CA1261481A

CA1261481A - Printed circuit board capable of preventing electromagnetic interference

Info

Publication number: CA1261481A
Application number: CA000531921A
Authority: CA
Inventors: Kazumasa Eguchi; Katsuya Nakagawa; Fumio Nakatani; Shinichi Wakita; Hisatoshi Murakami; Tsunehiko Terada
Original assignee: Nintendo Co Ltd; Tatsuta Electric Wire and Cable Co Ltd
Current assignee: Nintendo Co Ltd; Tatsuta Electric Wire and Cable Co Ltd
Priority date: 1986-03-13
Filing date: 1987-03-12
Publication date: 1989-09-26
Also published as: EP0238267A2; DE3751323T2; KR930011606B1; US4801489A; AU592627B2; DE3751323D1; EP0238267B1; AU7001287A; KR870009612A; EP0238267A3

Abstract

ABSTRACT

There is described an improved method of printing and a new printed circuit board for preventing electromagnetic interference. The board comprises a base plate and a first electrically conductive layer formed on at least one of the main surfaces of the base plate. The first electrically conductive layer includes a signal electrode and a ground electrode in accordance with the desired circuit pattern on the board. A second electrically conductive layer is formed to cover the first electrically conductive layer and is electrically insulated from the signal electrode thereon. The second electrically conductive layer is connected to the ground electrode of the first electrically conductive layer to act as a shield against electromagnetic interference.

Description

4~

The present invention relates to a pri.nted circuit board for preventing e],ectromagnetic interference.
More specifical,ly, the present invention re],ates to a pri.nted circuit board capab],e of preventing electromagneti.c interference as part of the e].ectroni.c circuitry, for example, a home TV gaming machine which is connected to other equipment by a cable and hand].es hi.gh-frequency signals.
In recent years, regu],ations on electromagnetic interference have become severe in every country. One example of an apparatus which can prevent such an electromagnetic interference is di.sclosed, for examp],e, in Japanese Patent Laid-Open No. 72895/1983 lai.d open on May 15, 1983.
This prior art is very effective, for examp],e, for personal computers and other stand-alone equipment because a shi.eld case is used to surround the whol,e unit.
However, this is insufficient to prevent e],ectromagnetic interference of home gami,ng machines, such as the FAMILY
COMPUTER (registered trade mark). The reason is that the gaming machine s main unit is connected to other equipment, for example, a TV receiver or a control].er, through a ],ong cable. This means that the above-described prior art prevents electromagnetic interference on],y by confining electromagnetic energy in the shield case, and is not effective in preventing e],ectromagnetic waves radiated through the cable extending from the gaming machine.
In Japanese Patent Lai,d-Open No. 8900/1981 ],ai.d open on January 29, 1981, Japanese Patent Laid-Open No.
20662/1984 laid open on February 2, 1984, and Japanese Patent Laid-Open No. 116437/1985 lai,d open on June 22, 1985, various shield plates or shi,e],d sheets are disclosed which are considered to be effective substitutes for the above-described shield case. However, a prob],em simi,],ar to that in the above-described prior art is left even when such a shield plate or shield sheet is used.
In Japanese Patent Laid-Open No. 4160/1982 ],aid 4~

open on January 9, 1982, a semiconductor device, for example, a charge transferring device is di.sclosed. To prevent electromagneti.c radiation from a hi.gh frequency signal generating circuit, an electric conductive layer is S provided above that high frequency signa], generating circuit with an insu].ati.ng layer in between, and thi.s electrically conducting ],ayer is held at a constant potential. In this prior art, e]ectromagnetic radiation from a semiconductor chi.p itse],f is eliminated, but electromagnetic radiation from a printed pattern of a printed circuit board for mounting the chip, that is, from a signal electrode portion of the printed circuit sti].l cannot be suppressed.
An object of the present invention is to provide a printed circuit board having a nove]. configuration which is capable of preventing electromagnetic interference.
Another objective of the present invention is to provide a printed circuit board capable of preventing electromagnetic interference by effective],y suppressing spurious radiation of e],ectromagnetic waves from a signal electrode portion formed on the printed circuit board.
In accordance with the present i.nventi.on, there is provided a printed circui.t board for preventi.ng electromagnetic interference, comprising a base plate, a first electrically conductive ].ayer formed on at least one of the main surfaces of the base p],ate, the first electrica],ly conductive layer inc],uding a signa], electrode portion and a ground electrode portion i.n accordance wi.th a desired circuit pattern; and a second e].ectrica].].y conductive layer formed so as to cover the first e].ectrica].ly conductive layer and being e].ectrica],],y insulated from the signa], electrode portion thereof, the second electrica],ly conductive ],ayer bei.ng connected to the ground electrode portion of the first e].ectrica].ly conductive ].ayer to act as a shield agai.nst e].ectromagnetic interference.
In a conventiona], printed circuit board having no second e],ectrica].ly conductive layer on the first ~2~48~.

electrica].].y conductive ].ayer, a stray capacity or a distributed capacity is formed between adjacent signa]
electrodes in the first electrica].ly conductive ]ayer. On the other hand, in the printed circuit board i.n accordance with one aspect of the present invention, the second electrica]].y conductive layer is formed on the fi.rst electrically conductive layer close thereto, and therefore each signal e].ectrode of the first electrica].].y conducti.ve layer forms a distributed capacity between the second electrica]ly conductive layer close thereto rather than between the adjacent signal electrodes. Thi.s second electrically conductive ]ayer is connected to the ground electrode portion and is therefore grounded as to the high frequency components. Accordingly, spurious electromagnetic energy produced in each signa] electrode of the first electrically conductive layer, for example, by induction, flows to ground through the distributed capacity formed between the above-described second e]ectrica]ly conductive ]ayer. Consequent].y, the spurious electromagnetic energy is e]iminated in the printed circuit board itse]f.
In accordance with another aspect of the present invention, spurious e]ectromagnetic energy is reduced in the printed circuit board, itse]f constituti.ng e]ectroni.c circuitry. Therefore, even if for example, a cable is connected to it, no electromagnetic waves are radiated through that cable. Accordingly, the present invention can be very effective for preventing e].ectromagnetic interference in a]l types of e]ectroni.c equi.pment. More specifically, in the conventiona]. system for preventing electromagnetic interference using the shi.e].d case, spurious electromagnetic waves are radiated through a cable or the like extending from the printed circuit board itself or the electronic circui.try. However, by employing a printed circuit board in accordance with the present invention, the spurious e]ectromagnetic waves are eliminated in advance in the printed circuit board itse]f, and therefore spurious radi.ation can be prevented even when for examp]e, a cable is connected thereto.
The second e]ectrica]]y conductive ]ayer may be formed by printing with copper ink. According]y, the second electrica]]y conductive ]ayer can be formed very simp]y in comparison with the case where the second electrically conductive ]ayer is formed with copper foi].
According]y, the rise in the cost of the printed circuit board itse]f is very slight.
The copper ink to be used is made by mixing and kneading meta]lic copper powder, resin mixture and fatty acid or its meta]lic salt. The resin mixture acts as a binder of metallic copper powder and other components.
The fatty acid acts as a dispersant. Either a saturated fatty acid or an unsaturated fatty acid may be used.
Unsaturated fatty acid is preferable. Further, a solvent of a reducing agent, an agent for adjusting coefficient of viscosity or the like may be added.
In one embodiment, the copper ink is made by b]ending 15 - 45 PHR in weight of a mixture of reso] type phenol resin and p-tert-buty] phenol resin and 0.5 - 7 PHR
in weight of unsaturated fatty acid or alka]i meta]]ic salt thereof with 100 PHR in weight of meta]]ic copper powder. When such a copper ink is used, no deterioration of electric conductivity is caused due to oxidation thereof, and the ink is stable with time.
For example, in Japanese Patent Laid-Open No.
199778/1984 laid open on November 12, 1984 and Japanese Patent Laid-Open No. 156773/1985 laid open on August 16, 1985, electrica]]y conductive paints are disc]osed.
However, these conventiona] electrica]]y conductive paints are not used for the printed circuit board, but are used to obtain an effect equiva]ent to the aforementioned shield case, shield plate or shield sheet by coating the housing portion with it. According]y, such a printed circuit board in accordance with the present invention cannot be obtained by using these conventiona] paints.
In another embodiment, the copper ink is made by blending 15 - 50 PHR in weight of resin mixture (composed 4~

of 20 - 60 weight percent of me]amine resi.n and 80 - 40 weight percent of polyo] and po]yester resin and/or a]kyd resin) and 1 - 8 PHR in weight of saturated fatty acid or unsaturated fatty acid or its meta].lic sa].t thereof with 100 PHR in wei.ght of meta].].ic copper powder.
In still another embodi.ment, a meta].]i.c chelating agent and a so].dering acce].erating agent are added to the copper ink, and a solder layer is formed on the second e].ectric conductive ].ayer formed by such a copper ink. One example of the above-described copper ink, a copper ink is made by b].ending 1 - 8 PH~ in weight of saturated fatty acid or unsaturated fatty acid or its metallic sa].t thereof, 1 - 50 PHR in weight of metal3ic chelating agent and 0.1 - 2.5 PHR in weight of soldering accelerating agent with a tota]. of 100 PHR in weight of 85 - 95 weight percent of meta].lic copper powder and 15 - 5 weight percent of resin mixture (resin mixture composed of

2 - 30 weight percent of meta]. surface activating resin and the rest of the thermosetting resin).
By using the copper ink having the above-described composition, the electric conductivity is improved, and a soldering is easily app].ied to the who].e surface of the cured copper ink ].ayer.
According to another aspect of the present invention, there is a].so provided a method of manufacturing a printed circuit board for preventing electromagnetic interference, comprising the steps of forming in accordance with a desired circuit pattern a first electrica].].y conductive ].ayer inc].ud;.ng a signa].
electrode portion and a ground e].ectrode portion on at least one of the mai.n surfaces of a base p].ate composed of an insu].ating materia]., and forming a second electrica].].y conductive layer so as to cover said fi.rst electrica].].y conductive layer and bei.ng e].ectrica]].y insu].ated from said signal electrode portion, sai.d second e].ectrica].].y conductive layer being connected to said ground e].ectrode portion.
These objects and other objects, features, 6 ~
aspects and advantages of the present invention wi],l become more apparent from the following detai.],ed description when taken in conjuncti,on with the accompanying drawings in which:
Fi,gure 1 is a cross-sectional view showing one embodiment in accordance with the present invention, Figure 2 through Figure 7 are cross-sectiona], views showing one example of a method of manufacturing a printed circuit board of Figure 1 embodiment in the sequence of production, Figure 8 is a cross-sectiona], view showing another embodiment in accordance with the present invention, Figure 9 and Figure 10 are cross-sectional views showing a part of a method of manufacturing a printed circui.t board of Figure 8 embodiment, Figure 11 and Figure 12 are equiva],ent circuit diagrams for explaini,ng effects of the embodiments i.n accordance with the present invention, and Figure 13 is a graph for explaining effects of the embodiments in accordance with the present invention.
The abscissa represents frequency and the ordi.nate represents the intensity of radiati,on e].ectric fie],d.
Referring to Figure 1, a printed circuit board 10 includes a base plate 12 composed of an insu],ating material, for example, synthetic resin or cerami.cs. This base plate 12 is a double-sided board, and on each of the main surfaces of the base p],ate 12, an electri.ca],]y conductive layer 14 as a first e],ectrica].]y conducti.ve layer composed, for examp],e, of copper foi.], is formed.
This electrica],ly conductive layer 14 inc],udes a circuit pattern portion having a signa], e],ectrode portion and a ground e]ectrode portion 14a which are formed by means of etching.
A through-hole 16 is formed i.n the base p].ate 12, and a plating ],ayer 18 is formed on the inner wa].], of this through-hole 16. Thi.s plating ],ayer 18 is formed i.n the case where interconnection of the electric conductive ? ~

layers 14 on the both surfaces of the base p],ate 12 is required. Both ends of the plating ~.ayer 1~ are connected to the correspondi,ng e]ectri.ca].ly conductive ],ayers 14.
In addition, the plating layer 18 may be unnecessary in the case where the through-hole 16 is used on].y for inserting parts (not illustrated).
A solder resist layer 20 is formed on each of the main surfaces of the base plate 12 so as to cover the e].ectrica]ly conductive layer 14, except for a part of the ground electrode portion 14a. This solder resist layer 20 is formed where solder is not to adhere i.n the later process on the electrica].ly conductive layer 14. The solder resist layer can be a],so utilized to secure insulation between the copper ink ],ayer 22 as described later and the electrically conductive layer 14. A],so, the copper ink layer 22 as described ],ater is connected to the ground electrode portion 14a which i.s not covered by the solder resist layer 20.
On each of the mai.n surfaces of the base plate 12, the copper ink ],ayer 22, a second electrica],ly conductive layer, is formed on the solder resist layer 20 over nearly the whole surface of the base plate 12 so as to cover the electric conductive ],ayer 14, and particularly to cover the signa], e].ectrode portion of electrical].y conductive layer 14. The copper ink formi,ng this copper ink layer 22 may have, for example, the following composition.
To be brief, the copper ink is made by mixi.ng metallic copper powder as a filler with a binder for firmly sticking the meta],],ic copper powder to other materia],s. The particle size of meta].].ic copper powder is sma].ler than the mesh size of the si].k screen used i,n printing this copper ink ].ayer 22. For the binder, a solvent of thermosetting synthetic resin, for example, phenol resin wherein electrolytic carriers are dispersed, is used.
The specific resistance of such a copper ink layer 22 after curing is, for example, 10-3 - 10-5 Q.cm.

On the surface of the base p].ate 12, a so],der resist layer 24 as a second insulating ],ayer is formed so as to cover the copper ink layer 22.
The above-described copper ink ].ayer 22 is effective as a measure for preventing electromagneti,c interference. More specifica],ly, the signa] e],ectrode portion of the e]ectrically conductive ],ayer 14 is located close to the copper ink ].ayer 22, and therefore a stray capacity or distributed capacity is formed between the signal electrodes of the e].ectrica].].y conductive ].ayer 14 and the copper ink ],ayer 22 rather than between the signa].
e],ectrodes. Accordingly, spurious e],ectromagneti.c energy induced in the signa]. e],ectrode of the electrica].]y conductive layer 14 flows into the copper ink ],ayer 22 through the formed distributed capacity. The copper ink ]ayer 22 connected to the ground electrode portion 14a of the electrically conductive layer 14, is grounded in relation to high frequency components. Accordingly, the electromagnetic energy f].owing into the copper ink ],ayer 22 through the above-described distributed capacity eventua]ly fl.ows into high-frequency ground.
Consequently, no spurious e].ectromagnetic energy is stored in the signal e].ectrode portions of the e].ectrica].].y conductive ].ayer 14. Accordi.ngly, even i.f an e].ectric circuit is made using the printed circui.t board 10 and a cable or the like is connected thereto, no radiation energy is transferred through this cab].e.
This is explained more specifically in reference to Figure 11 and Figure 12. Figure 11 is an equi.va].ent circuit di.agram of a conventiona]. printed circui.t board, and in this equivalent circuit, signa]. e].ectrodes 2 and 3 connecti.ng elements la and lb and a ground e].ectrode 4 each having inductances according to their lengths and having distributed capacities in accordance with the distance between the e].ectrodes are formed between the signal e],ectrodes 2 and 3 and between the signa]
electrodes 2 and 3 and the ground electrode 4. If the ground electrode 4 has an inductance component, the ground 4~

electrode 4 does not act as an idea] ground Eor a high-frequency component of the signa], a potentia] difference is produced between both ends of the ground electrode 4 by thi.s inductance, and energy by thi.s potentia]. difference remains on the ground e]ectrode 4. When this remaining energy becomes large, it ]eaks outside as noise and produces electromagnetic interference with the surroundi.ng electronic components and equipment.
On the other hand, i.n the printed circuit board of this embodiment, the equiva]ent circuit thereof is as shown in Figure 12. The copper ink ].ayer 22 and a ground electrode 4' cover nearly the whole of the surfaces of the signal electrodes 2 and 3. This ground e].ectrode 4' thus does not contain an inductance component and no high-frequency potentia] difference is produced. Thereforethere is ]ittle chance that energy remai.ns in the ground electrode 4'.
A].so, in the conventiona]. printed circuit board, distributed capacities di.ffer depending on the distance between the signa]. electrodes 2 and 3 and the ground electrode 4. The distributed capacity is thus non-uniform, and the impedance varies on the path of the signal. Therefore, mi.smatching of transmission of hi.gh frequency waves is produced. Consequently, the spurious electromagnetic energy in the signal stays on the signal electrodes 2 and 3, and this energy either leaks as noise to external electrodes or radiates away.
On the other hand, in the printed circuit board of this embodiment, the first e].ectri.ca].].y conductive layer 14 and the second e].ectrica]].y conductive ].ayer 22 are laminated through the insu].ating layer 20 which has nearly a uniform thi.ckness. Therefore the distance between each of the signa]. e].ectrodes 2 and 3 and the ground electrode 4' is near].y uniform, and the distributed capacity between them both is made uniform. The distributed capacity becomes a ]arge va].ue to the extent that the distributed capacity between the signa].
electrodes 2 and 3 can be neglected. Accordi.ng]y, the 8J~

e].ectromagnetic energy which, conventiona],]y, wou],d have been stored in the signa]. e].ectrodes 2 and 3 f].ows i.nto the ground e].ectrode 4 through that distributed capacity, and therefore no spurious radi,at.i,on takes place.
In Figure 13, a ].i,ne A shows the radiation ].eve].
when the conventional printed circuit board ;,s used, and a line B shows the radi.ation ],eve]. when the pri.nted circui.t board of the embodi,ment in accordance with the present invention is used. As is understood from Figure 13, i.n the conventiona]. case, spurious radiation as large as 50.60 dB~V was produced at 67.03 MHz. On the other hand, in accordance with the present invention, the radiation level is almost the noise component a].one. Regu],ations on electromagnetic interference can thus be met.
Next, one example of a method of manufacturing the printed circuit board 10 of Figure 1 is described.
First, as shown i.n Figure 2, the base p]ate 12 is prepared. This base plate 12 is made, for example, of synthetic resin, such as epoxy resin, pheno]., or cerami.cs with a thi.ckness of, for example, 1.2 - 1.6 mm. Then, on each of the main surfaces of the base plate 12, the electrica].ly conductive layer 14 is formed with copper foil with a thickness of between 30 to 70 ~ m, onto which is later placed a signal e]ectrode pattern matchi.ng the circuit pattern of the first electrica],ly conductive layer 14.
Subsequently, as shown in Figure 3, the through-hole 16 is formed in the base plate 12 so as to penetrate the electric conductive ],ayers 14 , using, for example, a multispindle drilling machine. Thi.s through-ho].e 16 is utilized to interconnect the e].ectrica].ly conductive layers 14 of both mai.n surfaces, and can be a],so utilized as a ho],e for inserting leads of e].ectronic parts. Then, the end faces of the dri],led hole are ground and the base plate 12 is transferred to the next process.
Next, as shown in Figure 4, the plati,ng layer 18 is formed on the inner wall of the through-ho],e 16, by, for example, electrolytic plating or chemi,ca], plating.

ll Accordingly, the e],ectrica],]y conductive ],ayers 14' on the both surfaces of the base plate 12 are connected to each other.
Subsequently, the e]ectrica],],y conductive layer 14' is etched to form the signa]. e]ectrode portion according to the required circuit, inc],uding the ground e].ectrode portion 14a as shown in Figure 5. More specifica],].y, etching resistant is first printed i,n accordance with the pattern of the requi,red signal e],ectrode, the through-hole 16 is filled and wet etching or dry etching is then app]ied. The signa], electrode portion and ground electrode portion are thus formed.
Thereafter, as shown in Fi,gure 6, the so]der resist ].ayer 20 which functions as the first insulating layer is printed. At this time, rust preventing treatment may be applied to prevent oxi.dation and deterioration of the electrically conductive ].ayer 14.
The above processes are well known as genera]
manufacturing processes of the conventiona]. pri,nted circuit board.
Next, as shown in Figure 7, the copper ink ].ayer 22 is formed on the first insulating layer, that is, the solder resist layer 20 over nearly the whole surface so as to cover the electrica].].y conductive layer 14. To be detailed, a silk screen (not il]ustrated) having a printed pattern is required because the copper ink ],ayer 22 is deposited through the screen onto the main surface of the base plate 12.
In addi.tion, when a copper ink having a sufficiently small specific resistance is used, the copper ink layer 22 may be formed so as to complete],y cover the ground e]ectrode portion 14a.
Thereafter, the printed copper ink i,s cured by heating. Resin mixture used as a binder is of thermosetting type and is cured by a condensation reaction when heated. In this curing, the copper ink layer 22 shrinks not only in the direction of the film surface but also in its thickness. In addition, the resu].ts of the experiment conducted by the inventors show that the strength of adhesion of the copper ink ~.ayer 22 after curing to the base plate 12 can withstand, for examp]e, 3 kg of tensi.],e load by with a 3 land, being near]y equa].
to that of the el,ectric conductive ],ayer 14 composed of copper foil.
Fina],]y, as shown in Figure 1, the solder resist ]ayer 24, a second insu]ati.ng layer is formed over the whole area of both surfaces of the base plate 12, by means of coating or printing, for example. Thus, the printed circuit board 10 is manufactured.
For the embodiment shown in Figure 1 though Figure 7, the copper ink is used, made by b]ending 15 - 45 PHR in weight of a mixture of resol type phenol resi.n and p-tert-butyl pheno], resin and 0.5 - 7 PHR in weight of unsaturated fatty acid or its alka]i metal]ic sa]t with 100 PHR in weight of metal]ic copper powder.
More preferab]y, the mixing ratio i.n wei.ght of resol type phenol resin and p-tert-butyl phenol resin is 65:35 - 97:3.
The degree of polymerization of p-tert-butyl phenol resin is preferably not more than 50.
Meta],lic copper powder is preferab]y of a dendrite shape, and the average partic],e size is preferabl,y 2 - 20 ~m. For the specific example, the electrolytic copper powder CE lllOA manufactured by Fukuda Meta]. Foil & Powder Co., Ltd., and the MF-D3 manufactured by Mitsui Mini.ng & Sme],ting Co., Ltd. and others are listed.
In the copper ink of thi.s embodi.ment, a mi.xture of resol type phenol resin and p-tert-butyl pheno], resin acts as a bi,nder, a],so acting effective],y to maintain the electric conductivity for a long time peri.od.
Norma]. resol type phenol resin can be used for this purpose. The above-described p-tert-buty], pheno], resin is obtained by heat-polymerizing p-tert-butyl pheno], and forma],in under the presence of an a],ka],i catalyst.
The degree of polymerization is preferably not more than 50. When using a resin the degree of po]ymerization of which exceeds 50, formation of the network structure of resol type phenol resin is hindered during the thermosetting of the copper ink. Thus contact between the metallic copper powder mo]ecu]es cannot be obtained, resulting in a reduction in e]ectric conductivity.
A]so, the combining ratio of the binder composed of the above-described resin mixture is 15 - 45 PHR in weight, or preferably 20 - 40 PHR in weight, to 100 PHR in weight of meta]lic copper powder. When the binder is ]ess than 15 PHR in weight, the amount of the binder is insufficient, resu]ting in poor f]uidity of the copper ink obtained, reduced printabi]ity and increased copper powder oxidization. The net result is a reduction in the e]ectric conductivity of the copper ink ]ayer. When the amount of the binder exceeds 45 PHR in weight the copper powder amount is insufficient, and the electric conductivity is reduced.
A mixture of 65 - 97 weight percent of resol type phenol resin and 35 - 3 weight percent of p-tert-butyl phenol resin is preferable. When p-tert-butyl phenol resin exceeds 35 percent by weight, the copper ink layer becomes brittle after thermosetting. Formation of the network structure of reso] type phenol resin is thus hindered, contact between copper powder mo]ecules cannot not be obtained, and reduction in e]ectric conductivity occurs. When p-tert-buty] phenol resin is not more than 3 weight percent, the electric conductivity immediately after thermosetting is adequate but the e]ectric conductivity of the copper ink ]ayer reduces with time.
Furthermore, unsaturated fatty acid or its alkali metallic sa]t acts as a dispersant and as a weak reducing agent to prevent oxidation of meta]]ic copper powder, thereby contributing to the maintenance of electric conductivity. Specifica]]y, the unsaturated fatty acid is absorbed on the surface of copper powder, which accelerates dispersion of copper powder, thus resulting in a copper ink layer having a good e]ectric .

$~ 8~

conductivity. Examp]es of unsaturated fatty acid are olein acid and linoleic acid. Examples of alka]i, meta],],ic salt are sodium salt and potassium sa]t. Furthermore, vegetable oil containing not ]ess than 60 weight percent of unsaturated fatty acid, for example, bean oil, sesame oil, olive oil or saff]ower oi,], can a]so be used. The amount of vegetab]e oil added is 0.5 - 7 PHR in weight, preferab],y 2 - 6 PHR in weight to 100 PHR in weight of metallic copper powder. If ]ess than 0.5 PH~ in weight of vegetable oil is added, dispersion of meta]]ic copper powder in the binder becomes poor and the electric conductivity is reduced. If the vegetab]e oil added exceeds 7 PHR in weight, not on]y no improvement in dispersion corresponding to the added amount, but the electric conductivity of the copper ink ]ayer is reduced.
Thus, a copper paste or copper ink used for thi,s embodiment is obtained by mixing and kneading meta],lic copper powder, a binder composed of a specific resin mixture and a dispersant composed of unsaturated fatty acid or its alkali meta],lic sa]t. In addition, a reducing agent conventiona]]y used may be blended as desired.
Here, a more detailed description is made of the above-mentioned copper ink in comparison with other examples. 5 Embodied sam les 1 - 12 p Electrolytic copper powder having an average particle size of 3 ~m, for example, the "CElllOA"
manufactured by Fukuda Meta] Foi], & Powder Co., Ltd., resol type phenol resin, for examp],e, the "PL2211", 58 percent in resin concentration, manufactured by Gunei Chemical Industry Co., Ltd., p-tert-butyl pheno], resin and unsaturated fatty aci,d or its a],ka]i meta]lic sa],t were mixed and kneaded in the composition shown in Tab]e 1.
The degree of polymerization of p-tert-buty], pheno], resin (I) in Table 1 is 50 or less.
The copper ink samples 1 - 12 were screen-printed in a band shape of 2mm in width and 35 - 45 ~m in thickness between electrodes (interva],s of 60 mm) on a glass-epoxy resin base p]ate. The samp],es underwent thermosetting at 150C for 60 minutes to form conductors tcopper ink layers). The volume resistivity of the samples was measured using a digita]. mu].timeter. In order to ascertain whether or not an e],ectric conductivi,ty capable of withstanding a long time period of use is obtainable, the samp],es were subjected to two kinds of oxidation acceleration tests. These tests were the humidity cabinet test (40C at 95% RH for 500 hours) and the heating test (100 Eor 500 hours). The rate of vo],ume resistivity change (hereinafter referred to as "resistance change rate") was measured from the tests. Table 1 shows the results of the measurements.
In addition, calcu].ations of the volume resistivity and resistance change rate were performed according to the following equations (1) and (2).
Volume resistivity (Q.cm) = R x t x W/L ~
where, R: Resistance va].ue between e],ectrodes (Q ) t: Thickness of coated film (cm) W: Width of coated film (cm) L: Distance between electrodes.
Resistance changing rate (~)=lOOX(R500-Ro)/Ro~ (2) where, Ro Resistance value before test (Q) R500 Resistance va].ue after humidity cabinet test or heating test for 500 hours.
Furthermore, the printabi],ity of each sample was studied according to the following judging standard.
O : Good printabi].ity ~ : Capab],e of printing X : Incapab].e of printing The results of the study are shown in Table 1.
Comparative samples 1 - 8 Mixtures having compositions as shown in Tab],e 2 were prepared, and conductors were formed on the base plates as with the embodied samples, and the volume resistivity, the resistance change rate after the humidity cabinet test and after the heating test were performed and L~ 481 the pri.ntability was a].so studied. Table 2 shows the results of the measurement and the study. In addition, p-tert-butyl phenol resin (II) in Table 2 contains 30 weight percent of p-tert-buty]. pheno], resin with degree of polymerization exceedi.ng 50.
Comparative samp]e 9 A copper i.nk composed of 100 PHR in wei.ght of copper powder, 25 PHR in weight of resol type phenol resin, 4 PHR in weight of o],ei.n acid and 0.6 PHR in wei.ght of organic titanium compound was prepared. The volume resistivity, the humidi.ty cabinet test, the heating test and the printability were studied as in the embodied samples. The resu],ts of the study are shown in Tab],e 2.
In addi.tion, tetra t2,2 - dially],oxymethy],-l butyl) bis [di(tridecil)] hosfitetinate was used as an organic titanium compound.
Comparative samp]e 10 A copper ink composed of 100 PH~ i.n weight of copper powder, 25 PHR in weight of resol type phenol resin and 1.25 PHR in weight of anthracene as a reducing agent was prepared. The volume resistivity, humi.dity cabi.net test, heati,ng test and the printability were studi,ed as in the embodied samples. The results of the study are shown in Table 2.
As is apparent in the comparison of the resu].ts in Table 1 and Tab],e 2, by b].ending p-tert-butyl phenol resin with the copper inks having the above-described compositions, a conductor, that is, an e],ectrica],],y conductive ].ayer capab],e of withstandi.ng a ].ong ti.me period of use without adverse],y affecting the pri.ntabi].ity is obtainable. This resu].t is particu].ar],y remarkab],e where the degree of polymerization of p-tert-buty], pheno], resin is 50 or less. Furthermore, it is found that the effect is excellent withi.n a mixing ratio range of 65:35-97:3 of reso]. type phenol resin and p-tert-buty], phenol resin. It is a],so obvious that when the amounts of binder and unsaturated fatty acid added to meta],lic copper powder are within ranges as shown in Table 1, exce].lent electric .~2'~

conductivi,ty and a ].ong time peri.od of stabili.ty are obtainable.
On the other hand, the copper ink of the comparative samp].e 9 made by blendi.ng an organi.c titani.um compound, as is obvious from the resu].ts of the humidity cabinet test and the heating test, cannot withstand a ].ong time period of use. The copper ink of the comparative sample 10, made by blending anthracene has inferior va].ues for any of the initial, volume resisti.vity, the resistance change rate based on the humidity cabinet test and the resistance change rate based on the heating test.
In another embodi.ment, in order to form the copper ink layer 22, a copper ink i.s used which is made by blending 15 - 50 PHR in weight of resin mi,xture (resin mixture composed of 20 - 60 weight percent of me],amine resin and 80 - 40 wei,ght percent of polyol and polyester resin and/or alkyd resin) and 1 - 8 PHR in weight of saturated fatty acid, unsaturated fatty acid or its metallic salt with 100 PHR in weight of meta],].ic copper powder.
More preferab].y, the blendi,ng ratio of po],yester resin and/or a].kyd resin and polyol is 95 - 50: 5 - 50.
Meta],lic copper powder may have any shape;
strip, branch, sphere or unfixed shape, and the particle size thereof is preferably less than 100 ~ m, and most preferab]y 1-30 ~m. Meta],],ic copper powder whose particle size is l.ess than 1 ~ m is easily oxidized, and the electric conductivity of a coated fi],m i.s reduced. The blended amount of meta],],ic copper powder used is a],ways 100 PH~ in weight.
The binder, that is, me],ami,ne resin in the resin mixture, is alkyrated melamine resin. Ei,ther methylated melamine resin or butylated me].amine is used. Me].ami,ne resin binds well to meta]]ic copper powder and other components. The amount of melamine resin in the resin mixture blended with polyol and polyester resin and/or alkyd resin which are used as other binders is wi,thi,n a range of 20 - 60 weight percent, and preferab].y 30 - 50 12t;~l~81 weight percent. When the b]ended amount of me],ami.ne resin is less than 20 weight percent, enough meta].]ic copper powder cannot be bound, the network structure of melamine resin becomes unstable, and the electric conducti,vity of the copper ink ].ayer is remarkably reduced. If the amount exceeds 60 percent by weight the e].ectric conductivi,ty of the copper ink ].ayer is remarkably reduced.
Polyol in the resin mixture is polyester polyo],, and makes cross linking with me].amine resin.

r HO -- H2C O O ,CH2H
HO t CH2 - ,C CH2 C - O - CH - C - CH2O t C2H5 ~ C2H5 J n The tota], hydroxyl group va],ue and acid value of the polyol used is lOOmg/g or more, and preferably 130mg/g or more. Use of polyol with a tota], of hydroxyl group value and acid value is less than lOOmg/g causes the copper ink layer to lose e].ectric conductivity.
The amount of polyol in the resin mixture blended with polyester resin and/or a].kyd resin is within a range of 50 - 95 weight percent, and preferab].y 60 - 90 weight percent. When the blended amount of po].yol is less than 50 weight percent, the electric conductivity of the copper ink layer is not good, and in reverse, when exceeding 95 weight percent, a good adhesion of the copper ink layer to the base plate cannot be obtai,ned.
Polyester resin and/or a].kyd resin in the resin mixture suppresses the condensation reaction of me].amine resin and po].yol, and improves the vehi,cu],ar property of the copper ink ].ayer.
The average molecu].ar weight of po],yester resin and/or alkyd resin used is preferab].y 5000 or more, and more preferably 8000 or more. When the average mo].ecu].ar weight is less than 5000, the adhesion of the copper ink layer to the base plate is remarkab].y reduced.

48~

The amount of polyester resin and/or alkyd resin blended with po].yo] is withi.n a range of 5 - 50 weight percent, and preferably 10 - 40 weight percent. When the blended amount of po]yester resin and/or a]kyd resi.n i.s less than 5 weight percent, the adhesi.on of the copper ink layer is not good, and when exceeding 50 weight percent, electric conductivity of the copper ink ]ayer is remarkably reduced.
The amount of po]yo]. and polyester resin and/or alkyd resin in the resin mixture blended with me].amine resin is within a range of 80 - 40 weight percent, and preferably 70 - 50 weight percent.
The blended amount of the binder, that is, the resin mixture tresin mixture composed of 20 - 60 weight percent of melamine resin and 80 - 40 weight percent of polyol and polyester resin and/or a]kyd resin) is within a range of 15 - 50 PHR in weight and preferably 20 - 40 PHR
in weight to 100 PHR in weight of meta]].ic copper powder.
Saturated fatty acid, unsaturated fatty acid or its meta].lic salt acts as a dispersant dispersing meta].lic copper powder in the resin mixture. Saturated fatty acid such as palmitic acid, stearic acid, arachic acid or acids having a carbon number of 16 - 20 is used. Unsaturated fatty acid such as zoomari.c acid, olein acid, linolenic acid or the like having a carbon number of 16 - 18 are used. Metallic sa].ts of these acids may be sodium, potassium, copper, zinc, a].umi.num or the ].ike.
The blended amount of saturated fatty acid, unsaturated fatty aci.d, or its meta].].ic sa].t is within a range of 1 - 8 PHR in weight and preferab].y 2 - 6 PHR in weight to 100 PHR in weight of metal].ic copper powder.
When the blended amount of di.spersant is ].ess than 1 PHR
in weight, excessive kneadi.ng time is required to microdisperse meta].].ic copper powder in the resin mixture, and in reverse, when exceeding 8 PHR in weight, the e].ectric conductivity of the copper ink ].ayer is reduced.
Furthermore, to adjust the coefficient of viscosity, a norma]. organi.c solvent can be used. For 8~

exampl,e, ethylene g].yco] meno ethy]. ether acetate (ethy]
cellosolve acetate) and ethy].ene glycol meno n-buty] ether acetate (n-butyl ce].],oso].ve acetate) are wel], known solvents.
Here, a more detai].ed description is made of the copper ink having the above composition i.n comparison with other examples.
Branched-shaped meta].lic cop~er powder having a particle size of 5 - 10 ~m, stearic acid, olei.n acid and potassium oleinate as dispersants and melamine resin, polyester po].yo],, polyester resin and a],kyd resin as the binding resin mixture were blended by the ratios (PHR in weight) as shown in Table 3. Some amount of n-butyl cellosolve acetate was added thereto as a solvent, and the mixture was kneaded by a three ax],e roll for 20 minutes to prepare the embodied samp]es 1 - 7. Five e].ectric conductive lines of 2mm in width, 30+~5 m in thickness and 100 mm in length were printed on a g]ass-epoxy resin base plate by screen printing. The copper ink was cured by heating to 130 - 180C for 10 - 60 minutes, and the volume resistivity, that is, the electric conductivity of the cured copper ink ].ayer was measured.
To observe adhesive properties, the copper-foil surface of a printed wire board underwent a cleaning treatment, and thereafter copper ink 50 x 50 mm2 in area, was printed on that copper-foil surface by screen printing. The copper ink was cured by heating as in the embodied samples, and para],le]. ].ines orthogona]. to one another were then cut in with the copper ink ].ayer interva].s of 1 mm in accordance wi.th the cross cut test, JIS tJapan Industria]. Standards), test i.tem K5400 (1979).
Checker-shaped cuts were then made so that 100 squares were formed in lcm2 and the copper ink ]ayer was then peeled off the copper-foil surface. Tab].e 3 shows the resu],ts of the study on adhesion characteristics.
As is understood from Table 3, embodied samp],es 1 - 7 excel in the characteristics such as e].ectric conductivity of the copper ink ].ayer, that is, the vo].ume ~26~

resistivity and the adhesion of the copper ink ].ayer to the copper-foil surface.
However, the comparative sample 1 contains large amounts of butylate me],ami,ne resi.n, po],yester polyol and polyester resin, and therefore the e],ectric conductivity and adhesion of the copper ink ],ayer are reduced.
Comparative sample 2 has no e],ectric conductivity at a].], because of the ],ow hydroxyl group va],ue of po],yester polyol. For the comparative sample 3, the adhesion of the copper ink ],ayer is not preferable because the average molecular weight of a],kyd resin to be used is ]ess than 5000. The comparative samp],e 4 contains a ],arge amount of meta],lic copper powder and does not contain po],yester resin and/or a].kyd resin, and therefore the electric conductivity and adhesion of the copper ink ],ayer are reduced.
In Figure 8, the copper ink layer 22' and the solder layer 26 prevent electromagnetic interference, unlike the previous embodi.ment, in which the copper ink layer 22 is effective for preventing electromagnetic interference.
To be detailed, the copper ink ],ayer 22' is formed using the copper ink previ.ous],y used but when the binder is cured, a so].derab].e layer i.s formed on the surface of copper ink ],ayer 22'. Then, the solder ],ayer 26 is formed on copper ink ],ayer 22' (so].derable layer), the p],ating layer 18, the inner wa].l of the through-hole 16, and the electrica],].y conductive ],ayer 14, by so].der dipping. Thi.s solder ],ayer 26 i.s formed on near],y the who].e area of the main surface of the base p].ate 12 as was the solderab],e ],ayer (copper ink ],ayer) 22'. At this time, the solder resist layer 20 is removed on a segment of the ground electrode porti.on 14a, and the so],der ].ayer 26 i.s connected to that ground electrode portion 14a.
The solder layer 26 serves to reduce the specific resistance of the copper i.nk ].ayer 22' (improves the electric conductivity) and to increase the mechani.ca].
strength. Assuming that the specific resistance of on],y ~ 8 the copper ink layer 22' after curing i.s, for examp].e, about 10 4 ~ .cm, the speci.fic resistance becomes, for exampl.e, about 10 5 Q .cm after the solder ].ayer 26 has been formed. The copper ink layer 22' and solder ]ayer 26 S can thus function together against electromagnetic interference.
Note that the so].der layer 26 need on].y to be formed so as to cover at ]east the copper ink ].ayer 22', and not the signa]. electrode formed by copper foil (the electric conductive ].ayer 14) or the p].ating layer 18.
On the surface of the base plate 12, so]der resist layer 24 as the second i.nsu]ating layer i.s formed as the second insulating ]ayer so as to cover the solder resist layer 20 and the solder layer 26.
Next, one example of the method of manufacturi.ng the printed circuit board of the embodi.ment shown in Figures 8 through 10 is described.
The processes as shown in Figure 2 through Figure 6 are first employed for this embodiment. Then, after the process of Figure 6, as shown in Figure 9, the copper ink ]ayer 22' is formed on nearly a]]. of the first insulating layer, that is, the solder resist ].ayer 20 and/or the electric conductive layer 14. To be detai.led, a silk screen (not il]ustrated) having a printed pattern is used to print copper ink on the main surface of the base p].ate 12.
Thereafter, the printed copper ink i.s cured by heating. When the copper ink i.s cured, a so].derab].e ].ayer is formed on the surface thereof. This means that the surface of the copper ink ].ayer 22' becomes so].derab]e.
Thereafter, as shown i.n Figure 10, the solder layer 26 is formed on a].]. portions whereto so].der actua].ly adheres so as to cover at ].east the copper ink ].ayer 22'.
To be detailed, in this process of Figure ].0, solder is made to adhere on the main surface of the base p].ate 12 by means of solder leveller, reflow soldering or solder di.pping.
As described above, this solder layer 26 mechanica],],y rein~orces the copper ink ]ayer 22' and i.mproves the e].ectric conductivity.
Fina],l,y, as shown i.n Figure 8, the solder resist layer 24, the second i.nsu],ating layer, is formed on both surfaces of the base plate 12 by coating or printing. The printed circui.t board 10 is thus manufactured.
In the above-described embodi.ment, to form the solderable layer, a copper ink havi,ng a re],ative],y ],ow specific resistance is used. However, thi.s so],derab],e layer may be formed by an electrically conductive ink having a low e],ectric conductivi,ty, or even an i.nsu],ating ink having a specific resistance of, for example, about 106 _ 108 ~ .cm. In summary, a so],derab],e layer has only to be formed thereof because the so],der ]ayer 26 formed in the process thereafter has a sufficient electric conductivity. The copper ink 22' must be formed to completely cover the signa], electrode portion because the solder layer 26 must be i,nsu],ated from the signa], electrode portion of electric conductive layer 14' by the copper i.nk layer 22'.
In the case where the solderab],e layer havi.ng insu].ating property is formed, i,t will be unnecessary to form the solder resist layer 20 as the first i.nsu].ating layer because insu],ation between the solder ].ayer 26 and the electric conductive ],ayer 14 is provided by the solderable layer itself.
In the embodi,ment as shown i,n Figure 8 through Figure 10, a conductive copper ink havi,ng the fo],].owing composition is uti],ized. To be described specifi.ca].].y, a copper ink is used which is made by b].endi.ng 1 - 8 PHR in weight of saturated fatty aci.d, unsaturated fatty acid, or its metallic sa],t as a dispersant, 1 - 50 PHR in weight of metallic chelating agent and 0.1 - 2.5 PHR in weight of solder accelerating agent, with a tota], of 100 PHR in weight of 85 - 95 weight percent of meta].],ic copper powder and 15 - 5 weight percent of resin mi.xture as a binder.
For the resin mixture, a resin mixture composed of 2 - 30 weight percent of meta]. surface activati.ng agent and the ~26P48~

rest of thermosetting resin is used.
The meta]].ic copper powder may be of any shape:
strip, branch, sphere or unfixed shape, and the particle size thereof is more preferab]y not more than 100~ m, and particularly 1 - 30 ~ m is preferab].e. Powder havi.ng a particle size of ].ess than 111 m is easi].y oxidized, the electri.c conductivity of the copper i.nk layer is reduced, and the solderability is poor.
The amount of meta].].ic copper powder blended with the binder, that is, the resin mi.xture is within a range of 35 - 95 weight percent, and preferably 87 - 93 weight percent. When the b]ended amount is ].ess than 85 weight percent, the electric conductivity of the copper ink layer is reduced, the solder is britt].e, the e]ectri.c conductivity is reduced, and the screen-printabi]ity i.s poor.
For the meta]. surface activating agent in the resin mixture, at least one i.s se]ected from among denatured rosin such as active rosin, partia].].y hydrofined rosin, fully hydrofined rosin, esterifined rosin, ma].ei.c rosin, disproportiona] rosin and polymerized rosin.
Active rosin or maleic rosin is preferab].e.
The blended amount of meta]. surface activating resin in the resin mixture is within a range of 2 - 30 weight per cent, and preferably 5 - 10 wei.ght percent.
Even when the blended amount of meta]. surface acti.vating resin is less than 2 weight percent, if the meta]].ic chelating agent and the solder accelerati.ng agent as described later are b]ended by proper amounts, so].dering can be performed di.rectly on the Eormed copper ink ].ayer.
By adding them withi.n such a preferable range of b].endi.ng, the so].dered surface can be made smoother and glossier.
When exceeding 30 weight percent, the electric conductivity of the copper ink ]ayer is reduced and solderabi].ity is not increased.
Thermosetting resin in the resin mixture serves to bind metallic copper powder and other components, and has on].y to be a ].ow-molecular substance being ]iquid at normal temperature that becomes a higher molecul.ar substance with thermosetting. Phenol, acry], epoxy, polyester or xylene may be used, but the use i.s not limited to these resins. Reso]. type phenol resin i.s preferable. The blended amount of thermosetting resin in the mixture is withi.n a range of 98 - 70 wei.ght percent.
The amount of the above-described binder, that is, resin mixture, blended with meta]]ic copper powder i.s within a range of 15 - 5 weight percent, taki.ng a tota].
b].ended amount of meta].].ic copper powder and resin mi.xture as 100 PHR i.n weight. When the blended amount of resin mixture is less than 5 weight percent, metallic copper powder is not bound sufficiently, the copper ink ].ayer is brittle, the electric conductivity is reduced and the screen-printability i.s poor. In reverse, when exceeding 15 weight percent, the so].derability is poor.
Saturated fatty acid, unsaturated fatty acid, or its metallic sa].t acts as a di.spersant. For a saturated fatty acid, pa].mitic acid, stearic acid, arachic acid, or an acid having a carbon number of 16 - 20 can be uti].i.zed.
For an unsaturated fatty acid, zoomaric acid, o]ein aci.d, linolenic acid or an acid having a carbon number of 16-18 can be utilized. The meta].]ic salt may be with meta].
such as potassium, copper or a]umi.num. In the b]end of metallic copper powder and resin mixture, the use of a dispersant accelerates microdispersion of meta]lic copper powder in the resin mixture, thus increasing el.ectric conductivity.
The blended amount of saturated fatty acid, or unsaturated fatty acid, or its meta].li.c sa]t is withi.n a range of 1 - 8 PHR in weight and preferably 2 - 6 PHR i.n weight to a total of 100 PHR in weight of meta].]i.c copper powder and resin mixture. When the blended amount of dispersant is ].ess than 1 PHR in weight, excessive time is required to microdisperse metallic copper powder in the resin mixture, and i.n reverse, when exceeding 8 PHR in weight, the electric conductivity of the copper ink ].ayer and the adhesion of the copper ink ].ayer to the base p]ate are reduced.
For the meta] 1 ic che] ating agent, fatty ami.nes such as monoethanolami.ne, di.ethanolamine, triethanolamine, ethylene diamine, triethy].ene diamine and triethylene tetrami ne are used . The meta].lic che].ating agent prevents oxidation of meta].lic copper powder, thus improving the e].ectri.c conductivity and the so]derabi] ity. For example, a b] end of meta] 1 ic copper powder, thermosetting resin and metal surface activating resin, will resu]t in poor solderability. But by addi.ng the metallic chelating agent to the mix, a good solder can be obtai ned .
The blended amount of metallic chelating agent is within a range of 1 - 50 PHR in weight and preferab] y 5 - 30 PHR in weight to a total amount of 100 PHR in wei.ght of metallic copper powder and resin mixture. When the blended amount of meta] lic che].ating agent is less than 5 PHR in weight, the electric conductivity and the solderability are reduced. In reverse, when exceedi.ng 50 PHR in weight, the viscosity of the copper ink is low and the so].derability is reduced.
For the solder accelerating agent, at least one selected f rom among oxidicarboxy].ic acid, aminodicarboxylic acid and its meta].lic sa].ts is used.
For example, tartaric acid, ma].eic acid, glutamic acid, aspartic acid and its meta].lic sa].ts may be used. The solder accelerating agent improves the solderability through synergism with the meta] lic chelating agent. By b].ending the metal surface activating resin, the meta].] ic chelating agent and the so] dering acce].erating agent, and the soldered surface of the copper i.nk ].ayer can be made smoother and g].ossi.er.
The blended amount of solder accelerating agent is within a range of 0.1 - 2.5 PHR i.n weight, and preferab].y 0.5 - 2.5 PHR i.n weight, to a tota]. of 100 PHI~
in weight of meta].lic copper powder and resin mixture.
Even when the blended amount of so].dering acce] erating agent is less than 0.1 PHR in weight, if the meta]. surface activating agent and the meta] ].ic chelating agent are ~2~

blended i.n proper amounts, soldering can be performed di.rectly onto the copper ink ].ayer. But by setting the amount of solder accelerating agent within the preferab].e range, the so].dered surface can be made smoother and 5glossier. In reverse, when exceedi.ng 2.5 PHR in weight, the electric conductivi.ty of the copper i.nk ].ayer and the solderability are reduced.
To adjust the coefficient of viscosi.ty, norma]
organic solvents such as diethylene glycol mono-n-buty].
lOether (n-butyl-carbitol), diethylene glycol-mono-buty].
ether (n-butyl-carbitol acetate), ethylene glycol mono-n-butyl ether tn-butyl cel]oso]ve), methy] isobutyl ketone, toluene, and xylene can be used.
Copper ink having the above composition i.s now 15compared with the various samples.
Branch-shaped meta].lic copper powder having particle si%es of 5 - lO ~ m, a resin mixture (resin mixture consisting of lO weight percent of ma].eic rosin and 90 weight percent of resol type pheno] resi.n), 20potassium oleinate, oleinic acid, triethanolamine and glutamic acid were blended by the ratios (PHR in wei.ght) as shown in Table 5, and of n-butyl-carbitol was added as a solvent. The mixture was kneaded for 20 mi.nutes by a three axle roll to prepare an embodi.ed sample. An S-25shaped pattern of 0.4mm i.n width, 30 + 5~ m in thickness, and 520mm in length was formed on a glass-epoxy resin base plate by screen printing. The samples were then heated to 180C for 20 - 60 mi.nutes to cure the copper ink.
Subsequently, in order to app].y so].dering to the 30formed copper ink layer, the base p]ate went through the solder leveller machine, was di.pped i.n a f].ux bath for 4 seconds, di.pped in a melted solder bath of 250C (Pb/Sn =
40/60) for 5 seconds, blown by hot ai.r of an atmospheric pressure of 2-6 and 220-230C, and c]eaned. Soldering was 35then applied to the whole surface of the copper ink ].ayer.
Tab]e 5 shows the results of study on various characteristics of the copper ink ].ayer obtai.ned i.n the above-described process. In Tab].e 5 and Table 6, ,8~

polyester po].yol (I) is of 280 - 300 mg/g in hydroxyl group va]ue, not more than 4 mg/g in acid va],ue and 1200 in average molecular weight, po],yester polyol (II) is of 160 - 180 in hydroxyl group va],ue, not more than 2 mg/g in acid value, and 2500 in average molecu],ar weight, polyester po]yol (III) is of 40 - 50 mg/g in hydroxy], group val,ue, not more than 2 mg/g in acid value and 4100 in average molecular va]ue, polyester resin i,s of 4 - 8 mg/g in hydroxy], group va],ue, not more than 5 mg/g in acid value and 18000 in average mo]ecu]ar weight, a],kyd resin (I) is of 60 mg/g in hydroxyl group va],ue, not more than 3 mg/g in acid va],ue and 9800 in average mo],ecu].ar wei,ght, and a].kyd resin (II) is of 120 mg/g in hydroxyl group va].ue, not more than 5 mg/g in acid va],ue and 2200 in average molecu]ar weight.
In Table 5 and Table 6, the observation of the soldered state of the copper ink layer solderabi],ity was made with a low-magnification physica], microscope, based on the following standards:
~ : Solder adheres to the whole area and has smooth and glossy surface.
O : Solder has an uneven surface but adheres to the who]e area.
~ : The copper ink ]ayer is partly exposed.
X : Solder adheres on]y part].y.
The humidity cabinet tests refers to the resistance change rate after the soldered copper ink ],ayer has been ],eft in an atmosphere of 55C and 95% RH for lO00 hours.
The heating test refers to the resistance change rate obtained after the so]dered copper ink ],ayer has been heated at 80C for lO00 hours.
The film thickness of the so],der layer on the copper ink ],ayer of the embodi,ed samples in Tab]e 5 is 10 ~m in average. The embodied samples l - 8 have desired va].ues, regarding the vo]ume resistivi,ty of the copper ink layer (electric conductivity, adhesion of the copper ink layer, solderability onto the copper ink ]ayer, and ~2~8~

printability of the copper i,nk and the like) because the specific materia],s to be used for the copper i,nk are suitably b]ended.
Particu],arly, soldering can be performed directly on the copper ink layer using a norma], organic acid flux agent, thus improving the electric conductivity from the order of 10 4 Q.cm to the order of 10 5 Q.cm.
The e]ectric conductivity of the copper ink layer on whi,ch the solder layer is formed has high heat resistance and moisture resistance and possesses a ],ow resistance change rate. Therefore, this invention can be used i,n an atmosphere of high temperature and hi,gh humidi,ty.
In Table 6, comparative sample 1 contai,ns a large amount of metallic copper powder and a sma]l amount of thermosetti,ng resin. Meta],lic copper powder i,s not bound sufficiently, the copper ink ]ayer obtained is brittle and it is di,fficu]t to print.
Comparative samp],e 2 contains a sma]l amount of metallic copper powder, and solder thus on],y partly adheres to the copper ink ],ayer. The comparative sample 3 is not added meta]]ic salt of unsaturated fatty acid, and therefore the solderability is slightly reduced, and the resistance change rates in heat and moisture are increased. Comparative sample 4 has a ]arge amount of a meta]lic salt of unsaturated fatty acid, and the adhesion of the copper ink layer to the base plate is thus poor.
Comparative sample 5 does not possess the metallic chelating agent. The electric conductivity of the copper ink layer and its solderabi],ity thereto are reduced, and the resistance change rates in heat and moisture are increased. Comparative samp],e 6 contains a ]arge amount of metallic chelating agent, the coefficient of viscosity of the copper ink is thus reduced, resu],ting in difficu],ty in printing.
Comparative samp]e 7 does not possess the acce],erating agent, but suitable amounts of meta] surface activating resin and meta],],ic chelating agent are blended, therefore the so],derability is reduced on]y s],ight]y.

Comparative sample 8 contains a ]arge amount of so]der accelerating agent the e].ectric conductivity of the copper ink ].ayer and the sol.derabi]ity are thus reduced.
In al] of the above-described embodi.ments the copper ink ]ayer 22 (22 ) and the so]der layer 26 were formed on both surfaces of base plate 12. However the resu].ts of experiments conducted by the inventors et a].
show that these ].ayers may be formed on on].y one of the surfaces of the base plate 12.
Where the copper ink ].ayer 22 (22 ) and the solder layer 26 were formed on both main surfaces of the base p]ate 12 the ground e].ectrode portion 14a is formed on only one of the main surfaces then through-holes at severa]. places are connected to ground and the copper ink layer 22 and the solder ~.ayer 26 on the other main surface are connected to those through-ho].es.
A].though the present invention has been described and i.]]ustrated in detai.l it is c]early understood that the same is by way of i]lustration and example only and is not to be taken by way of limitation the spirit and scope of the present invention being limited on]y by the terms of the appended c].ai.ms.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A printed circuit board for preventing electromagnetic interference, comprising:
a base plate, a first electrically conductive layer formed on at least one of the main surfaces of said base plate, said first electrically conductive layer including a signal electrode portion and a ground electrode portion in accordance with a desired circuit pattern; and a second electrically conductive layer formed so as to cover said first electrically conductive layer and being electrically insulated from said signal electrode portion thereof, said second electrically conductive layer being connected to said ground electrode portion of said first electrically conductive layer to act as a shield against electromagnetic interference.

2. A printed circuit board for preventing electromagnetic interference in accordance with claim 1, further comprising an insulating layer formed on said base plate except for a part of said ground electrode portion of said first electrically conductive layer for insulating said signal electrode portion of said first electrically conductive layer from said second electrically conductive layer.

3. A printed circuit board for preventing electromagnetic interference in accordance with claim 2, wherein said second electrically conductive layer is formed so as to cover nearly the whole area of said signal electrode portion on said base plate.

4. A printed circuit board for preventing electromagnetic interference in accordance with claim 3, wherein said second electrically conductive layer includes a layer of material containing copper.

5. A printed circuit board for preventing electromagnetic interference in accordance with claim 4, wherein said layer of material containing copper is formed by a copper ink which is made by mixing metallic copper powder, a binder and a dispersant.

6. A printed circuit board for preventing electromagnetic interference in accordance with claim 5, wherein said binder is composed of a resin mixture including at least thermosetting resin.

7. A printed circuit board for preventing electromagnetic interference in accordance with claim 6, wherein said dispersant includes saturated fatty acid or unsaturated fatty acid.

8. A printed circuit board for preventing electromagnetic interference in accordance with claim 7, wherein said copper ink is made by blending 15-45 PHR in weight of a mixture of resol type phenol resin and p-tert-butyl phenol resin and 0.5-7 PHR in weight of unsaturated fatty acid or alkali metallic salt thereof with 100 PHR in weight of metallic copper powder.

9. A printed circuit board for preventing electromagnetic interference in accordance with claim 8, wherein the blending ratio in weight of said resol type phenol resin and said p-tert-butyl phenol resin is 65:35-97:3.

10. A printed circuit board for preventing electromagnetic interference in accordance with claim 8 or 9, wherein the degree of polymerization of said p-tert-butyl resin is not more than 50.

11. A printed circuit board for preventing electromagnetic interference in accordance with claim 7, wherein said copper ink is made by blending 15-50 PHR in weight of a resin mixture and 1-8 PHR in weight of saturated fatty acid or unsaturated fatty acid or metallic salt thereof with 100 PHR in weight of metallic copper powder.

12. A printed circuit board for preventing electromagnetic interference in accordance with claim 11, wherein said resin mixture is composed of 20-60 weight percent of melamine resin and 80-40 weight percent of polyol and polyester resin and/or alkyd resin.

13. A printed circuit board for preventing electromagnetic interference in accordance with claim 12, wherein the blending ratio in weight of said polyester resin and/or said alkyd resin and said polyol is 95-50:5-50.

14. A printed circuit board for preventing electromagnetic interference in accordance with claim 1, wherein said second electrically conductive layer is solderable and further includes a solder layer formed on said solderable second electrically conductive layer.

15. A printed circuit board for preventing electromagnetic interference in accordance with claim 14, wherein said solderable second electrically conductive layer contains high-resistance material to provide a predetermined specific resistivity.

16. A printed circuit board for preventing electromagnetic interference in accordance with claim 14, wherein said solderable second electrically conductive layer contains an electrically conductive material dispersed therein.

17. A printed circuit board for preventing electromagnetic interference in accordance with claim 16, wherein said electrically conductive material includes copper powder.

18. A printed circuit board for preventing electromagnetic interference in accordance with claim 17, wherein said solderable second electrically conducting layer is formed by a copper ink which is made by mixing metallic copper powder, resin mixture, saturated fatty acid or unsaturated fatty acid or metallic salt thereof and a metallic chelating agent.

19. A printed circuit board for preventing electromagnetic interference in accordance with claim 18, wherein said copper ink further includes a soldering accelerating agent.

20. A printed circuit board for preventing electromagnetic interference in accordance with claim 19, wherein said resin mixture is made by mixing metal surface activating resin and thermosetting resin.

21. A printed circuit board for preventing electromagnetic interference in accordance with claim 20, wherein said copper ink is composed of a total of 100 PHR
in weight of 85-95 weight percent of metallic copper powder and 15-5 weight percent of resin mixture, 1-8 PHR
in weight of fatty acid or metallic salt thereof, 1-50 PHR
in weight of metallic chelating agent and 0.1 - 2.5 PHR in weight of soldering accelerating agent.

22. A printed circuit board for preventing electromagnetic interference in accordance with claim 21, wherein said resin mixture includes 2-30 weight percent of metal surface activating resin and the remainder being thermosetting resin.

23. A printed circuit board for preventing electromagnetic interference in accordance with claim 22, wherein said base plate includes an additional main surface having thereon first and second electrically conductive layers.

24. A printed circuit board for preventing electromagnetic interference in accordance with claim 23, further comprising a second insulating layer formed on said base plate so as to cover said second electrically conductive layer.

25. A method of manufacturing a printed circuit board for preventing electromagnetic interference, comprising the steps of:
(a) forming in accordance with a desired circuit pattern a first electrically conductive layer including a signal electrode portion and a ground electrode portion on at least one of the main surfaces of a base plate composed of an insulating material, and (b) forming a second electrically conductive layer so as to cover said first electrically conductive layer and being electrically insulated from said signal electrode portion, said second electrically conductive layer being connected to said ground electrode portion.

26. A method of manufacturing a printed circuit board for preventing electromagnetic interference in accordance with claim 25, wherein after forming said first electrically conductive layer and before forming said second electrically conductive layer, an insulating layer is formed on said base plate except for a part of said ground electrode portion, said ground electrode portion being exposed so that said second electrically conductive layer contacts said part of said ground electrode portion.

27. A method of manufacturing a printed circuit board for preventing electromagnetic interference in accordance with claim 25, wherein said step (b) includes a step of printing a copper ink made by mixing metallic copper powder, binder resin and a dispersant so as to cover said first electrically conductive layer and being electrically insulated from said signal electrode portion and which further includes a step of curing said printed copper ink to form a copper ink layer as said second electrically conductive layer.

28. A method of manufacturing a printed circuit board for preventing electromagnetic interference in accordance with claim 27, wherein said binder resin includes at least thermosetting resin, and said step of curing said copper ink includes a step of heating said printed copper ink.

29. A method of manufacturing a printed circuit board for preventing electromagnetic interference comprising steps of:
(a) forming in accordance with a desired circuit pattern a first electrically conductive layer including a signal electrode portion and a ground electrode portion on at least one of the main surfaces of a base plate composed of an insulating material;
(b) forming a solderable layer so as to cover said signal electrode portion on said first electrically conductive layer while insulated therefrom and so as to be connected to said ground electrode portion, and (c) forming a solder layer on said solderable layer by means of soldering.

30. A method of manufacturing a printed circuit board for preventing electromagnetic interference in accordance with claim 29, further comprising the step of forming an insulating layer on said base plate except for a part of said ground electrode portion so as to cover said first electrically conductive layer, wherein step (b) includes a step of forming said solderable layer on said insulating layer.

31. A printed circuit board constructed for preventing electromagnetic interference, comprising:
a base plate having at least one electrically insulated main surface;

a first electrically conductive layer formed on said electrically insulated main surface of said base plate, said first electrically conductive layer including a signal electrode portion and a ground electrode portion in accordance with a desired circuit pattern; and a second electrically conductive layer formed so as to cover said first electrically conductive layer and being electrically insulated from said signal electrode portion, said second electrically conductive layer connected to said ground electrode portion of said first electrically conductive layer so that electromagnetic energy generated in said signal electrode portion of said first electrically conductive layer is capacitively coupled to said second electrically conductive layer and from there passes into said ground electrode portion such that electromagnetic interference does not radiate from said printed circuit board.

32. A printed circuit board constructed for preventing electromagnetic interference in accordance with claim 31, further comprising an insulating layer formed on said base plate except for a part of said ground electrode portion of said first electrically conductive layer for insulating said signal electrode portion of said first electrically conductive layer from said second electrically conductive layer.

33. A printed circuit board constructed for preventing electromagnetic interference in accordance with claim 31, wherein said base plate has an additional electrically insulated main surface and wherein additional said first and second electrically conductive layers are formed on said additional electrically insulated main surface.

34. A printed circuit board constructed for preventing electromagnetic interference in accordance with claim 31, further comprising an insulating layer formed on said base plate so as to cover said second electrically conductive layer.

35. A method of manufacturing a printed circuit board capable of preventing electromagnetic interference, comprising the steps of:
(a) forming in accordance with a desired circuit pattern a first electrically conductive layer including a signal electrode portion and a ground electrode portion on at least one of the main surfaces of a base plate composed of an insulating material;
(b) forming a first insulating layer on said base plate except for a part of said ground electrode portion so as to cover said signal electrode portion of said first electrically conductive layer;
(c) forming a second electrically conductive layer so as to cover said first insulating layer, said second electrically conductive layer connected to said ground electrode portion of said first electrically conductive layer so that electromagnetic energy generated in said signal electrode portion of said first electrically conductive layer is capacitively coupled to said second electrically conductive layer and from there passes into said ground electrode portion such that electromagnetic interference does not radiate from said printed circuit board, said second electrically conductive layer being formed by the steps of:
(i) printing a copper ink made by mixing metallic copper powder, binder resin including at least a thermosetting resin, and a dispersant on said first insulating layer; and (ii) curing said printed copper ink by heating to form a copper ink layer as said second electrically conductive layer; and (d) forming a second insulating layer so as to cover said second electrically conductive layer.

36. A method of manufacturing a printed circuit board capable of preventing electromagnetic interference in accordance with claim 25, further comprising the step of forming an insulating layer on said base plate 50 as to cover said second electrically conductive layer.

37. A method of manufacturing a printed circuit board capable of preventing electromagnetic interference in accordance with claim 29, further comprising the step of forming an insulating layer on said base plate so as to cover said solder layer.

38. A printed circuit board constructed for preventing electromagnetic interference in accordance with claim 14, wherein said solder layer is in electrical contact with said copper ink layer and said ground electrode portion.

39. A method of manufacturing a printed circuit board capable of preventing electromagnetic interference in accordance with claim 29, wherein said solder layer is in electrical contact with said copper ink layer and said ground electrode portion.