Reduction of QFN Voids with I/O Pad Overprinting

This technical article discusses a novel approach for reducing voiding in Quad Flat No-lead (QFN) packages during surface mount technology (SMT) manufacturing. The focus shifts from traditional methods that modify ground pad designs to a technique that involves altering the I/O pad stencil apertures. The study investigates the effectiveness of various overprint patterns on three Micro Lead Frame (MLF) devices, examining print patterns that extend beyond the I/O leads by 10, 20, and 30 mils. Results indicate a consistent reduction in void formation, with an average decrease of over 50% in voiding across different device types. The article also proposes a hypothetical explanation for these results, suggesting that the timing of melting between the I/O pads and the center pad may facilitate gas outgassing. The findings imply significant potential for optimizing solder assembly processes without requiring new equipment or materials, paving the way for future research into different solder paste types and long-term reliability studies.