JP2002009440A - Composite wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high density multi-layered composite wiring board at a low cost in high yield. SOLUTION: The composite wiring board is constituted by putting a hard printed wiring board 7 which has a wiring part 8 on one surface and a flexible substrate 1 which has wire parts 2 on both surfaces and a hole 3 penetrating the substrate from the wire part on one surface to that on the other surface one over the other in one body across an adhesive sheet 4. The adhesive sheet 4 has a conductive via hole 5 formed by charging conductive resin paste in a through hole bored in the sheet and a conductive bump 6 formed of conductive resin paste on the top surface of the sheet or on the via hole, and the wire parts of the flexible substrate 1 and hard printed board 7 or the wire parts 2 on both surfaces of the flexible substrate 1 are electrically connected together through the conductive via hole 5 or bump 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite wiring comprising a printed wiring board, in particular, a rigid printed wiring board and a flexible wiring board, which are integrated by pasting together and electrically connecting wiring portions provided on both boards. Regarding the substrate.

[0002]

2. Description of the Related Art In recent years, the number of I / O terminals of semiconductor devices or semiconductor packages has been increasing more and more with the degree of integration, and the number of such devices exceeds 1000, for example. In order to accommodate this in the smallest possible package area, there is a tendency to shift from conventional peripheral arrangement to grid arrangement. A printed wiring board on which these semiconductor elements or semiconductor packages are mounted has a very high density, such as a wiring width and a wiring interval of 50 μm or less, respectively, for arranging I / O pads and lead wires for connection. High-definition arrangement rules are required.

[0003] As a conventional multi-layering technique, for example, a plurality of superposed substrates are mechanically integrated by pressurizing and heating via an insulating layer called a prepreg, which is a so-called plating method of punching and plating. It is general to form an electrical junction between the layers by a through-hole method. However, the wiring width and the wiring interval of this technology are each about 100 μm minimum, and furthermore, the layout area of the through-hole and the through-hole It has become impossible to respond to the increase in density due to the routing of wiring to avoid the problem.

[0004] Build-up boards have come into widespread use as wiring boards that meet such fine disposition rules. The build-up board is a board formed by sequentially stacking a thin insulating resin layer and a wiring layer with a double-sided printed board as a core. The insulating resin layer is coated with a photosensitive insulating material or laminated in the form of a sheet. Next, by applying a photomask and irradiating with ultraviolet rays and developing, a hole is formed only in the portion of the conduction hole. Next, the surface of the insulating resin layer is made of, for example, CrO ₃
And a solution containing H ₂ SO ₄ to chemically roughen the surface. Next, a required wiring pattern is formed by using electroless plating or a combination of electroless plating and electroplating. With this process as one unit, the required number of layers is sequentially repeated to form a multilayer.

However, the current minimum wiring width and wiring interval of the build-up board is about 40 μm. This is because, since the insulating resin layer and the wiring layer are sequentially stacked, it is difficult to form a finer pattern than this due to the unevenness of the lower wiring pattern. There is a method in which the resin layer is thickly coated and polished after curing. However, it is difficult to form small-diameter via holes, which hinders high density. In addition, there is a problem that the polishing process increases the cost. Therefore, it is difficult for build-up boards to comply with very fine arrangement rules. Further, when the wiring density is high, it is difficult to form a required circuit pattern with high accuracy over the entire surface of a large-sized substrate. However, the wiring substrate cannot be used as a product if there is any defective portion. As described above, it is difficult and expensive to achieve high yields due to the sequential manufacturing method.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art,
It is an object of the present invention to provide a high-density multilayer composite wiring board with high yield and low cost.

[0007]

In order to achieve the above object, a composite wiring board according to the present invention has a hard printed wiring board having a wiring portion on at least one side and a wiring portion on both sides and has a wiring portion on one side. A composite wiring board obtained by integrally polymerizing a flexible substrate having a hole reaching the wiring portion on the other surface via an adhesive sheet, wherein the adhesive sheet has a through hole formed in the sheet. A conductive via formed by filling the hole with a conductive adhesive, and a bump formed of a conductive adhesive on the surface of the sheet or on the via, and between the wiring portion of the flexible substrate and the hard printed board or The wiring portions on both sides of the flexible substrate are electrically connected via the conductive vias or bumps.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on illustrated embodiments. FIGS. 1A and 1B are diagrams showing respective constituent elements of a composite wiring board according to the present invention, wherein FIG. 1A is a cross-sectional view of a flexible substrate, and FIG. 1B is a view of an insulating resin adhesive sheet formed with vias and bumps made of a conductive resin. Sectional view,
(C) is a cross-sectional view of the rigid printed circuit board.

Although the conventional method can be used for forming the wiring of the flexible substrate, according to the present invention, the step of connecting the double-sided wiring becomes unnecessary. Hereinafter, an example of the wiring forming method will be described. First, a substrate material such as a polyimide film having copper foils formed on both sides is prepared. Then, after applying a photosensitive resin or laminating a photosensitive dry film on both surfaces, a photomask is applied and ultraviolet rays are irradiated to develop.
A pattern is formed on the photomask so that the copper foil on the via portion on one side is etched along with the region other than the wiring portion on both surfaces. After etching both sides of copper foil at the same time,
A hole (non-through hole) is formed by irradiating a laser beam from the copper foil opening at the via position to the copper foil on the opposite side. Next, the remaining photosensitive resin is peeled off to complete a flexible substrate having two layers of wirings (see FIG. 1A). Apart from this method, the copper foil on one side is etched only in the via part,
There is also a method in which the polyimide is chemically etched using the remaining copper foil as a resist to form the non-through holes, and then the wiring is formed by a photoetching process in the same manner as described above. The thinner the insulating layer of the flexible substrate is, the smaller the hole can be processed. For example, if the thickness is 25 to 75 μm, a micro via having a diameter of 40 to 100 μm can be formed. However, since an inorganic material such as glass fiber is difficult to be laser-processed or chemically etched, it is preferable to use an insulating layer that does not use an inorganic fiber. The material of the insulating layer can be selected from at least one of the group consisting of a polyamide film, a polyester film, a polytetrafluoroethylene (PTFE) film, and a polyphenylene sulfide film in addition to the polyimide film.

When a wiring pattern is formed on a flexible tape, there are no irregularities, so that fine wiring can be formed. Moreover, if the tape is a reel-to-reel, it can be processed continuously, so that inexpensive wiring can be formed. To make the wiring finer, the copper foil may be made thinner. For example, when the wiring layer is formed using a copper foil having a thickness of about 15 to 18 μm, the wiring width / interval can be set to about 25 μm. Further, when the thickness of the copper foil is about 10 μm, the wiring width / interval can be made about 20 μm each.

As the insulating resin adhesive sheet, a commercially available epoxy-modified polyimide, epoxy-based, acrylic-based, or poimide-based thermoplastic resin or thermosetting resin sheet can be used, and is used to adjust the coefficient of thermal expansion and thermal conductivity. May contain an inorganic filler such as silica powder. In order to dispose the two wiring boards facing each other via the insulating resin adhesive sheet and absorb the unevenness of the wiring of both substrates by the resin layer, the thickness of the insulating resin adhesive sheet is the same as the thickness of the wiring of both boards. It is preferable that the total be equal to or more than the total.

A hole is formed by a technique such as punching, chemical etching, laser etching, or plasma etching, and the filling of the conductive resin into the hole and the formation of the bump are performed simultaneously (see FIG. 1B). For example, a conventional method such as a method in which a mask having the same opening as the opening pattern and the bumps of the insulating resin adhesive sheet is overlapped and a conductive resin paste is press-fitted from above the mask, a method using screen printing or a dispenser, etc. In order to improve the contact between the conductive resin and the conductor pattern of the wiring board, it is desirable that the via portion slightly protrudes from the front and back surfaces of the sheet. The conductive resin is composed of the same resin component and conductive powder as the conductive resin adhesive sheet, and a commercially available paste is easy to handle. As the conductive powder, a copper powder, a silver powder, a nickel powder, a gold powder, a solder powder, a palladium powder, or a mixture thereof is used.

The insulating resin adhesive sheet in which the vias and bumps are formed of a conductive resin and the flexible substrate on which the wiring has been formed are cut into predetermined sizes in advance, and are cut by automatic mounting by image processing or positioning by pins. They are sequentially mounted on a rigid printed circuit board and joined by heating and pressing. The heating and pressing conditions are appropriately selected depending on the type of the insulating resin adhesive sheet to be used. If further multi-layering is required, the flexible substrate and the insulating resin adhesive sheet may be stacked and heated and pressurized, and the interlayer connection is completed simply by pasting, so that a low-cost multi-layer substrate is completed.
The unevenness of the wiring is absorbed by the insulating resin adhesive sheet and becomes flat.

The rigid printed wiring board of the present invention may be an inexpensive one having a usual level of wiring density manufactured by the prior art, and is required to be rigid or rigid. A single-sided or double-sided wiring board or a multilayer substrate can be used if necessary. The need to be rigid or rigid is to mount a flexible board with high accuracy or to efficiently mount a large number of electronic components on a composite wiring board. It is good if you have. The material of the insulating base material of the hard printed wiring board is glass-epoxy, glass-bismaleimide triazine,
Used by selecting from ceramics and the like.

[0015] As the material embodiment the flexible substrate 1, was prepared Poimidotepu that adhering a copper foil having a thickness of 18μm on both surfaces in a thickness of 50 [mu] m. A 10 μm-thick dry film photoresist is stuck on both sides of this polyimide tape, a photomask is applied thereon to expose and develop, and a wiring portion 2 of the dry film photoresist remains, and a via portion 3 is formed on one surface. Was patterned so as to be etched. Next, the copper foil is etched using an aqueous solution of copper chloride to remove the minimum wiring width 30.
μm, minimum wiring interval 30 μm, via part 3 on one side
An opening having a diameter of 100 μm was formed in the substrate. Next, using a YAG fundamental wavelength laser, a hole (non-through hole) having a diameter of 70 μmφ reaching the copper foil opening in the via portion or the copper foil on the opposite surface from the polyimide surface was formed by the focusing method.

On the other hand, as a material of the adhesive sheet 4, an insulating resin adhesive sheet having a thickness of 40 μm (DF-Hitachi, manufactured by Hitachi Chemical Co., Ltd.)
400) is prepared, a through hole having a diameter of 100 μmφ is formed by punching at a predetermined position, and a conductive resin paste (T-303 manufactured by Sumitomo Metal Mining Co., Ltd.) is formed by printing.
After filling with 0) to form the conductive vias 5 and the conductive bumps 6, the paste was temporarily cured at 100 ° C. for 5 minutes. In this sheet, a reference hole for positioning was previously formed by punching.

Further, a commercially available glass epoxy board is prepared as a material of the hard printed wiring board 7, and the adhesive sheet 4 prepared as described above is made flexible by fitting the reference holes into the reference pins. Substrates 1 were sequentially laminated. Then, using a thermocompression bonding device,
Temporarily pressure-bonded at 180 ° C. and 0.5 MPa for 30 seconds, and then passed through a hot roller to remove the voids. By this process,
Wiring part 2 of flexible substrate 1 and hard printed wiring board 7
Are electrically connected via the conductive vias 5 of the adhesive sheet 4, and the wiring sections 8 of the hard printed wiring board 7 are formed of the adhesive sheet 4 fitted into the via sections 3 of the flexible substrate 1. It is electrically connected to the wiring portion 2 on the other surface of the flexible substrate 1 via the conductive bump 6.

The multilayer substrate thus obtained can achieve electrical connection of the double-sided wiring portion of the flexible substrate and interlayer connection between the flexible substrate and the necessary portion of the rigid printed circuit board simply by sticking, and at low cost. A high-density composite wiring board was obtained.

[0019]

As described above, according to the present invention, it is possible to provide a composite wiring board which can be continuously manufactured at a low cost despite its high density.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows each component body of a composite wiring board according to the present invention, (a) is a cross-sectional view of a flexible substrate, and (b) is a cross-section of an insulating resin adhesive sheet on which vias and bumps made of a conductive resin are formed. FIG. 1C is a cross-sectional view of the rigid printed circuit board.

FIG. 2 is a sectional view of a composite wiring board according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flexible board 2, 8 Wiring part (copper foil) 3 Via part 4 Adhesive sheet 5 Conductive via 6 Conductive bump 7 Rigid printed wiring board

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E317 AA21 AA24 BB02 BB03 BB11 CC25 CC53 CC60 CD32 GG14 GG16 5E346 AA22 AA35 AA43 BB01 BB16 CC09 CC10 CC32 DD02 DD32 EE02 EE06 EE07 EE12 EE44 FF18 FF24 FF28 H

Claims (1)

[Claims] 1. An adhesive sheet comprising: a rigid printed wiring board having a wiring portion on at least one surface; and a flexible substrate having a wiring portion on both surfaces and having a hole extending from one surface to the wiring portion on the other surface. Wherein the adhesive sheet comprises a conductive via formed by filling a through hole formed in the sheet with a conductive adhesive, and a surface of the sheet. Or a bump made of a conductive adhesive on the via or between the flexible substrate and the wiring portion of the hard printed board or between the wiring portions on both sides of the flexible substrate, via the conductive via or bump A composite wiring board which is electrically connected.