Assessment on the effects of electroless nickel plating on the reliability of solder ball attachment to the bond pads of PBGA substrate

This paper presents an experimental study to assess the reliability of solder ball attachment to the bond pads of PBGA substrate with various plating schemes. The basic structure of under bump metallization is Cu/Ni/Au. Three different kinds of electroless plating solutions are used to deposit the Ni layer, namely, Ni-B, Ni-P (5%), and Ni-P (10%). Also, the conventional electrolytic Ni/Au plating is performed for benchmarking. After solder ball attachment, mechanical tests are conducted to characterize the ball shear strength for comparison. Furthermore, some specimens are subjected to multiple reflows to investigate the thermal aging effect. The testing results reveal that, compared to the electroless Ni-P plating, the electroless Ni-B plating may lead to better solder ball shear strength. However, the conventional electrolytic plating still gives the highest ball shear strength. For most cases under investigation, multiple reflows seem to slightly reduce the solder ball shear strength. In addition to the ball shear tests, scanning electron microscopy is performed to inspect the cross-section and the fracture surface of the tested specimens. From the failure analysis, certain characteristics are identified for various Ni plating schemes