JPH0251297A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To make it possible to obtain a printed wiring board which is small in warp and small in lowering of adhesion even after soaking in fused solder, generation of blister and rise of resistance value by covering it with electron beam hardening covering composition and hardening it by electron beam irradiation after printing conductive paste on a substrate and hardening it by electron beam irradiation so as to form an electric circuit. CONSTITUTION:After printing conductive paste, which has conductive fine powder and electron beam hardening resin for its main ingredients, onto, e.g., a one-side copper clad paper-phenol resin laminate using a screen print made of stainless steel, electron beams are applied from the conductive paste printed face side of the laminate using an electron beam irradiation device so as to harden the conductive paste printed part. Next, electron beam hardening resin, or electron beam hardening covering composition which has it and inorganic filler for its main ingredients is printed onto the conductive past printed hardened part using a screen print made of nylon, and then electron beams are applied under the same conditions as the case of hardening of the conductive paste so as to harden an electron beam hardening covering composition printed part, thus a printed wiring board is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method of manufacturing a printed wiring board used in electronic equipment and the like.

(Conventional technology) In recent years, electronic devices have been rapidly becoming smaller and lighter, more densely packaged, and more energy efficient, and along with this, the requirements for printed wiring boards used in electronic devices are becoming more diverse. Protection of conductive layers and circuits in printed wiring boards is also becoming increasingly important. Conventionally, conductive pastes mainly composed of conductive fine powder, thermosetting resins, and organic solvents have been used for such conductive layers and conductive circuits.
As protective coating materials for these conductive layers and conductive circuits, materials containing thermosetting resins, organic solvents, or these and inorganic fillers as main components have been used.

In order to cure conductive pastes and protective coatings containing these thermosetting resins, multiple heating steps at high temperatures and long periods of time are required, which can cause warping and deterioration of the substrate due to heating.

This causes shrinkage, which lowers the yield of two-component mounting, and also reduces energy savings, resource savings, and environmental protection.

There was a problem due to solvent volatilization.

In order to solve these problems, conductive layers and conductive circuits are
Consideration has been given to using a conductive paste whose main components are conductive fine powder and ultraviolet curable resin.

However, these conductive pastes containing high concentrations of conductive fine powders such as metal fine powders, metal oxide fine powders, carbon black, and graphite do not absorb or reflect ultraviolet rays due to the ultraviolet rays being absorbed or reflected by the conductive fine powders. The drawback was that even when irradiated with ultraviolet light, the inside was not sufficiently cured.

For this reason, 1 the present inventors have developed an ultraviolet curable resin, or a UV curable resin and an inorganic filler as main components, as a protective coating material for a conductive layer or a conductive circuit obtained by curing a thermosetting conductive paste. It was investigated. However, the conductive layers and conductive circuits obtained by curing these conductive pastes are extremely porous, and the protective coating that has penetrated deeply into the pores of the conductive layers and conductive circuits cannot be sufficiently cured even when exposed to ultraviolet light. 1
In the next process, when the parts are mounted and immersed in solder, the protective coating may blister or break.

Therefore, the present inventors coated or printed a conductive paste mainly composed of conductive fine powder and electron beam curable resin on a substrate, and cured it by electron beam irradiation to form a conductive layer or a conductive circuit. Furthermore, it was considered that a thermosetting coating composition containing a thermosetting resin and an organic solvent, or a thermosetting resin and an inorganic filler as main components, was coated thereon and cured by heating. However, in this method, the organic solvent contained in the thermosetting coating composition causes the conductive layer or conductive circuit to swell, changing the conductivity of the conductive layer or conductive circuit and reducing its adhesion to the substrate, resulting in reliability. In addition, when a protective coating is provided after one component is mounted, the mounted component is subject to thermal deterioration.

(Problems to be Solved by the Invention) The present invention provides a method for manufacturing a printed wiring board that has less warpage, less decrease in adhesion, less occurrence of blisters, and less increase in resistance value even after being immersed in molten solder.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides the following: (1) A conductive paste containing conductive fine powder and a thermosetting or electron beam curing resin as main components is coated or printed on a substrate, and heated. Alternatively, after curing by electron beam irradiation to form a conductive layer or a conductive circuit, an electron beam curable resin or an electron beam curable resin containing these and an inorganic filler as main components is applied on the conductive layer or conductive circuit. Coat the coating composition.

A method for manufacturing a printed wiring board characterized by curing by electron beam irradiation, (2) further comprising mounting electronic components, coating with an electron beam curable conformal coating agent, and curing by electron beam irradiation. 1) The method for producing a printed wiring board according to (1) or (2) above, wherein the electron beam curable coating composition does not substantially contain a solvent. and (4
) The method for producing a printed wiring board according to (2) above, wherein the electron beam curable conformal coating agent does not substantially contain a solvent.

In the present invention, the substrate includes 1 paper-phenol resin,
Substrates commonly used for printed wiring boards can be used, such as resin laminates made of glass-epoxy resin, paper-polyester resin, etc., flexible substrates made of polyimide, polyester, etc., ceramic substrates, metal substrates coated with insulation, etc. As a substrate, a metal foil such as copper foil, aluminum foil, or iron foil is applied and etched and polished to form a circuit, and/or a conductive paste, a resistive paste, and/or an insulating paste are applied or A printed version may also be used.

In the present invention, as the conductive fine powder, one or more of conductive metal fine powder, conductive metal oxide fine powder, carbon black, and graphite can be used. Gold and silver are used as conductive metal fine powder.

It is possible to use metals such as platinum, copper, nickel, chromium, palladium, aluminum, and tungsten, fine powders made of alloys thereof, fine inorganic powders coated with these metals or alloys, or mixtures thereof. As conductive metal oxide fine powder, soot,
Fine powder of oxides of metals such as titanium and iron, or mixtures thereof can be used. 2. Graphite is refined natural graphite such as scale graphite and earthy graphite.

Artificial graphite or a mixture thereof is used.

When the conductive fine powder is made of conductive metal fine powder such as silver powder, the resulting conductive paste has high conductivity, and the conductive fine powder is a conductive metal oxide fine powder.

When the paste is composed of one or more of carbon blank and graphite, the resulting conductive paste becomes a resistance paste with low conductivity.

By appropriately selecting the composition of the conductive fine powder and its content in the conductive paste, a conductive paste having desired conductivity can be obtained.

In the present invention, thermosetting resins include thermosetting epoxy resins, phenolic resins, modified phenolic resins,
Alkyd resins, polyamide resins, polyimide resins, amino resins, acrylic resins, urethane resins, unsaturated polyester resins, etc., or appropriate combinations thereof can be used.

Examples of electron beam curable resins include polyallyl compounds such as diallyl orthophthalate and diallyl isophthalate;
Unsaturated polyesters, epoxy (meth)acrylates such as bisphenol A type epoxy poly (meth)acrylate, novolac type epoxy poly (meth)acrylate, polyurethane poly(meth)acrylates,
Trimethylolpropane tri(meth)acrylates, polyether polyol poly(meth)acrylates, polyurethane poly(meth)acrylates, divinyl compounds, phenoxyethyl(meth)acrylate,
Tetrahydrofurfuryl (meth)acrylate, (meth)acrylic acid alkyl ester, oligoester mono (meth)acrylate, (meth)acrylic acid alkyl 3 (meth)acrylic acid 2-hydroxyalkyl,
In addition to radically polymerizable resins made of monomers such as glycidyl (meth)acrylate, styrene, and α-alkylstyrene, tris(2-acryloyl ethyl ester) isocyanurate, and mixtures thereof, cationic photopolymerization initiators and A cationic polymerizable resin containing an epoxy resin as a main component can be used.

The conductive fine powder is preferably contained in a proportion of 5 to 95% by weight based on the conductive fine powder and the thermosetting or electron beam curing resin. If the amount of the conductive fine powder exceeds 95% by weight, the co-adhesive curing of the conductive fine powder by the thermosetting or electron beam curable resin may be inhibited.
If it is less than 5% by weight.

Formation of a conductive circuit due to contact between conductive fine powders may be inhibited.

In addition to conductive fine powder and thermosetting or electron beam curable resin, methyl ethyl ketone as required.

Ethyl Cellosolve 2 Ethyl Cellosolve Acetate.

Organic solvents such as ethyl acetate, butyl acetate, toluene, xylene, butylcarpitol, coupling agents such as silane coupling agents, thermoplastic resins, etc.? n combined, 2
A conductive paste can be obtained by cross-dispersing using a conventionally known cross-dispersing means such as a main roll, a three-roll roll, a ball mill, a paint conditioner, a disper, or a kneader.

The conductive paste obtained in this way is placed on the substrate.
It is applied in a solid manner using a coating machine such as a roll coater, or printed in the desired pattern using a printing machine such as a screen printer, and if the conductive paste contains a solvent, the solvent is removed as necessary. .

The applied or printed conductive paste is cured by heating if the conductive paste is made of thermosetting resin, or by electron beam irradiation if the conductive paste is made of electron beam curable resin. It is cured to form a conductive layer or circuit. When curing by heating, 8 usually heat curing is carried out at 130 to 200°C for about 10 to 30 minutes, and when curing by electron beam irradiation, 1 usually,
Accelerating voltage 150-300kV, absorbed dose 3-30M
Electron beam curing is performed under conditions of approximately rad.

The conductive layer or conductive circuit thus formed is coated with an electron beam curable resin or an electron beam curable coating composition containing these and an inorganic filler as main components, and cured by electron beam irradiation. be done.

As the electron beam curable resin, the same resin as the electron beam curable resin described above can be used. As the inorganic filler, one or more of talc, barium sulfate monocalcium carbonate, fine silica, clay, kaolin, diatomaceous earth, etc. can be used.

Among these, talc has an average particle size of 1.5 to 3.5 μm.

Particularly preferred are those containing talc treated with a silane compound. In addition to the above electron beam curable resin or these and an inorganic filler, the electron beam curable coating composition may contain, if necessary,
A small amount of the above organic solvent, silane coupling agent, thermoplastic resin, organic pigments such as phthalocyanine blue, phthalocyanine green, titanium white 1 yellow lead, or other additives such as inorganic pigments and dyes can be added, but the organic solvent is substantially It is preferable that it not be included. The above electron beam curable resin,
Or by mixing, dispersing, or kneading these, an inorganic filler, and, if necessary, additives using a conventionally known mixing, dispersing, and kneading means such as a disper, paint conditioner, two-roll, three-roll, ball mill, or kneader. An electron beam curable coating composition is obtained.

The electron beam curable coating composition thus obtained is applied onto the conductive layer or conductive circuit in a solid manner using a coating machine such as a roll coater, or by a printing machine such as a screen printer. It is coated by printing in the desired pattern and cured by electron beam irradiation. Electron beam irradiation is 2 normal.

Accelerating voltage 150-300kV, absorbed dose 3-30Mra
It is done at about d. Coatings cured by electron beam radiation act as solder resists, insulation coatings, and/or overcoats.

When the coating cured by electron beam irradiation is an insulating coating or solder resist, an electromagnetic shielding printed wiring board is manufactured by further providing a conductive layer on top of it and then applying an insulating coating or protective coating on top of it. You can also. The above conductive paste may be used as a conductive layer when forming an electromagnetic shield printed wiring board, and/or the above electron beam curable coating composition may be used as an insulating coating or protective coating. The electromagnetic wave shield printed wiring board thus obtained can shield the printed wiring board circuit and electromagnetic waves from the outside, and can prevent malfunction of electronic equipment and damage to electronic components.

If the coating cured by electron beam irradiation is a solder resist, solder cream is printed in synchronization with the metal foil part by screen printing, and the chip capacitor,
Chip resistors, chip inductors.

Equipped with electronic parts such as transistors and diodes,
Electronic components are mounted by heating.

An electron beam curable conformal coating is applied and cured by electron beam radiation. The electron beam curable conformal coating agent can be the same as the electron aN curable coating composition described above, and can be coated by applying it in a solid state with a coating machine such as a spray coater, curtain coater, or roll coater. However, it can be cured under the same conditions as for the electron beam curable coating composition.

When the coating cured by electron beam irradiation is an insulating coating, a multilayer structure can be formed by forming a conductive layer or a conductive circuit, coating the electron beam curable coating composition thereon, and repeating the curing process. Printed wiring boards can be manufactured.

Furthermore, on the printed wiring board thus obtained.

An electromagnetic shield printed wiring board can also be manufactured by applying an insulating coating or a solder resist, providing a conductive layer thereon, and further applying an insulating coating or a protective coating thereon. The electron beam curable coating composition may be used as an insulating coating, solder resist, or protective coating that forms the shield portion of an electromagnetic shield printed wiring board, and/or the conductive paste may be used as a conductive layer. The electromagnetic wave shield printed wiring board thus obtained can shield the printed wiring board circuit and electromagnetic waves from the outside, and can prevent malfunction of electronic equipment and damage to electronic components.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, 2 parts represents parts by weight.

Production Example 1 A mixture having the following composition was kneaded using three rolls to obtain electron beam curable conductive paste A.

Trimethylolpropane triacrylate 2 parts Electron beam curable spiran resin "Spirac U-3000J (manufactured by Showa Kobunshi ■, trade name) 10 parts T
-Methacryloxypropyltrimethoxysilane 1.5 parts Silver powder rD-15J (manufactured by Degussa Japan, trade name)
28 parts Silica powder "Aerosil-200" (manufactured by Nippon Aerosil ■, trade name) 2 parts Production example 2 A mixture having the following composition was kneaded using three rolls to obtain an electron beam-curable conductive paste 1-B.

Trimethylolpropane triacrylate 30 parts Tris(2-acryloylethyl ester) isocyanurate 30 parts Diallylisophthalate oligomer 30 parts 2-hydroxyethyl methacrylate 10 parts Carpitol acetate
80 parts Furnace Black “Ketchen Black ECJ (manufactured by Lion Akzo ■, product name)
15 parts acetylene black "Denka Black" (Denka Kagaku Kogyo a@ Seisakubu product name 18
Production Examples 3 and 4 The mixtures having the compositions shown in Table 1 were each kneaded using three rolls to obtain electron beam-curable coating compositions C and D.

Note that in Table 2, the symbols are as follows.

TMPTA: Trimethylolpropane triacrylate "Lipoxy": Epoxy acrylate manufactured by Showa Kobunshi ■,
Product name.

3-HPMA: 3-hydroxypropyl methacrylate.

MAOEP: methacroyloxyethyl phosphate.

N-VCZ: N-vinylcarbazole.

[Micro Ace-IJ: Shiraishi calcium talc,
Average particle size: 3.3 μm, trade name.

"Lionor Green": Phthalocyanine green manufactured by Toyo Ink Manufacturing ■, product name.

Table 1 Production Example 5 A mixture having the following composition was kneaded using three rolls to obtain an ultraviolet curable coating composition E.

Trimethylolpropane triacrylate 50 parts “Lipoxy” 90 parts 3-hydroxypropyl methacrylate 20 parts N-vinylcarbazole 5 parts 2-chlorothioxanthone 5 parts “Microace K
-IJ 100 parts calcium carbonate
Part 5 “Lionor Green”
5 Parts Example 1 The conductive paste A obtained in Production Example 1 was applied onto a single-sided steel-clad paper-phenolic resin laminate on which a copper foil electrode portion had been provided in advance, and the conductive paste A printed portion between the copper foil electrodes was applied. After printing using a 200-mesh stainless steel screen plate with a size of 4 mm vertically and 4 mm horizontally, it was printed at an accelerating voltage in a nitrogen gas atmosphere using an energy science 150B-15 electron beam irradiation device. 160
kV, absorption! An electron beam was irradiated from the conductive base 1-A printed surface side of the laminate under the condition that the amount of tlA was 10 Mr ad to cure the printed part of the conductive paste A). Next, the electron beam curable coating composition C obtained in Production Example 3 was printed on the printed hardened part of the conductive paste A) using a 200 mesos nylon screen plate, and then the conductive paste L
-The printed portion of electron beam curable coating composition C was cured by irradiation with an electron beam under the same conditions as in the case of curing A, and a printed wiring board was obtained. At this time, using the laminate without warpage before printing the conductive paste I-A as a standard, visually evaluating the occurrence of warpage after printing and curing of the electron beam curable coating composition C, and After curing, the resistance value before printing of electron beam curable coating composition C and the resistance value after printing and curing of electron beam curable coating composition C were measured, and the rate of change in resistance value before and after coating was calculated. Table 2 shows the evaluation results for the occurrence of warpage and the calculated rate of change in resistivity. Further, the adhesion of the printed cured portion of the electron beam curable coating composition C was evaluated by a cellophane adhesive tape peel test. The evaluation results are also shown in Table 2.

Next, the obtained printed wiring board was immersed in a molten solder (tin/lead = 60/40, weight ratio) bath at 260° C. for 10 seconds, taken out from the solder bath, and cooled to room temperature.

The external appearance of the printed cured part of electron beam curable coating composition C after immersion was visually evaluated, the adhesion was evaluated by a cellophane adhesive tape peel test, and the resistance value after immersion in the molten solder bath was measured. The rate of change in resistance after immersion was calculated. Table 2 shows the evaluation results of adhesion and the calculated rate of change in resistance value.

In addition, the resistance value is that between the copper foil electrodes using a wide range digital ohmmeter DR-100CU manufactured by Sansho Keiki Seisakusho.
(trade name), and the resistance change rate was calculated using the following formula, and those whose resistance change rate exceeded +1.5% were rejected.

or Resistance change rate (χ) = Resistance value after immersion - resistance value before immersion ×100 Resistance value before immersion In addition, in Table 2, the display of evaluation results, etc. is as follows.

Occurrence of warpage ◎: No warpage occurred; O: Slight warpage occurred, but there was no practical problem. ×: Significant warpage.

Adhesion after printing cures ○: Good Appearance after solder immersion ○: Good, ×Niblistering occurred, poor.

Adhesion after solder immersion O: Good, ×: Poor.

Example 2 Conductive paste B obtained in Production Example 2 was used instead of conductive paste I-A, and after printing and before curing conductive paste B, far infrared rays were irradiated for 1 minute at an ambient temperature of 180 ° C. Table 2 shows the results of the test and evaluation carried out in the same manner as in Example 1 except that tall acetate was removed.

Example 3 Thermosetting silver paste rFA instead of conductive base l-A
Table 2 shows the results of a test evaluation conducted in the same manner as in Example I, except that -620TJ (manufactured by Fujikura Kasei ■, trade name) was used and the conductive paste was cured by heating at 150°C for 30 minutes. Shown below.

Comparative Example I Using the ultraviolet curable coating composition E obtained in Production Example 5 instead of the electron beam curable coating composition C, the ultraviolet curable coating composition E was heated at 2 kW and an ozone-free high pressure of 80 W/cm. Pass once under one mercury lamp at IQcm and conveyor speed at 1m/min (equivalent to 700mJ/cmz)
Example 1 except that it was cured by ultraviolet irradiation.
Table 2 shows the results of test evaluation conducted in the same manner as above.

Comparative Example 2 The ultraviolet curable coating composition E obtained in Production Example 5 was used instead of the electron beam curable coating composition, and the ultraviolet curable coating composition E was subjected to the same ultraviolet irradiation conditions as in Comparative Example I. Table 2 shows the results of a test evaluation conducted in the same manner as in Example 2, except that the cured product was cured by irradiation with ultraviolet rays under the same conditions.

Comparative Example 3 Thermosetting solder resist rS-222J (manufactured by Taiyo Ink GW, trade name) was used instead of electron beam curable coating composition C, except that rS-222J was heat-cured at 150°C for 10 minutes. Table 2 shows the results of the test evaluation conducted in the same manner as in Example 1.

Comparative Example 4 The results of a test evaluation were conducted in the same manner as in Example 2, except that rs-222 was used instead of the electron beam curing coating composition, and rS-222J was heat-cured at 150°C for 10 minutes. It is shown in Table 2.

Table 2 Example 4 Solder cream was printed on the copper foil electrode part of the printed wiring board obtained in the example process, a chip resistor (Hokuriku Electric Industrial characteristics, CRI/8.lkΩ) was mounted, and the solder cream was heated. , soldered the chip resistor.

The coating composition was applied as an electron beam curable conformal coating to a thickness of 100 μm, and cured by electron beam irradiation under the same conditions as those for conductive paste A in Example 1. At this time, no warping occurred on the printed wiring board.

Comparative Example 5 A chip resistor mounted printed wiring board was produced in the same manner as in Example 4, except that rS-222J was used instead of the electron beam curable coating composition and rS-222J was heated and cured at 150°C for 10 minutes. Obtained. At this time, the printed wiring board was severely warped and could not be put to practical use.

〔Effect of the invention〕

According to the present invention, it has become possible to obtain a printed wiring board with less warpage, less decrease in adhesion, less occurrence of blisters, and less increase in resistance value even after immersion in molten solder.

Claims (4)

[Claims] 1. A conductive paste consisting mainly of conductive fine powder and thermosetting or electron beam curable resin is applied or printed onto a substrate, and is cured by heating or electron beam irradiation to form a conductive layer or a conductive circuit. After that, the conductive layer or the conductive circuit is coated with an electron beam curable resin, or an electron beam curable coating composition containing these and an inorganic filler as main components, and cured by electron beam irradiation. A method for manufacturing a printed wiring board. 2. 2. The method of manufacturing a printed wiring board according to claim 1, further comprising mounting electronic components, coating with an electron beam curable conformal coating agent, and curing by electron beam irradiation. 3. 3. The method of manufacturing a printed wiring board according to claim 1, wherein the electron beam curable coating composition is substantially free of solvent. 4. 3. The method of manufacturing a printed wiring board according to claim 2, wherein the electron beam curable conformal coating agent is substantially free of solvent.