Challenges in Singulation Process of Corner Lead with Wet-Able Pocket on Thin QFN Packages

Saw singulation is an indispensable process to singulate the Micro Carrier Device (MCD) strips into individual units in assembling Quad Flat No-lead (QFN) packages. Mechanical saw, cutting the MCD strip along saw streets using dicing blade, is a mainstream mode in the saw singulation process. The growing variety and complexity of leadless packages present a true challenge to Back-End processes. Recent customer demand for a lead with side solder-able or wet-able pocket to ease their AOI has led to new challenges for conventional blade and dicing process. Due to this reason, this paper will reveal the challenges in singulation process to meet customer requirement over corner wet-able pocket design. All the activities towards burr-removal process on the corner lead involving process and method optimization through conventional sawing and advanced dicing method will be shared in this paper. Process and method optimization via mechanical dicing involving various blade selection, additional cut channel, different cut method and direction only able to minimize the occurrence of the burr but not eliminate the symptom. As part of the recommendation for future works, an advanced approach in dicing technology, namely laser singulation and water jet was proposed to mitigate the risk of burr on wet-able pocket. On one hand laser dicing showed better response over burr removal but on other hand pose a risk of laser ablation mark on EMC surface. In addition, suitable laser method selection is important to ensure the best performance. Finally, by performing water jet in between the singulation process, significant results were achieved with an improved and way better dicing responses and cutting quality-burr. Water jet pressure of max 600Bar and conveyor speed max 2m/min in combination with half cut mechanical sawing process found to be able to meet the expectation.