Fatigue properties of base copper materials used in the fabrication of TAB leads

An attempt was made to characterize the mechanical properties of various types of copper foils that are used for TAB (tape automated bonding) fabrication with a special emphasis on fatigue properties. Coffin-Manson plots of strain range versus cycles-to-failure and fatigue ductility values were generated from testing of specimens. In general, the wrought foils showed a high degree of anisotropy with up to a 5 to 1 difference in cycles-to-failure between machined and cross-machined directions. The anisotropy was observed to be much lower in the low-temperature annealable wrought foils, about 1.5 to 1. Observed grain structures of these materials correlated to their anisotropic behavior, with the low-temperature annealable materials showing smaller amounts of directionality in their microstructure. The ED (electrodeposited) coppers tested had fine-grained equiaxial structures with no significant effects from direction of test. Of the samples tested, the ED coppers performed better at low-cycle, high strain rates, while the wrought coppers had the best performance at high-cycle, low strain rates. The results of this work show that the fatigue performance of a particular type or temper of copper is an important consideration when designing a TAB tape