for low tech, low cost, low to moderate density double sided boards i
have taken to using 44/28 (mils) pad/hole for vias
this is not very aggressive even for that sort of board
40/22 should also be ok
you will note that leaves an 8 mil (or greater) annular ring
for higher density higher tech boards (generally using 5/5 mil trace/gap
we have sucessfully used 22/12
others have used 20/10 but some shops get a little nervous ($) at that range
but beware that these tiny vias are a REAL pain if you need to hack the
bd to make changes
wires don't fit in the holes and soldering to the pads can be an
adventure, especially if they were tented and need to be scraped
there isn't much 'there' there and they can come off real easily when
mucking about with the tiny vias
so the best practice is often to use the biggest vias (within reason)
that are practical
other than current considerations there really isn't a necessary direct
relation between trace width and via size to use
obviously at smaller trace widths the via site area becomes an issue
causing bulging of the nested traces
another point is drill breakage, the smaller the more fragile
a broken bit can sometimes cause a whole panel to be scrapped
most shops are pretty comfortable with a 15 mil drill not breaking too
often, this will finish out after plating to about 12 mils finished hole
size which is what you would call out
shops are doing smaller than that all the time but it take a bit more
finesse
Dennis Saputelli
_______________________________________________________________________
Integrated Controls, Inc. Tel: 415-647-0480 EXT 107
2851 21st Street Fax: 415-647-3003
San Francisco, CA 94110 www.integratedcontrolsinc.com
Brad Kosiance wrote:
Any recommendations for via/pad size for 10mil tracks?
I have a dense PCB and require the smallest via/pad size that won't violate
manufacturability of the PCBs.
The signal lines are low voltage and low current.
I assume there is a rule of thumb for 10mil, 20mil, 30mil. track widths?
Thanks,
Brad.
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