Synergistic Interactions Between Water-Soluble Solder Paste and Ultrasonic Flux Cleaning in Producing Zero Solder Ball Rejects

The semiconductor packaging industry is growing rapidly driven, in part, by the booming sales of high-performance electric vehicles with advanced Internet of Things (IoT) features. As a result, the reliability requirements for the packages are getting more and more stringent. In common solder paste die attach applications, the presence of solder balls is often a roadblock to the reliability performance of the packages. Optimizing the reflow profile is the typical and straightforward approach to minimize the chances of solder ball formations by adjusting parameters such as the temperature ramp rates and peak temperatures. Nevertheless, getting the optimized parameters is very challenging and time consuming due to the necessity for extensive experimentations. Yet, this approach is still unable to ensure zero solder ball rejects. In this study, a robust solution is proposed to remove the solder balls completely. This solution utilizes the synergistic interactions between water-soluble solder pastes and ultrasonic flux cleaning as the mechanism to remove the solder balls effectively. In addition, the proposed solution is deemed to be applicable to other packages with solder paste die attach.