The increase in board routing density, decrease the hole-to-hole spacing and lower to 0.30mm. High aspect ration PTH reliability is not the major issue since the plating copper has at least 20% elongation, but conductive anodic filaments (CAF) and laminate crack are to be concerned since the lead-free assembly and the application of fine pitch components. The lead-free assembly will require higher peak reflow temperature of up to 250degree, and the high temperature will cause thermal damage to PCB, on the other hand, the fine pitch component will require very close hole-to-hole spacing and hole-to-trace spacing, these factors will cause PCB to be easy damaged by the mechanical and thermal stress. The article introduces how to evaluate and avoid these risks.
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