Electronics > PCB/EDA/CAD

silkscreen underneath SMT components...

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westfw:
I'd like to put some identifying silkscreen "underneath" SMT components so that I can easily identify the type of component (assuming, say, otherwise identical 0805 SMT pads) on the completed board.  Will this work, or will the thickness of the silkscreen interfere with SMT component placement?  (assume for the moment that the symbols will be possible to read; these are relatively large components...)
Here's a picture of what I had in mind:

jaqie:
if their height may interfere, what about making it a negative instead so that the height isn't unpredictable and uneven?  basically a solid silkscreen color for the entire underside of the part, with the text you want missing from that solid color?  that could give it a solid platform to sit on instead of a possible teeter totter effect?

fcb:
Don't do it for passives - you'll risk having misaligned silk on the pads and if they use a thick ink the part may ride up and encourage tombstoning. Your probably OK with the SOIC, although I put a box round the outside.

If I'm hand-building small runs of boards I just print out multiple copies of the top silk and colour in the parts, so I end up with flip-book (page for 10K's, page of 100n's, etc...).

free_electron:
Down to 0805 no problem. Smaller gives risk of tombstoning.

NEVER do this under QFN as it may prevent the pads from wetting during reflow

Kremmen:
Yep, doing it all the time and no problems so far. Down to 0805, SOT23 and similar; iron soldering, heat gun, pizza oven - all work with no probs whatever. 0402 and below could be an issue but i don't do that size so wouldn't know.

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