I prefer specified finished hole tolerances.
Hypothetically, what your colleague said is true, but it's just stupid to
think any company would actually do (drill 20, plate to 10) such a dumb
thing.
Keep in mind that the internal pads and clearances (pad-to-pad,
pad-to-trace), board thickness, copper weight (starting and finished) all
contribute to the drilled hole size requirement and many shops will make
fabrication adjustments to any or all of these to ensure a quality product
meeting your requirements is the final result.
These of course are just my opinion...
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wilson
Sent: Monday, January 16, 2006 5:06 PM
To: [log in to unmask]
Subject: [TN] Drill and plated hole callouts
Hello,
I am a designer (...wait! wait! Don't throw anything yet!...) and we are
discussing hole and drill callouts in standard high Tg FR4 material on the
design side and I'd like to hear from ya'll.
I specify a hole of .020 and a tolerance of plus .003 and minus .003
(inches), along with a note stating ALL HOLE SIZES ARE FINISHED. Now I
don't care how the hole is made: drill, laser, plasma, teeth. As long as
the hole is as I specify, I figure the board house knows what their best
method would be. And I request electrical test before I see the boards on
my loading dock.
A well-respected colleague says that he specifies the drill hole and
tolerance before finish. He maintains the fab house could drill a via hole
at up to .020 and plate it down to .010, and that it will punch out any
traces as the hole is made. Further, he says that electrical test isn't
enough and when the board is stuffed and under full load that the heat could
cause further problems.
Make sense?
How do you prefer to see the holes called out?
Regards,
Bob Wilson
Electro-Mechanical Designer
SpectraSensors, Inc.
972 N. Amelia Ave.
San Dimas, CA 91773
800-619-2831 x239
www.spectrasensors.com
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