| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1992: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1991: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
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.
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