JPH01232791A - Manufacture of circuit board - Google Patents

Abstract

PURPOSE:To improve the breakdown strength of an electric circuit having an organic polymer insulating layer by applying a photosetting coating material over the entire surface on which the electric circuit is present, masking, irradiating the surface, and removing the coating material from the nonirradiated portion. CONSTITUTION:A photosetting coating material 4 is applied over the entire surface of the electric circuit 3. Then, a mask having a desired light-permeating hole pattern is placed on the photosetting coating material 4 to irradiate thereto light such as an ultraviolet ray. Lastly, the non-set coating material on the non-irradiated portion is removed by dissolving with an appropriate organic solvent to obtain a circuit board having a photosetting coating portion 4'. The application of the coating material over the entire surface is easier compared to the partial application thereof only on an edge portion 32, and the masking process can be performed by simply arranging and using the finely structured mask. Accordingly, it is possible to manufacture on a commercial basis a circuit board, in which it is ensured that at least all the edges 32 of the electric circuit 3 are coated with the completely photoset organic polymer and that at least any portions 31 on which electric connections are required to be made will be left uncoated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing a circuit board that can be used for forming an electric circuit in an electronic device or the like.

[Prior art]

2. Description of the Related Art With the recent miniaturization of electronic devices, so-called hybrid ICs, in which various components such as resistors, capacitors, transistors, etc. are mixed together and installed on a single substrate to realize electronic functions, are becoming more important.

Conventionally, hybrid ICs made of ceramic plates whose insulating layers are mainly made of alumina have been mainly used, but ceramic plates are easily broken, making it difficult to manufacture large-sized ones, and they are difficult to manufacture with metal heat sinks. Since adhesion is also a complicated process, there has recently been a trend to use insulating organic polymers such as polyimide resins and epoxy resins instead of ceramics. These insulating organic polymers are easy to form into films and adhere to metal materials, so
It is used in a structure in which a metal material layer serving as a heat sink is adhered to one side of an insulating organic polymer film, and an electric circuit layer is adhered to the remaining side.

[Problems that need to be solved]

By the way, the electrical circuits on circuit boards are sometimes formed by simply gluing foils of conductive metals such as copper or nickel that are cut into the desired circuits in a separate process, but this is not possible with mass production. In this case, a method is adopted in which a conductive metal foil is adhered onto an insulating permanent polymer film, and this foil layer is subjected to an etching treatment to finish an electric circuit in the desired shape. Regardless of which method is used, the electrical circuit is
It is raised from the surface of the insulating layer by the thickness of the conductive metal foil, that is, it has a side surface that corresponds to the thickness of the foil, and has a structure in which corona is likely to occur due to the concentrated electric field at the edge portion on this side surface. There is. Moreover, the organic polymer insulating layer has a drawback of having lower corona resistance than the conventional ceramic insulating layer, and as a result, organic polymer insulating circuit boards have the problem of being susceptible to corona damage. In order to solve the problem of corona destruction at the edges, the present inventors attempted to coat these parts with an insulating material, but the surface of the electric circuit is not covered by electrical connection work. For example, there are some areas that should not be covered with insulating material, such as areas where wire bonding is performed and where resistors, capacitors, transistors, etc. are mounted, so it is necessary to ensure that only the edges are covered with insulating material on a commercial production scale. turned out to be quite difficult.

[Means for Solving the Problems] In view of the above-mentioned problems, an object of the present invention is to provide a circuit board having an organic polymer insulating layer and improved voltage strength, and a method for manufacturing the same. That is.

That is, the present invention targets a circuit board that has an organic polymer electric insulating layer on a metal substrate and further has an electric circuit thereon, and coats the entire surface on which the electric circuit is present with a photocurable paint. At least all the edges of the electrical circuit are coated without a mask, while at least the parts of the surface of the electrical circuit that require electrical connection work are masked and irradiated with light to remove the paint on the irradiated parts. The present invention relates to a method for manufacturing a circuit board, which comprises curing the coating material and then removing the paint from the non-irradiated areas.

r Actions and Effects] The present invention is characterized by applying a photocurable paint to the entire surface where an electric circuit is present, masking, irradiating it with light, and removing the paint (therefore, uncured paint) in areas that have not been exposed to light. However, the entire surface application of the paint is easier than the partial application only to the edges, and the masking itself can be done by preparing and using a mask with a fine structure. A commercially available circuit board that ensures that at least all edges of the electrical circuit are coated with photocured organic polymer, and that at least the surface of the electrical circuit that requires electrical connection work is left uncovered. It can be manufactured on a large production scale.

Further, since the circuit board manufactured by the method of the present invention maintains excellent withstand voltage strength, it can be suitably employed in the production of various high-quality electronic devices.

In the present invention, the photocurable paint only needs to be photocurable, and has a volume resistivity of 10' in the cured state.
Electrical insulation of Ωcm or more, or volume resistivity of 10
Various chemical materials can be used without restriction as long as they have semiconductivity of about '-1o9 ΩCm, especially those with excellent corona resistance. If it is insulating, all edges of the electric circuit are covered with insulating material, making it difficult for dielectric breakdown to occur from the edges, and if it is conductive, electric field concentration at all edges of the electric circuit is alleviated. As a result, the withstand voltage strength of the substrate is improved.

The photocurable paint is one whose main ingredient is an organic polymer containing an acryloyl group.

This type of paint is known as a photopolymerizable prepolymer, in other words, it has a low degree of polymerization, for example, a polymer with a degree of polymerization of about 2 to 100, which has about 1 to 10 acryloyl groups as a functional group in the molecule. Various photocurable resins are preferred. Examples of the curable resin are shown below.

Polyurethane acrylates: Examples of polyurethane acrylates include polyether polyol-based polyurethane acrylates, polyester polyol-based polyurethane acrylates, and polyurethane acrylates having an ether group and an ester group in the molecule.

Examples of the above polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, neopentyl glycol, cyclohexane dimetatool, Examples include 2゜2-bis(4-hydroxycyclohexyl)propane, and bisphenol A to which ethylene oxide or propylene oxide is added. Examples of polyester polyols include reaction products of one or more of the above-mentioned polyether polyols and dibasic acids such as adipic acid, sebacic acid, azelaic acid, and dodecanedicarboxylic acid, or their acid anhydrides. Can be mentioned. Diisocyanates used when producing polyurethane acrylate using the above materials include tolylene diisocyanate, 4,4゛-
Aromatic diisocyanates such as diphenylmethane diisocyanate, isophorone diisocyanate, 4,4“-
Alicyclic diisocyanates such as dicyclohexylmethane diisocyanate, hexamethylene diisocyanate,
Examples include aliphatic diisocyanates such as 2,2°-trimethylhexamethylene diisocyanate. Examples of the hydroxy group-containing polymerizable monomer include hydroxy group-containing methacrylates such as β-hydroxyethyl methacrylate, β-hydroxypropyl methacrylate, β-hydroxylauryl methacrylate, and ε-caprolactone-β-hydroxyethyl methacrylate.

Epoxy acrylates: As epoxy acrylates, the epoxy groups of various epoxy resins are esterified with acrylic acid or its derivatives to form acryloyl groups. Examples include bisphenol A type, novolak type, polyhydric alcohol type, polybasic acid type, and polybutadiene type.

Polyester acrylates: Examples of polyester acrylates include ethylene glycol, diethylene glycol, 1.4-butanediol, 1.6-hexanediol, trimethylolpropane, dipropylene glycol, polyethylene glycol,
At least one polyhydric alcohol such as polypropylene glycol, pentaerythritol, and dipentaerythritol and a polyhydric alcohol such as phthalic acid, adipic acid, maleic acid, trimellitic acid, itaconic acid, succinic acid, terephthalic acid, and alkenylsuccinic acid. Examples include those obtained by acrylicizing a polyester obtained from at least one type of polyester.

Polysilicon acrylate R: Examples of polysilicon acrylates include those obtained by reacting a polysiloxane containing a hydroxyl group with an alkoxysilane containing a methacrylic group, those obtained by reacting a polysiloxane containing a hydroxyl group with a compound such as allyl methacrylate, and polysiloxane containing a hydroxyl group. Compounds using cinnamoyloxymethyljethoxysilane, compounds made by adding a bisazide compound to polydiorganosiloxane, photosensitive silicones reacted with acryloyl chloride or p-azidobenzoate, silicones introduced with mercapto groups, etc. These include silicone, which is made by introducing a photoreactive functional group into siloxane and adding a photoinitiator or sensitizer.

In addition to the above, urethane-epoxy acrylates, polyester-urethane-acrylates, polyether acrylates, polyol acrylates, alkyd acrylates, polyacrylates, or even US Pat. No. 3,876,432, US Pat. No. 3,673,140, US Pat. , acryloyl group-containing organic resins described in the same No. 4099837 and the like can also be suitably used. Paints made of ultraviolet curable compositions comprising the photocurable resin described above and various agents such as photocurable monomers, polymerization initiators, photosensitizers, and polymerization inhibitors can also be suitably used.

1 to 4 show cross-sectional views of a circuit board at each step in the method of the present invention.

The circuit board 1 shown in FIG. 1 has a structure having an organic polymer insulating layer 2 and an electric circuit 3 on a metal substrate l. First, a photocurable paint 4 is applied to the entire surface of the electric circuit 3. It is (
(Fig. 2), then place a mask with a desired light-transmitting hole pattern on the photocurable paint 4, irradiate it with light such as ultraviolet light, and finally dissolve the uncured paint in the unirradiated area with an appropriate organic solvent. Figure 3 or 4 with the photocurable paint section 4° removed.
A circuit board having the structure shown in the figure is obtained. In the circuit board shown in FIG. 3, an electrically insulating photocurable paint is used to cover all parts of the surface of the electric circuit 3 except for the part 31 that requires electrical connection work, that is, the surface of the electric circuit 3. The edge portion 32 and the space 5 between the electric circuits 3 are covered with a photocurable paint portion 4°, and in the circuit board of FIG. 4, the electric circuit 3 is coated with a semiconductive photocurable paint. Only the edge portion 32 is covered with the photocurable paint portion 4''.

5 and 6 are both enlarged cross-sectional views of a portion of the surface of the electric circuit 3 where only the edge portion 32 is covered with the photocurable paint portion 4'; It is preferable that the distance α from the edge edge where the surface of the electric circuit 3 is covered by the cured paint portion 4'' be at least 0.1 mm.

Further, as shown in FIG. 6, the edge portion 32 has a cross section with a radius of about 0.0 mm centered on the edge end. It is preferable that it has a circular shape or a shape close to it with a diameter of about 01 to 1.0 mm. The circular cross-sectional coating at the edge portion 32 is coated with the photocurable paint 4.
This can be achieved by coating the film to the required thickness and irradiating it with light using a mask with a circuit pattern shape that is 0.1 to 0.3 mm smaller than the original circuit pattern.

Note that the photocurable paint 4 used in the present invention has a molecular weight of 100 to 10,000 cps, particularly 500 to 5.0 cps, at room temperature. O
It is preferable to have a viscosity in the range of OOcps, and it may contain inorganic powder such as alumina or zirconia to improve corona resistance, or it may contain carbon blank, conductive metal powder, etc. to make it semiconductive. It is okay if it is

So far, we have shown technology using photocurable resin, but
The same results can be obtained by using a photodegradable resin, masking parts other than the circuit pattern, irradiating light to decompose the resin in the circuit pattern part, and then dissolving and removing it with an organic solvent or the like.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples in any way.

Example 1 A polyimide film (thickness: 25u*) with a 15μ-thick adhesive layer on both sides was placed on a 2.0-thick aluminum plate, and a 35μ-thick copper foil was placed on top of it. were stacked and heat pressed at 170°C for 160 minutes at 30kg/cd to obtain a circuit board material.

A 100mm square piece was taken from this circuit board material, and then the copper foil layer was etched to form a 30mm square piece in the center of the 100mm square piece.
A large number of simulated circuit boards were obtained in which the copper foil layer was left only at the 11I11 corners. The side surface of the copper foil layer of the sample was completely coated with an ultraviolet curable paint made of an epoxy acrylate-based chemical composition.
Apply a mask and irradiate ultraviolet rays for about 30 seconds to harden.
A portion 31 of the surface of the electrically insulated electrical circuit 3 that requires electrical connection work, such as the circuit board shown in FIG.
A circuit board was obtained in which all other parts except for the edges 32 of the electric circuits 3 and the gaps 5 between the electric circuits 3 were covered with the photo-curing paint part 4°. The covering distance α from the edge of the portion 31 requiring electrical connection work was 0.3 mm.

Example 2 A circuit board was produced in the same manner as in Example 1 except that a polysilicon acrylate material was used as the ultraviolet curable paint. The covering distance α from the edge of the portion 31 where electrical connection work is required was 0.2-.

Comparative Example 1 An etched sample was prepared in the same manner as in Example 1, and then used as an evaluation sample without using an ultraviolet curable paint.

For each sample of Examples 1 to 2 and Comparative Example 1, AC 2 kV (60 tlz) was applied between the aluminum plate and the copper foil layer, and the time until dielectric breakdown occurred, that is, the applied life (unit: : Time) was measured. At that time, the corona onset voltage (CV, unit: ■) was also measured.

The measurement results for the average value (Av) and standard deviation (σ) of the charging life (L) and the corona onset voltage (CV) are shown in the table below.

table

[Brief explanation of the drawing]

1 to 4 show cross-sectional views of a circuit board at each step in the method of the present invention. 5 and 6 are both enlarged sectional views of a portion of the surface of the electric circuit 3 in which only the edge portion 32 is covered with the photocuring paint portion 4'. 1 Circuit board 2 Organic polymer insulating layer 3 Electric circuit 31 Portion where electrical connection work is required 32 Edge portion 4 Photo-curing paint 4゛ Photo-curing paint portion 5 Between the electric circuits 3 Figure 1 Figure 2 Figure 4 Figure SFigure 6

Claims (1)

[Claims] For circuit boards that have an organic polymer electrical insulating layer on a metal substrate and an electrical circuit on top, a photocurable paint is applied to the entire surface on which the electrical circuit is present, and at least the electrical All edges of the circuit are left unmasked, while at least the parts of the surface of the electrical circuit that require electrical connections are masked and exposed to light to harden the paint on the irradiated areas. A method for manufacturing a circuit board, characterized by removing paint from non-irradiated areas.