WO2000041447A1

WO2000041447A1 - Method for producing a multilayer printed circuit board

Info

Publication number: WO2000041447A1
Application number: PCT/CH1999/000625
Authority: WO
Inventors: Thomas Widmer
Original assignee: Ppc Electronic Ag
Priority date: 1999-01-05
Filing date: 1999-12-24
Publication date: 2000-07-13
Also published as: AU1646500A; EP1142457A1

Abstract

The invention relates to a method for producing a multilayer printed circuit board which is produced by bonding laminate layers (20, 30, 40, 50) which each consist of a conductor layer (24, 25, 31, 32) and an insulating layer (16, 17; 28, 29) to a laminate core (10). According to the invention the via holes (33, 34) between the conductor layers (24, 32 and 25, 31) are formed by laser drilling through the individual laminate layers (40, 50) and then plated through.

Description

DESCRIPTION

METHOD FOR PRODUCING A MULTI-LAYER PCB

TECHNICAL AREA

The present invention relates to the field of printed circuit board technology. It relates to a method for producing a multilayer printed circuit board which comprises a plurality of conductor layers which are arranged one above the other and are separated from one another by insulating layers, the conductor layers being conductively connected to one another by via openings arranged one above the other in an axis in the respective insulating layers.

Such a method is e.g. known from US-A-5,662,987 or US-A-4,258,468.

STATE OF THE ART

In the production of multilayer printed circuit boards, it is in most cases necessary to arrange them in a stack with insulating intermediate layers to conductively connect individual structured conductor layers at certain points to one another by means of via openings (so-called "via holes" or "vias"). When through-contacting three or more conductor layers lying one above the other, it is expedient and desirable for reasons of space saving and the short line connections to arrange the via openings between the different levels in a line one above the other and to choose the diameter of the via openings as small as possible.

In the publication US-A-5,662,987 mentioned at the outset, a conventional method is first described in connection with FIGS. 1-6, in which the via openings lying one above the other are successively opened in the various insulating layers and then metallized by chemical wet etching. This conventional method has the disadvantage that the plated-through holes cannot be adjusted sufficiently precisely one above the other, and that the diameter of the openings is relatively large and therefore takes up a lot of space (column 2, lines 28-52). In a further known method (FIGS. 7-11), conductive posts are produced for the plated-through hole, in which, however, the conductive connection to the conductor layers has major problems (column 3, lines 8-21). Finally, a method is proposed (Fig. 12-19), in which the individual plated-through holes are filled with a filling material after the metallization. However, this technique requires a large number of additional process steps, which complicate and make the entire production process more expensive.

The method described in US Pat. No. 4,258,468 is also very complex, in which openings are first created in the individual conductor layers by means of an etching process into the conductor layer islands provided for through-plating, and then the stack of insulating layers in the region of the openings by means of a Laser beam is pierced and then metallized. PRESENTATION OF THE INVENTION

It is therefore an object of the invention to provide a method for producing through-contact multilayer printed circuit boards which ensures reliable through-plating, manages with a small number of easily controllable process steps, and enables through-plating with a minimum of space requirement.

The object is achieved by the entirety of the features of claim 1. The essence of the invention is to open the plated-through holes of a laminate layer by means of a laser beam through the respective conductor layer and the insulating layer underneath. As a result, very fine openings with a diameter of less than 100 μm can be produced quickly, cleanly and precisely one above the other, which ensure reliable through-plating during the subsequent metallization.

A first preferred embodiment of the method according to the invention is characterized in that the laminate core comprises a third insulating layer provided on both sides with first conductor layers, and in that first and second laminate layers are applied to both sides of the laminate core and in each case through-contacted. As a result, the number of conductor layers and levels can be significantly increased while maintaining a laminate core. A further increase in the number of conductor levels is of course possible if more than two laminate layers are applied one above the other on one or both sides.

A second preferred embodiment of the method according to the invention is characterized in that the through-openings are introduced into the respective insulating layers by means of the laser beams in two steps, in a first step with a first laser beam of a first power, the conductor layer lying over the insulating layer and a Part of the underlying insulating layer of the respective laminate layer is removed, and in one second step with a second laser beam of a second, compared to the first, reduced power, the remaining part of the insulating layer is removed. A relatively high beam power or intensity of the laser beam is required for the removal of the metallic (Cu) conductor layer in the area of the via openings to be produced. If the insulation layer underneath was also completely removed with this power, there would be the risk that the next conductor layer underneath, to which the via should be produced, would be damaged and the via would possibly be faulty. This is certainly avoided by the fact that after the removal of the upper conductor layer, the power of the laser beam is reduced to such an extent that when the insulation layer is subsequently removed, the next conductor layer underneath is not damaged. The ratio of the first power to the reduced second power is preferably about 3: 1.

A further preferred embodiment of the method according to the invention is characterized in that the conductor layers applied with the laminate layers are each reduced in thickness before the through-hole openings are introduced, and are reinforced again after the through-hole openings have been introduced by the metallizations used for the through-hole connection. The reduction in thickness of the conductor layers enables a total reduction in the laser beam power used or a higher processing power with the same laser beam intensity. As a result, greater precision in machining and thus an overall reduced diameter of the openings can be achieved. The conductor layers of the laminate layers preferably initially have a thickness of 10-20 μm, in particular 12 or 18 μm, and they are removed down to a thickness of approximately 6-7 μm for the laser drilling of the plated-through holes.

The plated-through holes also have a diameter of 50-150 μm. Cu films are preferably used as the laminate layers as conductor layers with an epoxy resin layer as the insulating layer, the laminate layers each having an initial thickness of approximately 70-100 μm.

Further embodiments result from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

The invention will be explained in more detail below on the basis of exemplary embodiments in connection with the drawing. 1-14 show in detail sectional views different stages or steps in the production of a plated-through multilayer printed circuit board according to a preferred embodiment of the invention.

WAYS OF CARRYING OUT THE INVENTION

The exemplary embodiment for the method according to the invention shown in FIGS. 1-14 is based on a flat laminate core 10 according to FIG. 1, which comprises a central insulating layer 11, each provided with a conductor layer 12 and 13 on the top and bottom is. As in the other figures, the thicknesses of the individual layers are not drawn to scale in FIG. 1 for reasons of better visibility. The thickness of the laminate core is, for example, 1.2 mm. The insulating layer 11 is made of a conventional epoxy resin. The conductor layers 12 and 13 are usually made of Cu and have a thickness which is adapted to the respective requirements and e.g. is a few 1/10 mm.

In a first step, the two conductor layers 12 and 13 are structured according to FIG. 2 by means of conventional lithographic and etching methods in accordance with an existing circuit board layout, by structures 14 and 15 in the Conductor layers 12, 13 are etched free. 3, two identical first laminate layers 20 and 30 are then applied to the laminate core 10 from both sides by lamination or pressing. Each of the laminate layers 20, 30 consists of a conductor layer 18 or 19 in the form of a copper foil, which is provided on the underside with an insulating layer 16 or 17 made of an epoxy resin. The thickness of the laminate layers 20, 30 is preferably between 70 and 100 μm, and the initial thickness d1 of the conductor layers 18, 19 is preferably 12 or 18 μm. When pressing the laminate layers 20, 30 with the laminate core 10, the material of the insulating layers 16, 17 completely fills out the etched structures 14, 15 in the conductor layers 12, 13.

In the further course of the method (FIGS. 4-6), the first via openings are then introduced into the laminate structure according to FIG. 3. First of all, wet chemical etching, the thickness of the conductor layers 18, 19 reduced from the original value d1 (12 or 18 μm) to a value d2 of approximately 6-7 μm. A laminate structure according to FIG. 4 then results. According to FIG. 5 in a laser processing center with a laser beam 39 (indicated by the arrow bundle in FIG. 5) at predetermined points, which are provided for through-plating, from this side Through openings 21 and 22, respectively, are introduced by locally removing (evaporating) both the (reduced-thickness) conductor layer 18 and 19 and part of the underlying insulation layer 16 and 17 to a certain depth. The plated-through holes 21, 22 are preferably produced in succession in the same laser processing center with the same laser beam 39.

The plated-through holes 21, 22 are preferably produced with a diameter D1 of 50-150 μm. The laser beam 39 has only a diameter of approximately 25 μm and is moved across the laminate structure on a predetermined travel line across the laminate structure in order to lift the larger through-hole 21, 22. To remove the conductor layers 18, 19, the laser operates in a first mode with increased beam power or beam intensity. For the removal of the remaining thickness of the insulating layers 16, 17 is the bearing the remaining thickness of the insulating layers 16, 17, the laser is operated in a second mode with a beam power attenuated to approximately 1/3 (indicated in FIG. 6 by a smaller number of arrows in the laser beam 23). The insulating layers 16, 17 can thus be cleared out precisely and completely within the plated-through holes 21, 22 without the underlying conductor layers 12, 13 being damaged.

In the next step (FIG. 7), by applying a metallization 24 or 25, conductive connections are made between the areas of the conductor layers 12, 13 exposed in the via openings 21, 22 and the areas of the conductor layers 18, 19 bordering the via openings 21, 22. Since the metallization takes place over the entire area, the conductor layers 18, 19, which were previously reduced in thickness, are again reinforced overall by the metallization and can subsequently be structured in the usual way, i.e. can be provided with structures 26, 27 (FIG. 8).

The laminate structure according to FIG. 8 is now ready for the lamination (pressing with) of the next following laminate layers 40 and 50 (FIG. 9), which in turn each consist of a conductor layer 31 or 32 (Cu foil) with an insulating layer 28, 29 underneath (made of epoxy resin) and the laminate layers 20, 30 same. In these laminate layers 40, 50, the same steps for producing the plated-through holes are carried out according to FIGS. 10-14 as those shown in FIGS. 4-8 for the laminate layers 20, 30 and have already been explained. This includes reducing the thickness of the conductor layers 31, 32 (step from FIG. 9 to FIG. 10), clearing the conductor layers 31, 32 in the plated-through holes 33, 34 with a laser beam 35 of increased power (FIG. 11), clearing out the rest Insulating layers 28, 29 down to the level of the underlying conductor layers 18, 19 or 24, 25 by means of a laser beam 38 of reduced power (FIG. 12), the metallization of the via openings 33, 34, the reduced-thickness conductor layers 31 being formed by the metallizations 41, 42 , 32 are reinforced again (FIG. 13), and the final structuring of the conductor layers 31, 32 and 41, 42 by means of the structures 43, 44 (FIG. 14), which are also used for term multi-layer circuit board 100 leads. In principle, further laminate layers can then be applied and plated through accordingly.

The plated-through holes 33, 34 are made directly through the previously created plated-through holes 21, 22 by suitable adjustment of the laminate structure in the laser processing center and corresponding control of the laser beam. Due to the 2-stage laser processing, an island 36, 37 made of insulating material remains within the lower plated-through holes 21, 22 (FIG. 12), which is subsequently covered by the metallization 41 and 42, respectively. In this way it is possible to limit the metallization to only the depth of one laminate layer.

Overall, the method according to the invention makes it easy and safe to produce a multilayer plated-through circuit board which is characterized by space-saving and precisely arranged plated-through holes.

REFERENCE SIGN LIST

10 laminate core

11 insulating layer 12.13 conductor layer (Cu) 14.15 structure (etched)

16, 17 insulating layer (epoxy resin)

18.19 conductor layer (Cu foil)

20.30 laminate layer

21, 22 via hole (via)

23 laser beam

24.25 metallization

26.27 structure (etched)

28.29 insulating layer (epoxy resin)

31, 32 conductor layer (Cu foil) 33.34 via hole

35,38,39 laser beam

36.37 island (insulating material)

40.50 laminate layer

41, 42 metallization

43.44 structure (etched) d1, d2 thickness (conductor layer)

D1 diameter (through hole)

100 multi-layer circuit board

Claims

PATENT CLAIMS

1. A method for producing a multilayer printed circuit board (100) which has a plurality of conductor layers (12, 18, 24, 32; 42 or 13, 19) which are arranged one above the other and are separated from one another by insulating layers (16, 28 or 17, 29), 25, 31, 41), the conductor layers (12, 18, 24, 32; 42 or 13, 19, 25, 31, 41) through plated-through holes (22, 34 or 21, 33) arranged one above the other in an axis in the respective insulating layers (16, 28 and 17, 29) are conductively connected to one another, characterized in that

(a) a first laminate layer (20 or 30) on a flat laminate core (10) provided with a first conductor layer (12 or 13), which first layer (20 or 30) is applied to a first insulating layer (16 or 17) 19) is laminated on,

(b) first via openings (22 and 21) are introduced into the first insulating layer (16 and 17) at predetermined points by means of a laser beam (39, 23) through the second conductor layer (18 and, 19), respectively, in such a way that the first conductor layer (12 or 13) is freely accessible from above through the first plated-through holes (22 or 21),

(c) the first conductor layer (12 or 13) is conductively connected to the second conductor layer (18 or 19) through the first plated-through holes (22 or 21) by a first metallization (24 or 25),

(d) a second laminate layer (40 or 50), which comprises a third conductor layer (32 or 31) applied to a second insulating layer (28 or 29), is laminated onto the first laminate layer (20 or 30),

(e) via the first via openings (22 or 21) by means of a laser beam (35, 38) through the third conductor layer (32 or 31) second via openings (34 or 33) into the second insulating layer (28 or 29) are introduced in such a way that the second conductor layer (18 or 19) is freely accessible from above through the second plated-through holes (34 or 33), and (f) through a second metallization (42 or 41) the first and second conductor layers (12, 18 or 13, 19) with the third conductor layer (32 or 31) through the second plated-through holes (34 or 33) is connected.

2. The method according to claim 1, characterized in that the laminate core (10) comprises a third insulating layer (11) provided on both sides with first conductor layers (12, 13), and that on both sides of the laminate core first and second laminate layers (20, 40 and 30, 50) are applied and plated through.

3. The method according to any one of claims 1 and 2, characterized in that the introduction of the plated-through holes (22, 34 or 21, 33) into the respective insulating layers (16, 28 or 17, 29) by means of the laser beams (23, 35 , 38, 39) takes place in two steps, in a first step with a first laser beam (39, 35) of a first power the conductor layer lying above the insulating layer and part of the underlying insulating layer of the respective laminate layer is removed, and in a second step the remaining part of the insulating layer is removed with a second laser beam (23, 38) of a second, reduced power compared to the first.

4. The method according to claim 3, characterized in that the ratio of the first power to the reduced second power is about 3: 1.

5. The method according to any one of claims 3 and 4, characterized in that the conductor layers (18, 32 or 19, 31) applied with the laminate layers (20, 40 or 30, 50) in each case before the introduction of the via openings (22, 34 or 21, 33) are reduced in their thickness (d1) (d2), and after the introduction of the plated-through holes (22, 34 or 21, 33) by the metallizations (24, 42 or 25, 41) are reinforced again.

6. The method according to claim 5, characterized in that the thickness reduction of the conductor layers (18, 32 or 19, 31) is carried out by etching over the entire surface.

7. The method according to any one of claims 5 and 6, characterized in that the conductor layers (18, 32 or 19, 31) of the laminate layers (20, 40 or 30, 50) first a thickness (d1) of 10-20 microns , preferably 12 or 18 μm, and that they are removed for the laser drilling of the plated-through holes (22, 34 or 21, 33) to a thickness (d2) of approximately 6-7 μm.

8. The method according to any one of claims 1 to 7, characterized in that the plated-through holes (22, 34 or 21, 33) have a diameter (D1) of 50-150 μm.

9. The method according to any one of claims 1 to 8, characterized in that as laminate layers (20, 40 or 30, 50) Cu foils as conductor layers (18, 32 or 19, 31) with an epoxy resin layer as an insulating layer 16, 28th or 17, 29) can be used.

10. The method according to claim 9, characterized in that the laminate layers (20, 40 and 30, 50) each have an initial thickness of about 70-100 microns.

11. The method according to any one of claims 5 and 6, characterized in that a structuring of the conductor layers (18, 32 or 19, 31) takes place only after the reinforcement by the metallization (24, 42 or 25, 41).