PRECISION HEIGHT STAND-OFF BLOCK WITH INLINE HIGH SPEED PLACEMENT MACHINE

摘要

Feasibility of using high speed inline placer to pick a block, place it on a pad at the comer of Ball Grid Array (BGA), and reflow during SMT process to maintain a minimum stand-off height and prevent subsequent corner bridging is investigated. A test vehicle is designed and assembled with four DOE factors, including block height/diameter, pad size, stencil aperture, and placement offset. Based on the analysis, Ni block with Au plating has the most consistent post reflow height. The pad diameter should be larger than the block by 15mil or more. And, with the optimized pad size, stencil aperture does not seem to have strong correlation with post reflow height, if it is within block size +10mil range. It is planned to run the 2nd Phase with one block size, 11mil height Ni block plated with Au. The target post reflow height is 12mil with ±1mil tolerance.