Doug,
Is there solder mask under the conformal coat? Some of what Bob says would make sense if bare copper could touches the conformal coat. Circuit could have been hot when coffee spilled, making a "caffine oxide" over the one circuit.
Denny Fritz
-----Original Message-----
From: Bob Landman <[log in to unmask]>
To: TechNet <[log in to unmask]>
Sent: Wed, Oct 27, 2010 3:02 pm
Subject: Re: [TN] Disappearing Fluorescence
I agree Bev. We used to make spectrofluorometers. Oxygen also will quench
luorescence. As will Cu2+ and amines and a lot of organic chemicals. A good
eference is Joseph R. Lakowicz's book "Principles of Fluorescence
pectroscopy".
Could the current, however small, with the spilled coffee, somehow created an
onized copper trail?
Having just returned from Costa Rica where I went on a coffee plantation tour,
'm chock full of caffene and the knowledge that coffee is an incredibly complex
rganic stew. Perhaps the caffene is the quencher?
And what does this tell us about the conformal coating's qualities that it can
e penetated by coffee?
Bob Landman
&L Instruments, LLC
-----Original Message-----
rom: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
ent: Wednesday, October 27, 2010 8:38 AM
o: [log in to unmask]
ubject: Re: [TN] Disappearing Fluorescence
Doug,
t was a looong time ago, but I did take a fourth year course in photochemistry.
luorescence can be "quenched" in a variety of ways. For instance quinine
luorescence can be quenched by chloride. See the Wikipedia link.
http://en.wikipedia.org/wiki/Quenching_(fluorescence)
Bev
IM
-----Original Message-----
rom: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
ent: Wednesday, October 27, 2010 8:30 AM
o: [log in to unmask]
ubject: [TN] Disappearing Fluorescence
Good morning all,
I posted a picture to the IPC Technet gallery.
http://ipc-technet.groupsite.com/gallery/16251
This is taken from a failure analysis effort I am working on. Its amazing what
appens to electronics when you spill coffee into them.
One of the assemblies I have been looking at has a very odd visual effect that I
ave never seen before. The conformal coating has a fluorescing dye to it that
lows blue under black light, which is common. Notice how the fluoresence has
isappeared from the areas over one set of traces. I have seen fluorescence
isappear before, but it usually heat releated and over a large area, nothing
ighly localized like this. My first thought was that there had been a jumper
ire installed in these locations, but that is not the case.
I showed this to my good friend Phil Kinner at Humiseal, who is no stranger to
he wierd and wacky world of conformal coating oddities, and he has not seen
nything like this either.
Anyone else seen this?
Doug Pauls
Maybe this could be one of Inge's Friday quiz items............
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