http://www.dtic.mil/dtic/tr/fulltext/u2/249378.pdf > I have seen the effects of corona consuming carbon impregnated ABS > plastic, I wish I had the photos to share. The device lasted less than six > months before the corona consumed the plastic and potting material. This > was a device that was placed on a high voltage transmission line and a > portion of it had to be at or near line potential to function correctly. I > do not think we concluded if it was the actual corona that destroyed the > plastic and potting material or the high concentration of ozone being > produced. My guess it was a combination of both. > > Ted > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne Oosterhof > Sent: Tuesday, March 21, 2017 10:16 AM > To: [log in to unmask] > Subject: Re: WG: [TN] Screen On Insulation > > The high field strength allows corona to develop and corona "eats" plastic > materials. Therefore no sharp ends on high voltage components and no sharp > corners in high voltage conductors !!!!!!!! > > Experience is a very strict task master, > > Bin der, done dat, > Ahne > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Giamis, Andy > Sent: Tuesday, March 21, 2017 8:03 AM > To: [log in to unmask] > Subject: Re: [TN] WG: [TN] Screen On Insulation > > That's very interesting Carl. > > I have never considered a polymer degrading and breaking down as a result > of electric field strength. I suppose it is possible. What did it look > like. What led you to that conclusion? > > Thanks, > Andy > > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl Van Wormer > Sent: Tuesday, March 21, 2017 8:46 AM > To: [log in to unmask] > Subject: Re: [TN] WG: [TN] Screen On Insulation > > My experience with safety regulation electrical spacing has always > required guaranteed distances and multiple barriers. For example, where a > plastic spacer/insulator had pin-hole fault possibilities, a double layer > was required. I would be concerned about a cleanliness fault (a chunk of > debris, a protrusion from a mechanical impact, or a filament of PCB edge > fiber) preventing a thin-layer applied coating from achieving its nominal > protection characteristics. I have seen double layer spacing requirements > met by a notch in the PC board with an inserted Kapton shield. > Also, beware of sharp edges and corners in HV environments. I had one > product fault that resulted in long-term (after 1-year) dielectric > break-down of an insulated video HV anode wire near a sharp sheet-metal > edge. The electrical field strength is related to inverse radius of the > physical elements. The silicone wire insulation broke down because of the > field strength, not because of abrasion from the sharp edge. > > Later, > Carl > > > Carl B. Van Wormer, P.E., AE7GD > Senior Hardware Engineer > Cipher Engineering LLC > 21195 NW Evergreen Pkwy Ste 209 > Hillsboro, OR 97124-7167 > 503-617-7447x303 > [log in to unmask] http://cipherengineering.com > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Torsten Hagge > Sent: Tuesday, March 21, 2017 2:49 AM > To: [log in to unmask] > Subject: [TN] AW: [TN] WG: [TN] Screen On Insulation > > Hi Bob, > > parylene is closed at about 0,6µm, so at 1 mil you have a safety margin > of about 4200 %. > > We have payed about 1500€ for a batch of 32pcs bio sensor PCBs with 40mm > diameter... > > Take care, > Torsten > > > Best Regards > > KRISTRONICS GmbH > > Dipl.Ing. (FH) Torsten Hagge > team leader HW development > Gewerbegrund 5-9 > 24955 Harrislee > Telefon +49 (0) 461 7741-624 > Telefax +49 (0) 461 7741-642 > [log in to unmask] > www.kristronics.de > Place of jurisdiction: Flensburg, commercial register: HRB 1433 FL CEO > Dipl.-Ing. oec. Thormod Ohm VAD-Id DE 811182059 Bank account: Deutsche > Bank AG Flensburg, account 4216610, bank number 21570011 > IBAN: DE32 2157 0011 0421 6610 00, BIC: DEUT DE HH 215 Please consider > the environment before printing this e-mail > > > > > -----Ursprüngliche Nachricht----- > Von: Robert Kondner [mailto:[log in to unmask]] > Gesendet: Montag, 20. März 2017 17:06 > An: 'TechNet E-Mail Forum'; Torsten Hagge > Betreff: RE: [TN] WG: [TN] Screen On Insulation > > Torsten, > > Do you know how thick a parylene coating is? My recollection is pretty > thin. > > So I checked, very high dielectric strength, thickness typically under 1 > mil but it can be built up further with longer processing time. > > Any idea wat coating with parylene cost for a small batch of boards? > > Thanks, > Bob Kondner > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Torsten Hagge > Sent: Monday, March 20, 2017 9:17 AM > To: [log in to unmask] > Subject: [TN] WG: [TN] Screen On Insulation > > Hi, > > cheap solution could be a 1mil kapton tape with the mention risk of air > gaps, fine and cost expensive solution parylene HT coating before placing > the ferrite cores... > > Take care > Torsten > > > > Best Regards > > KRISTRONICS GmbH > > Dipl.Ing. (FH) Torsten Hagge > team leader HW development > Gewerbegrund 5-9 > 24955 Harrislee > Telefon +49 (0) 461 7741-624 > Telefax +49 (0) 461 7741-642 > [log in to unmask] > www.kristronics.de > Place of jurisdiction: Flensburg, commercial register: HRB 1433 FL CEO > Dipl.-Ing. oec. Thormod Ohm VAD-Id DE 811182059 Bank account: Deutsche > Bank AG Flensburg, account 4216610, bank number 21570011 > IBAN: DE32 2157 0011 0421 6610 00, BIC: DEUT DE HH 215 Please consider > the environment before printing this e-mail > > > > -----Ursprüngliche Nachricht----- > Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Robert Kondner > Gesendet: Freitag, 17. März 2017 21:11 > An: [log in to unmask] > Betreff: [TN] Screen On Insulation > > Hi, > > > > We have a PCB that turns out to require 2500VAC test for 60 seconds and we > had some flash over on pads to vias. We also have a planar ferrite > transformer with primary windings on one side. > > > > Does anyone know of a screen on insulation material that can be used to > increase flash over voltages? I would like to get a 2 or 3 mils of > material. > My other option is to have a laser cut layer of isolation but that could > leave air paths under the material. > > > > Any other ideas welcome. > > > > Thanks, > > Bob K. >