JPH0358497A - Manufacture of multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To prevent voids from remaining in resin of a clearance hole by employing a conductor foil provided with an air flowing groove communicating with the hole. CONSTITUTION:A copper foil is formed on a base material 11, air flowing grooves 13 are formed in communication with clearance holes 12 on the surface, and the grooves 13 are extended to the end of the foil 10. A plurality of such materials 11 formed with the foil 10 formed with the grooves 13 on the surface and another base material are laminated through a prepreg (adhesive sheet) 14, and thermally press-adhered. In this case, when the boards 11 are thermally press-adhered, the airs in the holes 12 are escaped externally through the grooves 13. Thus, it can prevent voids from remaining in the resins of the holes.

Description

[Detailed Description of the Invention] [Summary] Regarding a multilayer printed wiring board in which a base material with a relatively thick conductive foil provided on the surface is laminated in multiple layers, voids occur in the clearance holes provided in the conductive foil during thermocompression bonding. (
In order to eliminate air bubbles and prevent cracks, conductive foil with air circulation grooves that communicate with the clearance holes is used, or the base material has air circulation holes that communicate with the clearance holes. Either a metal mold with a protrusion placed on the opposite side corresponding to the clearance hole is used for crimping, or a conductive foil whose edge portion forming the clearance hole has a sloped cross section is used.

[Industrial application field]

The present invention relates to a multilayer printed wiring board in which a base material having a relatively thick conductor layer on its surface is formed into multiple layers.

In recent years, large combinations have been required to operate at increasingly high speeds, and in order to meet this demand, multilayer printed wiring boards, especially i4i11!, used for arithmetic circuits, etc. The copper foil for the IT and ground layers must have a large capacity, for example, a thickness of 70 μm or more. When the thickness of the copper bar becomes thick in this way, voids are likely to be formed in the clearance holes provided there during thermocompression bonding, and moreover, large stress is generated and cracks are likely to occur. Therefore, it is necessary to eliminate voids in the clearance holes and prevent cracks during manufacture of multilayer printed wiring boards using such relatively thick sti.

[Conventional technology]

A multi-shouldered printed wiring board consists of a plurality of base materials each having a copper foil wiring pattern (IJI) on the surface and a copper foil (III source layer, ground layer) formed almost all over the surface, and a pre-reg (IJI) layer between them.
via appetizer sheet)! aWJt, which is naturally pressed together and through-holes are formed in predetermined portions. Here, the thickness of the copper foil for the power supply layer and the ground layer is 70 μm or more, which is more than twice that of the copper foil for the signal layer. Especially in the through-hole area, a clearance hole is provided in the copper foil to make the through-hole. There is a part that prevents electrical continuity with the copper.

In the conventional manufacturing method, as shown in FIG. 5(A), a base material 3 is formed with a copper foil 2 for an electric layer or a ground layer having a clearance hole 1 on the surface, and a copper foil pattern for a signal layer is formed on the surface. As shown in the figure (B), the formed base material (not shown) is layered with a plurality of M4 sheets with prepregs 4 interposed therebetween, and these are thermocompression bonded as shown in the figure (C). After thermocompression bonding,
A hole 6 having a smaller diameter than the clearance hole 1 is bored in the base material 3 exposed in the clearance hole 1, and a through hole (copper) is formed here.

[Problem to be solved by the invention]

When thermocompression bonding the base material 3 through the prepreg 4, especially II
If a is thick, the resin of prepreg 4 may not reach the corners of the clearance hole, so the thermocompression bonding device is evacuated to release the air in clearance hole 1, but in reality this is insufficient. In the clearance hole 1, the melted prepreg 4 is
Void 5 remains inside. In particular, there is no difference between the diameter of clearance hole 1 and the diameter of the through hole.
If the portion 1m is small, sparks may occur at the void 5, causing a problem that may cause malfunction.

In addition, since the thickness of the copper foil 2 is relatively thick at 70 μdays or more, the bending becomes large when the buripreg 4 enters the clearance hole 1 during thermocompression bonding, and stress is applied to the copper foil ridge 1a forming the clearance part 1. There was a problem in that the resin in this area was concentrated and cracked, resulting in a short service life.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a multilayer printed wiring board that can eliminate voids in clearance holes provided in a conductor cage and prevent cracks during thermocompression bonding.

[Means to solve the problem]

The above problem can be solved by using a conductor foil with air circulation grooves that communicate with the clearance hole, or by using a base material with air circulation holes that communicate with the clearance hole, or by using a conductor foil that has air circulation holes that communicate with the clearance hole. Solved by a method for producing a multilayer printed wiring board characterized by pressing using a mold with a protrusion in the groove or using a conductor foil with a clearance hole consisting of circular parts of different diameters. It will be done. ．． (Function) If the conductor foil is thick, it is difficult for the melted resin of the adhesive sheet to penetrate into the corners of the clearance hole during thermocompression bonding, and voids are likely to occur in the resin. However, if the conductor foil is provided with an air circulation groove that communicates with the clearance hole, or the base material is provided with an air circulation hole that communicates with the clearance hole, then during thermo-compression bonding, the air in the clearance hole will not be filled up or Since the resin is released through the resin to the outside, no voids remain in the resin.

In addition, if thermocompression bonding is performed using a mold with a protrusion at a position corresponding to the clearance hole, the base material of the clearance hole will bend slightly in the compression direction, allowing the resin to penetrate into the corners of the clearance hole, thereby eliminating voids in the resin. Extruded. Moreover, since the base material is slightly bent during thermocompression bonding, the amount of resin that enters the clearance hole is reduced, and the rate of cracks is reduced.

Furthermore, if you use a conductor foil with a clearance hole made of stacked circular parts with different diameters, even if the conductor foil is thick, the adhesive sheet will not bend when it enters the clearance hole during thermocompression bonding. becomes smaller, and the stress is distributed to the ridges of the two circular parts of the clearance hole, so that no cracks occur in these parts. Furthermore, upon heating (1'), even if the conductor foil is thick, the resin can sufficiently penetrate deep into the clearance hole, reducing the occurrence of voids.

〔Example〕

FIG. 1 shows a diagram illustrating a first embodiment of the present invention. In the same figure (A>, 10 is a copper foil (conductor foil), which is formed on a base material 11, and air circulation grooves 13 are formed on the surface of the copper foil, which communicates with the clearance holes 12. 13 extends to the end of the copper foil 10. A base material 11 on which the copper foil 10 with such grooves 13 is formed, and another base material (not shown) are shown in the same figure. As shown in (B), multiple pre-regs (adhesive sheets) 14 are interposed between them!i141
m and heat-press them as shown in the same figure (C).

After thermocompression bonding, a hole 15 smaller than the clearance hole 12 and having a diameter of 0 is bored in the base material 11 exposed in the clearance hole 12 to form a through hole. When forming the fill hole 13 and the clearance hole 12 in copper II 10, a mask for W413 is formed on the base material on which the copper foil has not been formed, and the base material is moved at high speed and etched with an etching solution sprayed at low pressure. A groove 13 is formed in the portion. Subsequently, a mask for the clearance hole 12 is formed in this base material, and the clearance hole 12 is formed so that the base material 11 is exposed by an etching solution that is sprayed at high pressure while moving the base material at a low speed.

In this way, since the grooves 13 were formed on the surface of the copper foil 10,
When the base material 11 is heat-pressed, the air in the clearance hole 12 is released to the outside through the groove 13 (at this time, the heat-press bonding apparatus is kept in a vacuum as in the conventional example). As a result, no voids remain in the 1jAti of the melted Bripreg 14 in the clearance hole 12,
Therefore, no sparks are generated.

Note that the groove 13 does not extend to the end of the copper foil 10;
A similar effect can be produced even if the length is about several shoes from the clearance hole 12.

FIG. 2 shows a diagram illustrating a second embodiment of the present invention. In the same figure (A), 20 is a base material, and the copper foil (
Air circulation holes 23 are formed in the surface exposed by the clearance holes 22 of the conductive foil 21. As shown in FIG. 8 (8), a plurality of such base materials 20 and a base material 25 on which another copper foil 24 is formed are stacked together with a prepreg (adhesive sheet) 26 interposed therebetween and bonded by thermocompression. .

As described above, since the holes 23 communicating with the clearance holes 22 are formed in the base material 20, when the base material 20 is bonded by thermocompression, the air in the clearance holes 22 escapes to the outside through the holes 23. Similar to the first embodiment, no voids remain within the clearance hole 22. In addition, in the case of a type in which copper foil is formed on both sides of the base material 20, when the holes 23 are formed in the base material 20, the holes may also be formed in the copper strip.

FIG. 3 shows a diagram illustrating a third embodiment of the present invention. As shown in the same figure (A), a conductor foil (for example, 17
Two base materials 33 each having a thickness of 5μ thick) 31 on the front side and a copper foil 32 of the copper foil layer on the back side are bonded together by thermocompression via a Bripreg (adhesive sheet) 34, and these are bonded together, for example, with one intermediate layer. Used as a base material, a plurality of these are further laminated with prepreg interposed between them. Clearance hole 30 for thermocompression bonding
Using a mold 35 having a protrusion 35a at a position corresponding to
The protrusion 35a is opposed to the clearance hole 30.

As shown in <8> of the same figure, the portion of the base material 33 exposed in the clearance hole 30 is slightly bent toward the center (in the crimp direction) due to the pushing by the protrusion 35a during thermocompression bonding.
As a result, the resin of the buripreg 34 penetrates into the corners of the clearance hole 30, and voids in the resin are easily pushed out. In addition, since the base material 33 is slightly bent within the clearance hole 30, the amount of resin that enters the clearance hole 30 is reduced compared to the conventional example, and this reduces the rate of cracks (the more the resin hangs, the more , the proportion of cracks will increase). After thermocompression bonding, a hole 36 having a smaller diameter than the clearance hole 30 is bored to form a through hole.

FIG. 4 shows a diagram illustrating a fourth embodiment of the present invention. As shown in FIG.
Further, an etching resist 42 having a diameter larger than the original clearance hole is formed on the surface of the copper foil 41, and the surface of the copper foil 41 is shallowly etched to form a circular portion 44. Next, as shown in FIG. 4B, an etching resist 4 with the same diameter as the original clearance hole is formed on the surface of the copper foil 41.
3 is formed and the copper foil 41 is etched so that the base material 40 is exposed to form a circular portion 45. Next, when the etching resist 43 is removed, a clearance hole 46 consisting of a circular portion 45 and a circular portion 44 having a larger diameter than the circular portion 45 with approximately the same center as the circular portion 45 is formed above the circular portion 45, as shown in FIG. The provided copper foil 41 is completed. Next, the same figure (
The material shown in C) is thermo-compressed with a plurality of sheets of prepreg (separate sheet) of mm+,., in between, and after the crimping, a hole 47 with a diameter smaller than the circular part 45 is bored to form a through-hole here. do.

As shown in FIG. 4(C), the clearance hole 46 formed in the TJ4 foil 41 has a circular portion 44.45 and an inclined portion 44.
a is formed, even if the copper foil 41 is thick, the pre-reg (not shown) will close the clearance hole 4 during thermocompression bonding.
The deflection when entering 6 is smaller than the conventional example, therefore,
Stress is not concentrated on one copper foil ridge of the clearance hole as in the conventional example, but is dispersed on the inclined portion 44a. This prevents cracks from occurring in the resin in this area, making it possible to extend the service life. In addition, since the clearance hole 46 is inclined, the resin of the prepreg can sufficiently penetrate into the deep part of the clearance hole 46 (the corner of the circular part 45) during thermocompression bonding compared to the conventional example, thereby eliminating voids. 1. In the above embodiments, a copper clad plate was used to display the copper foil on the base plate, but in the first, third and fourth embodiments, excluding the second embodiment, the base material was It is also possible to use only copper foil.

〔Effect of the invention〕

As explained above, according to the present invention, since air circulation grooves or air circulation holes are provided in the conductor foil or the base material in communication with the clearance holes, the air in the clearance holes is removed during thermocompression bonding. It can escape to the outside and no voids remain in the resin in the clearance hole. In addition, since thermocompression bonding is carried out using a mold that has a protrusion at a position corresponding to the clearance hole, the protrusion can push out voids in the resin in the clearance hole, and the wood inside the clearance hole can be Since the amount is reduced, cracks can be prevented. Furthermore, since we use a conductor foil with a clearance hole made of stacked circular parts with different diameters, the bending of the adhesive sheet when it enters the clearance hole during thermocompression bonding is reduced even without the conductor foil. Stress is dispersed to the ridge, preventing cracks from occurring in this area, and even if the conductor foil is thick, the resin can penetrate deep into the clearance hole, reducing the occurrence of voids. .

[Brief explanation of drawings]

1 to 4 are diagrams for explaining the first to fourth embodiments of the present invention, respectively, and FIG. 5 is a diagram for explaining a conventional example. In the figure, 10, 21, 24, 31, 32, 41 are copper foils (conductor foils)
, 11, 20.25, 33.40 is the base material, 12.22.3
0.46 is a clearance hole, 13 is an air circulation groove, 14.26.34 is a pre-reg (adhesive sheet), 23 is an air circulation hole, 35 is a mold, 35a is a protrusion, 42, 43 is an etching resist, 44, 45 indicates a circular portion.

Claims (4)

[Claims] (1) Conductor foil (1) with clearance hole (12)
0) through an adhesive sheet (14) to form a multilayer structure, and then a through hole is formed in the clearance hole. (
12) A method for manufacturing a multilayer printed wiring board, characterized in that a multilayer printed wiring board is provided with an air circulation groove (13) communicating with the board. (2) Conductor foil (2) with clearance hole (22)
1) is a method for manufacturing a multilayer printed wiring board, in which a substrate formed on the surface of a base material (20) is bonded by thermocompression via an adhesive sheet (26) to form a multilayer structure, and then through holes are formed in the clearance holes. , As the base material (20), the clearance hole (2
2) A method for producing a multilayer printed wiring board, characterized in that a board is provided with air circulation holes (23) communicating with the base material (20) and extending to the outside of the base material (20). (3) Conductor foil (3) with clearance hole (30)
1) to form a multilayer structure by thermocompression bonding via an adhesive sheet (34), and then forming a through hole in the clearance hole. Using a mold (35) having a protrusion (35a), the protrusion (35a) is
A method for producing a multilayer printed wiring board, characterized in that a) is thermocompression bonded with the material facing the clearance hole (30). (4) Conductor foil (4) with clearance hole (46)
1) to form a multilayer structure by thermocompression bonding via an adhesive sheet, and then forming through holes in the clearance holes, the clearance hole (46) of the conductor foil (41)
1. A method for manufacturing a multilayer printed wiring board, characterized in that the cross section of the edge portion forming the board is sloped.