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April 2004

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 27 Apr 2004 13:35:29 -0700
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>       Another possibility could be that a piece  or pieces of metal debris might have shorted several leads of  the QFPs.
>       Ramon
>
> -----Original Message-----
> From: Steve Gregory [SMTP:[log in to unmask]]
> Sent: Tuesday, April 27, 2004 2:08 PM
> To:   [log in to unmask]
> Subject:      [TN] Interesting Occurance...
>
> Hi All!
>
> Just had an interesting occurance that I thought I'd share with you. We build
> this 14-layer assembly here that has 10 Altera FLEX 240-pin QFP's on it...4
> on one side, 6 on the other. We've been building this assembly for some time
> now with no problems.
>
> After SMT, the board goes through AOI, gets some connectors hand soldered on,
> then goes to ICT. After ICT it goes into a Thermotron for some power-on
> thermal cycling for eight hours.
>
> Last week, after a cycle was done, the test technician went to retrieve the
> boards from the oven. Upon opening the oven door, he noticed this funky
> smell....kinda like burnt fiber glass. At one of the twelve positions in the test
> rack he found this:
>
> Go to http://www.stevezeva.homestead.com and look at "Smoking Hole" and
> "Smoking Hole 2" (NOTE: DUE TO THE GRAPHIC NATURE OF THESE IMAGES, PARENTAL
> DISCRETION IS ADVISED)
>
> We don't have a clue how this happened. ICT on this assembly was fine, there
> were no problems found in the test fixture position in the oven (other
> assemblies have gone through the temp cycle in the same position without a problem).
> And supposedly, there is only 5V and 3.3V being applied during the thermal
> cycle.
>
> Obviously there had to be more voltage than that to cause the kind of damage
> you see in the pictures, but nobody knows where it came from. Smoking Hole is
> a QFP on one side of the board, and Smoking Hole 2 is on the other. The leads
> are vaporized in the pictures. This only happened to one board, and the
> fixture was loaded up with another 11-assemblies.
>
> I don't expect we'll ever figure out what happened unless it somehow happens
> again. I know one thing, if it does, I don't want to be anywhere near the
> oven!
>
> Thought you might find the pictures interesting...these are $4000 images.
>
> -Steve Gregory-
>
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