Roger, in hearing the many discussions on this subject at J-STD-001 and IPC-A-610
meetings, I feel pretty confident in saying that height has nothing to do with
failure mechanisms.  Studies done by Roger Wild, Colin Lea and others showed that
PTHs that had solder fill edges near the center of the PTH experienced fractures to
the barrel plating and internal layer connections when there was a high degree of
thermal stress applied (rapid rather than slow ramp rate).

We have a bunch of the papers that the committee reviewed in electronic format
available for download from our FTP site.  It's a few MB worth, and you probably
wouldn't want to do it with a slow modem connection, but let me know if you would
like to review them and I'll tell you how to do it.  Reply to my regular e-mail
[log in to unmask] rather than here to the technet.  Jack

==========================================
APEX - the industry's premier trade show in Electronics
Manufacturing, March 12-16, 2000, Long Beach, California.
More information on website www.ipc.org/html/apex.htm
-----------
Jack Crawford, IPC Director of Assembly Standards and Technology
2215 Sanders Road, Northbrook IL  60062-6135
[log in to unmask]
847-790-5393
fax 847-509-9798

>>> "Deakin, Roger" <[log in to unmask]> 09/13/99 08:54AM >>>
HI ALL !!!!
I HAVE A BACKPLANE WITH 14 LAYERS. THE PANEL IS 6.8mm THICK.

IPC CAT 3 REQUIRES 75% FILL ON PECS WHICH ARE UP TO 3.8mm THICK ?

MY QUESTION IS, WHAT DICTATES THE REASON FOR 75% FILL ? I WOULD LIKE
TO ACCEPT THE PANEL WITH ONLY 40% FILL. THIS WOULD STILL HAVE A
FILLET OF 2.72mm. WOULD THIS FAIL IPC-610 CAT 3 ?

Regards  -  Roger Deakin.

EMAIL           [log in to unmask]
TEL             +44 (0)1983 202632
FAX             +44 (0)1983 202106
COMPANY         BRITISH AEROSPACE  LAND AND SEA SYSTEMS
                NEWPORT ROAD
                COWES ISLE OF WIGHT
                PO31 8PF
                ENGLAND

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