Do you have that Black TyveK tape? PDR gave us some for use with metal
case components. I think that metal top may reflect more energy than the
black plastic. I bet the temperature difference is enough to crack the
package. It might be lot dependent, There is probably some variation in
the actual thickness of the plastic over the metal spreader. I don't
think this was due to moisture.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, September 16, 2003 12:03 PM
To: [log in to unmask]
Subject: [TN] Strange part cracking...


Hi All!

I had something strange happen yesterday. Was reworking a Altera Flex
240-pin RQFP, and after the part was removed, noticed a semi-circular
crack going about a quarter the way around the heat sink in the top of
the part. The part was reworked shortly after reflow (within a hour of
reflow), and prior to original assembly had been stored in a desiccant
cabinet. The part was reworked with a PDR LightMaster Pro under a
profile that was developed for that part. This part was the only one
I've seen do this.

I don't think it was a true popcorn job, because doesn't popcorning
usually happen on the bottomside where the die usually is? But I suppose
popcorning can happen anywhere...I've just never seen a part crack like
this.

Go to:

http://www.stevezeva.homestead.com

and look at "Top Crack", "Crack Close", "Heat Sink", and "Heat Spreader"

After I saw the crack, I just had to take it apart. The heat sink in the
top of the part was attached to a heat spreader inside the part by what
looks like dots of silver filled epoxy...

Anybody ever see this happen before?



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