Hi, David,
So is it true that contamination has to be on a copper trace to start with
in order to grow? If contamination is only on the solder mask or other
non-metallic surface, there's no harm?
Hmmm! Further light is glimmering on this contamination business (or is it
yet another train coming through the tunnel?)
Peter
David Douthit <[log in to unmask]> 06/02/2003 12:49 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to David Douthit
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] Dendrites
Peter,
They "grow" by chemically desolving the metal in the traces and
redepositing
the metal ions. The reason they have that shape (fern like)
is because it is a metallic based crystal structure.
You are "growing" new traces!
David A. Douthit
Manager
LoCan LLC
[log in to unmask] wrote:
> Hi, Wee Mei,
>
> Dendrites can be (and usually are) on top of Solder mask but underneath
> conformal coating. Solder mask, of course, leaves exposed metal where
> components are soldered, test pads are located, etc. It just takes a bias
> voltage to make microscopic "seeds" of ionic contamination on the surface
> grow between the points of differential voltage.
>
> On top of conformal coating, if dendrites happen at all, it doesn't
matter.
> The metal they would short to is on one side of the coating and the
> dendrites would be on the other side, so they never come into contact.
>
> I've always been curious to know, though - where do these beautiful and
> quite substantial fern-like growths get all the material from to grow
like
> that? Their botanical look-alikes draw nutrition from the soil they grow
in
> - what do dendrites draw on to grow? It's not like they're "alive" or
> anything. What are dendrites composed of (in general terms, not specific
> chemical analysis, which will differ from specimen to specimen)?
>
> Peter
>
> Lum Wee Mei <[log in to unmask]> 06/02/2003 07:22 AM
> Sent by: TechNet <[log in to unmask]>
>
> Please respond to "TechNet E-Mail Forum."; Please respond to Lum Wee Mei
>
> To: [log in to unmask]
> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
> Subject: Re: [TN] Dendrites
>
> Susan,
>
> I am not a reliability gal but curious to learn. While it is
understandable
> that dendrites can formed under moisture condition between conductive
> patterns, how dendrites can be present on top of solder mask or conformal
> coating? Just my curiousity?
>
> Regards,
> Wee Mei
>
> [log in to unmask] wrote:
> It would be good to know where the dendrites are located. You
might
> be able
> to determine this with stereo microscropes. You need to determine
if
> they are under the solder mask or on top of the solder mask.
>
> The main way to get the dendrites to grow would be to add moisture
> and a bias.
>
> Are the assemblies conformally coated? Have you done a simple
ionic
> cleanliness test?
>
> Susan Mansilla
> Robisan Lab---------------------------------------------------
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