JPH0453188A - Manufacture of through hole printed wiring board - Google Patents

Abstract

PURPOSE:To improve conductivity, migration resistance, etc., by previously forming a copper or nickel film of predetermined thickness on the wall surface of a through hole of a board in which the hole is opened. CONSTITUTION:A board (1) in which a through hole is opened and a copper or nickel film of 0.3-3mum of thickness is previously formed on the wall surface of the hole, is used. The film formed on the wall of the hole is a copper film. The film is formed by holding copper formate within 5cm from the hole of the board (1) and heating it to a predetermined temperature of a range of 165 deg.C to a deformation deteriorating temperature or lower of the board (1) under reduced pressure of 30Torr or less. A copper formate plating method of heating the copper formate is heated at 1 deg.C/min or more at least up to 130-165 deg.C and holding it is employed. Conductive paste is silver, copper or carbon paste, and a screen printing method using suction means is performed to inject the paste.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improved method for manufacturing through-hole printed wiring boards using conductive paste, and in a particularly preferred method, a novel and essentially non-conductive method is provided. By using a phase-based through-hole plating method, the disadvantages of conductive pastes, such as conductivity and migration resistance, are improved while minimizing cost increases.

[Conventional technology and its problems]

The most common method for making electrical connections between the eyebrows in multilayer or double-sided printed wiring boards is the through-hole plating technique, in which a through hole is formed at the connection part and the wall surface of the hole is plated with copper. Although this method is highly reliable, it requires complicated steps and has the disadvantage of increasing processing costs.

On the other hand, in consumer electronic equipment, mainly audio equipment, due to the demand for cost reduction, conductive paste through-holes, in which a conductive paste made of silver powder mixed with a thermosetting resin is filled into the holes and hardened, are widely used.

This conductive paste method is simple and inexpensive to manufacture.

However, when voltage is applied in environments such as high temperature and high humidity, silver tends to migrate, increasing the risk of short circuits. Therefore, for example, the insulating layer of the substrate to be used, the gap between the matrix resin and the base gusset real should be selected to have low hygroscopicity and migration is unlikely to occur, or the distance between the silver through holes should be kept sufficiently wide. There were design issues such as:

As a method to solve this migration problem, a method has been proposed that uses a copper conductive paste containing copper powder mixed with a thermosetting resin. However, copper is easily oxidized, which poses problems in electrical performance and reliability.Furthermore, it is possible to use carbon conductive paste, which is a mixture of carbon and thermosetting resin, but it has the disadvantage of high resistance, so it is currently not possible. Exclusively silver base is used.

[Means for Solving the Problems] The present inventors have previously discovered a through-hole plating method that is essentially a vapor phase method using copper formate. In the process of intensively studying the practical application of this method, it was discovered that this method could also be used as a base copper plating for conductive paste through-hole plating, and based on this, the present invention was completed.

That is, the present invention provides a method for manufacturing a through-hole printed wiring board in which electrical connections between printed wiring layers are made by injecting and curing a conductive paste into the through-holes. This is a method for producing a through-hole printed wiring board, characterized in that a copper or nickel film having a thickness of 0.3 to 3 caps is formed in advance on the through-hole printed wiring board. Further, the present invention provides that the film formed on the wall surface of the through-hole is a copper film, that the formation of the copper film is carried out by an acid group Fj, and that copper formate is maintained within 5 cm of the through-hole in (1). , under a reduced pressure of 30 Torr or less
℃ or above and below the deformation deterioration temperature of the substrate (1), and the copper formate is heated to a temperature of at least 130'.
The conductive paste must be silver, copper or carbon paste, and the conductive paste must be injected. This is a method for manufacturing a through-hole printed wiring board, characterized in that it is carried out by a screen printing method using a suction means.

The present invention will be explained below.

Substrate (1) used for conductive paste through holes of the present invention
means a large number of through-holes (usually about 10,000 to 50,000 holes/bore) at a predetermined position on a copper-clad board or double-sided copper-clad multilayer board, that is, at the through-hole position of the desired printed wiring pattern, based on the reference hole. Of course, it is also possible to use one in which a printed wiring network is formed in advance and then holes are punched.

Furthermore, since the conductive paste is embedded in the through-holes, a thinner substrate (1) can be used more preferably.

The materials used to manufacture the board (1), such as copper-clad boards, prepregs, and laminates, are usually thermosetting resins or thermoplastic resins that are resistant to soldering heat.
Fibers made of glass (E-1T-1D-1S-1 quartz glass), fully aromatic polyamide, super heat-resistant resins such as fluororesin, ceramics such as alumina, silica, boron nitride, aluminum nitride, silicon carbide, cellulose, etc. quality woven fabric,
Base material is nonwoven fabric, paper, etc.
ial), a copper clad board made by integrating this prepreg with electrolytic or rolled copper foil, and a printed wiring board for inner layers obtained by processing this copper clad board for inner layers.

Here, as the thermosetting resin, phenol resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, polyamine-bismaleimide resin, polymaleimide-epoxy resin, borimaleimide-isocyanate resin, cyanato resin, cyanate-epoxy resin , cyanate-polymaleimide resin, cyanate-polymaleimide resin, thermosetting resin such as cyanate-polymaleimide resin; thermosetting resins thereof and polyamide (nylon), aromatic polyester, polyetherimide, polyetheretherketone,
Thermosetting so-called "rlPN" is made by blending engineering plastics such as polysulfone and polyphenylene ether with the addition of appropriate catalysts; Examples include cross-linked curable resins made by blending oxides, radically polymerizable polyfunctional compounds, thermosetting resins, etc. Examples of thermoplastic resins having soldering heat resistance include polyethylene-2. ,6
- naphthalate, polyoxyhendiyl polyester,
Fully aromatic polyesters mainly containing P-hydroxybenzoic acid, phthalic acid, bisphenol, etc., aromatic polyesters obtained by grafting polyethylene terephthalate, etc. to these polyesters, liquid crystal polymers, polyetherimides,
polysulfone, polysulfone, polyethersulfone,
Examples include polyether ether ketone, polyphenylene ether, polyphenylene sulfide, polyimide, polyhenreimidazole, polyphenylene sulfide, and wholly aromatic polyamide.

Among these, in the present invention, it is preferable to use phenol resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, which have conventionally been used for conductive paste through holes, and matrix resins containing these as main components. However, since the conductivity and migration resistance are improved, it is also applicable to those using a higher grade heat-resistant resin as the matrix resin.

The substrate of the present invention (
1), with at least 0.3 units in the through hole, preferably 0
．． After forming a copper or nickel film of 7- or more, especially 100% or more, a conductive paste is embedded in the hole and heated and hardened to establish through-hole conduction.

The method for forming this copper or nickel film may be a conventionally known electroless plating method for copper, nickel, etc., but in the present invention, the copper film is formed essentially by applying a vapor phase through-hole plating method using copper formate. is suitable.

This vapor phase through-hole plating method uses 5 cm of the plated area.
Copper formate is held at a temperature of at least 130°C to 165° C. and heated to a predetermined temperature in the range below the deformation deterioration temperature of the substrate (1) at 165° C. or higher under a reduced pressure of 30 Torr or less. The method is to raise the temperature to 1°C at a rate of 7 minutes or more and maintain the temperature.

The copper formate used in the above method is a cupric formate compound such as anhydrous copper formate, copper formate 4-eternal compound, or a mixture thereof, and any of them can be used, but in particular, it is used as a fine powder of anhydrous copper formate. It is preferable that the amount used (the total amount of copper formate placed) is mainly determined by the surface area of the substrate (1) to be plated and its holes, and the total surface area of the copper formate placement tool, and the amount per this surface area is O,001g/af
1 or more, preferably 0.002 to 0.3 g/cIIN
, especially 0.002 to 0.1 g/cffl. The placement method is to simply place the copper formate in the hole of the substrate (1), or to place the copper formate at a distance of within 5cIII, preferably within 1.5cm, more preferably within 1.0cm from the hole. There is a method of allowing vapor of copper formate to pass through, and any of these methods can be used preferably.

The former arrangement method involves applying copper formate to the entire surface of the through-hole board (1) by brush coating, screen printing, roll coating, dipping, etc., and then applying copper formate into the holes using a roll, squeegee, etc. Examples include a method of pressing, removing copper formate on the surface as necessary, and drying. Also,
In the latter method, the copper formate is placed on a plate-like material that can withstand the processing temperature, such as a metal, resin, or other sheet or film, and a thin isolation material is inserted as appropriate to prevent direct contact with the copper formate. A method is mentioned as a structure in which hole substrates (1) are stacked.

When placing copper formate in the above-mentioned through holes or sheets, it is done by dissolving or uniformly dispersing the powder in a relatively low boiling point solvent that does not substantially react with copper formate.
Preferred methods include heating at a temperature at which copper formate does not decompose, usually 130° C. or lower, or drying under reduced pressure.

The substrate (1) described above and copper formate are heat-treated and through-hole plated. The atmosphere for this plating treatment is preferably under reduced pressure, and the degree of reduced pressure is 30 Torr or less, preferably 5 Torr.
r or less. For heating, radiation heating such as infrared rays, electron beams, and microwaves, electric furnace, oven, oil heating, pressurized steam heating, nichrome wire, and other means are appropriately selected. Further, from the viewpoint of reducing dimensional changes, it is preferable that the set temperature has small variations. It is also preferable from the viewpoint of productivity to obtain a good copper film by increasing the heating rate and shortening the plating time. In this case, the method is to preheat it to a temperature of 130°C or less and then feed it into a heating device with a heater as a heating section set to a predetermined temperature; heating using infrared rays, especially far-infrared ceramic heaters, etc. Methods: Furthermore, a combination of both methods may be mentioned. In particular, the latter method can efficiently heat only the plated surface.

The heating temperature is 165°C or higher and the through-hole substrate (1)
A predetermined temperature in the range below the deformation deterioration temperature of 170 to 300
℃ and below the deformation deterioration temperature of the through-hole substrate (1), particularly 170 to 230℃.
It is preferable to select from the range of . On the other hand, copper formate is heated at a temperature of 130° C. to 165° C. at ldeg/min or more, preferably 1 to 50° C./min, especially 2 to 35° C./min, and maintained at a predetermined temperature. Further, the heating time is 3 hours or less, preferably 1 to 60 minutes, and it is preferable to devise a shorter heating time.

In the case of the method using copper formate, it is preferable that the surface of the substrate (1) is cleaned using a cleaning liquid, and the surface is leveled by drying. Examples of the surface preparation solution include cleaning with an acidic or alkaline degreasing solution, a volatile organic solvent, and a volatile organic solvent solution containing acid or alkali.

After the heat treatment in the above manner, the substrate is cooled to room temperature to obtain a through-hole base plated substrate on which a copper film of 0.3 or more is formed in the through-holes, which is used for forming the conductive paste through-holes described above.

Examples of the conductive paste of the present invention include silver, copper, or carbon paste, and silver paste is preferably used when complete curing is performed in an air atmosphere. There are various methods for filling through-holes, such as brush painting, screen printing, roll coating, and dipping, but screen printing is preferable. It is preferable to carry out this method while

Next, the conductive paste is semi-cured or hardened, and a solder resist or the like is further applied to form the through-hole printed wiring board of the present invention.

〔Example〕

Next, an example of the manufacturing method of the present invention will be explained with reference to the accompanying drawings.

FIG. 1 shows a manufacturing process flow of a through-hole printed wiring board of the present invention, and FIG. 2 shows an enlarged sectional view of a through-hole portion in each step of FIG. 1.

In FIG. 1, the substrate (1) is a double-sided copper-clad laminate or a printed wiring network forming board with drill holes (a) formed at required through-hole positions. This substrate (1) and the copper formic anhydride arrangement plate (2) are stacked with a spacer interposed therebetween so that the periphery thereof is sealed, and then this stack is preheated in a preliminary vacuum chamber, and then the pressure is reduced. Heating in the plating room (
b) After that, the substrate is transferred to a preparatory vacuum chamber for removal, cooled appropriately, and then taken out as a through-hole substrate (3) with a copper film formed on the hole wall surface. Next, a conductive paste such as silver paste is printed (C
) and heat cured (d) to form the through-hole (4) filled with the paste of the present invention. Here, the board (1
) If a printed wiring network forming board is used in advance, it is subjected to a post-treatment such as applying and curing a solder resist as required) to form a paste through-hole printed wiring board. On the other hand, in the case of using a copper-clad laminate that does not have a printed wiring network formed thereon, an etching resist layer is formed, the printed wiring network is formed by etching (e), and the post-processing (
f) Manufacturing a paste through-hole printed wiring board.

Fig. 2 is an enlarged view of the through-hole part in the manufacturing flow shown in Fig. 1 above, where a indicates the drill hole processed in (a) of Fig. 1 on the board (1), and b indicates the drill hole in the substrate (1) shown in Fig. 1. (b) shows a through-hole board (3) with a copper film formed on the hole wall, and C shows a paste through-hole board (4) that has been processed as shown in (C) to (f) in Figure 1, respectively. It is something that

As is clear from C in FIG. 2, since the paste through-hole substrate of the present invention has a copper film as a base for a conductive base such as a silver base, the silver can pass through this copper film. It is easily understood that migration does not occur and that the occurrence of migration is greatly suppressed. In addition, even when copper paste or carbon paste is used as this conductive paste, due to the electrical conductivity of the copper film, if a large current does not flow, the electrical resistance value becomes the resistance value of the copper film, and the conductivity It is also easy to understand that it has excellent properties.

[Operation and effects of the invention]

As described above, according to the method of the present invention, a conductive base is embedded after a copper film is attached to the wall of a through-hole. It is clear that the size of the problem is largely eliminated.

Moreover, according to the preferred method for forming a copper film of the present invention, the copper film can be formed at low cost essentially by a dry method.

Therefore, it is possible to manufacture a paste through-hole printed wiring board with high reliability at low cost, and its significance is extremely high.

[Brief explanation of drawings]

FIG. 1 shows a manufacturing process flow of a through-hole printed wiring board of the present invention, and FIG. 2 shows an enlarged sectional view of a through-hole portion in each step of FIG. 1. Patent applicant Mitsubishi Gas Chemical Co., Ltd. agent (9070) Patent attorney Sadafumi Tebori Figure 1 Figure 2

Claims (1)

[Claims] 1. In a method for manufacturing a through-hole printed wiring board in which electrical connection between printed wiring layers is made by injecting and curing a conductive paste into the through-holes, a through-hole hole in a substrate (1) having through-holes formed therein. Thickness 0.3~3μ on the wall surface in advance
1. A method for manufacturing a through-hole printed wiring board, characterized in that a through-hole printed wiring board is formed using a copper or nickel film formed thereon. 2. The method for manufacturing a through-hole printed wiring board according to claim 1, wherein the film formed on the wall surface of the through-hole is a copper film. 3. The formation of the copper film is carried out by holding copper formate within 5 cm of the through-hole of the substrate (1), under a reduced pressure of 30 Torr or less, at 165° C. or higher and below the deformation deterioration temperature of the substrate (1). Claim 2, characterized in that the plating is carried out by a copper formate plating method in which copper formate is heated to a predetermined temperature of at least 130°C to 165°C at a rate of 1°C/min or more and maintained. A method of manufacturing the through-hole printed wiring board described above. 4. The method for manufacturing a through-hole board according to claim 1, wherein the conductive paste is silver, copper or carbon paste. 5. The method of manufacturing a through-hole plate according to claim 1, wherein the conductive paste is injected by a screen printing method using a suction means.