The effect of underfill on the pressure cooker test performance of flip chip on board assembly

摘要

The use of polymer underfill in Flip chip on Board (FCOB) assembly can significantly enhance assembly reliability performance compared to un-underfilled assembly in the temperature cycling test. This is achieved by reducing the strain on solder joints caused by thermal mismatch of silicon chip and organic substrate. Although reliability performance of FCOB assembly in accelerated testing environment, such as thermal shock and temperature cycling, has been widely reported, the reliability performance data in Pressure Cooker Test (PCT) is not widespread. This paper addresses the above issue. Several types of underfill from different sources were used in FCOB assembly and PCT was performed. FCOB assembly without underfill was also tested for reference. It was found that underfill can either enhance, be compatible with, or deterirate the PCT performance as compared to that of un-underfilled FCOB assembly. It was also found that the adhesion of underfill to organic passivation material on the chip has a significant impact on PCT performance.