Morphological evolution and migration behavior of silver thin films on flexible substrates during thermal cycle testing

Abstract

To understand morphological evolution and migration behavior caused by stress migration and thermal fatigue of silver thin films on flexible substrates, bending tests were conducted with different bending angles for two types of thermal tests. Furthermore, the effect of stress migration and thermal fatigue on the electrical conductivity of the silver thin films was discussed. The experimental samples were silver thin films printed on flexible paper for these tests. In an ultra-low cycle thermal test, the electrical conductivity of a silver film decreased with increasing bending angle because of the occurrence of voids caused by stress migration. Meanwhile, a high-cycle thermal test caused cracks to form and caused further deterioration of the electrical conductivity owing to a combination of stress migration and thermal fatigue.

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“…In metallic wires, the wind force causes preliminary damage (voids) on the cathode side and hillocks on the anode side, whereas the direct force produces void on the anode side and hillocks on the cathode side [99]. Quan Sun and his team [100] studied the effect of stress migration and thermal fatigue of silver thin films on the flexible substrate. Their results indicated that the combination of thermal fatigue and stress migration increases the number of atomic diffusions then causes the thin films to experience cracks, voids, and hillocks, which could cause the electrical conductivity to deteriorate [100].…”

“…Quan Sun and his team [100] studied the effect of stress migration and thermal fatigue of silver thin films on the flexible substrate. Their results indicated that the combination of thermal fatigue and stress migration increases the number of atomic diffusions then causes the thin films to experience cracks, voids, and hillocks, which could cause the electrical conductivity to deteriorate [100]. According to Liu et al [101], copper diffuses into the silver layer's vacancies after the annealing process, and then the vacancies transfer to the copper layer.…”