Phil,
I assume that CCA stands for Conformally Coated Assembly. If so what chemical family did the coating
fall into (acrylic, urethane, etc...)
How long was this device "in the field" and how much exposure did it receive to humidity above 80%?
BTW those "faint carbon tracks" are usually all that left when the dendrite vaporizes due to current
flow.
I will send you a copy of my paper "Avionics Systems, Reliability, and Harsh Environments". it should
provide some useful info for your investigation.
David A. Douthit
Manager
LoCan LLC
phil bavaro wrote:
> OK, here is the background on this particular dendrite growth:
>
> It is a field failure unit and upon closer inspection, this dendrite
> follows a crack in the capacitor from one termination to the other. In my
> opinion, the crack was there first, and was filled with contaminated
> moisture while the cap had battery voltage (5V) across it, causing the near
> perfect dendrite to form along the walls of the crevice.
>
> This CCA was produced on our no clean assembly line, of which the
> cleanliness is monitored on each lot of boards produced. We believe that
> the solder flux residues are not related to this defect. The soldering
> residues do not migrate to this area of the capacitor.
>
> The condensation moisture alone would not seem to be enough to have
> generated this dendritic growth so we are investigating other possible
> contamination that may have been present such as moisture dripping off of a
> dirty shelf above, and also the component cleanliness itself. If the crack
> was there from the beginning then the contamination could have been as well.
>
> We have seen shorts across this capacitor before but usually only as random
> faint carbon tracks that are nowhere as defined as this one was.
>
> This one is so perfect, it almost looks like an organic plant like a small
> fern.
>
> This is an ongoing investigation so all comments are welcome and I will
> provide an update at some point in the future.
>
> Phil
>
> At 06:51 AM 2/25/02 -0700, [log in to unmask] wrote:
> >Doug,
> >Isn't that known as the Mountain "Dew"lution Test?
> >Dewey
> >
> > > -----Original Message-----
> > > From: [log in to unmask] [SMTP:[log in to unmask]]
> > > Sent: Monday, February 25, 2002 6:31 AM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] Dendritic Growth...
> > >
> > > Sunny asks:
> > > I'd like to know which type of Ion Chromatography can measure the local
> > > dot ionic cleanliness. Anyone can tell me which company produce this
> > > equipment?
> > >
> > > Doug Pauls responds:
> > >
> > > No company that I know of builds ion chromatography equipment to do spot
> > > ionic checks. IC equipment merely analyzes extract solutions. If you
> > > want
> > > to measure localized ion concentrations, you have to develop a localized
> > > extraction technique. This might involve immersion of a portion of the
> > > assembly in extract solution, or building some time of non-contaminating
> > > enclosure around the area to be extracted. Once you can localize the
> > > extraction, collect the solution an analyze it with the IC equipment
> > >
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