JPH0931210A - 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 a non-polar solvent. SOLUTION: Before base paper is impregnated with a thermosetting resin (e.g. a phenolic resin), the base paper is impregnated with a non-polar solvent in an amount of 5-20%. The solvent is preferably toluene, acetone, methylethylketone, diethylether, methanol, ethanol or propanol. For example, the base paper is preferably impregnated with the solvent and subsequently subjected to two stage impregnation treatments (containing the impregnation of the base paper with a low mol.wt. resin).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silver through-hole printed wiring board for producing a laminated board which is less likely to cause a silver migration phenomenon which causes deterioration of reliability of electrical characteristics and the like, that is, excellent in silver migration resistance. It provides a method.

[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]

According to the present invention, prior to the step of impregnating a base paper with a thermosetting resin, the base paper is impregnated with a non-polar solvent in an amount of 5 to 20% by weight, and then the thermosetting resin is impregnated. The present invention relates to a method for producing a laminated sheet, which is characterized in that the base paper is impregnated with a non-polar solvent in advance, and the thermosetting resin impregnated thereafter is evenly distributed inside the paper fiber of the base paper. As a result, it is possible to obtain a laminate having high silver migration resistance.

The impregnation amount of the non-polar solvent is 5 with respect to the weight of the base paper.
-20%, preferably 7-15%. When the amount of impregnation is in this range, only the silver migration resistance can be improved without affecting the productivity of the laminate and the workability after molding. If it is less than 5%, the effect of improving the resistance to migration of silver is insufficient, and if it exceeds 25%, the above-mentioned processability and productivity are deteriorated.

Examples of the base paper used in the present invention include kraft paper and linter paper. The non-polar solvent referred to in the present invention is a solvent that does not substantially swell the base paper,
Aromatic hydrocarbons such as toluene and xylene, acetone,
Examples thereof include ketones such as methyl ethyl ketone, ethers such as diethyl ether, alcohols such as methanol, ethanol, and propanol. As a preferable solvent, toluene, acetone, methyl ethyl ketone (MEK), diethyl ether, methanol, ethanol, purpanol and the like are suitable because they are easily evaporated and are easily available.

As the thermosetting resin, a phenol resin,
Epoxy resin, unsaturated polyester resin, melamine resin, etc., or these, tung oil, tall fatty acid, cashew oil, linseed oil, castor oil, linolenic oil, linole oil, epoxidized vegetable oil and other drying oils, semi-drying oils, glycerides of these , Epoxidized polybutadiene, polyethylene glycol, polyester, polyether, and the like, which are modified with a flexibilizing agent, and these may be used alone or in combination.

In this method, when two-stage impregnation is performed after impregnation with a non-polar solvent (the base paper of the low molecular weight resin has a primary treatment), only one-stage impregnation (the base paper does not have a primary treatment).
However, the effect is greater when applied to the two-stage impregnation.

[0013]

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 A prepreg a was obtained by previously impregnating a base paper with 7% toluene based on the weight of the base paper and then impregnating a phenol resin so that the resin content was 60%.
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 The base paper was previously impregnated with 15% toluene based on the weight of the base paper, and then impregnated with a phenol resin so that the resin content was 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 The base paper was previously impregnated with 7% of isopropanol based on the weight of the base paper, and the resin content was 60%.
Prepreg c impregnated with phenol resin so that
I got Eight sheets of this prepreg and copper foil with adhesive are laminated on both sides and heat-pressed to obtain a plate thickness of 1.6 mm.
A laminated plate C of was obtained.

Example 4 The base paper was previously impregnated with 15% of isopropanol based on the weight of the base paper, and the resin content was 60%.
% To obtain a prepreg d. Eight sheets of this prepreg and copper foil with adhesive on both front and back sides are laminated, and heat and pressure molded to obtain a plate thickness of 1.6 m.
A laminated plate D of m was obtained.

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

Comparative Example 2 The base paper was previously impregnated with 3% toluene based on the weight of the base paper, and then impregnated with a phenol resin so that the resin content was 60% to obtain prepreg g.
Eight prepregs and copper foil with an adhesive were superposed on both the front and back surfaces of the prepreg and heat-pressed to obtain a laminated plate G having a plate thickness of 1.6 mm.

Comparative Example 3 The base paper was previously impregnated with 25% toluene based on the weight of the base paper, and then impregnated with a phenol resin so that the resin content was 60% to obtain prepreg g. Eight prepregs and copper foil with an adhesive were superposed on both the front and back surfaces of the prepreg and heat-pressed to obtain a laminated plate G having a plate thickness of 1.6 mm.

The silver migration resistance of each laminate obtained by the above method was measured, and the results are shown in Table 1.

[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.

[0023]

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

Claims (2)

[Claims] 1. A laminated sheet characterized by impregnating a base paper with a non-polar solvent in an amount of 5 to 20% by weight prior to the step of impregnating the base paper with the thermosetting resin, and then impregnating the thermosetting resin. Manufacturing method. 2. The method for producing a laminated sheet according to claim 2, wherein the non-polar solvent is toluene, acetone, methyl ethyl ketone (MEK), diethyl ether, methanol, ethanol or purpanol.