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January 1998

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Subject:
From:
Joe Reichert <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 30 Jan 1998 16:47:12 -0500
Content-Type:
text/plain
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text/plain (125 lines)
Hello,

I have had limited experience with IR reflowing PCB's with gold fingers
but it seems that it would be possible for the nickel plating under the
gold to somehow be "mixed in" with the gold during a IR reflow.  I do
not know at what temperature gold or nickel would "reflow" or
"liquefy"(so I may be way off base here), but if one of the two was in
anyway to "liquefy" they would either mix or appear contaminated.  Hope
this helps.

Joe Reichert
LakeShore, Inc.


>----------
>From:  annie laberge[SMTP:[log in to unmask]]
>Sent:  Friday, January 30, 1998 4:35 PM
>To:    [log in to unmask]
>Subject:       Re: [TN] Solder spots on gold fingers
>
>Hi Richi.
>
>I am not shure I can help you but at least I can share with you what we are
>experiencing over here: The same thing as you are.We have solder spot on
>gold fingers  (We assemble PCBs).
>
>The board is a double sided 0.062" SMOBC board with goldfingers( 30
>microinches of gold over 100 microinches of Nickel) The assembly process
>consists of screen printing of solder paste, pick and place SMT machines ,
>Reflow, manual insertion of through hole
>components and finally wave solder. The problem manifests itself after IR
>reflow. There are tiny silverish/grey spots on the goldfingers, on solder
>side and componant side.
>
>What is strange is that we don't see any tendancy in terms of Manufacturers
>or part numbers.  At least 6 manufacturers are involved with this issues,
>and almost all part numbers has this issue on and off.
>
>We also put Kapton tape BEFORE assembling to see if the problem comes from
>the board or the process.  And after SMT assembly, we remove the tape and
>find solder spot on gold fingers.  So it definitively comes from the PCB.
>At incoming inspection, we don't see those solder spots  (the inspection
>may not be as rigorous as on the assembly line).  What we think it could be
>is tinny solder flakes on the boards which with manipulation fall on gold
>fingers during assembly (before reflow oven).
>We will investigate futher for this  point.
>
>But if anybody can give us more input, it will be greatly appreciated.
>
>ALaberge
>Quality Eng.
>Matrox Electronic systems
>
>_____________________________________________________________________________
>
>At 05:04 PM 1/29/98 EST, [log in to unmask] wrote:
>>We are PCB manufacturers and seem to be having a enigmatic problem on one of
>>our boards we manufacture for one of our customers.
>>
>>The board is a double sided 0.062" SMOBC board with flash gold goldfingers(
>>1-3 microinches). The assembly process consists of screen printing of solder
>>paste, pick and place SMT machines , Reflow, manual insertion of through
>>hole
>>components and finally wave solder. The problem manifests itself after IR
>>reflow. There are tiny silverish/grey spots on the goldfingers. Suspecting
>>that the spots were caused by solder paste particles which were either
>>deposited because of contaminated equipment or degassing from the PTH
>>causing
>>splattering of solder paste we ran the next batch of boards using Kapton
>>tape
>>on the gold fingers. Unfortunately we saw the same spots again. The straw
>>which broke the camels back was when a recent datecode boards fresh out of
>the
>>cartons were run without Kapton tape and exhibited the same symptoms.
>>
>>Our dilemma:
>>
>>We manufacture 30 P/Ns for this customer. The problem is only on this P/N.
>The
>>same lines are used to run all the boards.
>>
>>We have manufactured thousands of these boards without any problem and now
>>suddenly we have this issue.
>>
>>The same assembly line used to assemble this board is used to run other
>boards
>>we manufacture and no other P/N exhibits this problem.
>>
>>Hope somebody has seen such a manifestation and can advise.
>>
>>Thank you.
>>
>>Richi
>>
>
>>
>
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