Enabling Wettable Flank Technology: Insights, Challenges and Perspectives

The market drive towards visually detectable solder joints for high reliability applications calls for the implementation of robust wettable flank technologies, wherein copper terminations at the package edges exposed after package singulation are made solderable by plating the exposed copper to prevent oxidation and promote consistent solderability. Herein, we present the diverse technologies explored to realize the wettable flank technology in a QFN platform. Tin immersion plating, ultra-short pulsed laser ablation technology, and laser guided-surface responsive singulation system were explored. Product innovation and process development activities related to each technology are presented, where technical insights into their manufacturability and reliability are identified. More importantly, the challenges encountered and their resolution were reported to provide key learnings for future product development. In addition, the evaluation results highlight the potential of these technologies in achieving the desired geometry in QFN packages, and by extension the possibility of achieving visually detectable solder fillet on package edges.