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Solder Mask Keepout or small Solder Mask patch area.

Question asked by on Feb 1, 2015
Latest reply on Feb 3, 2015 by sajivnglnice

This PCB will be used in a high vacuum cryogenic instrument.

Normally I have a surface plane on top and bottom.  These are done with Gold flash or similar and No Solder Mask.

This metal layer keeps the total exposed FR4 surface area to a minimum, which reduces the effects of outgassing for the FR4.  The Gold finish is also easy to clean from finger prints and oils.


However for this design I have some small pitch SMT parts and the assembler really wants Solder Mask to keep the solder on the pads from wicking between lands. ( I can certainly sympathize with his perspective. )

So I want to put a small area of Solder Mask only where it is needed for manufacturing.


I.E. What I am looking to achieve is to maximize the total area of bare metal and minimize the total area of Solder Mask exposed to the vacuum.


I do not seem to be able to produce Keepouts on the Solder Mask layer like we can with copper pours.


Any hints would be greatly appreciated.


Kevin Hanna

Gemini Observatory

Hilo, Hawaii

(352) 278-4326