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August 2010

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Subject:
From:
Reuven Rokah <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Reuven Rokah <[log in to unmask]>
Date:
Tue, 10 Aug 2010 13:48:32 +0300
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Hi Krishnan,

Some time, boards stuck in the reflow oven because of power failure or conveyor problem.
How many assemblies have this failure?

Anyway, discoloration (brownish) may affect the electrical / physical performances of the laminates / PCBs.

Reuven

e mail: [log in to unmask]
Think green before printing this mail... Thanks


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Krishnan (Radhakrishnan) Chezhian
Sent: Tuesday, August 10, 2010 1:54 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Discoloration

Hi All,

This is a double sided board, we did not see this defect when the boards
were shipped. This is a pretty straight forward process for double sided
boards with red soldermask. The only heat  cycle it sees is during the
soldermask pre-cure and final cure. So based onour records and data we did
not see any abnormality during the curing process. Also the only other area
we suspected was at final visual inspection where an inspector found exposed
copper and touched-up the copper surface with mask and wanted to bake it. So
we baked a board at 250F for 60 hours, simulating extreme conditions and did
not see any discoloration, at least to this extent.
We are not sure what processes the boards go through at the assembler in
Jabil Shanghai, we are getting back some baords for FA. So we are open to
resolve this issue ad if anyone has any suggestions pls feel free to
comment.....

Thanks,
Krishnan



On Tue, Aug 10, 2010 at 1:12 AM, Genny Gibbard <[log in to unmask]>wrote:

> I am late into this discussion, since I have been on holidays, but did
> anyone consider the possibility that the layers were stacked together in
> the wrong order internally?  I have seen colour changes like that on one
> batch that was made wrong.  If the internal copper plane layer is closer
> to one surface than it normally should be, it would appear darker on one
> side and lighter on the other than normal, which is what I see with the
> ring.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dan Skweres
> Sent: July 30, 2010 10:59 AM
> To: [log in to unmask]
> Subject: Re: [TN] PCB Discoloration
>
> Looks almost like one is FR-4 and the other is Polyimide. There was
> mention that they are from different lots. Call the supplier and see.
> Perhaps they (the board supplier) messed up and pulled one sheet of
> Polyimide and figured that it would be okay to send based on the fact it
> met or exceeded requirements per print.
> Dan S.
> ----- Original Message -----
> From: "Steve Gregory" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, July 29, 2010 9:34 PM
> Subject: Re: [TN] PCB Discoloration
>
>
> > Hi Linda!
> >
> > While discoloration in itself is not a defect, I would be a little
> > worried about these seven boards. Especially since the rest of the lot
>
> > are not discolored like this:
> >
> >
> > http://stevezeva.homestead.com/PCB_Discoloration1.jpg
> >
> >
> >
> > I don't see any delamination in the photos, but it sure looks like the
>
> > boards got pretty toasty. I wonder if it was because the boards were
> > sitting over a preheater or hot plate too long. From the looks of the
> > components on the board, most of it was probably hand soldered (those
> > PTH caps converted to SMT couldn't have taken reflow), and I imagine
> > that the solid plane on on the backside of the board was a real
> heatsink.
> > Preheating the board would have helped with soldering the PEM nuts for
>
> > sure, but maybe the preheater was set too high. I know a Hakko IR
> > preheater can smoke a board if you're not careful (not that I've ever
> > done that, but I know a friend of a friend who did. Hehehehe).
> >
> >
> >
> > Anyways, those seven boards saw more heat than the rest of them did
> > based on the appearance in the photos. I don't think I'd buy off on
> them...
> >
> >
> >
> > Steve
> >
> >
> >
> >
> >
> >
> >
> > From: Linda Langley [mailto:[log in to unmask]]
> > Sent: Thursday, July 29, 2010 1:42 PM
> > To: Steve Gregory
> > Subject: FW: PCB Discoloration
> >
> >
> >
> > Hi Steve,
> >
> >
> >
> > Here I go again asking for help from my experts! Can you please post
> > these pictures? So I don't have to bother the whole forum, would you
> > know the name of the board guru that could answer my questions?
> >
> >
> >
> > I am not sure if the discoloration is a defect, is this a form of
> > delaminating? Why would only seven boards turn this color? They are
> > all from the same lot.
> >
> >
> >
> > Any information will be greatly appreciated.
> >
> >
> >
> >
> > Linda Langley CIT
> >
> > Training Specialist
> >
> > Jabil Circuit
> >
> > 248-292-6176
>
>
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