ULTRA-LOW VOIDING HALOGEN-FREE NO-CLEAN LEAD-FREE SOLDER PASTE FOR LARGE PADS

摘要

The electronic industry is evolving rapidly toward miniaturization, with major emphasis on thin product profiles. This is particularly true for portable devices, such as smart phones. To facilitate the implementation of thin profile, use of thin components such as LGA and QFN becomes mandatory. This means the solder paste will have great difficulty in venting the volatiles at reflow due to the low standoff. In the case of QFN, due to the incorporation of large thermal pads, therefore a significantly higher difficulty for the escape of flux volatiles at reflow, formation of large voids virtually becomes inevitable. Apparently the presence of large voids will greatly jeopardize the reliability of devices. While board design and process adjustment may alleviate the voiding challenge somewhat, an intrinsically voiding-free solder paste will be the most desirable solution. With the elucidation of voiding mechanisms and a deep understanding of the material factors contributing to the voiding, a new halogen-free, lead-free, and no-clean solder paste 44-29-3 was developed. The test results showed this paste was significantly lower in voiding than any other solder pastes tested in this study. It also exhibited nearly none solder beading, and a very acceptable performance on non-slump, wetting on OSP and ENIG under air, solder balling, and graping.