Oh,
I see you found a faster way!!
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Thursday, October 19, 2006 10:05 AM
To: [log in to unmask]
Subject: Re: [TN] Oxidized PCBs
Rich,
Rich,
Sorry I just got to this email.
I believe I have a way for you to recover them economically providing that
NO COMPONENTS HAVE BEEN LOADED on the reverse side.
If this is the case, cut a stainless steel stencil say 6 mils thick for the
component pads.
Align the stencil to the board pads using a frame which you are going to
make cheaply at your local tooling house to hold the loaded board in a nest
and hold the stencil frame.
Then you are going to use an airbrasive micro blaster loaded with something
like coconut shell to remove the oxide. The stencil will mask the board
material and so only the solderable areas will get the treatment.
You will then clean the assembly thoroughy agitating in DI water, followed
immediately by a rinse in IPA which will remove any residual water.
Then you are going to assemble them the same day.
Have fun
Any other method I believe may involve you in field failure which would be
far more expensive potentially than scapping the boards
If you need any clarification call me please any time after 08-30 AM pacific
time on my mobile.
408 515 4992
Kind regards,
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of JaMi Smith
Sent: Wednesday, October 18, 2006 9:04 PM
To: [log in to unmask]
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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