Have you done any cross sectioning or SEM work on fracture?


My guess is that fracturing is due to a small stress built into solder
joints by operators pushing (very slightly) on some of the joints during
reflow and the joint can (depending on thermal mass etc.) freeze with a
certain amount of stress still built in and the solder joint creeps (even at
room temp) over time and ultimately fractures.  Roger Wild did some
excellent work on this problem.

Re you fixes, while another solder alloy (suggest Sn96 or one of Sn/Ag/Cu
lead free alloys) will help it's still (IMO) a bandaid on a poor process.
If you can't use a reflow oven, then I suggest one of the solder "dam" tips
where you set a large wedge shaped tip w/solder and don't touch the device
at all but essentially transfer the solder from tip to lead(s) by drawing
the tip down a line of pads.  Most solder iron vendors make some form of
this (I'm familiar with Metcals.)

Good luck
Jim

-----Original Message-----
From: Patricia Volkman [mailto:[log in to unmask]]
Sent: Tuesday, June 25, 2002 2:18 PM
To: [log in to unmask]
Subject: [TN] fractured solder joints


Fractured Solder Joints

My company has been doing hand assembly/soldering on a driver IC board for a
display that is used on a military airplane.  The board uses 8 Holt ICs -
HI-8010SM-32 - http://www.holtic.com/ProPDFs/8010.C.pdf

The boards we provide have been in use for between 1 year and 8 years, the
actual time is unknown, but it is likely that they have been in place for a
long period of time.

The IC is a 44 pin QFP J-lead with 0.050 center spacing on the leads.

Our customer has recently found fractured solder joints associated with
these ICs (identical to those in photo - IPC-A-610C page 12-85 )

It is assumed that the fractured solder joints occured after leaving our
facilities, caused by airplace stress cycles or ???

I am looking for any information on why these fractures would occur, the
boards are spring mounted on the plane, the boards measure about 1.5" x 5".

Most importantly, I am looking for a solution to this problem, I am
currently looking for a more ductile solder...the solder used in the past
was Kester SN60PB40.  I can also change the assembly process if that is
determined to be the root cause (all hand soldered)

thanks for any information you can provide.


Patti Volkman
(1-800-823-5588)



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