In the development of highly heat resistant modules containing SMDs (surface mount devices) that are used in automotive electronic equipment, it is important to study the degradation behavior of SMD solder joints at high temperatures. We compared the high-temperature degradation behaviors of solder joints in SMDs with different electrode structures and studied the relationship between electrode structure and degradation behavior. We exposed this module to high temperatures and observed the sections of SMDs with solder joints. Our results showed that an intermetallic compound layer is formed between the joint boundary layers of the solder and the electrode and its thickness increases with elapse of time. Furthermore, when the modules were exposed to high temperatures for extended periods, the other degradation modes shown below were observed depending on the electrode specifications of SMDs. (1) Exfoliation of the interface caused by embrittlement of intermetallic compound layer and cracks formed in the interface of the intermetallic compound layer or solder (2) Exfoliation of the interface caused by interconnection of voids formed in the interface In addition, we estimated the thickness of the intermetallic compound layer that would be generated at high temperatures, and made a life prediction for the SMD at 150 °C. Our results suggest this to be approximately 15,000 hours for a thickly plated electrode. Accordingly, we found that SMDs with thickly plated electrodes that have a stress relaxation layer were ideal for creating reliable solder joints at high temperatures.
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