If the alignment is off by 2mils or more, sounds like your fab house
needs to check their drilling machine, or else use a better, more
accurate one than typically used. The issue is one of positional
accuracy plus repeatability. If a machine has a drilling accuracy of
+/-.001, positional accuracy of +/-.0005, and repeatability of +/-.0005,
then the total accumulated tolerance can be as large as +/-.002.
Sound like you need to specify a location tolerance (true position) of
+/-.0015 (or better) for the holes in question. The wider the tolerance
for hole diameter, the narrower the tolerance for location accuracy, and
vice versa, for press-fit connectors. IPC-2221 9.2.2 says you can
expect +/-.002 for fabs built to level B. Asking for Level C would give
you +/-.0015 tolerance. (If I'm missing something, somebody *please* set
me on the straight and narrow...)
Use of GD&T (IPC-2615) would help in specifying what you really want,
because tolerance zones with GD&T are round, not square as in the
(unfortunately) typical drawing practice.
All said and done: it's up to you to specify hole size, tolerance, *and*
accuracy for your design. If you don't specify accuracy, the board
vendor may provide you with what's easy for them to make, to the widest
tolerances possible.
Best Regards,
Roger
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Scott Lefebvre
Sent: Wednesday, May 04, 2005 6:10 PM
To: [log in to unmask]
Subject: [TN] Through hole drill accuracy
I have looked profusely at IPC-6012 for a specification I could not
find. I need to know if there is a specification for PTH drill accuracy
and repeatability. We have a press-fit connector we are having problems
with. The component manufacturer tested one of our boards and said the
alignment is off 2 mils or more in some locations. I could not find
what is the spec in IPC to reference to, could someone please point me
to the correct document I should look at.
Sincerely,
SCOTT L
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
