Minus 16F....pFF...we have had minus 40F. But very little snow. Alpine
world championship games were stopped for three days because of hard
winds. In January, we had as much as five storms.
Plasma cleaning does not seem to be a hit for the electronics industry,
at least not for PCBs and general electronic modules. Not even for most
microelectronics. If contamination layers are thicker than nanometers,
it takes one hour or hours to get rid of the stuff, and sometimes you
get unwanted depositions somewhere else. We do have areas where the
plasma equipment is used successfully, namely optic lenses for missiles
and thinfilm substrates or semiconductor wafers. We remove most
contaminations by means of chemical cleaning methods, like vapour
degreaser, ultrasonic cleaners, UV radiation, inline washing machines
etc.
Two months more, and you'll be amongst the eagles again, Steve!
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven
Sent: den 6 februari 2007 20:37
To: [log in to unmask]
Subject: Re: [TN] Plasma Surface Treatment For Conformal Coat
Joe,
From a microelectronics standpoint [hermetic type of stuff] I have
always been under the impression that removal of silicone residue with
standard gases such as Argon, Oxygen, Nitrogen, or Argon+Hydrogen mixes
was not reasonably possible - talking RF plasmas in a partially
evacuated chamber, here. Our best plan, was not to have it [silicone]
there in the first place - silicones have a really nasty tendency to
migrate all over the place, on occasion.
The greatest part of my fear of placing a silicone containing part
within the chamber is that some of what gets dislodged from the piece in
question may deposit on the chamber walls [instead of getting sucked out
the vacuum]. This can mean that the next part to go into the chamber
may get a smattering of this as it becomes knocked from the chamber
walls. This would not be good for a part which was going to be wire
bonded, for example.
At our power levels, angstoms, or atomic layers, of contaminates are
removed. I don't normally attempt to remove visibly thick layers of
contaminates with the plasma because doing so usually either takes a
long, long, time and/or the parts become hot and/or discolored [eg O2
will turn silver black. Go long enough and SnPb solder will get dark
and dull looking, etc.].
A 'quicky' O2 plasma - say 5 minutes, at 150W, at about 150-200 mT will
do a nice job of activating the surface of many plastics for promotion
of adhesive adhesion though. I have little doubt that it would also
improve the wetting characteristics of your bare laminate and/or solder
mask, but I would not necessarily lay claim that it would remove gobs of
organics [within a reasonable time frame, that is].
I'm interested in hearing what Yoda Ingemar and D Hillman have to say on
the matter.
PS - Ingemar, I had -16F, outside air temp this morning [-14F
yesterday]. Getting more like your neck of the woods each day! Have
had enough, thank-you.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Joseph E (US
SSA)
Sent: Tuesday, February 06, 2007 11:23 AM
To: [log in to unmask]
Subject: [TN] Plasma Surface Treatment For Conformal Coat
While we're on the subject of CC, does anybody use plasma to remove
stubborn organic residues (e.g. silicones) from board surfaces, or
otherwise change the surface energy to promote coating adhesion?
We're not talking about long or aggressive exposure here, just enough to
remove a thin layer of contaminant, or roughen the surface of a glossy
soldermask. So I'm not much concerned about removing markings or
anything, but are there any other potential pitfalls?
Joe Kane
BAE Systems
Johnson City, NY
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