Research On Reliability Of Silicon Via Interconnect Technology

IC Packaging is the key technology semiconductor industry. Semiconductor process has been developed rapidly followed by Moore's Law. The IC packaging has become the bottleneck of IC performance. Demand for high speed, high density, small size, and multi-functional electronic devices (particularly mobile devices) have driven the development of 3D integration, in which different functional devices are integrated into one package. Among 3D integration technologies, it is believed that through silicon via (TSV) interconnection is the ultimate way for 3D die stack application. With the development of IC packaging aim to smaller size and higher performance,3D integration based on TSV interconnect technology has been applied to the flash and image sensor. However, the research of reliability of through silicon via interconnect technology are not sufficient.In this study, TSV samples were assembled on PCB board and the reliability were evaluated by temperature cycling, thermal shock, drop test and moisture sensitivity level test according to the JEDEC standards for electronic assembly. The failure mechanism and the influence of underfill on the reliability of the TSV devices were discussed.Thermal-mechanical reliability of TSV device was researched by temperature cycling and thermal shock experiments. TSV device showed excellent reliability in temperature cycling due to the tiny packaging size. However, TSV device failed to-55℃～125℃thermal shock test. Failure analysis was performed to investigate the failure mechanism. The thermal expansion mismatch of four packaging materials applied constant thermal stress on aluminum layer, the fracture on aluminum layer results the failure of TSV device. Two different underfills were applied and the reliability was improved.PCB board has been designed followed by JEDEC standard of drop test.1500G, 0.5ms, half sine pulse was selected as the test condition. Except static electrical test, transient signal during the drop was detected by high speed acquisition device. Solder ball was the lower reliability part in TSV interconnection system, the application of underfill between PCB board and device could improve reliability obviously.TSV devices have passed moisture sensitivity test level 1-3 without any failure. However, the application of two underfills result a severe failure after MSL1. Humidity absorption by underfill was the failure mechanism. During reflow process, polymer cracked due to underfill expansion. Two failure modes were discussed:open circuit and short circuit. Stress which applied on silicon and break the aluminum layer result to open circuit failure. Solder ball was melt during reflow and solder flows along the crack in Polymer A and B, copper lines were shorted by solder, which caused short circuit failure.