I cannot tell from the picture but it doesn't look like the silkscreen
is discolored? From past experience the silk was the first to turn
colors before the PCB material, when the boards were over cooked. Also
when are the labels applied, prior to or after SMT? I know they can be
replaced but operators never take the time to get all the goo off the
board from the smoked label or get the label back on the board in the
same exact spot.
What is the number of boards in assembly array? I am guessing this
happened during the HASL process and wasn't caught until final
inspection.
Regards,
Ted T.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, July 29, 2010 8:34 PM
To: [log in to unmask]
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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