Kathy,
one word of caution... the 1st failure may not be the 40% dewetted PWA...
visual may not reveal the weakest spot on the assembly...PTH for example may
be the 1st to go...Try to correlate the visual dewet with functional result
may have some difficulty...(wetting balence or oxide/contamination thickness
measurement using Auger may provide better correlation...but it is
costly)...Good luck...
jk
At 10:00 AM 7/29/99 -0700, you wrote:
>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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