We are investigating a higher than normal defect rate on a QFP 208 part
being soldered on our boards.

This part looks much like a conventional QFP, but it is not molded, it has
two sealed slabs of anodized aluminum, and between these there is a die
cavity.

Some of these defects, occurring mainly near the "corner" pins, give the
appearance of strain cracks in which the joint is broken as by shearing.

My thoughts are that the TCE mismatch between Al and FR4 may be problematic.

If anyone has guidance for me after considering my rambling on this matter,
please advise.

My references show these data:

TCE for the substrate laminate (FR4) = 120 x 10^-6
TCE for the QFP package (Al) = 25 x 10^-6

If we have excursions of 160 C in our reflow, are we not seeing a strain of
20-30 mils across the diagonal of the package, about 1.6" or so.

Can a QFP gullwing lead accomodate this safely?

What could be done to increase the window...
slow the cooling rate after the reflow spike zone in the furnace?
use a really slow conveyor rate?

Is anyone else seeing issues with soldering MQUAD packages?




Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################