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December 1998

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Subject:
From:
Rick Thompson <[log in to unmask]>
Reply To:
Date:
Mon, 14 Dec 1998 15:47:25 -0800
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Todd,

I can't offer a solution, but can validate what you're seeing. We use a
similar TI 100-pin QFP and consistently get bad solder joints. We also
switched from OA 596 to 598 but haven't seen much improvement. There are
some good documents detailing TI's palladium plating including test results
from their testing on the TI web site.  Bottom line is that after talking
with a TI engineer and looking at the documentation noted above, it appears
that paste chemistry is a big factor in soldering to palladium plated leads.
As a result, we're currently evaluating other pastes to see what seems to
work better.

Rick Thompson

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Todd Ness
> Sent: Monday, December 14, 1998 8:42 AM
> To: [log in to unmask]
> Subject: [TN] Fine-Pitch Soldering Problem
>
>
> 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
>
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