Abstract
Lead-frames have been widely used in the semiconductor package assembly field, and QFN (Quad flat no leads) has the advantages of miniaturization and cost reduction of the semiconductor package. It has had limited use in automotive or defense products because of its board-level reliability. Nevertheless, due to the advantages of QFN packages, there is a trend toward using QFNs in automotive packaging. Automotive use would also require a wettable flank design of the QFN leads and automated optical inspection (AOI) of solder joints. New lead forming and surface finish technologies, including wettable flank design, are expected to improve reliability and enable AOI inspection, but much research is needed. This study investigated the board-level reliability of various QFN lead designs and surface finishes. All lead frames with different structures and surface finish types were assembled under the same conditions and then mounted on a daisy chain printed circuit board to evaluate board-level reliability. Accelerated thermal cycling (TC) tests were performed per IPC-9701A rev 2/2006 over a temperature range of -40°C to 125°C and 6080cycles. Lastly, each package type tested was cross-sectioned, and failure analysis was performed by observing the solder joint crack for all leg samples.
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