Daan,
The sizes you quote are not especially small, nor is the difference between
them. I'm not totally clear from your description what you are meaning,
but, (converting to my old-fashioned language), do you have 12 mil diameter
holes going through 24 mils diameter exclusion zones in the copper planes?
Unless your Fab House's registration accuracy is very bad, you will have a
nominal 6 mils all-round clearance and in practice, shouldn't have less
than 3 to 4 mils clearance. Is this OK electrically if your small
clearances are, for example, at layers with high power? It should not be a
difficult job for a decent Fab House to make this board for you, though.
Pete Duncan
"d. terstegge"
<[log in to unmask] To: [log in to unmask]
GROUP.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Sent by: TechNet Subject: [TN] Clearance area around holes
<[log in to unmask]>
07/27/01 04:37 PM
Please respond to
"TechNet E-Mail Forum.";
Please respond to "d.
terstegge"
Hi Technet,
Here's a question for the bare board experts out there:
One of our pcb-suppliers had rejects on a complete batch of our boards
because the clearance between the via's and the surrounding copperplane was
so small that it resulted in short circuits.
The holes were designed 0.3 mm (finished hole size) and the openings in the
copperplane were 0.6 mm, leaving only a small clearance area. The board
measures about 20*15 cm.
What do you think, is a board like this manufacturable for a decent board
shop, or is it really that difficult? Could you give me a typical value
for the minimum clearance around the finished-hole that board vendors need
?
Best regards,
Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net
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