Insulating and heat resistant cardboard/paper? - Page 1
Forum section: electronics / beginners

author: analogix
author_rank: Frequent Contributor
timestamp: October 21, 2020, 06:15:23 pm
content: I have a computer power supply which used to have a type of thin cardboard underneath the power supply's PCB, to insulate against any short-circuiting of the through-hole components and its metal frame. I believe it's heat resistant as well (so as not to start any fire because of the PSU heat).What are these boards called, and what kind of places sell them?

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 21, 2020, 06:39:05 pm
content: Brands:PresspahnElephantide

author: madires
author_rank: Super Contributor
timestamp: October 21, 2020, 06:49:26 pm
content: fish paper

author: drvtech
author_rank: Regular Contributor
timestamp: October 21, 2020, 09:29:47 pm
content: Nomex

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 21, 2020, 11:03:35 pm
content: pizza box

author: andy3055
author_rank: Super Contributor
timestamp: October 22, 2020, 12:03:57 am
content: Leatheroid paper:https://www.google.com/search?rlz=1C1CHBD_enUS923US923&source=univ&tbm=isch&q=leatheroid+paper&sa=X&ved=2ahUKEwiYwqqB8sbsAhXmJDQIHdG9CpwQjJkEegQIAhAB&biw=1366&bih=625Motor winding shops carry this always for insulation along with Milinex paper (the plastic like transparent stuff).https://www.google.com/search?q=milinex&tbm=isch&ved=2ahUKEwjPpdjM8sbsAhUiPH0KHfFgBdcQ2-cCegQIABAA&oq=milinex&gs_lcp=CgNpbWcQAzICCAAyBggAEAoQGDIGCAAQChAYOgQIABBDOgUIABCxAzoICAAQsQMQgwE6BwgAELEDEENQ3ckEWMPdBGCI4wRoAHAAeACAAWGIAdMEkgEBN5gBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=ysuQX8-YDKL49APxwZW4DQ&bih=625&biw=1366&rlz=1C1CHBD_enUS923US923

author: tkamiya
author_rank: Super Contributor
timestamp: October 22, 2020, 12:37:25 am
content: I think it's fish paper. Anyone know why it's called FISH paper??These days though, most PC power supply I took apart had plastic sheeting glued to the bottom. Ordinary paper tends to dry and degrade to crumbling mess in moderate to high heap application.

author: analogix
author_rank: Frequent Contributor
timestamp: October 24, 2020, 12:16:43 pm
content: Thanks for all your suggestions.Unfortunately none of them seem to be available here in Norway. I suppose they're commonly sold in bulk for industry-use and don't pop up as something consumers generally can buy.I originally bought an acrylic plastic display stand for this, but decided against using it because I don't know how it handles heat (fire hazard?) and if it'll emit dangerous chemical fumes when heated, which I definitely don't want.An idea struck me though: how about those silicone baking mats? They're made to handle high temperatures no doubt, and silicone should insulate electrically as well.Even cheaper: baking paper. Equally well for high temperatures, but would it do for constant heat, or will they break up or something? I'd place several sheets on top of each other for suitable electrical insulation.I don't know how hot a computer power supply PCB would become from underneath, but they do at least give off some heat as long as they're turned on, so the material should be able to handle long-term heat, even if it won't be very high.

author: Gyro
author_rank: Super Contributor
timestamp: October 24, 2020, 12:49:05 pm
content: Quote from: analogix on October 21, 2020, 06:15:23 pmJust to clarify the issue. These sorts of insulating sheets are only suitably for supplemental insulation, to allow reduction of clearance distance. You still need mechanical standoffs for the board mountings to define the clearance, to avoid board stress, and to prevent the real danger of sharp points punching through the sheet over time.Sheets are fine, but don't forget the standoffs.The insulating sheets should carry the appropriate flammability rating. Stick with the proper brands, eg. as mag_therm listed.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 24, 2020, 01:41:17 pm
content: These materials are mostly used for construction of wound/magnetics devices so not much demand for hobbiests.There is a vendor in USA with a shopping cart for one off purchases, where I get C-Cores.If the power supply is 100% for your own use for rest of its life, you might consider press-board instead of cooking paper.Press board is a dense cardboard available in craft shops for artists and photo mounting etc.Also you may be able to purchase a roll of "adhesive Kapton tape" in 25mm width or less.It is a high performance insulation. tough mechanically and rated temp class C (I think).I use this, laying down overlapping strips, in cases like yours, and even use it as heatsink insulator.

author: tkamiya
author_rank: Super Contributor
timestamp: October 24, 2020, 04:38:59 pm
content: Inside of power supply should not get any hotter than 80C or 105C. That's the temperature electrolytic capacitors can withstand. Those phenolic circuit-board can do less.Silicone cooking sheet is more than adequate.

author: tkamiya
author_rank: Super Contributor
timestamp: October 24, 2020, 04:42:19 pm
content: Does anyone know WHY they put those sheets in first place? Inside of those power supplies reach 400 volts+ but those "insulating papers" are poor ways to handle it. In fact, leads and traces shouldn't even have a possibility of touching anything metal. Is it insurance?

author: Gyro
author_rank: Super Contributor
timestamp: October 24, 2020, 05:55:32 pm
content: Effectively insurance, yes, in terms of meeting safety specs. As I mentioned above, supplementary insulation allows them to 'push' the board to chassis clearance (which must of course be still be defined and present) when they're trying to cram everything in - especially when taking cropped lead length into account.

author: analogix
author_rank: Frequent Contributor
timestamp: October 24, 2020, 06:30:10 pm
content: Quote from: tkamiya on October 24, 2020, 04:38:59 pmGood point about the electrolytic capacitors!I see thatIkea sells some cheap silicone rubber baking mats("Baktradition", suitable for up to 225 C/435 F), so that appears to be the easist and cheapest way to go.Mag_Therm: I'll likely sell the computer so it's best to do it properly. I've found a place which sells Kaption tape (which I plan to buy for fastening loose wires on top of motherboards etc.) but it's very narrow and would take several (expensive) rolls to cover the underneath of the PSU PCB.Gyro: The standoffs are already taken care off. I don't know why the insulating sheet was missing in the first place, but likely after a recapping job from the previous owner of the computer. Here's a photo of the PSU. It goes underneath the circuit board (through hole components). There's a spacing of around 7mm from underneath the PCB to the "floor" of the metal chassis.I don't know where to get any of the mentioned brands/types of sheets here, and ordering from abroad will likely make them very expensive with shipping, import duties etc. so I'm hoping the Ikea silicone baking sheet mentioned above will suffice.

author: cdev
author_rank: Super Contributor
timestamp: October 24, 2020, 07:20:24 pm
content: Here in the US they call cooking paper parchment paper. I use it all the time to save the PITA of greasing baking sheets, etc. It seems quite resistant to the heat levels you encounter in baking. But it would most certainly burn if subjected to an open flame.Personally, I wouldn't use it in any device where it might pose a fire hazard, definitely not in a computer power supply.Whatever you use, make sure you don't block ventilation holes especially, and bear in mind the convection may not go in the direction you expect. A computer may not always be placed with the side up you would expect also. Most tape wont do to hold it because tape dries out.Polyamide (Kapton) tape sticks and protects even under high heat. It is a known quantity. Its fire resistant and doesn't dry out that rapidly but eventually it does lose its sticking power and becomes just a sheet of material, not tape. However as a data point, I have a big roll of wide polyamide tape that must be at least 15-20 years old and it still works and resists heat, in soldering scenarios. Its still usable.

author: ledtester
author_rank: Super Contributor
timestamp: October 24, 2020, 07:26:42 pm
content: Quote from: analogix on October 21, 2020, 06:15:23 pmDoes it look like this?I can't remember the name of this stuff (perhaps someone can help out here), but it's a fibrous material with some sort of coating on it. It's about 1-2mm thick.

author: cdev
author_rank: Super Contributor
timestamp: October 24, 2020, 07:44:51 pm
content: Is it "Masonite" ?It used to be used on the backs of old radios, typically with a warning to to look in there, unless you were qualified to do so.But I doubt if it would be up to today's fire codes.

author: ledtester
author_rank: Super Contributor
timestamp: October 24, 2020, 07:56:59 pm
content: no, not Masonite (like the stuff pegboard is made out it).It's much more fibrous - it's like interwoven horizontal and vertical strands. For some reason I am under the impression that it is resistant to heat... I probably should just test it.

author: andy3055
author_rank: Super Contributor
timestamp: October 24, 2020, 09:05:24 pm
content: Type of Paxolin:https://picclick.co.uk/One-NOS-B9A-Vintage-Silver-Plate-Paxolin-Wafer-193701751014.html

author: DanielCorwen
author_rank: Newbie
timestamp: October 24, 2020, 10:02:59 pm
content: NOTE: This message has been deleted by the forum moderator Halcyon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.If you believe this to be in error, please contact the moderator involved.An optional additional explanation is:

author: Cerebus
author_rank: Super Contributor
timestamp: October 24, 2020, 10:51:33 pm
content: Quote from: ledtester on October 24, 2020, 07:26:42 pmIf it's old, then it's probably linen (flax) bonded with phenolic resin. If it's relatively recent then the reinforcing fibre is more likely to be fibreglass. I don't know any trade names for either material.

author: connectTek
author_rank: Regular Contributor
timestamp: October 26, 2020, 07:34:27 am
content: Takeaway or frozen?

author: connectTek
author_rank: Regular Contributor
timestamp: October 26, 2020, 07:35:18 am
content: Quote from: Doctorandus_P on October 21, 2020, 11:03:35 pmTakeaway or Frozen?

author: Sampea
author_rank: Newbie
timestamp: October 26, 2020, 09:18:19 am
content: I guess frozen

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 26, 2020, 02:04:16 pm
content: I have seen polycarbonate sheets (0.5mm thick or so) used in several PC power supplies, between the metal covers and PCBs.The optimum stuff would be mica sheets. Maximum temperature is around 480°C - 650°C / 900°F - 1200°F, depending on the binder; dielectric strength close to 20kV per mm (~500V per 0.001"). Some varieties have silicone binders, so the sheet can be quite flexible and not as rigid/flaky as pure mica is (various phyllosilicates). Flame retardant, UL94 V-0.