JP2886503B2 - Multipoint conductive sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipoint conductive sheet in which a large number of conductive members penetrating in the thickness direction are arranged at arbitrary positions in the plane of an insulating sheet.

[0002]

2. Description of the Related Art In recent years, in the field of the electronics and electric industries, there has been an increasing need for higher density and higher insulation reliability of printed wiring boards due to demands for smaller and lighter equipment. As one of the methods, many cases using a multilayer printed wiring board have been studied and reported. Multi-layer printed wiring boards are different from single-sided or double-sided printed wiring boards in which conductive wiring is provided only on one or both sides of an electrically insulating plastic board, and have conductive wiring inside the insulating substrate together with the surface. is there. Therefore, there is a feature that the degree of freedom of the wiring is increased and the accommodation amount of the wiring is large.

[0003] Printed wiring boards include a rigid board having a hard insulating substrate and a flexible board having a flexible insulating board. Most multilayer printed wiring boards are rigid boards, but recent changes in the mounting style of electronic components have resulted in the use of multilayer flexible printed wiring boards, or the use of flexible rigid multilayer boards that integrate both. The case is seen.

[0004] In the use of these multilayer printed wiring boards, it is necessary to provide a conductor wiring penetrating in the thickness direction inside the insulating substrate with high precision at a required place, and the method is industrially produced. Is known as a plating through-hole method, and there are other methods, but this method is currently the main method. This method requires a high precision and many steps by a method of drilling a hole (called a through hole or a via hole) penetrating an insulating substrate with a small diameter drill and plating a metal on the inner wall of the hole. In addition, there is a disadvantage that a cut piece generated in drilling with a drill causes poor connection at a plated portion.

[0005] In order to overcome such disadvantages, attempts have been made to embed conductor wiring in advance in an insulating substrate. One example is a method in which a thin metal wire is embedded in an epoxy resin block, which is a thermosetting resin, and sliced to a certain thickness in a semi-cured state.
According to this method, the conductor wiring is provided inside the insulating substrate. However, there is a technical limit in reducing the thickness of the insulating substrate that can be provided, and the size that can be provided is also limited.
Furthermore, when thermocompression bonding with metal foil or the like to provide conductor wiring on the surface of the insulating substrate, the thermosetting resin is cured,
It is easy to cause abnormal peeling off at the interface with the conductor wiring embedded in advance.

Further, as an attempt to provide a conductor inside the insulating substrate, a substrate material having conductivity imparted by kneading a conductive powder into a resin of the same material as that of the insulating substrate is prepared, and is thermally pressed to the insulating substrate material in a thickness direction. A method has been proposed in which a laminated block in which a conductive layer is provided at a specific portion of a cross section is manufactured and sliced to a certain thickness. In this method, the insulating part and the conductive part are sufficiently bonded, but the conductor part provided inside the insulating substrate is continuous in one direction, which has a new disadvantage that the wiring design of the multilayer printed wiring board can be restricted. is there.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a simple and highly reliable multipoint conductive sheet in which conductive wiring (conductive material) is embedded, which is useful in forming a multilayer printed wiring board. The structure is to provide.

[0008]

SUMMARY OF THE INVENTION According to the present invention, it is an object of the present invention to remove a large number of particles embedded in an insulating sheet made of a thermoplastic synthetic resin sheet or the like and to penetrate the sheet in the thickness direction of the sheet. This is achieved by a multipoint conductive sheet having a structure in which a large number of through holes for each particle are formed in the surface of the sheet, and a conductive material is retained in each through hole.

In addition, a large number of through holes due to an explosion are formed in an insulating sheet made of a thermoplastic synthetic resin sheet or the like in the plane of the sheet, and a conductive material is held in each of the through holes to form the multipoint conductive sheet. Is achieved by

As the conductive material, a conductive metal paste is suitable. The insulating sheet is a thermoplastic synthetic resin sheet, and the conductive material is bonded to the insulating sheet by thermoplasticity of the insulating sheet.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1A, a thermoplastic synthetic resin sheet is used as an insulating sheet 1, and a sheet in which a large number of particles 2 are embedded in the thermoplastic synthetic resin sheet is prepared. The particles 2 are removed from the thermoplastic synthetic resin sheet, and a large number of through holes 3 penetrating in the thickness direction of the sheet are formed in the plane of the sheet as shown in FIG. 1B. As shown in FIG. 1C, a conductive material 4 is held in the through hole 3 to form a multipoint conductive sheet 5. The conductive material 4 can be used as a wiring contact for connecting between wiring patterns when a multilayer wiring board is formed.

The particles serving as the conductive materials 4 apply heat to the insulating sheet 1 to soften or melt the insulating sheet 1 so that the sheet 1
And is tightly bound. That is, the conductive material 4 is bonded to the sheet 1 by the thermoplasticity of the sheet 1.

The method for removing the particles 2 is achieved by incorporating the particles 2 easily soluble in water or a specific solvent into the insulating sheet 1 and dissolving and removing the particles. In particular, it is preferable to mix a substance that easily dissolves in water from the viewpoint of hygiene and handleability. Such particles 2 include neutral water-soluble salts such as rock salt and potassium chloride and weakly acidic water-soluble salts such as ammonium sulfate. And the like. In addition, metal particles such as copper particles and aluminum particles can be embedded in an insulating sheet and eluted with an acid or alkali solution or eluted by electromagnetic heating to form a large number of through holes 3.

When the diameter of the particles 2 is extremely smaller than the thickness of the insulating sheet made of a synthetic resin sheet, it is difficult to elute or a hole is formed only in the surface portion and no penetration occurs.
Conversely, when the diameter of the particles 2 is extremely larger than the thickness of the insulating sheet 1, the particles are mixed and contained, and when melt extruded to form a film into a sheet shape, a through hole is opened to break the insulating sheet 1. Occurs. Therefore, the average diameter of the particles 2 is 1.2 to 1.2 with respect to the target thickness of the insulating sheet 1.
Preferably, the ratio is in the range of 0.9. When the diameter of the particles 2 is small and buried in the insulating sheet 1, the surface of the particles is covered with a thin resin film, but the elution of the particles is performed by performing polishing with a dense wire brush. Can be promoted.

One method of uniformly containing the particles 2 in the insulating sheet 1 is a method of mixing the particles with a thermoplastic resin to form a melt-extruded film. In this case, the dispersibility of the particles is made more uniform. It is preferable to use a twin-screw extruder for this purpose, and the melt extrusion screw is not particularly limited, but those skilled in the art can easily determine these conditions in order to enhance the mixing property.

As shown in FIG. 2A, immediately after the molten synthetic resin is extruded from the die 5 to form a film (when in a softened state), as shown in FIG. A method is adopted in which the resin is spread almost uniformly on the surface of the synthetic resin sheet, and is pressed and embedded by a press roll 6 using an elastic roll. In this method, it is possible to use particles 2 having a larger particle diameter than the thickness of the formed synthetic resin sheet (insulating sheet 1).

The synthetic resin sheet is extruded substantially horizontally from the die 5 and the sheet is passed just below the particle supply tank 7, while a mask 8 is provided at the lower supply port of the particle supply tank 7 so as to face the sheet surface. The particles 2 supplied into the tank shown are spread as uniformly as possible on the surface of the sheet 1 through the mask 8.

After the spraying, the sheet 1 is passed between the press rolls 6 to embed the particles 2 to obtain the sheet 1 holding the particles by sheet curing.

By removing the embedded particles 2 in this manner, the intended through-holes 3 can be provided to the insulating sheet 1. The size of the through hole 3 governs the size of the metal conductive material 4 in the present invention. As a result of intensive studies by the present inventors, the average diameter of the metal conductive material 4 could be controlled from 0.02 mm to 0.2 mm.

The proportion occupied by the through holes 3 governs the proportion occupied by the metal conductive material 4. The area occupancy of the metal conductive material (the ratio of the surface area of the metal conductive material to the total surface area) is preferably from 10% to 40%. When the area occupancy of the metal conductive material is small, its usefulness is not sufficiently exhibited because the number of conductive portions to be aimed at is small. If the area occupancy of the metal conductive material is too large, the insulating sheet 1 is easily broken.

The thickness of the insulating sheet 1 made of the thermoplastic resin is related to the shape of the particles to be mixed.
mm and 0.02 mm or more are preferable. If the thickness is larger, it is necessary to increase the size of the particles 2. If such particles are aggregated, a very large through hole is formed, and the sheet 1 is easily broken by an external force. When the thickness is thinner, not only the strength of the thermoplastic resin sheet 1 alone becomes weak, but also the handleability becomes worse.

As another example of the formation of the through hole 3, a large number of point explosions are generated in the plane of the insulating sheet 1, and the point explosion breaks the sheet 1 into dots to form the through hole 3 penetrating in the thickness direction. it can. As a specific example, as shown in FIG. 3A, a metal sheet 10 having a fine concave portion 9 on the surface is used, and as shown in FIG. 3B, an insulating sheet 1 made of a thermoplastic resin is thermocompression-bonded to the metal sheet 10. After the bubbles are contained in the fine irregularities, the bubbles are rapidly heated to a temperature near the melting temperature of the thermoplastic resin to expand the internal bubbles and generate an explosion.

In order to fix the shape of the through hole 3,
It is necessary to immediately cool below the heat distortion temperature. Such a method is achieved by passing through a hot blast stove maintained near the melting temperature of the thermoplastic resin, and the residence time and the cooling temperature can be controlled to control the size of the through-hole and the proportion of the through-hole 3. The through hole 3 thus formed
As shown in FIG. 1C, a multipoint conductive sheet is formed by holding a conductive material. As an example of a method for uniformly forming the fine concave portions 9 in the metal sheet 10, a film in which an opening 12 is formed at a specific position of an elastic polyethylene film 11 is brought into close contact with the metal sheet 10, and then sandblasted. The concave portion 9 is provided only in the opening by a method known as a method. The size of the through hole 3 formed at a specific position of the thermoplastic resin sheet (insulating sheet) 1 can be controlled by the size and depth of the concave portion 9.

Metal sheet 10 having fine irregularities on its surface
Also by changing the thermocompression bonding force with the thermoplastic resin sheet by applying a release agent in advance,
It is possible to control the size of the through hole 3 and the proportion of the through hole. It is preferable that this release agent is not transferred to the thermoplastic resin sheet. As a result of intensive studies by the present inventors, it has been found that transfer is not performed if a specific type of silane-based release agent is applied and thermally cured.

A conductive metal paste is filled in the through-hole 3 formed at an arbitrary position in the plane of the insulating sheet made of the thermoplastic resin sheet or the like, and a heat treatment is performed to harden the conductive metal paste. By performing the application (when a thermosetting resin is used as the metal paste), the conductive material 4 exposed on the front and back surfaces of the sheet is held in the through hole 3.

As the conductive metal paste, as is well known to those skilled in the art, fine powder of an alloy such as gold, silver, copper or solder and an organic binder such as a resol type phenol resin are used as a butyl cell solvent. And a paste mixed with a solvent such as an antioxidant or an antifoaming agent, and has a shape that can be easily roll-printed. Copper paste and solder paste are preferred from the viewpoint of ease of printing and economy.

The filling of the paste into the through holes 3 can be easily performed by applying a pressing force by a pair of printing rolls. It is preferable that the thermoplastic resin sheet is placed on a metal or plastic plate and provided to a printing roll from the viewpoint of filling uniformity.

By thermosetting the conductive metal paste, it is possible to secure adhesion to the insulating sheet made of the thermoplastic resin sheet or the thermosetting resin sheet or the like. As the thermosetting conditions, thermosetting conditions of a metal paste well known to those skilled in the art can be applied. In this thermosetting, some types of thermoplastic resin may cause shrinkage or curl. These abnormalities are more likely to occur as the glass transition temperature is lower, and a thermoplastic resin having a glass transition temperature of 120 ° C. or higher is preferable.

In this thermosetting, depending on the type of the thermoplastic resin, partial peeling from the metal paste may be recognized. This is due to the difference between the thermal expansion of the metal paste and that of the thermoplastic resin sheet. Partial failure is not a problem in most applications, but if the size of the conductive part is made smaller, higher conduction reliability may be required, and as a thermoplastic resin that is unlikely to cause such abnormalities Is exemplified by a polymer capable of forming an optically anisotropic molten phase (hereinafter referred to as a liquid crystalline polymer). Since the thermal expansion of the liquid crystalline polymer is close to that of a metal, such abnormalities hardly occur.

These liquid crystalline polymers preferably have a transition temperature to an optically anisotropic molten phase in the range of 250 to 350 ° C. in view of heat resistance and workability of the sheet. In addition, within a range that does not impair the effects intended by the present invention,
A lubricant, an antioxidant, a filler and the like may be blended.

Since the liquid crystalline polymer has a sufficiently high glass transition temperature, it is characterized in that shrinkage and curling hardly occur even when blended with another thermoplastic resin having a low glass transition temperature. Therefore, other thermoplastic resins can be blended with these liquid crystalline polymers as long as the effects intended by the present invention are not impaired. The thermoplastic resin used in this case is not particularly limited, but examples thereof include polyolefins such as polyethylene and polypropylene, aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, and the like.
Examples include polystyrene, polyamide, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyphenylene ether, and fluororesin.

As the particles 2 to be embedded and removed in the insulating sheet 1, a metal wire such as copper, aluminum or the like is finely divided in the axial direction, and the finely divided dimension is made larger than the thickness of the sheet 1. It can be embedded by each of the above methods. In this case, the hole shape such as the diameter of the through-hole 3 can be made uniform in conformity with the subdivided wire rod diameter and form.

[0033]

According to the present invention, a multi-point conductive sheet having a conductive material penetrating in the thickness direction of the insulating sheet can be provided very easily, and it shows conductivity only at a specific position in the thickness direction, and shows electricity at other places. It is useful as a conductive sheet for a multilayer wiring board having insulation properties.

The above-mentioned multi-point conductive sheet is also effective as a contact means interposed between an electronic component such as an IC or the like and a wiring board, instead of a conductive elastomer serving as a contact medium between them.

Further, these multi-point conductive sheets for a multilayer wiring board,
Alternatively, a multipoint conductive sheet that replaces the conductive elastomer can be produced at low cost.

[Brief description of the drawings]

FIGS. 1A, 1B, and 1C are enlarged cross-sectional views illustrating a structure of a multipoint conductive sheet through a forming step.

FIGS. 2A and 2B are diagrams illustrating a method of embedding particles for forming through holes in the sheet in FIGS. 1A and 1B, and FIG. 2A is an example in which particles are scattered immediately after film formation of a synthetic resin sheet; And FIG. B is an enlarged plan view of the sheet for explaining the sprinkling state.

3A to 3C are views for explaining another method of forming a through hole in the sheet in FIGS. 1A and 1B. FIG. 3A is an enlarged sectional view of a metal sheet having a large number of concave portions, and FIG. An enlarged cross-sectional view showing a state in which an insulating sheet made of a plastic resin sheet is brought into close contact with air bubbles in the concave portion, C
FIG. 4 is an enlarged sectional view showing a state in which a through hole is formed in a sheet due to the explosion of air bubbles.

FIG. 4 is an enlarged cross-sectional view illustrating a case where a large number of concave portions are formed in the metal sheet by sandblasting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating sheet 2 Particle 3 Through hole 4 Conductive material

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H05K 3/46 H05K 3/46 X (72) Inventor Yoshiki Tanaka 1621 Sazu, Kurashiki-shi, Okayama Prefecture Kuraray Co., Ltd. (72) Inventor Yamazaki Hidehisa 3-28-7 Nakamagome, Ota-ku, Tokyo Yamaichi Denki Co., Ltd. (72) Inventor Akira Yonezawa 3-28-7 Nakamagome, Ota-ku, Tokyo Yamaichi Denki Co., Ltd. (72) Inventor Suzuki Etsushi 4 Yamanaka Denki Co., Ltd. 3-28-7 Nakamagome, Ota-ku, Tokyo (56) References JP-A-6-262375 (JP, A) JP-A-5-309793 (JP, A) JP-A Heisei 6-107865 (JP, A) JP-A-59-166540 (JP, A) JP-A-6-333984 (JP, A) JP-A-6-184349 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05K 3 / 32,3 / 00,3 / 46 H05K 1 / 11,3 / 40 H01R 11 / 01,43 / 00 C08J 9/26 101

Claims (4)

(57) [Claims] 1. A method for removing a large number of particles embedded in an insulating sheet, forming a large number of through-holes for each particle penetrating in the thickness direction of the sheet in the plane of the sheet, and forming a plurality of through-holes in each of the through-holes. A multipoint conductive sheet characterized by having a conductive material. 2. A multi-point structure wherein a plurality of through holes are formed in an insulating sheet in the thickness direction of the sheet due to an explosion in the surface of the sheet, and a conductive material is held in each of the through holes. Conductive sheet. 3. The multipoint conductive sheet according to claim 1, wherein the conductive material is a conductive metal paste. 4. The insulating sheet according to claim 1, wherein said insulating sheet is a thermoplastic synthetic resin sheet, and said conductive material is bonded to said insulating sheet by thermoplasticity of said insulating sheet.
Or the multipoint conductive sheet according to 2.