Since 90% of the designs that we work on are mixed technology, we
specify the finished hole size with tolerance. In the case of visa our
tolerance range is generally specified as +0/-nominmal via diameter to
allow maximum plating and make meeting our minimum annular ring
requirements (2mil/no breakout) easier for the fabricator. With a known
pad diameter and a minimum annulus specification for all internal and
external pads the possibility of drilling away the pad is mitigated.

We also require electrical net list testing to verify functionality.
Since our designs are for prototype quantities we do not require any
sectioning.    


Jeffrey McGlaughlin, CID 
Engineering Designer 
Battelle 
505 King Avenue 
Columbus Ohio 43201-2693 
(614)424-7582 Phone 
(614)458-7582 Fax 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wilson
Sent: Monday, January 16, 2006 6:06 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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