[luvdunhill]

I am in the need of a very thin piece of material that I can put between a PCB board and a aluminum chassis for insulation purposes. The amount of room between the PCB and the chassis is uncomfortable small, probably the width of a #6-32 nut plus a thin washer. My main concern is some tube sockets that will have around this much clearance, and the voltages present here. Would adding a sheet of silicone, or other plastic be beneficial here, or am I just pushing the envelope too much? If so, any recommendations? The chassis will be very rigid (top and bottom are 4mm aluminum), so I wouldn't worry about the chassis flexing and causing contact. There will also be standoffs from the top of the PCB to the top of the case, adding further support. I probably wouldn't even use real standoffs for the bottom side, just a nut and washer... I guess I didn't figure things would be this tight, and now I have a lot invested in this configuration so I'm trying to make it work.

 

[Uncle Erik]

How about a sheet of Lexan? You can find it at Lowe's and it comes in (I believe) fairly thin sheets. Lexan is tough and should be an excellent insulator.

Also, Lowe's will cut it for you, or you can cut it yourself with a coping saw. It's fairly easy to work and you can sand or file it to shape, as well.

 

[MisterX]

Teflon sheet.
The downside is the price......

 

[vixr]

those cheap plastic kitchen cutting boards work awesome...you can cut them with scissors and they are very tough.

 

[tomb]

MisterX's suggestion is a good route. If my Lowe's and Home Depot's are like yours, though, the thinnest sheet of Lexan or acrylic you will find will be 3/32" inch thick. I keep trying for 1/16", since that's what fits in a Hammond slot, but no luck with those two stores.

You might try a Hobby Shop or a craft store. There are often "Plastruct" displays that offer structural shapes of plastics - including thin sheets. They have thicknesses down to 0.3mm in various types of plastic.

EDIT: Looks like Vixr posted at the same time - sounds like a great idea, too!

 

[Bjornboy81]

Don't use something that can conduct across the surface like plastic. You need Nomex or Teflon.

To be honest you probably have enough clearance. If you have 1/4" or so of air, that will be enough to prevent arcing even from 300V on a tube pin.

 

[luvdunhill]

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif Don't use something that can conduct across the surface like plastic. You need Nomex or Teflon. To be honest you probably have enough clearance. If you have 1/4" or so of air, that will be enough to prevent arcing even from 300V on a tube pin.

I'm assuming Lexan is non-conductive?

TomB and others, what about something like this:

Parma 8x9" 0.030 Lexan Sheet PAR10415 - eBay (item 350021134400 end time Mar-01-08 17:21:41 PST)

 

[luvdunhill]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif Teflon sheet. The downside is the price......

seems cheap enough:

TEFLON SHEET ( VIRGIN ) .005 x 6" x 18" - eBay (item 120078575266 end time Feb-16-08 20:20:11 PST)

 

[Kees]

I don't know how large the sheet needs to be, but a large diameter heatshrink cut up to a sheet would do the trick.

 

[MisterX]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif seems cheap enough: TEFLON SHEET ( VIRGIN ) .005 x 6" x 18" - eBay (item 120078575266 end time Feb-16-08 20:20:11 PST)

I was thinking more like .03" thick and etched on one side so you can glue it down (like they offer here) but I have no idea what the actual insulation "rating" is for their teflon sheet so will see if I can find some data that might suggest one is better then the other for your application.

 

[Bjornboy81]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif I'm assuming Lexan is non-conductive?

Lexan is non-conductive (decently anyways).

I was talking about a materials ability to store a charge on the surface (think static charge) which could cause arcing at higher voltages. I think the teflon would be your best bet here if you wanted to insulate it.

 

[Bjornboy81]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif but I have no idea what the actual insulation "rating" is for their teflon sheet so will see if I can find some data that might suggest one is better then the other for your application.

I don't know the exact number, but it's electrical conductivity rating is very low making it a great insulator. 5 mil should be good for about 1000V or so.

 

[ecommerce813]

Quote:

Originally Posted by vixr /img/forum/go_quote.gif those cheap plastic kitchen cutting boards work awesome...you can cut them with scissors and they are very tough.

Agreed. These are also good for diffusers/reflectors in photography. I think boards about 13x10 can be picked up for around $2.

 

[luvdunhill]

Teflon sheet, or skived sheet conforms to AMS 3652. I cannot find a copy of this ... still hunting.

 

[pabbi1]

Tangent used to carry something, but I no longer see it... might be worth a ping.

Tangent's Parts Shop