Doped SAC Solder Ball Alloys Comparison for High Performance Automotive BGA Packages

BGA (Ball Grid Array) packages offer a wide range of applications such as mobile and automotive applications due to its flexible and easy integration. Following Moore's law, More-than-Moore growth and customer targets, package robustness plays a major role in thermo-mechanical performance nowadays, especially at board level. Most challenging customers may request BLR (Board Level Reliability) improvements, especially on TCoB (Thermo-Cycling on Board). However, drop and thermal cycling reliabilities are driving opposite material requirements for solder, even though they are equally critical to satisfy, this brings important challenges for interconnection solder material. Therefore, advances in solder materials are key to achieve balanced reliability performance. SnAgCu (SAC) alloys have become prevalent over other lead-free solder alloys due to low cost and good material properties. Recent studies revealed that introduction of dopants may improve drop test while maintaining good TCoB performance. When introducing new products, one of the biggest challenges is to select the most suitable alloy aligned BLR needs related to product application and expected performance. Several alloys were studied for BLR performances comparison, targeting automotive field specifications. TCoB and drop test trials were made using Daisy Chain BGA package mounted on PCB (according to JEDEC Standards [1], [2]), for this purpose all balls within the package were monitored. TCoB was performed using a dual chamber system from −40°C to 125°C with a temperature ramp of 28°C/min. Drop test conditions at 1500G peak acceleration and 0.5 ms pulse duration. Failure Analysis was realized with the aim of determining the failure mode observed after BLR testing. Also, microstructural characterization was done to develop a better understanding of stress behavior on different solder alloys. Finally, ball attach process validation at package level was compared in order to get a global comprehension tested material features and broaden comparison outputs/results.