Tin-Bismuth Low Temperature Homogeneous Second Level Interconnect Solder Joint Microstructure, Reliability, and Failure Mechanism
Authors: Nilesh Badwe, Kevin Byrd, Ou Jin, Pubudu Goonetilleke Company: Intel Corporation Date Published: 9/22/2019
Abstract: Tin-Bismuth (Sn-Bi) based low-temperature solder (LTS) paste materials were studied for surface mount technology (SMT) applications. LTS alloys have been shown to be compatible with Tin-Silver-Copper (SAC) Ball Grid Array (BGA) components where it forms a hybrid SAC-LTS joint without melting the SAC solder. These hybrid solder joints can be optimized through LTS solder metallurgy and SMT processes to maximize reliability performance. To reduce this complexity of materials-process optimization, the BGA component can be further modified to employ low temperature solder balls. We used two LTS paste materials to mount BGA components using both SAC solder balls as well as Sn-Bi based LTS solder balls on printed circuit boards at peak reflow temperatures 190°C or below. Microstructure studies revealed hybrid joint formation with the SAC BGA components whereas the LTS BGA components formed homogeneous LTS joints. Reliability studies indicated an improvement in the thermal cycling performance of homogeneous LTS joints compared to the hybrid joint for both of the paste materials. Drop shock reliability of the homogeneous LTS joints was also found to be better than hybrid LTS joints for both first-fail as well as critical-to-function (CTF) solder joints. Although the first-fail capability of homogeneous LTS was lower than homogeneous SAC, CTF failure capability was found to be comparable for both.
Sn-Bi solder, Hybrid vs homogeneous LTS joint, Thermal cycle, Drop shock, Reliability