Steve,

Several years back we saw the same thing with the Littlefuse series PGB
ESD suppressors.  We'd run them for a long time with no issues, then hit
a lotcode of parts where the green coating chipped or lifted off in the
process. Those assemlies were also seeing a fairly aggressive wash,
which included a saponified batch cleaning.

In the PGB series, I think that the round dots were a special composite
polymer and part of the ESD protection. The green coating was nothing
more than that.  What we observed was that when the coating pulled away,
it sometimes removed or tore part of that polymer. We replaced any parts
with a non-intact coating.  

Bruce Tostevin
Benchmark Electronics
Hudson, NH

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Gregory
Sent: Monday, March 06, 2006 10:19 AM
To: [log in to unmask]
Subject: [TN] A new one for me, ESD Suppressors...

Mornin' Everybody!

Last Friday, I had a problem with a new part that I've never used
before, and maybe somebody else has seen this problem. It's with
something called an ESD Suppressor. It's a little 0603 SMT part that
looks a lot like a LED...in fact, that's what I thought it was at first.
It's made by Littlefuse.

My problem is that there's a little green piece of plastic on the top of
it that looks like it's held there with a tiny dot of glue, that is
either coming off or breaking during wash. I'm washing the boards in a
batch cleaner using Kyzen Aquanox 4512P at 140 F. for 20-minutes
followed by a ambient temperature rinse cycle, and a 15-minute 100 F.
dry cycle.

I did read in the datasheet that I'm probably washing at too high a
temperature. The datasheet says that they have been tested IAW ASTM-543
for 4-hours at 40 C., with 3 solutions (H2O, detergent solution, and a
defluxer). I didn't know that there was this limitation until we
observed the little green pieces of plastic coming off. You can see a
picture at: 

http://stevezeva.homestead.com/files/ESD_Suppressor.jpg

My question is; what is that little green plastic piece? There's nothing
in the datasheet that describes it. Is it something functional to the
part? Or is it something there for pick and place? I've got a call into
Littlefuse and I'm just waiting for a call back. But I thought I'd ask
you all to see if someone else has run across these little guys before.
I don't have a clue about them...

Have a good Monday!

-Steve Gregory-



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