Low Melting Temperature Interconnect Thermal Cycling Performance Enhancement Using Elemental Tuning and Edgebond Adhesive
Authors: Andy Hsiao and Tae-Kyu Lee, Imbok Lee, Young-Woo Lee, Edward Ibe and Karl Loh Company: Portland State University, MK Electron Co., Ltd. and Zymet Date Published: 10/14/2018
Abstract: The adaptation of low melting temperature for solder interconnection comes with significant benefits to less warpage and component defect risk due to the lower assembly temperature. But one disadvantage is inferior thermal cycling performance due to the higher creep rate. Adding to the recent active efforts to improve the thermal cycling performance with maintaining the melting temperature, the degradation mechanism in low melting temperature solder alloys is critical to understand. Since the mitigation of the degradation mechanism will provide the key mechanism improving the thermal cycling performance. In this study, 12x12 mm chip array BGA (CTBGA) components on 62mil thick boards were thermal cycled from -40ºC to 125ºC with Sn based low melting temperature solder with control elements including In and Bi. The microstructure evolution during thermal cycling were observed and the correlation between crack propagation and localized recrystallization were compared in a series of cross section analyses via polarized imaging and Electron–backscattered diffraction (EBSD) imaging. It was found that the elemental impact, of In and of Bi, enhance thermal cycling due to creep rate changes compared to conventional Sn based alloys. To further enhance the performance, an edgebond adhesive was applied and investigated, to determine if it can increase the thermal cycle performance. An improvement of over 140% with dot-cornerbond and 280% with full-edgebond was observed.