JPH04185429A - Laminate and printed wiring board - Google Patents

Abstract

PURPOSE:To manufacture a wiring board of superior resistance to silver migration and resistance to electrolytic corrosion by forming an insulated layer composed of impregnation cured thermosetting resin on a paper base composed of fibers with specified maximum fiber length. CONSTITUTION:An insulated layer is formed by a paper base composed of fibers of maximum fiber length of 1.0mm or less impregnated with thermosetting resin. A laminate includes both of insulated sheets composed of insulated layers only and metallic foil clad laminates on which metallic foils such as copper foils are laminated on both faces. As for a paper base, kraft paper, linter paper or mixed paper is used. As for the thermosetting resin, phenol resin, dry oil modified phenol resin, epoxy resin, unsaturated polyester resin or the like is used. A printed wiring board is manufactured by circuit processing the laminate or a copper clad material, and the copper clad laminate is etched for manufacturing the printed wiring board.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laminate and a printed wiring board that have excellent silver migration resistance and electrolytic corrosion resistance.

[Prior art] Recently, as electronic devices have become more multi-functional and highly reliable, there has been an increase in the use of copper-plated through-holes and silver paste through-holes in laminates using paper base materials, and the demand for high reliability has increased. has been done. In particular, there is a need for a laminate with excellent silver migration resistance and electrolytic corrosion resistance.

To improve silver migration resistance and electrical corrosion resistance, there is a method of improving moisture resistance by treating the paper base material with water-soluble phenol resin, water-soluble melamine resin, etc.

[Problem to be solved by the invention] However, when improving the moisture resistance weakness of the base material using the above method, as the density of the circuit increases, the distance between the walls of the through holes between different poles becomes smaller. , the silver migration properties and the electrolytic corrosion resistance deteriorated rapidly, and it was not possible to obtain a laminate with sufficiently satisfactory properties using the above method.

An object of the present invention is to provide a laminate and a printed wiring board that are excellent in silver migration resistance and electrolytic corrosion resistance in view of the above problems.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors have conducted extensive studies on the relationship between the fiber length of the paper base material and the silver migration property and the occurrence of electrolytic corrosion. It has been discovered that when the distance between the walls of the through-holes is smaller than the fiber length of the filter paper base material used as the base material of the laminate, silver migration and electrolytic corrosion deteriorate rapidly, and based on this knowledge, the present invention was developed. It has been completed.

That is, the present invention provides a laminate having an insulating layer formed by impregnating and curing a thermosetting resin into a paper base material made of fibers having a maximum fiber length of 1.0 mm or less.

In the present invention, the laminate includes both an insulating board having only an insulating layer and a metal foil-clad laminate in which metal foil such as copper foil is laminated on one or both sides of the insulating board.

Paper base materials used in the present invention include kraft paper, linter paper, and mixed paper. Further, the paper base material may be treated with a phenol resin, melamine resin, etc. in advance.

The maximum fiber length of the fibers used for the paper base material is 1. When it exceeds 0 mm, silver migration resistance and electrolytic corrosion resistance deteriorate significantly. The length of the fibers only needs to satisfy the above conditions, but 0. Preferably, the diameter is 3 mm to 0.9 mm.

Examples of thermosetting resins include phenolic resins, drying oil-modified phenolic resins, epoxy resins, and unsaturated polyester resins. Thermosetting resins may be modified using drying oils such as tung oil, polyesters, polyethers, and epoxidized polybutadienes.

In order to impart flame retardancy, brominated epoxy resins, brominated phenols, phosphoric acid esters, etc. are added to thermosetting resins.

The laminate of the present invention is usually manufactured by the following method. That is, a fabric obtained by adjusting the viscosity of the above thermosetting resin with a solvent is impregnated into a base paper having a maximum fiber length of 1.0 mm or less, which has been previously treated with a water-soluble phenol resin, and dried to obtain a prepreg. A required number of sheets of this prepreg are stacked together and molded under heat and pressure to form a laminate. Further, a required number of prepregs and copper foils are stacked and heated and press-molded to form a copper-clad laminate. Adhesive strength is improved by using copper foil with adhesive.

Laminated boards and copper-clad laminates are processed into printed wiring boards by circuit processing, and copper-clad laminates are processed by etching into printed wiring boards. Silver through-holes are manufactured by filling holes formed by drilling or punching with silver paint and then drying them. Further, the copper-plated through hole is formed by electrolytic plating, electroless plating, etc. in a hole formed by drilling or punching.

Holes for components such as semiconductors and resistors in printed wiring boards are generally formed by drilling, punching, etc.

[Function] The reason why silver migration resistance and electrolytic corrosion resistance are improved when the maximum fiber length of the paper base material is set to 1.0 mm or less in the present invention is considered to be as follows.

Normally, in a humidified and heated current conduction test of a silver through-hole printed wiring board, silver ions migrate from the positive electrode to the negative electrode along the fibers of the paper base material. When the maximum fiber length of the paper base material is set to 1.0 mm or less, the migration of silver ions is suppressed, and the insulation properties of the laminate are less likely to deteriorate in an electrical conduction test under humidified and heated conditions. Conversely, if the maximum fiber length of the paper base material is 1. If it exceeds 0mm, especially the distance between the through hole and the wall of the through hole between different poles,
The migration of silver ions is promoted, and the insulation of the laminate deteriorates.
It is thought that as a result, silver migration resistance and electrolytic corrosion resistance deteriorate.

[Examples] The present invention will be explained in detail based on Examples below, but the present invention is not limited thereto.

Example 1 Kraft paper with a maximum fiber length of 0.9 mm and an average fiber length of 0.7 mm, which had been previously treated with a water-soluble phenol resin so that the resin adhesion amount was 14 to 20% by weight, was coated with a tung oil modification rate of 35.
It was impregnated with % by weight of resol phenol resin and dried to obtain a prepreg (resin adhesion amount: 48 to 60% by weight). Eight sheets of this prepreg and adhesive-coated copper foil were combined and heated and pressed to obtain a copper-clad laminate.

Comparative Example 1 The maximum fiber length was 1°3 mn+, which was previously treated with water-soluble phenol resin so that the resin adhesion amount was 14 to 20% by weight.
Kraft paper with an average fiber length of 1.1 mm+ was impregnated with a resol phenol resin having a tung oil modification rate of 35% by weight and dried to obtain a prepreg (resin coverage: 48 to 60% by weight). Eight sheets of this prepreg and adhesive-coated copper foil were combined and heated and pressed to obtain a copper-clad laminate.

The properties of the obtained laminate are shown in Table 1.

Table 1 Silver migration resistance test results Silver migration resistance test method Hole pitch 2. Omm, pitch between through hole and through hole wall 1.1 mm, hole diameter φ0.9, land diameter φ1
．． 5. It was measured as the circuit insulation resistance after processing for 500 hours and 1000 hours under the conditions of an applied voltage of 50 V, a temperature of 90% RH, and a temperature of 40° C. in a silver migration test pattern of two consecutive circuits of 90 holes.

[Effects of the Invention] The laminate obtained by the present invention has excellent silver migration resistance and also excellent electrolytic corrosion resistance.

Claims (2)

[Claims] 1. A laminate having an insulating layer formed by impregnating and curing a thermosetting resin into a paper base material made of fibers with a maximum fiber length of 1.0 mm or less. 2. A printed wiring board formed by processing a circuit on the laminate according to claim 1.