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From:
Steven Creswick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steven Creswick <[log in to unmask]>
Date:
Fri, 30 Jul 2010 12:37:45 -0400
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Doug,

 

I believe my extreme phobia came about in the days of us processing
'elephant snot' for potting automotive.  One had to be extremely careful not
to contaminate things with that silicone - cured or not.

 

I have basically adhered to that rule of thumb in the years since, and have
not experienced problems.  Possibly a case of being overly cautious, but it
sure beats the other extreme!

 

I would not process any uncured materials in the plasma chamber - silicone
or other.  I still avoid the cured silicones if at all possible.  I remember
one MEMs device that needed to be attached with a thick section of low
durometer silicone gel, then wire bonded - we did not plasma clean it.!

 

"power" is somewhat unique to each unit, but when I go to ash the chamber, I
will drive the power to 300-500W [whereas the Argon plasma may only be
150-250W], under higher than normal pressure for 20-30 minutes.  The 'dense'
energetic plasma seems to do a good job of cutting through the organics.
Make it a standard cycle and do it every Monday morning, for example  On
some units you can automatically have it cycle through an oxygen plasma then
finish up with an argon plasma

 

Being below the explosive limit at 4-5%, I don't think you will have
opportunity to eliminate any overlords, but do watch the addition of baked
beans to the recipie!

 

Look at the Diener cleaner .   http://us-plasma.com/    Their PlasmaBeam
atmospheric plasma units are kind of slick.  Is it 100% ESD safe is always
the question..

 

Steve

 

 

 

 

From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Friday, July 30, 2010 10:52 AM
To: TechNet E-Mail Forum; Steven Creswick
Subject: Re: [TN] Plasma Chamber Maintenance

 


Thank you Steve.   
Does your silicone rule refer to cured or uncured silicone or both?  And
when you talk about "high energy", what wattage level are we talking about?
How long an oxygen cycle do you recommend for burn off. 

I will have to play a little with hydrogen. 

Not sure if I know what you mean by arc plasma.  In in-line ones that I have
seen are largely made for things like bare boards, and not assemblies. 

Doug Pauls 




Steven Creswick <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]> 

07/30/2010 09:22 AM 


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Re: [TN] Plasma Chamber Maintenance

 

		




Doug,

One of our rules was - thou shalt not put silicones in the chamber!

Other than that, periodically we would use a really fine scotchbrite and
clean room vac to physically clean the interior of the chamber.

Then, as Joyce indicates, a nice high energy oxygen plasma to ash off any
remaining organics and argon to knock off a few more offensive molecules.  

From a wire bonding point of view, I have found argon with 4% hydrogen to
provide a slight edge on cleaning over straight argon.  Not sure if that
would apply to CC adhesion of not.

Have you tried the arc plasma cleaners/surface activators.  Can be made into
an in-line process much easier than the batch type plasmas.


Steve Creswick
http://www.linkedin.com/in/stevencreswick




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Friday, July 30, 2010 9:01 AM
To: [log in to unmask]
Subject: [TN] Plasma Chamber Maintenance

Good morning all,

On a topic other than rhubarb, raiding my cubicle for prizes, and selling 
off my children, I have an actual technical question.

We have started to use plasma chambers as a preparation for conformal 
coating and are having some excellent results.  One of our IEs, with a 
background in the semiconductor industry, had indicated that the chambers 
can be items that are hard to maintain or high in maintenance costs.

So, for you plasma chamber users out there, what have your experiences 
been with plasma chamber maintenance?

Doug Pauls

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