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I've never used stencils before, but now I'm going to have to (BGAs, lots of 0402 caps and resistors, etc).

How close together can the paste holes for say adjacent 0402 caps be for a stencil to work properly?

I tried calling my stencil manufacturer, and they basically said "I dunno, send us your board files and we'll let you know if it's too close"...

One person I know says 5 mils between paste holes, but that seems like an awfully awfully thin wall in the stencil.

What's a reasonable clearance value? Would that number be different for using a stencil by hand? (vs. a more controlled automated unit)

EDIT: I'm currently aiming for a 10 mil clearance between paste holes. It appears that should be perfectly doable (since providers like Pololu say they can do approximately 0.5mm pitch, which works out to a ~10 mil gap between pads) However, what's a good clearance value assuming a nice laser cut metal stencil?

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For laser-cutting, it seems like a few mils is enough precision to ensure you create the necessary "mask wire" for the paste. As long as your stencil is framed well and you are gentle with it, I doubt the application of paste would stress the stencil much...

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