Enhancing Die and Wire Bonding Process Reliability: Microstructure Evolution and Shear Strength Analysis of Sn-Sb Backside Metal

Abstract

In this study, we report the microstructural evolution and shear strength of an Sn-Sb alloy, used for die attach process as a solder layer of backside metal (BSM). The Sb content in the binary system was less than 1 at%. A chip with the Sn-Sb BSM was attached to a Ag plated Cu lead frame. The microstructure evolution was investigated after die bonding at 330 °C, die bonding and isothermal heat treatment at 330 °C for 5 min and wire bonding at 260 °C, respectively. At the interface between the chip and lead frame, Ni 3 Sn 4 and Ag 3 Sn intermetallic compounds (IMCs) layers and pure Sn regions were confirmed after die bonding. When the isothermal heat treatment is conducted, pure Sn regions disappear at the interface because the Sn is consumed to form Ni 3 Sn 4 and Ag 3 Sn IMCs. After the wire bonding process, the interface is composed of Ni 3 Sn 4 , Ag 3 Sn and (Ag,Cu) 3 Sn IMCs. The Sn-Sb BSM had a high maximum shear strength of 78.2 MPa, which is higher than the required specification of 6.2 MPa. In addition, it showed good wetting flow.