Electronics > Manufacturing & Assembly

Question about Soldermask

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lorth:
Dear all,

I've been working with the same PCB manufacturing for a couple of years now, but after a couple of bad experiences I'm switching to a new one.

There is one rule on the new company that is bothering me regarding Soldermask: "openings in the solder-mask layers should be 0.006" larger than the copper feature."

What does that mean? If I have a pad that is 40 x 9 mils, how should the soldermask aperture be?

Thanks!!!

c4757p:
52x21?

free_electron:
ehhh.  46 by 15 mils..

6 mils larger means they want a 3 mil wide ring around the copper.
3 mil is standard opening these days. 2 mil will cost extra. i use 4 mil by default.

for a 40 by 9 pad you will have a 46 by 15 opening in the soldermask centered on top of each other.

ddavidebor:
That their soldermask is not able to attach on pcb surface, but only on copper, and you must leave 6 mils of copper between nude pcb and soldermask.

gxti:
Don't be ridiculous, of course they can put soldermask on bare PCB. Like free_electron said, it means the "registration" between soldermask and copper could be up to 3 mils off, so the soldermask aperture radius must be 3 mils larger in order to guarantee that soldermask will not get on the pad.

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