Characteristics of the interfacial microstructure of chip-on-plastic joints under thermal cycling and aging treatment

Abstract

This study presents the change of contact resistance and microstructure evolution of chip-on-plastic (COP) joints during the thermal cycling (T/C) test and aging treatment. Results showed that the average contact resistance of COP joints decreased in the early stage of the T/C test as well as during aging treatment. It was observed that after 1,000 h of aging, the (Cu, Au)(3)Sn phase was completely consumed and transformed into (Cu, Au)(6)Sn-5. The dependence of the growth of interfacial intermetallic compounds (IMCs) on the time of T/C and aging was investigated. The IMC growth had parabolic kinetics with time. The time exponent n under the condition of T/C was approximately 0.5, which indicated that the IMC growth was diffusion controlled. However, the fitting results on the aging treatment showed that n was only about 0.37. The reason for this finding is considered to be due to the fact that after 250 h, the Cu in some areas was depleted; thus, the diffusion in these areas was restrained.