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
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Please respond to "TechNet E-Mail Forum."; Please respond to Lum Wee Mei
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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
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