Edgebond adhesive enhances the reliability of low-temperature solder in board-level assembly (IMPACT 2022)

Abstract

Low melting temperature solder, which enables a lower temperature assembly process comes with significant benefits for less warpage and lower component defect risk, but at a cost of a potentially inferior thermal cycling performance due to higher creep rate at an elevated temperature environment.The creep rate can be reduced by dispensing underfill between BGA and PCB to lower thermal stress concentrated on the corner. Thus, the thermal cycling performance would be improved. However, this would increase difficulty when replacing the BGA. For this reason, applying edgebond on the peripheral of the BGA in the assembly process makes it easier to operate on during the rework process. Additionally, it will reduce material consumption dramatically for big BGAs.In this study, we evaluate the reliability of low-temperature solders, Sn-58Bi, used in the BGA, 12mm*12mm, assembly without edgebond and with edgebond. Comparing the characteristic life cycle number of 3328 cycles with Sn-58Bi solder, the full edgebond BGAs’ does not show any failures up to the test completion at 4050 cycles.To extend edgebond applications for the strong need for extra-large BGA in today’s electronics industry, we use simulation methods to compare the thermal stress of the solder joints when BGA size increases from 12mm by 12mm to 70mm by 70mm, and up to 100*100mm. These include the BGA assembly without edgebond and with edgebond. As thermal stress increases, the thermal cycle reliability shortens. From simulated thermal stress results, we can predict the edgebond’s significant benefit for the thermal cycling reliability of extra-large BGA on the board level assembly.