Abstract
Adhesiveless materials are commonly used for electric or portable products that need high flexibility in operation. We studied a structure which included copper substrate and polyimide (PI) film without any resin to avoid residual resin issues during the manufacturing process. Life-time and fatigue characteristics require further study. Normally, the technique to measure life-time is by storing samples to monitor the changes over a long period, but this is time-consuming. An accelerated aging test is an alternative way to predict and evaluate the property shift in the short term; nevertheless, the test conditions will influence the results. Temperature and relative humidity are the major environmental parameters, and the conditions at 85°C/85% relative humidity (RH) and 150°C are discussed in this paper. A better prediction was found using accelerated testing at 85°C/85% RH after comparing with data from samples stored for 3 years, with errors <5%. Also, the copper grain microstructure affects the fatigue character and mechanical properties. The best flexibility is achieved when an appropriate copper and PI thickness has been identified.