A Comprehensive Test Method for Bridging the Gap between Product and Board Level Drop Tests

Due to rapid and continual changes in the components and designs of portable electronic devices, it is essential to have the ability to perform quick, cost-effective and accurate assessments of the drop impact performance of component interconnections for portable applications. In order to understand the phenomena of solder joint fatigue under impact-induced PCB bending, a tester was developed specifically for applying high bending strains at high strain rates to a PCB assembly. Fatigue characteristics of solder joints were determined for various PCB strains, allowing the construction of fatigue E-N (strain vs. cycles-to-failure) curves. Fatigue data was also generated for several bending frequencies in a study of the effect of strain rate on drop impact performance. Higher bending frequencies were found to reduce fatigue life. A comprehensive test method would also have to be capable of applying variable loading levels in order to replicate the complex loading spectrums seen in actual product drops. A variable amplitude study is presented, where crack propagation tracking shows the effect of changes in load levels on the crack growth rate. Finally, a study on the effect of low temperatures on drop impact reliability is presented, where fatigue characteristics were obtained using the bend tester fitted with a cold temperature chamber.