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An practical study on improving the lifetime of FPC with controlling the viscoelastic properties of adhesives

通过控制粘合剂粘弹性来提高 FPC 寿命的实践研究

基本信息

批准号：
03555021
负责人：
SUZUKI Hideto
金额：
$ 1.28万
依托单位：
IBARAKI UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

The fatigue reliability on the functional disorder of flexible printed circuit, FPC was experimentally studied upon the basis of the conventional works on the fatigue of structural materials. Especially, the size effect of component materials and mechanical properties of adhesives on NG life of FPC, Nf that is the electric resistance rising up to 10% of the original value, were examined under strain repetition.It was found by cyclic flexural testing that Nf could be improved by thinning the copper foil and also adhesives but inversely by thinning Kapton of the base material. Nf was related to the maximum strain of copper epsilon as the straight relation of epsilon * Nf in the log-log diagram. Then, it can be understood that the size effects in the copper conductor and the polyimide base are due to the strain of copper, epsilon. While, from the relation between the tensile properties of adhesives and Nf, it is suggested that the adhesive agent should be provided either flexibility and strength in order to improve FPC life.The fractography with SEM showed that the fatigue process of copper foil could be divided into three stages as follows:(1)the crack initiation, (2)the crack density increase, (3)the crack opening. Then, Nf was corresponded to the stage of (1), the crack initiation.Furthermore, it was experimentally found that the lifetime of FPC could be varried through controlling the glass transition temperature, Tg of adhesives and the tensile properties of cover films of super engineering plastic. By increasing Tg of adhesives or controlling its viscoelasstic property, the life time of FPC can be remarkably improved.

在结构材料疲劳可靠性研究的基础上，对柔性印刷电路板（FPC）功能紊乱时的疲劳可靠性进行了试验研究。特别地，在应变重复下，研究了元件材料的尺寸效应和胶粘剂的机械性能对FPC NG寿命的影响，即电阻上升到原始值的10%时的Nf，通过循环弯曲试验发现，Nf可以通过减薄铜箔和胶粘剂来提高，但相反地，通过减薄基材的Kapton来提高。在双对数图上，Nf与铜应变片的最大应变之间呈直线关系。然后，可以理解，铜导体和聚酰亚胺基底中的尺寸效应是由于铜的应变ε造成的。从胶粘剂的拉伸性能与Nf的关系来看，为提高FPC的使用寿命，胶粘剂应兼具柔韧性和强度. SEM断口分析表明，铜箔的疲劳过程可分为3个阶段：（1）裂纹萌生阶段;（2）裂纹密度增加阶段;（3）裂纹张开阶段.实验还发现，通过控制玻璃化转变温度、胶粘剂的Tg和超级工程塑料覆盖膜的拉伸性能，可以改变FPC的使用寿命。通过提高胶粘剂的玻璃化温度或控制胶粘剂的粘弹性能，可显著提高FPC的使用寿命。