Legit source for thick (4-5mm) thermal conduction pads??........ - Page 1
Forum section: electronics / projects

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 07:51:56 am
content: Problem:I have a 2" x 2" board with all components on the top side, including a through hole connector with leads soldered from the bottom. Unfortunately that through hole connector is non-optional. The board is mounted on short standoffs so the through hole pins don't touch the heatsink. I need to conduct heat from the bottom of the board to a heatsink so I need a thick thermal pad of some sort. Something in the 4-5mm range is about the spacing.I was looking at something like this:https://www.amazon.com/dp/B086VZ9YW3Problems with this:1) Amazon is not a reliable source2) I would need to stack two pieces... Anyone know of a comparable thermal pad type product that1) Isn't crazy expensive and comes from a reliable source?2) Ideally already about 4-5mm thick.3) Comes in a form factor (sheet) that can be die cut.Notes:1) Yes I could mill a little pocket in the heatsink where the through hole pins are, but I don't think people would appreciate paying for an extra machining op.2) Also the connector effectively snaps in, so it's not really possible to just solder it in so the pins don't stick out as much.3) Something like a thermal epoxy would need to be really thick to not run through/around the board and would make rework impossible, so that sucks.

author: jbb
author_rank: Super Contributor
timestamp: September 08, 2024, 08:02:01 am
content: In general, ‘wet’ processes like gluing, potting, painting etc are a pain in the production line. Unless you’re going to large enough volume to use glue robots etc. and you run enough units per day to amortise the setup and cleaning costs.I used Bergquist Gap-Pad for a smaller gap and had good results. I think it was:https://www.henkel-adhesives.com/cn/en/product/thermal-gap-pad-materials/bergquist_gap_padtgp1000vous.htmlThey are very squishy and I found that they cut quite nicely using a paper-cutting guillotine from the logistics department (clean it carefully before use so you don’t pick up a pile of paper dust).The thermal resistance of a gap filling pad 5mm thick will be quite high. So I suggest you do some thermal resistance calculations for any proposed material and then check them on a prototype.

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 08:08:54 am
content: Ya, it's not going to be great. Actual bench measurements show the converter by itself with no heatsink doesn't overheat, but it does get hotter than I want.Nice, the BERGQUIST® GAP PAD TGP 1000VOUS comes up to 6.35mm. I'll see what that looks like cost wise.https://datasheets.tdx.henkel.com/BERGQUIST-GAP-PAD-TGP-1000VOUS-en_GL.pdf

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 08:14:41 am
content: Oh, killer. It's available in distribution in all thicknesses.https://www.mouser.com/ProductDetail/Bergquist-Company/GPVOUS-0.160-01-0816?qs=N2Tevpb%252BvoZaQnofuUuuWA%3D%3DThermal Interface Products GAP PAD, 8" x 16" Sheet, 0.160" Thickness TGP1000VOUS/VO Ultra Soft, IDH 2166004$104.91 in 1s$86.41 in 100s.. and I can get 32 pads per 8x16 sheet. So $3.25 per pad in 1s, or $2.70 in 100s. That's more than I was looking for, but not a show stopper.

author: voltsandjolts
author_rank: Unknown
timestamp: September 08, 2024, 08:35:46 am
content: Quote from: Smokey on September 08, 2024, 07:51:56 amSounds like the THT connector is the issue. Maybe:(1) change the PCB shape, such that the THT connector is over the edge of your heatsink(2) raise the THT connector on a small carrier board(3) source SMD equivalent for the THT connector, if available(4) trim the THT pins to be flush with the underside before insertion to PCB (use a jig). Or trim with flush cutter after insertion and prior to soldering.

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 08:50:51 am
content: Quote from: voltsandjolts on September 08, 2024, 08:35:46 amYou are totally correct that the through hole connector is the problem. Without that I would just use whatever thickness pad and bolt directly to the heatsink....Unfortunately, as I said, I'm stuck with that connector. I'm not happy about it either. No SMD equivalent exists, and the board is mounted in the middle of the heatsink so no hanging it over the edge.Trimming the pins would be a production pain in the ass (lots of pins). That would probably cost more than the expensive pads. Also "flush" is never really flush, so I would still need to stand the board off the heatsink and that means I would still need a thicker pad.

author: voltsandjolts
author_rank: Unknown
timestamp: September 08, 2024, 09:34:39 am
content: What connector is it?How much do the pins protrude?Would using 2.0mm PCB substrate (instead of existing 1.6mm?) make the protrusion manageable, such that you could just tighten the PCB down onto a single sheet 2mm thermal pad.Quote from: Smokey on September 08, 2024, 08:50:51 amNote that it doesn't need to be perfectly flush, thermal pad thickness can accomodate to some extent.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2024, 09:55:14 am
content: Machine cavities into the heatsink, or use aluminium shims perhaps - will be better thermally than a thick pad

author: voltsandjolts
author_rank: Unknown
timestamp: September 08, 2024, 10:09:22 am
content: Quote from: Smokey on September 08, 2024, 07:51:56 amAlloy thermal shim is a good idea. Probably quite cheap at this size, especially atJLCPCB/ PCBWAY.

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 10:25:05 am
content: Quote from: voltsandjolts on September 08, 2024, 10:09:22 amInteresting. It would need to be stamped to have a chance of being cheaper than a thick pad. I wonder if it would be flat enough to make decent thermal contact with the heatsink without a pad or greese. Plus I would still need a pad to take up tolerances and electrically isolate from the PCB.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2024, 10:30:14 am
content: Quote from: Smokey on September 08, 2024, 10:25:05 amLasercut from sheet should be fairly cheap.

author: voltsandjolts
author_rank: Unknown
timestamp: September 08, 2024, 10:41:07 am
content: Quote from: Smokey on September 08, 2024, 10:25:05 amJLCPCB alloy pcbs are in effect 0.1mm of dielectric glued to the alloy (you choose thickness). No need for other insulator.Quote shows abut $20 for 20 shims at your 2" x 2" size.Just send them a gerber with cutout for your connector pins slot.

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 05:46:21 pm
content: Quote from: voltsandjolts on September 08, 2024, 10:41:07 amNow that is really interesting,... I bet tolerances would be pretty tight. Looking into this..

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 09:11:27 pm
content: JLCPCB aluminum boards only look to go up to 1.6mm. The 2mm option is greyed out.So I would be looking at two 1.6mm board shims (3.2mm) + 1mm sil-pad I guess = 4.2mm total stackup.250 shim boards are quoted at $34.90 + $40 shipping = $0.30 per shim, or $0.60 per assembly.Only finish option is HASL. I wonder if they would make a build with NO surface finish for less.I should probably also be using some thermal grease between the boards and heatsink.What sucks about this is it's a lot of line items and assembly steps to make that stackup. The cost is decent, but the production steps I'm not super excited about.UPDATE: PCBWay has way more options for aluminum boards. Up to 3.2mm with no copper layer. Interesting...