Ramon,
Gracias, muy rapido. It's not easy to arrange the first choice in open
ground conditions, even if you can hide in a big canvas tent. I'm afraid
DI water rinse will be necessary. Then you have to seal the cooling air
channels in the boards. And how do you get DI water in the Haggar
Mountains, or en las Selvas etc? We tried with an (earthed) black ESD
brush, but you still seem to remove electrons from the coating, thus
causing superficial charges on several hundred volts. I did not believe
it first, until I saw it myself. Maybe hundreds of boards to clean,
needs a lot of DI water. But you may be right, best way.
Inge
-----Original Message-----
From: Dehoyos, Ramon [mailto:[log in to unmask]]
Sent: den 27 mars 2007 14:33
To: TechNet E-Mail Forum; Hernefjord Ingemar
Subject: RE: [TN] ESD charges in conformal coatings
Inge:
There are ESD safe brushes that are impregnated with Carbon.
Also if the process is done in a chamber that is humidified by a
current of moist air and the air goes over ionization bars the problem
is diminished considerably. You may also consider a short rinse with
ionized water, blow them dry with ionized air and then a bake. Even
though you state that it is not allowed, from experience, it works well.
Regards,
Ramon
-----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,
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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