Copper ball bond shear test for two pad aluminum thicknesses

Abstract

Copper (Cu) wirebonds exhibit higher strength and stiffness as compared to gold (Au) wirebonds. Cu's higher shear strength is studied in this project. There is currently no industry standard specifically for the Cu ballbond shear procedure nor an appropriate bond reliability specification limit. The JEDEC industrial standard JESD22-B116A “Wire Bond Shear Test Method”, issued in 1998, covers Au ball bond reliability testing by shear. Companies typically apply the shear test limits of Au from this standard to Cu ball bonds on Al pads in manufacturing, though the Cu bonds may show significantly more shear strength than Au balls. Cu wirebonds have different failure modes, so a unique test method and reliability spec limit for Cu bonds is needed. ON Semiconductor has conducted experiments comparing shear test results for two Cu ball diameters on two different Al thicknesses, participating in the industrial committee to develop a new Cu shear test procedure (in progress). Selected data from the ON experiments are provided in this paper, demonstrating the behavior of Cu as compared with the limits that were developed for Au ball bonds.