Copper wire bond strength reliability assessment

Experiments have been completed on dependence of the wire pull strength on aging duration in TCB(Temperature Cycle B), HTS(High Temperature Storage), uHAST(unbiased Highly Accelerated Stress Test), THS(Temperature Humidity Soaking), and PCT(Pressure Cooker Test) for non-molded bare Cu and Pd coated Cu wire bonded devices. The data can be summarized as follows: 1. Bare Cu is less robust to temperature cycling than Pd coated wire. 2. There was no significant difference between the two types of wires when exposed to either THS or HTS as no interfacial degradation was found for aging up to 1000 hours in either stress condition. 3. In both uHAST and PCT degradation of the interface was observed. In both stress tests more ball lifts were observed for bare Cu than for Pd coated Cu. However the time for onset of ball lift failures was the same for both wires. Finally the wire strength degradation was more severe for the Pd coated Cu than for the bare Cu. We interpret these results to be related to electrochemical degradation of the IMCs and of the wire itself.