Werner,
I have sent modules out for thermal cycling from 0C to 100C. 500 cycles. 2
minute ramp. 1 minute transfer. 10 minutes hot. 10 minutes cold. The
modules will be powered up during the cycling process. The modules will be
pulled from the chamber every 25 cycles for full functional system testing.
The ones that fail will be analyzed and cross sectioned. The modules that
pass will go back into the chamber for more cycling.
The modules selected for cycling were worse case (dewetting more than 40% of
the pad), moderate (dewetting less than 30%), and mild (dewetting 5% TO
15%). The dewetting is random in location, and some areas on the PCB are
worse than other areas. Hopefully with this test we will get a good feel as
to what level of dewetting is okay or not okay. I expect the worse case
modules to fall out first, then the moderate, and then the mild.
As a side note the same exact design bulit on known good PCB's with no signs
of dewetting were cycled and tested in the same exact way, and all made it
through cycling/testing with no failures. This was a requirement for
qualifying in the design for our OEM customer.
I was really hoping someone might have the same kind of test data, so it
could back up the test data I will have. So far there has only been the
metion of the studies done at china lake back in the 70's and 80's, which I
have not been successful in finding as of yet. Anyone who has done any
temperature cycling/cross section with regards to dewetting and is willing
to share that data I will be forever greatful!
As always Thank You to everyone who responded for your wonderful support and
information.
Sincerely,
Kathy Palumbo
Sr. Mfg. Engr.
Viking Components, Inc.
-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Wednesday, July 28, 1999 8:39 PM
To: [log in to unmask]
Subject: Re: [TN] Dewetting Issues
Hi Kathy,
You have my sympathies; when people in the same company work at
cross-purposes you can expect nothing but trouble.
I certainly have no idea what 'evidence' your Purchasing people will
consider
being adequate, given the evidence you already have. However, perhaps you
need failed solder joints to convince them. Just cross-sectioning your SJs
with inadequate wetting will not convince them (given your statements), but
if you take some of the assemblies made (under protest as you state) and
T-shock them 25C<->110C, your product excursions, for about 30 cycles (they
are likely to fail much earlier), you would get some beautiful (?) fractured
solder joints showing failure at the interface in the absence of a
metalurgical bond (intermetalic compounds).
If that does not convince them, nothing will.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com
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