While the minimum is based on the PCB vendor's ability to properly register the solder mask when printing it, the maximum is all about the whether or not small-pitch components get solder mask between their pads or not. In the screen captures below, the component on the right is the Altera MAX V package that has 0.4mm pitch pins. With a 4 mil solder mask expansion there is no solder mask between the pins. With a 2 mil expansion some mask is placed between the CPLD's pads.
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| 4 mil solder expansion (bityExpress-B) |
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| 2 mil solder expansion |
It is possible that the lack of solder mask between the CPLD's (U4's) pads is why I had a few solder bridges.
2 comments:
Nice post. Is there a minimum feature width under which the PCB manufacturer will not print?
In theory, yes. Tiny features between pads are called 'solder mask slivers' and most PCB tools let you set a minimum rule. I dont know what OSH Park's minimum is but I may be able to measure some PCBs and get an idea.
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