WO2017082744A1

WO2017082744A1 - A method for forming a laminate for a printed circuit board

Info

Publication number: WO2017082744A1
Application number: PCT/PL2016/000122
Authority: WO
Inventors: Wojciech STRUŚ; Artur SKORUT
Original assignee: Skorut Systemy Solarne - Sp. Z O. O.
Priority date: 2015-11-13
Filing date: 2016-11-08
Publication date: 2017-05-18
Also published as: TW201729656A; PL414778A1; WO2017082744A4; AR106668A1

Abstract

The present invention relates to the method for modification of laminates used to manufacture printed circuit boards. The present invention allows to use the laminates used in the subtractive method for industrial manufacturing of printed circuit boards in semi-additive and additive processes. Modification of laminates used to manufacture printed circuit boards consist in using two processes: 1. Adding to the resin comprising the laminate a catalytic substance that is a photoactive titanium dioxide or TiO₂-Me_nO type complex oxides in the amount of at least 10% by weight as compared to the resin weight, preferably from 10% to 40% by weight. 2. Development of the surface of the laminate manufactured in the first process to at least 150%. To obtain the required copper adhesion to the dielectric substrate, the process of photoselective plating is used. Photoselective plating is a process wherein metal is deposited only on those sections of the dielectric surface where exposure to light results in a metal formation reaction. The principle of photoselective plating is that during the exposure of the dielectric photosensitive material in the sections where absorption takes place, catalytic centres are created, the nucleation seeds on which metal is deposited later during chemical plating. Such a process results in formation of a pattern drawing on the board surface consisting of metal particles. The process of formation of the printed circuit board is carried out when two conditions are met by the used dielectric substrate, wherein the base laminate forming the basic component for the manufactured printed circuit board is properly prepared. The laminate intended for manufacturing printed circuit boards should undergo an additional two-track treatment during its formation. To the known and used in the state of the art dielectric laminates or other materials during their formation a component with a significant catalytic or photocatalytic activity is added with a later appropriate laminate surface development.

Description

A METHOD FOR FORM ING A LAM INATE FOR A PRINTED CIRCUIT BOARD

The present invention relates to the method for modification of laminates used to manufacture printed circuit boards.

The present invention allows to use the laminates used in the subtractive method of manufacturing printed circuit boards for industrial manufacturing of printed circuit boards in semi-additive and additive processes.

Many companies and research groups have been searching for a long time for a possibility to replace the existing subtractive process of manufacturing printed circuit boards with semi-additive and additive processes. These searches are connected with defects typical for the subtractive method of manufacturing laminates used in printed circuit boards. The basic weaknesses of the subtractive technique involve the following:

- the use of copper-coated dielectric materials,

where in the process of circuit board preparation

most of the copper is etched,

- the need to use necessary photo resistors,

metal resistors,

- baths in expensive palladium salt solutions. In the subtractive process known from the state of the art, in the process of manufacturing a layer or a board with a printed circuit, there is the process of exposure to light of the photosensitive coat on the copper foil of the treated layer or board. The exposure to light is performed after application of a mask onto the treated layer or board which enables imaging on the photosensitive layer of the printed components that are to be preserved during the next operation of etching the treated layer or board.

The Polish patent specification No. PL 189558 entitled "A method for direct plating of dielectrics, in particular the walls of holes in printed circuits boards" reveals a method for subtractive plating of a board made of glass- epoxy laminate, copper coated on both sides, and with drilled holes . According to the method the board undergoes a process of electrochemical degreasing. Then it is treated in acetone. Then the holes in the board are conditioned in the Cleaner Conditioner 3223 solution by Shipley Co. which contains cationic surfactants, at the temperature of 60°C for 5 minutes. Then the copper foil is micro-etched in a solution containing 100 ml/1 of concentrated H2SO4 and 20 ml/1 of 30% H₂0₂- Then the board is covered with a palladium activator containing 50 g/1 of stannous chloride, 1 g/1 of palladium chloride and 150 ml/1 of concentrated hydrochloric acid. The activation is carried out for 5 to 25 minutes at the temperature of 60°C after which the acceleration process takes place, i.e. dipping the board for 5 to 10 minutes in 1M H₂S0₄solution . The prepared board is then plated in a galvanic bath containing 80 g/1 of CuS0₄ * 5 H₂0, 180 g/1 of concentrated H₂S0₄ and 0.1 ml/1 of concentrated HCl. In the known state of the art of manufacturing laminates intended for printed circuit boards, substrates with catalytic activity or photocatalytic activity are not used in these processes. The processes using catalytic activity or photocatalytic activity are economically more convenient and offer better prospects for their use. They require considerably less process operations and are far more environment-friendly. So far no process has been developed that would use either catalytic or photocatalytic activity in a satisfactory manner useful in industrial production .

United States of America patent specifications number US 7,468,175 entitled "Highly photosensitive titanium dioxide and process for forming the same" and number US 8,012,451 entitled "Highly photosensitive titanium dioxide and process for forming the same" reveal methods for forming the composition of highly photosensitive titanium dioxide. These methods include the steps of providing a titanium chloride compound, such as titanium trichloride or titanium tetrachloride, an oxygen-containing gas such as air and hydrogen. The concentration of the hydrogen is in a stoichiometric excess (H₂:0₂) -from 2.02:1 to 2.61:1. In the methods described in these previous patents number US 7,468,175 and number US 8,012,451, the titanium chloride compound is burned in the presence of oxygen from the oxygen-containing gas and hydrogen to form plurality of ultrafine (or so-called nanoscale) particles. The resulting T1O₂ containing particles according to the known inventions provide a magnetic susceptibility value (χ) of at least 0.8-lQ^"6 cm³/g at 300 K and are at least 30% by weight rutile, with the balance being essentially anatase. The percentage can be between 0.8xl0^~6 cm³/g and 2.4xl0^-6 cm³/g at 300 K. The very high paramagnetic susceptibility of the composition is an indicator of its high photocatalytic activity, such as a room-temperate photosensitivity of 1.4- 3.0 mg/ml min m², which is several orders of magnitude greater than the photosensitivity provided by conventional industrial Ti0₂ pigment product, usually 2.5-3.0 Ί0-5 mg/ml min m² at room temperature.

The process of manufacturing laminates and printed circuit boards known from the previous state of the art, including the subtractive process that has been known earlier, do not make it possible to obtain high-quality printed circuit boards, they are labour-intensive and expensive .

The method for modification of laminates used to manufacture printed circuit boards according to the invention consist in adding to the thermosetting epoxy and/or acrylic and/or phenolic resin or a different thermosetting resin a photocatalyst based on highly photosensitive T1O₂ in the form of TiC>₂-Me_nO_m in the amount ranging from 10% to 40% by weight as compared to the resin weigh. This photocatalyst is added to the thermosetting resin during the process of laminate manufacturing according to the requirements for the subtractive process. Preferably, the added TiC>₂-based photocatalyst in the form of Ti0₂-Me_n0_m is 15% to 20% by weight as compared to the weight of the resin. The thermosetting resin with added photocatalyst and other additives such as among others accelerating and setting agents then undergoes the homogenisation process. The additive to the thermosetting resin in the form of highly photosensitive Ti0₂ contains plurality of nanometric particles that contain titanium dioxide and titanium suboxide with added oxides of other metals. Such a homogenised mixture is then applied onto a tape or tapes made of a fibrous material, preferably a glass mat or a different mat, and then the entire structure undergoes the process of pressurised press moulding, preferably with the use of a compression rollers system. The finished, cured laminate then undergoes the process of laminate surface development by at least 150.0%. The purpose of the surface development process is to enhance copper adhesion to the laminate. Preferably, the laminate surface development process is performed with the use of chemical, physical or physical and chemical methods, depending on the manufacturer's abilities.

The prepared laminate undergoes the process of manufacturing printed circuit boards with the use of the semi-additive or additive method.

In the semi-additive method, the process of manufacturing printed circuit boards is performed as follows :

- the laminate cut into pieces with drilled holes is

coated with 1.5-2.0 μπι thick copper layer

on the entire surface;

- the inner surface of the drilled holes is also

coated with a copper layer with a 1.5-2.0 μηα thick copper layer, and the process, according to the semi-additive method, preferably carried out according to two methods:

In the first method of semi-additive process, pieces of cut laminate undergo the process of activation by palladium salts and then they undergo the drying process. After drying, the activated pieces of the cut laminate are placed in a chemical copper bath for 60 to 90 minutes. In the chemical copper bath, the entire surface of the pieces of cut laminate is coated with a 1.5-2.0 μιη thick copper layer. The same copper layer is applied on the inner surfaces of the drilled holes.

Such prepared pieces of cut laminate are coated with the photo resistor with imaged plate pattern and then by galvanisation in the chemical copper at the same time printed circuit traces are made with required dimensions and the drilled holes are coated with copper.

In the second method of semi-additive process, pieces of cut laminate undergo the process of activation of the dielectric surface and the inner surface of the drilled holes by bathing in the activation solution that preferably includes :

CuS0₄ x 5H₂0 in the amount ranging from 10% to 12% by weight,

Trilon B in the amount ranging from 20% to 25% by

weight ,

NaOH in the amount ranging from 10% to 12% by weight, a, ' -dipyridil in the amount of 10 mg/l, K3 [ Fe (CN) e] in the amount of 30 mg/l,

formalin in the amount of 10 mg/l,

solution temperature = approx. 65°C +/-5°C,

solution pH = 12.5-13.0.

After drying, there is the process of exposure of the entire laminate to UV radiation, as a result of which copper particles are formed on the surface of the laminate and in the drilled holes, according to the following reaction :

Ti0₂→UV→ = Ί Ο₂ ^"1 + Cu⁺¹→ Ti0₂ + Cu

Preferably, the exposure process is performed without masks by selective exposure with the use of a laser beam.

The copper treated with ionisation turns into metallic form. Such particles of metal form the centres of reaction during the bath in chemical copper. The chemical plating is carried out for 60 to 120 minutes. As a result, laminate is obtained with the surface and drilled holes coated with a 1.5-2.0 μπι thick copper layer. Such prepared substrate is used to manufacture printed circuit boards according to the subtractive method.

In the additive method, the process of manufacturing printed circuit boards is performed as follows:

the laminate manufactured according to the invention, with drilled holes, is cut into pieces;

then the surface of the laminate and the holes drilled in the laminate are activated in the copper salt base;

the activated surfaces of the laminate undergo the drying process and then after drying the surface of the laminate and the drilled holes are exposed to UV radiation.

As a result of these activities, during the chemical copper bath, catalytic centres are formed on the laminate and the inner surfaces of the drilled holes. After exposure to UV radiation, the pattern drawing is formed on the laminate and then by bathing in the chemical copper the drawing is coated with a copper layer of the required thickness. The time of exposure to UV radiations ranges from approx. 15 to 20 seconds.

Preferably, the exposure process is performed by selective exposure with the use of a laser beam.

The semi-additive and additive process of applying traces of printed circuits onto the dielectric substrate of laminates manufactured according to this invention are more economical, easy to carry out, allow to obtain printed circuit boards of high quality and fine pattern, small spaces and greater packing density, and these methods are considerably more environment-friendly.

Modification of laminates used to manufacture printed circuit boards consist in using two processes:

Adding to the resin comprising the laminate a catalytic substance that is a photoactive titanium dioxide or Ti0₂-Me_nO type complex oxides in the amount of at least 10% by weight as compared to the resin weight. Preferably the amount of the added photoactive titanium dioxide or Ti0₂-Me_n0 type complex oxides ranges from 10% to 40% by weight as compared to the resin weight.

Development of the surface of the laminate manufactu in the first process to at least 150%.

To obtain the required copper adhesion to the dielectric substrate, the process of photoselective plating is used. Photoselective plating is a process wherein metal is deposited only on those sections of the dielectric surface where exposure to light results in a metal formation reaction. The principle of photoselective plating is that during the exposure of the dielectric photosensitive material in the sections where absorption takes place, catalytic centres are created, the nucleation seeds on which metal is deposited later during chemical plating. Such a process results in formation of a pattern drawing on the board surface consisting of metal particles.

Therefore, the process of formation of the printed circuit board is carried out when two conditions are met by the used dielectric substrate, wherein the base laminate forming the basic component for the manufactured printed circuit board is properly prepared. The laminate intended for manufacturing printed circuit boards should undergo an additional two-track treatment during its formation. To the known and used in the state of the art dielectric laminates or other materials during their formation it is necessary to add a component with a significant catalytic or photocatalytic activity with a later appropriate laminate surface development.

Photosensitive titanium dioxide formed according to patent number US 8,012,451 or a different similar titanium oxide and Ti0₂~Me_nO_m type complex oxides are such components with significant catalytic activity. Examples of photoactivity results are included in Table 1 which provides physical and chemical properties of photocatalysts - dielectric material fillers, developed for the purposes of this invention. Table 1

Table 1 shows that the systems of complex oxides Si0₂ - Ti0₂, ZNO - Ti0₂, Bi₂0₃ - Ti0₂, W0₃ - Ti0₂ with no less than 30% of Si0₂ by weight, 50% of ZnO by weight, 10% of WO3 by weight and 10% of ΒΪ2Ο3 by weight respectively have appropriate photoactivity and dispersion and prove to be useful as photosensitive dielectric components of laminates. By incorporation of pressed catalysts in dielectrics the latter become photosensitive with example values of photoactivity listed in Table 2 and thus allow the reaction of Pd²⁺, Fe²⁺, Ni²⁺, Cu²⁺ ions formation as active centres of electrolyte-free plating. Table 2

Activity of dielectrics and adhesion achieved with photocatalyst - filler content of 20%.

Testing of polymer compositions with Ti0₂-based photocatalysts showed that their content of 15-20% by weight of the used laminate with the minimum photoactivity of the component of 1.0 x 10^-1 was enough for plated pattern formation.

The second condition required to obtain the required copper adhesion to the substrate is the development of the surface of the laminate containing a photosensitive component. The laminate surface development process is preferably performed with use of chemical, physical or physical and chemical methods, depending on the manufacturer's abilities. Combining polymer compositions containing Ti0₂-based photocatalysts with laminate surface development processes enables preparation of a laminate that could be fully dedicated to the industrial semi-additive and additive method for manufacturing printed circuit boards.

The advantage of the method of modification of laminates used to manufacture printed circuit boards according to this invention is the lack of electrolytic deposition of metals from saline solutions which has many important uses. They include, among others, plating of surfaces of dielectric materials containing additives with catalytic or photocatalytic activity. In the method according to the invention, photoselective plating is used wherein metal is deposited only on those sections of the dielectric surface where exposure to light results in a metal particle formation reaction. With the use of appropriate masks or selective exposure with the use of laser, this diversity of plating can be successfully used to carry out the additive and semi-additive method for the needs of the electronic industry. These technologies are far more economical, they offer better prospects, they are simpler and allow to obtain high-quality boards, with a fine pattern, small spaces, with the possibility of greater packing density and they require a smaller number of process operations. Moreover, combining polymer compositions containing Ti0₂~based photocatalysts with laminate surface development processes enables preparation of a laminate that could be fully dedicated to the industrial semi-additive and additive method for manufacturing printed circuit boards. The method for modification of laminates used to manufacture printed circuit boards was disclosed in examples of execution

Example 1.

Laminate manufactured according to the known process, containing a filler incorporated together with resin as a catalyst in the amount of 25% by weight as compared to epoxy resin, and the laminate surface was developed to approx. 170% and had drilled holes. The laminate was cut into pieces. The pieces of the cut laminate were activated with palladium salts and dried and after drying they were placed in chemical copper bath for approx. 110 minutes. In the chemical copper bath, the entire surface of the pieces of cut laminate was coated with an approx. 1.65 μπι thick copper layer. The same copper layer was also applied on the inner surface of the drilled holes.

After activation according to the above-mentioned method, the laminate was coated with the photo resistor with the imaged board pattern and then by bathing in the chemical copper at the same time the traces of printed circuits were made with required dimensions and the holes were coated with copper.

Example 2.

The surfaces of the cut pieces of the laminate prepared as in example 1 underwent the process of activation of the dielectric surface and the inner surface of the drilled holes by bathing in the activation solution that preferably includes: CuS0₄ x 5H₂0 in the amount of 10% by weight,

Trilon B in the amount of 22% by weight,

NaOH in the amount of 10% by weight,

a, ' -dipyridil in the amount of 10 mg/1,

K₃[Fe(CN)₆] in the amount of 30 mg/1,

formalin in the amount of 10 mg/1,

solution temperature = approx . 65°C +/-5°C,

solution pH = 12.5-13.0.

The pieces of cut laminate were coated with an approx. 1.50 μιη thick copper layer. The same copper layer was also applied on the inner surface of the drilled holes.

Further process of fabrication of the printed circuit boards fully complied with the subtractive process known earlier .

Example 3.

Onto the laminate prepared as in example 1, printed circuits were applied by means of the additive method which was carried out as follows:

Cutting laminate into pieces and drilling holes in the laminate;

Preparation of the surface and holes in the laminate ;

Activation of the cut laminate pieces in a copper salt- based solution;

Exposure of the surfaces of the laminate and inner surfaces of holes to UV radiation;

After activation, a mask that had been exposed to radiation from a UV lamp was applied onto the laminate. After the exposure, a pattern drawing appeared on the laminate, formed by copper particles. Next, by bathing in chemical copper the copper was applied to the required thickness. It follows from the above-mentioned examples that the performed tests demonstrated a full usefulness of dielectrics for introduction of the semi-additive and additive process on an industrial scale.

Claims

A method for modification of laminates used to manufacture printed circuit boards using the subtractive method, wherein a tape or tapes made of a fibrous material, preferably a glass mat, is saturated with thermosetting resin with a setting agent and an accelerating agent, and then such prepared material undergoes the process of pressure press moulding, preferably at a higher temperature and with the use of the system of rollers and the finished, cured laminate is cut into pieces with appropriate dimensions, characterised in that during the process of laminate formation, to the epoxy and/or acrylic and/or phenolic resin or a different thermosetting resin a photocatalyst is added in the amount ranging from 10% to 40% by weight as compared to the weight of the resin used, where the photocatalyst is a highly sensitive T1O₂ in the form of Ti0₂-Me_nO_m, and such a mixture is applied onto the fibrous material which then undergoes the process of pressure press moulding, and then the finished, cured laminate undergoes the process of laminate surface development up to at least 150.0%, then on such a laminate printed circuits are formed with the use of the semi-additive or additive process.

The method according to claim 1 characterized in that the added Ti0₂-based photocatalyst in the form of T1O₂- Me_nO_m is 15-20% by weight as compared to the resin weight .

The method according to claim 1 characterized in that the process of laminate surface development is performed with the use of chemical, physical or physical and chemical methods, depending on the manufacturer's abilities .

The method according to claim 1 characterized in that the forming of printed circuits with the use of the semi-additive process is that the entire surface of the cut laminate with drilled holes is coated with copper to the thickness ranging from 1.5 μια to 2.0 μκι, and the copper layer is also applied onto the inner surface of the drilled holes, where the process of copper-coating the laminate is performed by activation of the laminate with palladium salts and its drying and then the laminate is coated with copper in a chemical copper bath where the bath time ranges from 60 minutes to 90 minutes and then such prepared pieces of the cut laminate are coated with a photo resistor with the imaged board pattern and then by galvanisation in chemical copper at the same time traces of printed circuits are made with the required dimensions and the drilled holes are coated with copper.

The method according to claim 4 characterized in that the process of copper-coating the laminate consists in activation of the dielectric surface and the holes drilled in it by bathing in a solution including CuS0₄ x 5H₂0 in the amount ranging from 10% to 12% by weight, Trilon B in the amount ranging from 20% to 25% by weight, NaOH in the amount ranging from 10% to 12% by weight, , ' -dipyridil in the amount of 10 mg/1, K₃[Fe(CN)₆] in the amount of 30 mg/1, formalin in the amount of 10 mg/1, and the solution temperature is approx 65°C +/-5°C, while pH ranges from 12.5 to 13.0 and after drying the entire laminate is exposed to UV radiation.

The method according to claim 1 characterized in that the forming of printed circuits with the use of the additive process consists in that the cut laminate with drilled holes undergoes activation in a copper salt- based solution and then the process of chemical plating takes place by exposing the pieces of the cut laminate, the surface of the laminate and inner surfaces of holes to UV radiation for approx. 15 to 20 seconds with the use of a mask and then the surface of the laminate and the inner surfaces of holes are coated with a copper layer with the required thickness and after the activation process a mask is applied onto the laminate which is exposed to UV lamp radiation, and such a pattern drawing formed on the laminate by copper particles by bathing in chemical copper is copper-coated to the required thickness.

7. The method according to claim 5 or 6 characterized in that the process of exposure is performed by selective exposure with the use of a laser beam.