Effect of thermal aging on drop performance of chip scale packages with SnAgCu solder joints on Cu pads

Because of the trend of miniaturization, the drop performance of portable electronic devices is becoming increasingly critical. This study was focused on the influential factors in the drop performance of chip scale packages (CSPs) with Cu/SnAgCu solder joints after thermal aging. Assembled CSP test boards were thermally aged at 100-150 degrees C for up to 1,000 h before drop test. Microstructural evolution in the bulk solder and the interfacial region was investigated after drop test. Crack propagation by drop test and the fractured surfaces were examined by scanning electron microscopy. Kirkendall voiding at the solder/Cu interface and the thickness of interfacial intermetallic compounds did not have a significant effect on the occurrence of the first failure by drop test. Correlation between drop performance and microstructural changes was observed. A model was built to explain the complex drop test results based on the relationship between microstructure and mechanical properties of solder joints.