Oil: probably transformer oil, the stuff without the pcb-s, would work. I
have used silicon oil, somewhat messy stuff. My guess is that any oil with a
low dielectric constant will work.
==
Maybe the other stuff you are thinking of is "corona dope", which we used
(back in the good old days) on the high voltage connections in some
oscilloscopes.
==
Adding some flies to your ointment, many books and other documents give a
"V/mm" to help you calculate the minimum spacings between (high voltage)
conductors. Most of those numbers are given at sea-level. But when you go to
higher elevations, e.g. Denver or worse, those numbers need to be derated!
They also are typically derived for voltages between smooth surfaces. So
when you have sharp points, the numbers get worse too.
The only thing you are really left with is do some calculations and test a
design to breakdown and then apply your own safety factor. Of course you can
apply the already suggested and the thought of solutions to make
improvements. (But I don't trust the solder ridge on the edge of the board
run very much.)
==
Enjoy,
Ahne.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks,Bill
Sent: Monday, November 07, 2005 10:48
To: [log in to unmask]
Subject: Re: [TN] High voltage breakdown... solutions?
Thanks Phil.
The oil was thought of... although not a specific type.
The routed gap idea was thought of too... and also high insulation
resistance conformal coating...
The corona ball idea is an interesting method... fixing 'sharp points' in
the process... Of course a redesign of the old board is the appropriate
method...
Didn't Dupont or some other company have a 'corona coating' of some sort
back in the bad old days? I think they had some sort of shellac or something
they sold for high voltage applications to deal with things like this...
I just can't remember where I saw it...
Bill Brooks - KG6VVP
PCB Design Engineer, C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 Datron World Communications,
Inc.
_______________________________________
San Diego Chapter of the IPC Designers Council Communications Officer, Web
Manager http://dcchapters.ipc.org/SanDiego/
http://pcbwizards.com
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
Sent: Monday, November 07, 2005 9:50 AM
To: TechNet E-Mail Forum; Brooks,Bill
Subject: RE: [TN] High voltage breakdown... solutions?
Bill,
This is a constant problem that we solved by routing a slot between the two
traces. The slot or gap needs to be sufficient enough to prevent flash over
in air. That assumes your board is in air. You could also "sink" the board
in a dielectric oil or Sulfurhexaflouride, but these bring new issues to the
product.
Another quick solution would be to hand solder a high voltage "corona ball"
along the edge of the etch patterns. Consider the etched edge of a trace.
It is a huge sharp edge. Now if you were to add a blob of solder to make
the edge less sharp you may be able to fix your problem.
Keep in mind there are two issues here, surface tracking and an arc in air.
With surface tracking the routed slot works best.
Hope this is of some help.
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks,Bill
Sent: Monday, November 07, 2005 12:39 PM
To: [log in to unmask]
Subject: [TN] High voltage breakdown... solutions?
It's Monday... had your coffee yet?
I'm trying to gather together some potential solutions to High Voltage
breaking over and arcing between traces on board. The things I know
contribute to this are things like, too little spacing between traces on the
surface or in the inner layers, sharp points on traces, board cleanliness or
the presence of contaminants between the potential voltages.
It was suggested that conformal coating the boards after a real good
cleaning might improve the insulation resistance between traces, has anyone
done this successfully? Do you have any other ideas short of a re-layout of
the board that could perhaps repair a problem like this?
Any ideas are most appreciated.
Bill Brooks - KG6VVP
PCB Design Engineer, C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 Datron World Communications,
Inc.
_______________________________________
San Diego Chapter of the IPC Designers Council Communications Officer, Web
Manager http://dcchapters.ipc.org/SanDiego/
http://pcbwizards.com
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