Solderability and Reliability of Sintered Nano-Ag Bond Pads of Printed Re-Distribution Layer

Abstract

Redistribution layer (RDL) is one key enabling technology for advanced packaging. RDL is usually fabricated at wafer level by a photolithography process. An alternative approach for implementing RDL by additive manufacturing (AM) method is proposed in this study. This allows RDL to be fabricated on a singulated chip. Nanosilver (nano-Ag) ink is printed on the silicon chip to form routing traces and bond pads. However, the Ag pad may be consumed by the solder quickly if the reflow process is not properly controlled. The mechanical integrity of the solder joint was evaluated by both solder ball shear and die shear tests. A high temperature storage test and humidity test were carried out to evaluate the solder joint reliability. Experiment results showed that the Ag pad fabricated by AM is compatible with surface mount technology (SMT). Reliable solder joints on the Ag pad were achieved. There was no significant change in the Ag3Sn intermetallic compound (IMC) layer thickness and mechanical strength after aging at high temperature and high humidity conditions. There was no early solder joint failure observed. The finding of the present study will serve as a very useful reference for the future practice of forming solder joints on sintered nano-Ag pads.