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March 2007

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TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
Date:
Wed, 28 Mar 2007 19:08:24 +0200
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James,

thanks for the response. We bought some ESD brushes and found a big and 
professional ionized air blower. We placed the coated board on a grounded 
workbench and switched on the blower to stream ionized air across the board. 
And measured with a ESD instrument. Then we swept the ESD brush a couple of 
times across the board. Guess what happened. The instrument read 3,000 
Volts! I'm not going to try an explanation how this could happen. Got no 
time just now.

Next experiment. We took the 'charged' boards and dipped them in DI water 
for a couple of seconds, lifted them up and dried them rapidly with a dry 
nitrogen pistol. New ESD readout gave 0 Volts.

We skip all thoughts about ionizers and brushes and go for rinsing in DI 
water.

Thanks, you all that contributed with ideas.

Inge



----- Original Message ----- 
From: "James Verrette" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 28, 2007 2:52 PM
Subject: Re: [TN] ESD charges in conformal coatings


Inge,



Have you tried an Anti-Static Film Cleaner like "Film Kleen" from
Anchor? There is a Film Kleen, Film Kleen II, Diazo Film Kleen, not sure
what the difference is.  Circuit Check recommends the Diazo Film Kleen
for cleaning their fixtures.  I also stumbled across an Ionizer that
fits on can of compressed air.



http://www.kinetronics.com/cgi-local/SoftCart.100.exe/online-store/scsto
re/cai.html?L+scstore+zczg8040ff939793+1180305318



Jim Verrette

Electrical Engineer





-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar

Sent: Tuesday, March 27, 2007 7:09 AM

To: [log in to unmask]

Subject: [TN] ESD charges in conformal coatings





 Hi all gnus and gurus,

=20

Sometimes, we need clean boards from dust and dirt. Field practise, no

proffesional facilities. Not surprisingly, you move electrons from the

conformal coating's surface. I  have measured several kilovolts at a

distance of one inch from the board. The highly insulating acrylic

coating keeps the charges effectively for hours, quite expected too. ESD

brushes not much better. Not even grounded ESD brushes works. I get rid

of the surface charges if I dip the board in water, quite natural,

because of the large contact area and polarisation media. EE in the US,

did an investigation during 8 years. They ranged the 23 most common

electrical failures and their sources. Conformal coating charges came as

number 9.



Question: anyone who can recommend a dust and dirt removal method, when

dry brushes don't work and water is not allowed?



Inge



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