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July 1998

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Subject:
From:
"Frank, Jr. Komitsky" <[log in to unmask]>
Reply To:
Frank, Jr. Komitsky
Date:
Sat, 4 Jul 1998 10:38:01 -0400
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-----Original Message-----
From: Hooper Doug <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Friday, July 03, 1998 10:20 AM
Subject: [TN] Au/Ni/Cu PROBLEM



I am experiencing a problem with my Au/Ni/Cu circuit boards. During the
cleaning process in warm (120f) DI water some of them are exhibiting a
"contamination". In certain areas (random) I am getting a discoloration
on the pads. These are non-soldered connections of the board. Other areas
on the board are soldered (hand) and have excellent
solderability/wettability/solder coverage are generally bright, smooth
and shiny. Sometimes this does not occur until the assembly has been
washed 3 or 4 times throughout the production process. The discoloration
appears brown, orange (like rust) and even dark blue to black. It also
appears to be removed with an eraser. Does anyone know what is going on
that would cause this condition to occur? I am concerned about the
condition with respect to contact resistance (keypad/dome application).
Will it get worse even if I can rub it off?

My circuit board supplier is on plant shut-down today. Any input on this
matter would be greatly appreciated! Technet or otherwise.

Douglas A. Hooper, Sr.
Process Engineer
Luminescent Systems, Inc.
[log in to unmask]
(716)655-0800 x163
(716)655-0309 fax

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Doug,

Almost certainly your cleaning is insufficient. Can you get your water up to
150 deg F? This is considered a safe setting for a home water heater so it
should be ok for your equipment. You might also consider increasing your
dwell time in the cleaning cycle. Possibly you can increase the pressure of
impingement of water on your boards, also.
Make sure your reflow profile is not too hot in terms of length and top
temperature, this can burn the flux components, especially in a paste.
Also check the temperature of your wave solder. If all else fails or doesn't
apply, try a different flux or paste. If you are running mixed technologies
make sure your paste and wave solder flux are compatible. Some are not with
components reacting to give insoluble residues.

                                                        Frank Komitsky, Jr.

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