JPH0931211A - Production of laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laminate expressing extremely excellent silver transfer resistance and useful for silver through-hole wiring boards, etc., by preliminarily impregnating base paper with formaldehyde. SOLUTION: Before base paper is impregnated with a thermosetting resin (e.g. a phenolic resin), the base paper is treated with formaldehyde. The treatment method includes a method comprising impregnating the base paper with a formaldehyde aqueous solution (formalin) and subsequently heating the treated base paper to react paper fibers with the formaldehyde and simultaneously dry the treated base paper, and a method comprising reacting the base paper with the vapor of the formaldehyde in a gas phase. In either of the methods, the employment of a catalyst such as boric acid is preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a method of manufacturing a silver through-hole printed wiring board, in which a silver migration phenomenon which causes deterioration of reliability is less likely to occur (excellent silver migration resistance). It is a thing.

[0002]

2. Description of the Related Art Conventionally, a laminated board is obtained by impregnating a base paper with a thermosetting resin compound varnish, laminating a plurality of the impregnated papers, and laminating an adhesive-coated copper foil on one or both sides depending on the application. Manufactured by heat and pressure molding. It is well known that, after the laminated plate thus obtained is subjected to silver through-hole processing, if a voltage is applied between the silver through-holes under high temperature and high humidity conditions, a silver migration phenomenon occurs over time. There is. In particular, in a place where the distance between the silver through holes is close to each other, a silver transfer phenomenon occurs so as to connect the through holes inside the laminate, and eventually causes a short circuit.

The silver migration phenomenon occurs inside the paper fibers contained in the laminate. As a result of research on this phenomenon, it has been clarified that a large number of pores contained in the inside of the paper fiber are the pathway of the silver migration phenomenon. Therefore, during the thermosetting resin impregnation step, by impregnating the resin into the pores inside the paper fiber, the silver migration path can be blocked and the silver migration phenomenon can be suppressed.

Therefore, in order to impregnate the inside of the paper fiber with the resin, a method of swelling the paper fiber (increasing the pores inside the paper fiber) by impregnating the resin with a highly polar solvent such as water is proposed. However, in the presence of highly polar solvents, paper fibers are very likely to adsorb the resin, so only the solvent preferentially penetrates into the paper fibers, making it more likely than the surface of the base paper. It was found that the impregnation of the resin inside the paper fiber was insufficient at the central portion of the thickness.

In order to solve this problem, a method of extending the impregnation time or increasing the amount of resin has hitherto been taken, but it has a bad influence on the productivity and the workability (warping / punching) of the laminated plate. However, there was a limit to the method.
Further, as described in Japanese Patent Application No. 5-69770, a base paper is pretreated to reduce the swelling ratio with water, and as described in Japanese Patent Application No. 6-33938. Means have been taken for sufficiently impregnating the resin inside the paper fibers by a method such as using a base paper having a thin fiber wall.

However, Japanese Patent Application No. 6-27789,
Due to the development of a method for evaluating the impregnating property of paper fibers using a water-soluble paint as described in Japanese Patent Application No. 6-32678, there is uneven distribution of the resin impregnated inside the paper fibers of the laminated board, It was found that this is a major factor in preventing the silver migration phenomenon.

[0007]

The present invention has been completed as a result of various studies based on the knowledge about the silver migration phenomenon as described above to develop a laminated plate in which the silver migration phenomenon is less likely to occur. Accordingly, the present invention provides a method for manufacturing a laminated plate in which a silver migration phenomenon is less likely to occur.

[0008]

Means for Solving the Problems The inventors of the present invention treated the base paper with formaldehyde in advance, impregnated it with a predetermined amount of a thermosetting resin, and heat-pressed the formaldehyde so that the formaldehyde contained hydroxyl groups in the paper fiber. It has been found that, by reacting, the moisture resistance of the paper fiber is enhanced, the cellulose molecules are cross-linked and the pores inside the paper fiber can be reduced, and a laminate having excellent silver migration resistance can be produced.

As a method for treating the base paper with formaldehyde, a method of soaking the base paper in an aqueous formaldehyde solution (formalin) and then heating it to react the paper fiber with formaldehyde and drying the base paper is used. There is a method of reacting fiber with formaldehyde, and in any case, a catalyst such as boric acid can be used.

Examples of the base paper used in the present invention include kraft paper and linter paper. As the thermosetting resin, phenol resin, epoxy resin, unsaturated polyester resin, melamine resin, etc., or tung oil,
Dry oils such as tall fatty acid, cashew oil, linseed oil, castor oil, linolenic oil, linole oil, epoxidized vegetable oil,
Semi-drying oils, glycerides thereof, epoxidized polybutadiene, polyethylene glycols, polyesters, polyethers and the like modified with a flexibilizing agent may be used, and these may be used alone or in combination.

In this method, after the impregnation treatment with the non-polar solvent, 2
It can be applied to both step impregnation (primary treatment of low molecular weight resin on the base paper) and single impregnation (no primary treatment on the base paper), but the effect is better when applied to the two-step impregnation. large.

[0012]

The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Formaldehyde 37 was used as the base paper.
% Aqueous solution and dried, and then impregnated with a phenol resin to a resin content of 60% to obtain a prepreg a.
The eight prepregs and the copper foil with an adhesive were superimposed on both front and back surfaces, and were heated and pressed to obtain a laminate A having a thickness of 1.6 mm.

<Example 2> Formaldehyde 65 was used as the base paper.
% Aqueous solution and dried, and then impregnated with a phenolic resin to a resin content of 60% to obtain a prepreg b.
Eight prepregs and copper foil with an adhesive were superimposed on both front and back surfaces thereof, and heated and pressed to obtain a laminate B having a thickness of 1.6 mm.

Example 3 A prepreg c was obtained by allowing the base paper to stay in formalin vapor at 120 ° C. for 5 minutes to react with the paper fiber and then impregnated with a phenol resin so that the resin content was 60%. . Eight sheets of the prepreg and copper foil with an adhesive were superimposed on both front and rear surfaces thereof, and heated and pressed to obtain a laminate C having a thickness of 1.6 mm.

Comparative Example 1 A prepreg d was obtained by directly impregnating a base paper with a phenol resin so that the resin content was 60%. Eight prepregs and copper foil with an adhesive were superposed on both front and back surfaces of the prepreg and heat-pressed to obtain a laminate D having a thickness of 1.6 mm.

Table 1 shows the characteristics of each laminate obtained by the above method.

[Table 1]

(Test method for silver migration resistance) Land diameter 1.2 m
m, through hole diameter 0.5 mm, 10 silver through holes
Create a test pattern in which two circuits with 0 holes are arranged adjacent to each other so that the distance between the centers of the through holes is 1.5 mm. Under the conditions of a temperature of 40 ° C. and a humidity of 93% RH, the through holes are formed. A voltage (50 VDC) is continuously applied for a predetermined time, and the insulation resistance between through holes is measured thereafter. Judgment criteria: The one whose insulation resistance between through holes is less than 1 × 10 ⁸ is NG.

[0019]

As is clear from the above results, the laminated sheet obtained by the present invention has extremely excellent silver migration resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H05K 3/46 6921-4E H05K 3/46 H // H05K 1/03 610 7511-4E 1/03 610T

Claims (1)

[Claims] 1. A method for producing a laminated sheet, which comprises treating a base paper with formaldehyde prior to the step of impregnating with a thermosetting resin.