Another chance to quote Sir Doug; it depends. You need to determine the size
and tolerance of the lead, the number and relationship of the leads per
device, the capability of the fabricator to hold a finished hole tolerance,
the true position relationships, the reflow process, solder viscosity vs.
temperature, the ability to achieve thermal equilibrium, what class are you
building to of IPC-A-610( top side fillet requirements ), solderability,
final lead finish and PWB surface finish.
The short answer is on a 20 pin DIP, I would require a nominal finished PTH
0.014 of an inch greater than the nominal lead size.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Morse, Carrie
Sent: Thursday, April 28, 2005 6:31 AM
To: [log in to unmask]
Subject: [TN] Hole Size Recommendations

All right...I know this has been asked before (I may have even been the one
to ask at least once), but....
In what specification can I find recommendations for lead to hole ratios or
something that gives guidance to designers when specifying hole size for
soldered TH parts?  I thought it was IPC-2221A, but, I can't find it.  I've
only had one cup of coffee so far...should I get a second?

-Carrie



---------------------------------------------------
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
-----------------------------------------------------