High Shear Speed Characteristics of Sub-100 μm Low Alpha SAC105 Solder Bump Directly Fabricated on Cu Filled Through Si Via for 3D Integration

Abstract

Soft errors in microelectronics devices, responsible for the malfunction of electronic systems, have become a hot issue for miniaturized and high-density packaging like three-dimensional (3D) packaging. Low alpha solder generates very few α-radiation-caused errors and malfunction in electronic devices compared with regular solder. It can improve performance and reliability of through-Si-via (TSV) packaging, prompting the need to adopt low alpha solder for bumping in TSV packaging. TSV technology has emerged as a popular choice for 3D packaging and chip stacking. In this study, the bonding properties of low alpha solder on Cu-filled TSV were investigated. TSVs were fabricated in a Si wafer by deep reactiveion etching, and Cu was filled in the via by electroplating using the periodic pulse-reverse current waveform. Cu filling in the via was achieved in 4 h without any defects at a cathodic current density of −8 mA/cm2. The LC-3 class of a low alpha solder ball (alpha emission < 0.05 cph/cm2) having a composition of Sn-1.0 wt.% Ag-0.5 wt.% Cu (SAC105) and a diameter of 80 μm was reflowed on the Cu-filled TSV to form the solder bump. High-speed shear test was performed on the bumped low alpha solder ball to assess the shear strength and to investigate the fracture mode. The shear strength of the low alpha solder bump showed a maximum value of 369.63 mN at 1.0 m/s shearing speed and 17.6 μm tip height. The fraction of brittle fracture increased with increasing shearing speed.