Reliability Performance of Stretch Solder Interconnections

A wafer level packaging technique has been developed with an inherent advantage of excellent solder joint co-planarity essential for wafer level test and burn-in. A suitable weak metallization scheme has also been established for the detachment process. During the fabrication process, the compliancy of the solder joint is enhanced by stretching the solder joint to achieve high aspect ratio and small shape factor. Thermal cycling reliability of these hourglass-shaped, stretch solder joints has been found to be considerably better than that of the conventional spherical-shaped solder bumps.