In a message dated 12/14/98 3:28:13 PM Pacific Standard Time,
[log in to unmask] writes:

<< Technetters,

 We are currently having soldering problems with a QFP 100 package
 part. The part is a TI microprocessor component with a 0.0196" pitch.
 The problem we are having with this part is we are getting
 intermittent opens with corner leads. Other fine-pitch components on
 this board solder fine. We have been building these boards for about 1
 1/2  years in production with no problems until the last three months.
 I found out that TI recently switched the lead plating for this part
 from Tin/Lead to Nickel/Palladium. The solder paste we were using was
 Kester OA 596. However, due to the inability of this paste to solder
 to palladium parts, we switched to Kester OA 598. The profile was also
 tweeked per Kester's recommendations for soldering to palladium leads.
 All leads for this component and all other components on the board are
 soldering fine with the new paste and new profile, except for some
 intermittent opens on corner leads of the TI part with
 Nickel/Palladium leads. Component leads for this part were inspected
 prior to pick and place for coplanarity. Does anyone have any ideas of
 what may be happening and any recommendations for eliminating this
 problem.

 Happy Holidays
  >>

Hi there Todd!

     Boy, the problem you're having sure sounds similar to a problem I had
with a TQFP-144 MPEG processor from C-Cubed. Mine was 15.7mil pitch and didn't
have anything to do with palladium, the plating, or coplanarity. We were
getting opens around only the corners of the parts too, and upon looking at
them REAL CLOSE under a microscope, I could see some sort of contamination
that was on the backside of the leads at the corner we were having the solder
problem with, by turning the part upside down and looking at them underneath.
The contamination looked kinda brownish...kinda like overcooked flux residues
or something.

Once I noticed that, I separated them out from the others and that's what
turned out to be causing the problem...but I still didn't know what it was. We
sent the contaminated ones back to C-Cubed, and later I got a call from them
that it was encapsulating material or something (I'm not very knowledgable
about the QFP assembly process) that had oozed out when they were putting it
together and contaminated the leads...it was just on the corners, and that's
why it reminded me of your situation.

It's a long-shot I know...

-Steve Gregory-

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