JPH0971671A - Production of laminated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laminated sheet uniformly impregnated with a thermosetting resin until the central part of the thickness of raw paper and having excellent resistance to transfer of silver by previously humidifying raw paper with water before impregnating a thermosetting resin and drying the raw paper by a specific method. SOLUTION: Raw paper (e.g. kraft paper or linter paper) is humidified with water and dried while applying such pressure as to compress the thickness of the raw paper thereto. Then, a thermosetting resin (e.g. phenol resin or epoxy resin) is impregnated into the dried raw paper. Water content in an amount of >=20wt.% based on the raw paper is preferably attached to the raw paper in a step for humidifying the raw paper. The permeation time of water content is preferably >=20sec. Raw paper density after drying is preferably 0.6-0.9g/cm<3> and residual water content is preferably reduced to <=10% based on the weight of the raw paper in a compressing and drying step. Furthermore, after impregnating the resin, plurality of the resultant prepreg are usually laminated and a copper plate having an adhesive is superposed thereto and the laminate is heated and formed under pressure.

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 laminated board in which a silver migration phenomenon that causes a decrease in reliability is unlikely to occur in a silver through-hole printed wiring board, that is, silver migration resistance is excellent. 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. In order to prevent the occurrence of the silver migration phenomenon that occurs inside such a laminated plate, Japanese Patent Application Nos. 6-69770 and 6-339.
By the method as described in the specification of No. 38 and the like, a means for increasing the impregnation of the resin into the paper fiber has been taken.

However, due to the development of the impregnating property evaluation method as described in Japanese Patent Application No. 6-27789 and Japanese Patent Application No. 6-032678, the laminate is impregnated with resin inside the paper fiber. It was found that there was a bias in the occurrence of silver and this was a major factor in the occurrence of the silver migration phenomenon.

[0004]

The present invention has been completed as a result of various studies based on the knowledge of such a silver migration phenomenon, and provides a method for producing a laminated plate in which the silver migration phenomenon is less likely to occur. To do.

[0005]

According to the present invention, before the impregnation step of the thermosetting resin, after the base paper is moistened with water,
The present invention relates to a method for producing a laminated plate having high silver migration resistance by drying while applying pressure so as to compress the thickness of the base paper.

The silver migration phenomenon occurs inside the paper fibers contained in the laminate. It is known that this silver migration phenomenon has a large number of pores contained in the inside of the paper fiber as this route. Therefore, by impregnating the resin into the pores inside the paper fiber during the impregnation step, it is possible to block the silver migration path and suppress the silver migration phenomenon. Therefore, in order to impregnate and permeate the resin inside the paper fiber, the resin has been swelled (the pores inside the paper fiber have been enlarged) by impregnating the resin with a solvent having a high polarity such as water. But,
In the presence of a highly polar solvent, the paper fiber easily adsorbs the resin, so only the solvent preferentially penetrates into the paper fiber, and the central portion in the thickness direction of the base paper compared to the surface of the base paper. Then, the permeation of the resin into the paper fibers is remarkably insufficient.

In order to solve this problem, a method of extending the impregnation time or increasing the amount of resin has been conventionally used, but the productivity and the workability of the laminated plate (warpage / punching) have been improved. The method was limited because of the adverse effects.

However, the inventors believe that the swelling of the base paper in the thickness direction when the base paper is impregnated with the resin promotes insufficient resin impregnation in the central portion of the base paper, and after the base paper is moistened with water, the base paper thickness is reduced. By drying while applying pressure to compress the base paper, it is possible to prevent the base paper from swelling during resin impregnation and evenly impregnate the resin up to the center of the thickness of the base paper.After that, impregnate the required amount of resin. It was found that the laminated plate obtained by laminating pressing has excellent silver migration resistance.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the step of wetting paper fibers with water, it is preferable to attach 20% by weight or more of water to the base paper. The upper limit of the water adhesion amount is the upper limit of the water retention amount of the base paper and is 100 to 200% by weight depending on the type of the base paper.
In order to obtain such an adhesion amount, it is necessary to set the moisture penetration time to 20.
It is preferable to set it to be more than a second. In the next compression drying step, the density of the base paper after drying is 0.6 to 0.9 g / cm.
^{3. It} is preferable that the residual water content is 10% or less of the base paper weight.

Examples of the base paper used in the present invention include kraft paper and linter paper. As the resin, phenol resin, epoxy resin, unsaturated polyester resin, melamine resin, etc. , Semi-drying oils, or those obtained by modifying these with a flexibilizing agent such as glyceride, epoxidized polybutadiene, polyethylene glycol, polyester, polyether,
These are used alone or in combination. In the impregnation step of the thermosetting resin of the present invention, any impregnation method can be applied.

[0011]

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 30% by weight of water was made to adhere to the base paper to moisten it, and then the base paper density was 0.7 g / cm.
^3. After drying while compressing to a residual water content of 7% by weight, a prepreg a was obtained by impregnating a tung oil-modified phenol resin so that the resin content was 60% by weight. 8 pieces of this prepreg and copper foil with adhesive on both sides
Heat-press molding was performed to obtain a copper-clad laminate A having a plate thickness of 1.6 mm.

Example 2 As in Example 1, the base paper was moistened, compressed and dried, then primary impregnated with methanol and a low molecular weight phenolic resin varnish to a resin content of 10% by weight, and then the resin content. A prepreg b was obtained by second impregnation with a tung oil-modified phenol resin so that the amount of the prepreg b was 60% by weight. 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 copper-clad laminate B having a thickness of 1.6 mm.

Comparative Example 1 A prepreg c was obtained by impregnating a base paper with a tung oil-modified phenol resin so as to have a resin content of 60% by weight without water-wetting treatment. 8 pieces of this prepreg and copper foil with adhesive on both sides
Heat-press molding was performed to obtain a copper-clad laminate C having a plate thickness of 1.6 mm.

Comparative Example 2 The base paper was not impregnated with water but was first impregnated with methanol and a low molecular weight phenolic resin varnish to a resin content of 10% by weight, and then with a resin content of 60% by weight. Tung oil-modified phenol resin was secondarily impregnated to obtain prepreg d. This prepreg 8
Copper foil with an adhesive was placed on both sides of the sheet and heat-pressed to obtain a copper-clad laminate D having a thickness of 1.6 mm.

Table 1 shows the characteristics of each copper-clad laminate obtained by the above method. Table 1 Silver migration resistance (unit: Ω) ──────────────────────────── 250 hours 500 hours 1000 hours 2000 hours ─── ───────────────────────── Example 1 6.8 × 10 ⁹ 5.6 × 10 ⁹ 4.3 × 10 ⁹ 3.2 × 10 ⁹ Example 2 1.0 × 10 ¹⁰ 1.0 × 10 ¹⁰ 8.9 × 10 ⁹ 7.5 × 10 ⁹ Comparative Example 1 NG Comparative Example 2 8.4 × 10 ⁸ 3.2 × 10 ⁸ NG ────────────────────── ───────

(Test method for silver migration resistance) Two circuits each having 100 silver through-holes with a land diameter of 1.2 mm and a through-hole diameter of 0.5 mm are connected to the copper clad laminate obtained by the above method. Distance between through hole centers is 1.5 mm
Create a test pattern adjacent to each other so that a voltage (50VDC) is continuously applied between the through holes for a predetermined time under the conditions of temperature 40 ° C. and humidity 93% RH, and then insulation between the through holes is performed. Measure resistance.・ Criteria: If the insulation resistance between through holes is less than 1.0 × 10 ⁸ , it is judged as NG.

[0018]

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

Claims (3)

[Claims] 1. A method for producing a laminated sheet, characterized in that a base paper is wetted with water before the impregnation step, dried while applying pressure so as to compress the thickness of the base paper, and then impregnated with a thermosetting resin. Method. 2. In the step of wetting the base paper, 2 is added to the base paper.
The base paper density is set to 0.6 to 0.9 g / cm ³ after the compression drying step by adhering 0% by weight or more of water.
A method for producing the laminated plate described. 3. The method for producing a laminated board according to claim 1, wherein the thermosetting resin is a phenol resin.