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摘要

"Novel Approach to Void Reduction Using Micro-flux Coated Solder Preforms for QFN/BTC Packages that Generate Heat" Authors: Anna Lifton, Paul Salerno, Jerry Sidone and Oscar Khaselev. Abstract: Earlier work demonstrated use of micro-fluxed solder preforms as a mechanism to reduce voiding. The current work builds on these results to focus on developing an engineered approach to void reduction in leadless components (QFN) through increasing understanding of how processing parameters and use of custom micro-fluxed preforms interact. Leveraging use of a micro-fluxed solder preform in conjunction with low-voiding solder paste, stencil design and application knowhow are critical factors in determining voiding in QFN packages. The study seeks to understand vectors that contribute to voiding such as PCB pad finish, reflow profile, reflow atmosphere, via configuration, and ultimately solder design. A solder materials supplier, a power semiconductor supplier, and an electronic assembler worked together for an in-depth study into the effectiveness of solder preforms at reducing voiding under some of the most prevalent BTC packages. Effects of factors such as thermal pad size, finish on PCB, preform types, stencil design, reflow profile and atmosphere have been evaluated using lead-free SAC 305 low-voiding solder paste and micro-fluxed preforms. Design and manufacturing rules developed from this work are discussed. (IPC Apex Expo, February 2018).