Assembly Reliability of 3D Stacks under Thermal Cycles

Stack electronic packaging technologies have now been widely implemented to increase the capabilities of commercial electronics in order to overcome the limitation of die fabrication with extremely finer features. An special 3D leaded configuration using internally packaged memory has been widely used for high-reliability applications. Its new configuration comes in high-temperature ball grid array (BGA), which may be less robust than the leaded version. This paper compares thermal cycle reliability of 3D stack assemblies with two configurations-leaded and BGA. The two configurations were subjected to either accelerated thermal cycle (ATC) alone or with subsequent extremer thermal shock cycle (AT SC) in two ranges in order to determine robustness and to initiate earlier failures. The ATCs were in the range of - 55 degrees C to 100 degrees C whereas the ATSCs ranged from-100 degrees C to 125 degrees C. Extreme cold temperature exposure to -100 degrees C is representative of mild deep space environment whereas possibly none for industrial applications. Visual inspection with optical microscopy images dcoumented damage progression for leaded 3D assemblies with and without workmanship defects. However, daisy-chain resistance continuity monitoring was used as the key verification method for detecting failure of 3D BGA and using visual inspection as a secondary approach for monitoring damage progression. The inspection results were presented in detail for leaded assemblies with and without the edge adhesive staking. For 3D stack BGA assemblies, results of failure analyses were also presented. These were were performed by cross-sectioning with optical and scanning electron microscopy evaluation.