
Over the past few days, Workingbear came across an issue I hadn’t really considered before. Here’s the story: an EMS (electronics manufacturing service) factory reported that during SMT production, they were seeing solder shorts under BGA components. After digging into it, the root cause turned out to be excessive solder paste. And why was there too much solder paste? The PCB’s solder mask (the green layer) and silkscreen (the white ink) were printed too thick.
When you think about it, this makes sense. If the solder mask or silkscreen is unevenly thick, it can affect the solder paste thickness during solder paste printing through stencil aperture. A thicker layer lifts the stencil slightly, increasing the gap between the stencil and the PCB. With all other printing conditions unchanged, that small gap leads to extra solder paste being deposited.




