JPH10321977A - Multilayer printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a interlayer connection element superior in connection reliability even in the case of a high aspect ratio by forming a via having a major and minor axes in plan view for electrically connecting between conductors partitioned by an insulation layer. SOLUTION: A via having a minor and major axes 12, 13 is formed by a laser or a drill and pref. moving it during boring of the via, thus forming an elongated circular hole. The major axis 13 is pref. longer than the distance between conductors to be connected; if not longer, the connection reliability will deteriorate. If it is an elongated circular hole of 0.1 mm×0.3 mm, a conductive resin cam be filled enough. This is effective for the case of the connection reliability reduced owing to the increase of the aspect ratio. In application to a multilayer printed board having vias at a high density, interlayer connection electrodes can be independently mounted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a multilayer printed wiring board.

[0002]

2. Description of the Related Art Generally, a via hole is formed by a step of removing an insulating material between conductors and a step of forming a conductor at a position where the insulating material is removed. Methods for removing the insulating material include chemical removal (etching) using a chemical solution, thermal and physical removal (ablation) using plasma or laser, and mechanical removal using a drill. The method for forming a conductor is plating. And deposition of metal by vapor deposition, filling and curing of conductive resin liquid (ink).

In recent years, there has been a high demand for portable devices such as cellular phones and hand-held personal computers, and the size of electronic devices has been reduced, so that the sizes of various electronic components used in the devices have been increasingly reduced. By the way, a multilayer printed wiring board is provided with a via hole for connecting between conductors separated by an insulating layer, but the multilayer printed wiring board is also required to be downsized. You have to do it.

[0004]

In order to reduce the size of a via hole, as the aspect ratio of the via hole (the ratio of the depth of the hole to the diameter of the hole) increases, the connection reliability of the via hole significantly decreases. There are issues. That is, as the aspect ratio increases, the portion where the insulating material has been removed due to the surface tension or viscosity of an etching solution for removing the insulating material, a plating solution for forming a conductor, or a liquid such as a conductive resin solution. As the opening area of the hole becomes smaller, penetration into the inside and flow and diffusion in the removed portion are less likely to occur, and a defective portion such as a void is formed in the formed via hole, and as a result, connection reliability is reduced.

An object of the present invention is to provide a multilayer printed wiring board having via holes having excellent connection reliability.

[0006]

According to the multilayer printed wiring board of the present invention, the planar shape of the via hole for electrically connecting the conductors separated by the insulating layer is as shown in FIG.
It has a shape having a short axis 12 and a long axis 13.

As a result of intensive studies, the present inventors have found that the length of the long axis is preferably longer than the distance between the conductors to be connected.
It has been found that if the distance between the connecting conductors is the same or shorter, the connection reliability is not sufficient.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A shape having a short axis and a long axis is shown in FIG.
As shown in FIG. 5, there are ellipses and ellipses, but the ellipses are preferred from the viewpoint of ease of processing. The via hole forming method of the present invention can be performed by laser or drilling, and only needs to add an operation of moving a normal hole in one direction while drilling.

As a method of forming a conductor in a via hole, an ordinary method of forming a conductor in a via hole can be used. In the shape of the present invention, a small via hole is filled with a conductive resin. Conventionally, the conductive resin could not be filled sufficiently with a hole diameter of about 0.1 mm, but it could be filled sufficiently with a 0.1 mm × 0.3 mm ellipse, and the connection reliability was low. The nature is also high. As a method for filling the conductive resin, a screen method, a curtain coating method, a dipping method, or the like can be used. The conductive resin is a resin containing conductive particles, and the resin preferably has the same characteristics as the resin forming the insulating layer of the multilayer printed board, such as an epoxy resin and a polyimide resin. Is preferred. As the conductive particles, metal particles or resin particles whose surfaces are coated with a metal thin film can be used.

[0010] The multilayer printed board has a number of layers, a kind of insulating material,
It does not specify the specifications of the wiring pattern and the like, and may mount an arbitrary circuit. The material of the conductor layer may be arbitrary. As the insulating material, a resin generally available for a multilayer printed board can be used. Epoxy resin, polyimide resin,
BT (bismaleimide triazine) resin, phenol resin and the like are preferable. These insulating materials have electrical properties such as permittivity and dielectric tangent, thermal conductivity, thermal properties such as heat capacity,
Alternatively, it may contain various additives and reinforcing materials for controlling various properties such as bending properties and mechanical properties such as a coefficient of thermal expansion. Further, the type of the insulating material and the types of the additives and the reinforcing materials contained therein can be set for each layer.

[0011]

FIG. 3 (g) shows an embodiment of the present invention, in which 9 μm of base copper +
μm + 15 μm solder plating on both sides, insulation layer 1a
100 µm thick epoxy adhesive film AS-
3000 (trade name, manufactured by Hitachi Chemical Co., Ltd.), 18 μm of base copper + 40 μm of plated copper as an inner conductor layer 2 a inside thereof, and 0.2 m thick as an insulating layer 1 b inside thereof
m, two layers of glass cloth epoxy resin prepreg are provided, a wire wiring layer 3 formed therebetween is provided, and an inner conductor layer 2b is formed on the inside of the two layers of prepreg as base copper 35 μm;
A glass cloth epoxy prepreg having a thickness of 0.4 mm as an inner insulating layer 1c on the inside thereof, and an inner conductor layer 2b on the inner side thereof.
35 μm of copper, and two layers of a glass cloth epoxy prepreg having a thickness of 0.2 mm as an insulating layer 1 b are further provided inside, and a wire wiring layer 3 formed therebetween is provided, and an inner conductor layer is provided inside the two layers of prepreg. Copper 35 μm as 2b
Inside, a 0.6 mm thick glass cloth epoxy prepreg as an inner insulating layer 1d, 35 μm copper as an inner conductive layer 2b inside thereof, and 0.8 mm thick glass as a core insulating layer 1e inside thereof. An epoxy insulating layer is provided, the thicknesses of the core insulating layer are centered on the core insulating layer, and an interstitial via hole (hereinafter, referred to as IVH) connecting the surface conductor layer 2c and the inner conductor layer 2a is formed as a via hole. 4) a multi-wire wiring board having a thickness of about 5 mm (a product of Hitachi Chemical Co., Ltd.) having a through hole 5 penetrating all between the inner conductor layer 2b and the wiring layer, and an insulating layer for insulating the above conductor layers. (Product name). The wire wiring layer 3 was formed of a copper wire 7 having a diameter of 0.1 mm and coated with an insulating material, using 0HAW-1IMW (trade name, manufactured by Hitachi Cable, Ltd.). The method of manufacturing this multilayer printed wiring board is a method of manufacturing an ordinary multilayer printed wiring board.
MCL-E- which is a double-sided copper-clad laminate made of copper foil
Unnecessary portions of copper foil on both sides of 67 (trade name, manufactured by Hitachi Chemical Co., Ltd.) are etched and removed to form an inner-layer wiring board, and a 0.6 mm thick glass cloth epoxy prepreg and 35 μm copper foil are provided on both sides. 2.5MPa, 180
Laminate and unify by heating and pressurizing at 60 ° C for 60 minutes to form a laminated board. Unnecessary portions of copper foil on the laminated board are removed by etching, and an underlay made of glass cloth epoxy resin is laminated, and insulation is performed on it. The coated electric wire was bonded and fixed by a numerically controlled wiring machine, an overlay made of glass cloth epoxy resin was overlaid thereon, and a copper foil of 35 μm was further overlaid thereon, and 2 MPa, 180
The laminate was integrated by heating and pressing at 60 ° C. for 60 minutes, unnecessary portions of the copper foil were removed by etching, and a thickness of 0.1 mm was formed thereon.
A 4 mm glass cloth epoxy prepreg and a 35 μm copper foil are superimposed and laminated under heat and pressure under the conditions of 2 MPa, 180 ° C., and 60 minutes, and unnecessary portions of the copper foil are removed by etching. An underlay was laminated, an insulated wire was bonded and fixed on the underlay with a numerical control wiring machine, a glass cloth epoxy resin overlay was further laminated thereon, and an 18 μm copper foil was further laminated thereon.
Laminate and unify by heating and pressing at 80 ° C for 60 minutes, make a hole to be a through hole 5, and apply electroless plating to a thickness of 40
μm, an unnecessary portion of the copper foil and plated copper is removed by etching, and AS-3000 (trade name, manufactured by Hitachi Chemical Co., Ltd.) which is an epoxy adhesive film having a thickness of 100 μm, and 9 μm An ultra-thin copper foil with a 9 μm carrier (trade name, manufactured by Furukawa Electric Co., Ltd.) obtained by releasing a 70 μm copper foil onto a copper foil and laminating the same is superimposed on 2 MPa, 18
The carrier was mechanically peeled off by heating and pressing under the conditions of 0 ° C. and 60 minutes, the carrier was mechanically peeled off, and a dry film 6 for etching resist was laminated thereon, and exposed and developed through a photomask. An etching resist 8 is formed, and the short axis 0.0 is used so that a 9 μm copper foil serves as a mask for etching an insulating material when forming a via hole.
An opening 9 is formed by etching the copper foil into an elliptical shape of 5 mm and a major axis of 0.15 mm, and a laser is output from above the opening 9 with a laser output of 20.5 kV, 6 shots, and an aperture diameter of 0.3 mm. And then electroless plating is performed to deposit to a thickness of 12 μm.
Is formed, solder plating is performed on the shape of the etching resist, the plating resist 10 is peeled off and removed, and the copper exposed during the solder plating is removed by etching.
The solder was fused under the condition of 0 second to obtain a 16-layer multi-wire wiring board. There is no defect such as void in the inner wall conductor of IVH4, and thermal shock test (MIL-STD-202, m
For method 107), the resistance increase rate was less than 10% at 200 cycles. In the through hole 5, the insulating layer was removed by a drill, and the inner wall conductor was formed by copper plating. The cross-sectional shape in the layer direction is a circle having a diameter of 0.4 mm. The inside was filled with resin.

The via hole of the present invention can be applied to any component having a plurality of conductor layers. This is effective when the decrease in connection reliability due to the increase in the aspect ratio becomes a problem. Especially when applied to a multilayer printed board in which via holes are densely arranged, the effect is remarkable. The interlayer connection elements can be installed independently of each other. The cross-sectional shape and the like may be designed as needed. In this example, the present invention was applied only to IVH4, which required miniaturization of the size. The cross-sectional shape in the plane direction was an ellipse having a short axis and a long axis, and the long axis length was 0.15 mm.

[0013]

As described above, according to the present invention, it is possible to provide an interlayer connection element having excellent connection reliability even in a high aspect ratio. Further, according to the multilayer printed board of the present invention, even when the terminal density is high and the arrangement density of the interlayer connection elements is high, it is possible to eliminate a decrease in connection reliability.

[Brief description of the drawings]

FIG. 1 is a top view for explaining a configuration of the present invention.

FIG. 2 is a top view showing one embodiment of the present invention.

FIGS. 3 (a) to 3 (g) are cross-sectional views in respective steps for explaining a manufacturing method according to one embodiment of the present invention, and FIGS. 3 (b) to 3 (f) are cross-sectional views of a main part. is there.

[Explanation of symbols]

 1a. Adhesive sheet 1b. Glass cloth epoxy resin prepreg 1c. Prepreg 1d. Prepreg 1e. Core insulating layer 2c. Surface conductor layer 2a. Inner conductor layer 2b. 2. inner conductor layer Wire wiring layer 4. IVH5. Through hole 6. 6. Dry film for etching resist Copper wire 8. Etching resist 9. Opening 10. Plating resist 12. Short axis 13. Long axis

Claims (4)

[Claims] 1. A multilayer printed wiring board, wherein a planar shape of a via hole for electrically connecting conductors separated by an insulating layer is a shape having a short axis and a long axis. 2. The multilayer printed wiring board according to claim 1, wherein the length of the major axis is longer than the distance between the conductors to be connected. 3. The multilayer printed wiring board according to claim 1, wherein the shape having a short axis and a long axis is an ellipse. 4. The multilayer printed wiring board according to claim 1, wherein the via hole is filled with a conductive resin.