I will try to help....
I don't think you will find component leads less than AWG#26 because they
are too wimpy and won't stay formed, and I doubt there are many components
with leads above AWG#12, so here ya go:
AWG mils mm
26 15.9 0.404
24 20.1 0.511
22 25.3 0.643
20 32.0 0.813
18 40.3 1.024
16 50.8 1.29
14 64.1 1.628
12 80.8 2.052
From everything I have read, solder flows best (capillary action) if the
hole is 11-14 mils larger than the lead, so that gives your hole size for
most components with wire leads.
For stamped leads you have a square or rectangular cross section, so you
have to calculate the hypotenuse (distance to opposite corners), for example
a 25mil square pin is really 35.3 mils across diagonally, but since it is
square there is more room for solder to flow so you can ignore the 11-14
rule and just make sure it fits in the hole, so use like a 40mil for that
(since most holes are called out plus or minus .003 you need to make sure
the smallest accepted hole .037 will still work for the 35.3 lead, it will).
Etc etc...
From my experience, let the fab vendor worry about the ACTUAL drill sizes
and YOU just concentrate on the desired FINISHED hole sizes. If you tell him
you need a 40mil hole plus or minus .003, he can figure out what drill size
to use.
In my opinion, call out small plated holes +/-.003, larger plated holes
+/-.004, and nonplated holes call out as +.005/-.000 or +.004/-.001 (so you
really specify the minimum size for nonplated, with is usually all you care
about anyway)
Good Luck and happy "wading",
Jack
p.s. mils and inches are the same thing, just shifted three decimal places.
-----Original Message-----
From: Derek Wynne [SMTP:[log in to unmask]]
Sent: Thursday, August 20, 1998 7:39 AM
To: [log in to unmask]
Subject: [DC] FW: PTH Drill Holes ?
Hi Folks,
I am wading my way through my first "Major" PCB design and I have a
couple of simple questions/requests for you.
1/ Does anybody have a conversion table AWG to MILS to INCHES
to METRIC ?
Or at least AWG to Metric.
2/ And has anyone got a table of PCB drill hole sizes for
different PTH pin sizes.
3/ Also does drill oversize vary from one PCB manufacturer to
another or is the 0.006MIL that my vendor uses pretty much standard.
I would appreciate any help that you could give.
Regards
Derek J. Wynne
Design Engineer.
Toucan Technology Ltd.
I.D.A. Business Park
Dangan
Galway City
Ireland.
Telephone: +35391519913
Fax: +35391519901
E-mail: [log in to unmask] < mailto:[log in to unmask]
<mailto:[log in to unmask]> >
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