JPH0510840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a multilayer printed wiring board with improved reliability by preventing cracks in inner layer copper foil due to thermal stress. [Technical background of the invention and its problems] In recent years, multilayer printed wiring boards have become more multilayered, denser, and finely patterned. Requirements are also becoming stricter. As one of these requirements, it is desired to prevent cracks in the inner layer copper foil. That is, in general, a multilayer printed wiring board is produced by laminating a predetermined number of inner-layer circuit boards obtained by forming inner-layer circuits on epoxy resin copper-clad laminates with a prepreg adhesive layer interposed therein, and then adding copper foil to the outermost layer. , or manufactured by laminating single-sided copper-clad laminates with the copper foil facing outward, and electrically connecting the specified inner layer copper foil and the outermost layer copper foil with through-hole copper plating. . The electrolytic copper foil conventionally used for the inner layer has a thickness of 35 microns, an elongation of 2 to 3% at 180° C., and a tensile strength of 12 to 13 Kg/mm ² . However, in such multilayer printed wiring boards, there is a difference in the coefficient of thermal expansion in the thickness direction (Z direction) between the epoxy resin that is the base material and the through-hole plated copper. There was a problem in that when subjected to such thermal stress, cracks occurred in the inner layer copper foil adjacent to the through hole. [Purpose of the Invention] As a result of intensive studies in order to solve these conventional problems, the inventors of the present invention have solved the above-mentioned problems by using a copper foil with higher elongation and tensile strength at high temperatures than before as the inner layer copper foil. We have found that it is possible to prevent the occurrence of The present invention was made based on such knowledge, and aims to provide a highly reliable multilayer printed wiring board in which the inner layer copper foil does not crack after thermal stress. [Summary of the Invention] That is, the multilayer printed wiring board of the present invention has at least three or more layers of copper foil integrated through an insulating layer based on synthetic resin, and at least two or more layers of the copper foil are made of these. In a multilayer printed wiring board that is electrically connected by a through hole having a conductive coating on the inner wall that penetrates between the copper foils, the copper foil in the inner layer of the copper foil has an elongation of 25% when hot at 180°C. % or more, and has a tensile strength of 15 kg/mm ² or more. The inner layer copper foil of the present invention is a 1 oz.
Copper foil is used that has an elongation of 25% or more at °C and a tensile strength of 15 Kg/mm ² or more; below these values, it is not possible to prevent the occurrence of cracks due to heat stress, which is the objective of the present invention. Furthermore, for the outer layer copper foil, the insulating layer, and the through-hole plated copper of the present invention, publicly known materials that have been commonly used can be used, and although they are not particularly limited, they can be used as the base material for the insulating layer. When an epoxy resin is used, the difference in thermal expansion coefficient from that of plated copper is large and the copper foil tends to crack, so the effects of the present invention are particularly noticeable. The multilayer printed wiring board of the present invention can be manufactured by any known method. For example, first, an inner layer circuit is formed on an epoxy resin copper-clad laminate having high elongation and high tensile strength copper foil of the present invention on both sides to obtain an inner layer circuit board. It is obtained by laminating the laminate, overlapping ordinary copper foil on both sides of the laminate, and bonding them under heat using a hot press. [Examples of the Invention] Next, Examples and Comparative Examples of the present invention will be described. Example Hot elongation at 180℃: 25.0 % , tensile strength: 20.5
Kg/mm ² , a circuit pattern is formed using an etching resist on a 0.2 mm thick epoxy resin copper clad laminate made by laminating 35 micron thick copper foil (1 oz copper foil) on both sides, and a non-circuit pattern is formed using an etching resist. After removing the copper in the area by etching using ferric chloride and then peeling off the etching resist, the circuit copper foil was subjected to surface oxidation treatment to obtain an inner layer circuit board. The inner layer circuit board and prepreg obtained in this way are layered alternately, 18 micron thick ordinary copper foil is placed on both sides of the outermost layer, and the whole is heated with a hot press, pressurized, and laminated to form 14 layers. A multilayer printed wiring board was obtained. Comparative Example A printed wiring board was obtained using ordinary electrolytic copper foil (35 micron thick, elongation at 180°C hot is 2.5%, and tensile strength is 13 kg/mm ² ) as the copper foil for an epoxy resin copper-clad laminate. Ta. Next, regarding the multilayer printed wiring boards of Examples and Comparative Examples obtained in this way, MIL-STD-202E,
When we conducted a thermal shock test on 107D, we found that the example did not meet the quality standard MIL-P, as shown in the table below.
In the 1000 cycle test of -55110C, no cracks were observed in the inner layer copper foil, and good results were obtained that met the standards. [Table] [Effects of the Invention] As is clear from the above examples, according to the present invention, a copper foil that exhibits high elongation and high tensile strength at high temperatures is used for the inner layer copper foil, so it is difficult to solder or use environmental temperature. The occurrence of cracks in the inner layer copper foil after thermal stress such as changes in temperature is prevented, and reliability is improved.

Claims (1)

[Scope of Claims] 1. An inner wall in which at least three or more layers of copper foil are integrated through an insulating layer based on synthetic resin, and at least two or more layers of the copper foil penetrate between these copper foils. In a multilayer printed wiring board that is electrically connected by a through hole having a conductive coating,
A multilayer printed wiring board characterized in that the copper foil in the inner layer of the copper foil is a copper foil having an elongation of 25% or more and a tensile strength of 15 Kg/mm ^{2 or more} when hot at 180°C. 2. The multilayer printed wiring board according to claim 1, wherein the base material of the insulating layer is an epoxy resin.