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Subject:
From:
Rich Wolbert <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rich Wolbert <[log in to unmask]>
Date:
Thu, 19 Oct 2006 08:39:37 -0400
Content-Type:
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text/plain (119 lines)
Thanks to everyone who offered their suggestions but I have to give credit
to an old teacher of mine. He drilled Occam's Razor into our heads years ago
and it finally clicked, the easiest solution IS typically the best solution.

After some experimentation we've found the best way to approach this problem
is to use a fiberglass brush to remove the oxides on the fine pitch pads.
Since we will be conformal coating the assembly after testing, the brush
marks will be invisible. We ran a solder test and we have excellent wetting.
The whole rework operation takes less than 3 minutes per board.

Thanks again for all the help.

Rich
----- Original Message -----
From: "JaMi Smith" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 19, 2006 12:04 AM
Subject: Re: [TN] Oxidized PCBs


>I am going way out on a limb here, so please save the boo's and hiss's.
>
> 1. How much assembly is done on the other side? Anything that can be
> striped
> off without too much loss and without damage?
>
> 2. How much, if any, assembly is done on the affected side?
>
> 3. Can you liberally hand flux the problem areas / side with something
> like
> good old Kester 1544 Flux and do good scrub with an trimmed down acid
> brush,
> and then do a hot air reflow, followed by a good cleaning, and then try
> and
> start from scratch with paste on that side?
>
> Whatever you do, you are probably going to have to spend some rework money
> on this to get 170 units done, so the things to ask are what can be saved,
> and at what cost, and how much rework for each board is needed.
>
> You say that you have $600 tied up in each board at present. Where is that
> money? Is it in a few parts that could be pulled and used on another
> assembly? Is it in the board?
>
> I am looking at this as a "rework" problem, since even though the boards
> have never been finished, it appears that you are going to have to handle
> it
> in the same way. I am assuming that you do not have a rework department of
> your own, but you might consider setting one up, since the money you will
> spend on equipment may well be much much less than what you are about to
> lose. Another solution would be to look into someone who does rework.
>
> May just be time to looking into buying something like a "Chipmaster" from
> A.P.E., or something similar either from them or another vendor, assuming
> you have a good tech that can operate it.
>
> Time is also a big question . . . do you have any?
>
> JaMi
>
>
> ----- Original Message -----
> From: "Rich Wolbert" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, October 18, 2006 6:31 AM
> Subject: [TN] Oxidized PCBs
>
>
>> OK, I know you guys are probably going to shake your head on this one,
>> but
>> I have to ask. We have a double sided fine pitch SMT assembly and we
>> decided to go to white tin for the pad material. Here's where the problem
>> comes in, we ran one side and when we started process the other side we
>> found counterfeit chips. We stopped production for two weeks until the
>> correct parts came in. When we tried to run the boards again, the PCB's
>> oxidized so badly over the two weeks that we can not get the solder to
>> wet. Any suggestions, other than scrapping the 170 assemblies at $600 a
>> piece?
>>
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