JPH06152139A - Multilayer wiring board and adhesive film used for it - Google Patents

Abstract

PURPOSE:To provide a multilayer wiring board that requires no cover film or plating process and can respond to thinner circuits and contribute to reducing thickness and costs. CONSTITUTION:Relating to two or more double-side wiring boards bearing a wiring pattern 2 farmed on an insulation substrate 1, an adhesive layer 6, consisting of conductive particles and bonding agent, is formed on both sides of an insulation film having through holes anywhere required, then heated and pressurized far forming laminated one body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interlayer connection structure for a multilayer wiring board.

[0002]

2. Description of the Related Art Since a multilayer wiring board can contain a signal circuit, a power supply, an earth circuit, etc., it is widely used in various electronic devices as an effective method for increasing the wiring density. A typical manufacturing method of a conventional multilayer printed wiring board is to electrically connect the wiring patterns of each layer to each other by copper plating or the like while covering the parts other than the interconnection part with a coverlay film to obtain insulation. Has been done in. In addition, as a relatively new attempt, a coverlay film, a mask film, a resist film, etc. (these are collectively referred to as a cover film hereinafter) other than the interconnection portion are covered to obtain insulation, while the interconnection portion is covered with conductive particles. It is also proposed to connect the wiring patterns of the respective layers to each other by using a material composed of a dispersed adhesive (for example, JP-A-61-49499 and JP-A-2-3659).
No. 3), and solder particles are used as the conductive particles in this case.

[0003]

In any of the above-mentioned conventional methods, since the portions other than the interconnections are covered with the cover film, when two layers of cover films are present between the opposing wiring boards to form a multilayer wiring board, it is possible to reduce the thickness. It was difficult to obtain a decrease, and this was one of the causes of the cost increase. Further, regarding the interconnection method of the wiring patterns, the method of plating with copper or the like requires a complicated plating step, and the copper plating is easily broken when the cover film is thermocompression bonded. When connecting with a material consisting of conductive particles and an adhesive, the conductive particles are uniformly dispersed throughout the bonding, so the adhesive will flow due to thermocompression bonding at the time of connection, except for the part that requires connection of the wiring pattern. However, if the conductive particles are solder, the insulating property deteriorates because the cover film is scratched because it is hard below the melting point, especially if the conductive particles are solder, and if the melting point is higher than the melting point, the adjacent wiring pattern melts and leaks. It has become impossible to cope with the progress of thinner wiring. TECHNICAL FIELD The present invention relates to a multilayer wiring board using an interlayer connection which does not require a cover film or a plating step and can cope with a fine wiring.

[0004]

SUMMARY OF THE INVENTION According to the present invention, conductive particles and an adhesive are provided on both sides of an insulating film having a through hole in a main part between two or more double-sided wiring boards each having a wiring pattern formed on an insulating substrate. A multilayer printed wiring board is formed by arranging an adhesive layer made of, and laminated and integrated by heating and pressing, and an adhesive layer made of an adhesive and conductive particles is formed on both sides of the insulating film. The present invention relates to an adhesive film having a dynamic transformation point lower than that of an insulating film.

The structure of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view illustrating an embodiment of the present invention. Reference numeral 1 denotes an insulating substrate, which is made of phenol resin, epoxy resin, polyimide, etc.
And the like, which are impregnated into a base material such as, and heated and pressurized, plastic films such as polyester and polyimide, metals such as Al and Fe, and ceramics. Wiring pattern 2 is
Although it is formed on both surfaces of the insulating substrate 1 as shown in FIG. 1, the outermost layer when a multilayer wiring board is formed may be one surface. The wiring pattern 2 may be projected from the substrate surface as shown in FIG. 1 or may be flat or concave although not shown. From the viewpoint of connection stability, it is preferable that at least one of the opposing wiring patterns projects. These wiring patterns can be formed by general means such as a tenting method, an additive method, and a transfer method. An adhesive layer may exist between the insulating substrate 1 and the wiring pattern 2.

In the interlayer connection method, between the first and second wiring boards 3 and 4 having the wiring pattern 2 which requires connection,
An adhesive layer made of conductive particles 5 and an adhesive 6 is laminated and integrated using an adhesive film 10 formed on both sides of an insulating film 8 having a through hole 7 in a main portion, and two wiring boards are attached 3-4.
And to electrically connect the wiring patterns 2-2 ′ that require these connections. The wiring pattern 2 that needs to be connected may be the entire pattern or a part of the pattern, and the connection-free wiring pattern 9 (for example, a via hole portion) may be present on the connection surface.

The adhesive film suitable for the present invention will be described. As the adhesive 6, a thermoplastic material used for a sheet or the like and a curable material by energy of heat, light, electron beam or the like can be widely applied. Curable materials are preferred because of the excellent heat resistance and moisture resistance of the multilayer wiring board. Among them, epoxy adhesives and imide adhesives have excellent adhesiveness and heat resistance due to their molecular structure, and the curing time can be set widely. Is preferred. Epoxy adhesives include, for example, high molecular weight epoxy, solid epoxy and liquid epoxy, urethane, polyester, epoxy modified with NBR, etc. as a main component, and a curing agent, catalyst, coupling agent, filler, etc. added. Is common. When these materials are high-purity products having 20 ppm or less of Na ion and Cl ion of extracted water, it is preferable that the electrolytic corrosion resistance of the multilayer wiring board is improved.

As the conductive particles 5, Au, Ag, Ni,
There are metal particles such as Cu, W, Sb, Sn and solder, carbon, etc., and these, and non-conductive glass, ceramics, polymer core materials such as plastics, etc. formed with the above-mentioned conductive layer by coating, etc. But good. Furthermore, the insulating coated particles obtained by coating the conductive particles and the insulating layer as described above, the combined use of the conductive particles and the insulating particles, and the like are also extremely useful for thinning the circuit. A heat-melting metal such as solder or a polymer core material such as plastic with a conductive layer has a thermal transformation point such as a melting point or a glass transition point. It is preferable because the contact area with the circuit is increased at the time of stacking and the reliability is improved. In this case, if at least the thermal transformation point of the core material of the conductive particles is at a low temperature due to the insulating film, the insulating film 8 of the adhesive film is not damaged by heat and pressure during lamination integration, so that the interlayer insulating property is maintained at a high level. It is preferable because it will drip. In particular, when a polymer is used as a core, it does not exhibit a melting point like solder, so that the softened state can be widely controlled at the connection temperature, and it is more preferable because it can easily cope with variations in thickness and flatness of the wiring board or wiring pattern. Further, in the case of hard metal particles such as Ni or W, the conductive particles stick to the wiring pattern, so that a low connection resistance can be obtained even in the presence of an oxide film or a contaminated layer on the wiring pattern. It is also effective in suppressing expansion and contraction by fixing, and improves reliability. Therefore, in the case of hard metal particles, the particle size is the distance between wiring patterns that require connection (thickness after connection).
It is preferable that the particle size is slightly larger than that, and if the particle size is smaller than that, it is preferable that the particles are in an agglomerated state. In principle, the number of conductive particles may be one in the portion on the wiring pattern where connection is required, but it is preferable to set it to five or more because the connection reliability is further improved. Since the grain size corresponds to thinning, it is preferable that the grain size be equal to or smaller than the distance between adjacent wiring patterns.

The insulating film 8 having the through holes 7 in the main part may be a general insulating film such as polyimide, polyethylene terephthalate, or polyethylene, and the thinnest possible film is preferable from the viewpoint of reducing the thickness of the multilayer wiring board and reducing the cost. The contact through hole 7 is formed in a portion where conductivity between layers is required, but even if an adhesive layer composed of the conductive particles 5 and the adhesive 6 is included (FIGS. 1 and 7A), only the insulating film is included without including the adhesive layer. (FIGS. 1 and 7B). The latter is preferable in terms of workability. Adhesive film 1 in through-hole 7 before lamination integration
There may be 0.

When the layers are integrated, the portions of the wiring pattern surface that require connection are aligned and heated and pressed. At this time, a so-called pin lamination method in which, for example, through holes are formed in a predetermined number of wiring boards and an adhesive film that need to be laminated and alignment is performed with pins or the like is suitable, and as a method of integration, a press or roll laminator is used. A general method such as By filling the through holes of the pin lamination method with a conductive adhesive or by through-hole plating,
It is also possible to obtain electrical connection between all layers.

FIG. 2 is a schematic cross-sectional view showing the structure of FIG. 1 after lamination and integration. By heating and pressing, the adhesive flows and the conductive particles 5 need to be connected on the wiring pattern.
Concentrating on 2'to enable electrical connection, the adhesive flows to fill and bond between the substrates 1-1 ', and the insulating film 8 maintains the interlayer insulating property. In addition, the connection-free wiring pattern 9 also maintains its insulating property. An arbitrary multilayer wiring board can be obtained by stacking these layers arbitrarily. A conductive particle formed by forming a conductive layer on a hot-melt metal such as solder, which is a preferable conductive particle, or a polymer core material such as plastic is
Is deformed into a portion 2-2 'that requires connection on the wiring pattern and is sandwiched, the contact area with the pattern is increased, the connection resistance is stabilized, and the reliability is also improved. The optimum filling amount of the adhesive agent can be controlled by the thickness of the adhesive agent, but it is preferable to let the flow out to the end portion and remove the unnecessary portion by laminating and integrating so that air bubbles are less mixed.

[0012]

According to the present invention, an adhesive composed of conductive particles and an adhesive is provided on both sides of an insulating film having a through hole in a main portion between a plurality of double-sided wiring boards each having a wiring pattern formed on an insulating substrate. Since it is a multilayer printed wiring board that is formed by forming layers and laminating and integrating by heating and pressing, a cover film is not necessary because it contacts the insulating adhesive except for the interconnection part, and the interconnection part is electrically connected by conductive particles. Since it is obtained, plating is unnecessary. Since the conductive particles of the present invention are concentratedly flowed and arranged only in the main part of the wiring pattern due to the constant stacking, no leak occurs between the adjacent patterns, and the thermocompression bonding conditions can be widely applied. Even if there are conductive particles other than the connection portion, the insulating film is present between the layers, so that the insulating property is maintained and the concentration thereof is low, so that no leak occurs in the adjacent wiring pattern. Therefore, the connection resistance is stabilized, the reliability is improved, it is possible to cope with the thinning of the circuit, and in addition, the multilayer wiring board which is effective in reducing the thickness and cost of the multilayer wiring board can be obtained very easily.

Further, since the adhesive film suitable for the present invention is formed by forming an adhesive layer composed of an adhesive and conductive particles on both sides of an insulating film, a conventional cover film and an adhesive for adhering the same are used from the beginning. Since they are integrated, a multilayer printed wiring board effective for cost reduction can be obtained very easily. In particular, when a polymer is used as the core of the conductive particles, the softened state can be widely controlled at the connection temperature, and it becomes easy to deal with variations in the thickness and flatness of the wiring board or wiring pattern.

[0014]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Also, for the sake of clarity, a four-layer wiring board in which two double-sided boards are connected to each other will be described, but one of the two double-sided boards may be a single-sided board or a multilayer wiring board having more than four layers. Applicable.

Examples 1 to 4 Adhesive 10 was applied to both sides of a polyimide film having a thickness of 50 μm.
A double-sided board formed by forming a copper foil 18 μm through
A wiring board on which pattern printing and etching were performed was prepared. The minimum diameter of the wiring pattern that requires connection is 50 μm
Met. A polyimide film 25 μm is punched with a through hole corresponding to a wiring pattern that needs to be connected, and an adhesive having a thickness of 15 μm and containing a high molecular weight epoxy as a main component is formed on both surfaces of the through hole. Ion and Cl ion are each 10 ppm or less). 12% by volume of the following conductive particles were uniformly dispersed in this adhesive to obtain an adhesive film of the present invention. The conductive particles used here were plated plastic spheres having a Ni / Au composite conductive layer on the surface of a core material made of crosslinked polystyrene and having a particle diameter of 10 μm (Example 1), and a carbonyl method Ni having an average particle diameter of 7 μm (Example). 2), melting point 1 with an average particle size of 15 μm
80 ° C. solder particles (Example 3) and insulating coated particles (Example 4) obtained by coating the particle surfaces of Example 1 with nylon having a thickness of about 0.2 μm. After aligning the through holes formed on the four peripheral sides of the wiring pattern, the through hole of the adhesive film, and the other wiring board that require connection of one side of the wiring board with a pin, the through hole portion is electrically conductively bonded. Fill with the agent,
180 ° C 20kg / cm ² The adhesive was cured by heating and pressing for 30 minutes. As described above, a four-layer wiring board in which two double-sided boards were connected to each other was obtained. All of Examples 1 to 4 showed sufficient interlayer connection characteristics.

Example 5 Adhesive 1 was applied to both sides of a glass epoxy substrate having a thickness of 0.2 mm.
A wiring board was prepared by pattern-printing and etching a double-sided substrate having a copper foil of 18 μm formed with a thickness of 0 μm. The minimum diameter of the wiring pattern that requires connection is 20
was μm. Using the adhesive film of Example 1, the same positioning, heating and pressing, and adhesive curing as in Example 1 were performed to obtain a four-layer wiring board in which two double-sided boards were interlayer-connected.
Example 5 also showed sufficient interlayer connection characteristics.

[0017]

As described above, according to the present invention, there is no need for a cover film or a plating process, and it is possible to cope with the thinning of the circuit. In addition, the connection is effective for reducing the thickness of the multilayer wiring board and reducing the cost. It is very reasonably easy to obtain a multilayer wiring board with improved reliability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one example of the constitution at the time of manufacturing of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of the present invention after being laminated and integrated.

[Explanation of symbols]

 1 Insulating Substrate 2 Wiring Pattern 3 First Wiring Board 4 Second Wiring Board 5 Conductive Particles 6 Adhesive 7 Through Hole 8 Insulating Film 9 Wiring Pattern 10 Connection-Free Wiring Pattern 10 Adhesive Film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kyohisa Ota 1500 Ogawa, Shimodate, Ibaraki Shimodate Research Laboratory, Hitachi Chemical Co., Ltd. (72) Yutaka Yamaguchi 1500 Ogawa, Shimodate, Ibaraki Hitachi Chemical Co., Ltd. Company Shimodate Institute

Claims (2)

[Claims] 1. A wiring pattern formed on an insulating substrate. 2.
A multilayer wiring board in which an adhesive layer composed of conductive particles and an adhesive is disposed on both sides of an insulating film having a through hole in a main portion between two or more double-sided wiring boards and laminated and integrated by heating and pressing. 2. An adhesive film in which an adhesive layer composed of an adhesive and conductive particles is formed on both sides of an insulating film, and the thermal transformation point of the conductive particles is lower than that of the insulating film.