Methods of conducting heat from PCB to extruded aluminum enclosure? - Page 1
Forum section: electronics / projects

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 02, 2016, 02:07:43 am
content: I'm working on my next product and the board dissipates about 8W. I need to remove heat to the outside of the aluminum enclosure so ideas are to put a small fan and drill some holes in the end panels (not very nice looking) or (better) to somehow conduct the heat from the PCB to the enclosure. As the below picture shows (not actual enclosure but close enough), the PCB slides in so, perhaps, something could be attached to the sides of the PCB to decrease the thermal resistance between the PCB and enclosure? Or, perhaps there is some kind of foam (non-conductive) that can be attached under the PCB such in contact with both the PCB and bottom of enclosure? The surface area of the heat conduction would be much larger in idea #2 so perhaps best solution.http://g01.s.alicdn.com/kf/HTB1yO1OKFXXXXa2XpXX760XFXXXc/224624606/HTB1yO1OKFXXXXa2XpXX760XFXXXc.pngAny other ideas?

author: samnmax
author_rank: Regular Contributor
timestamp: June 02, 2016, 12:22:42 pm
content: You could fill the space between the PCB and the case with some thermally conductive material, although it would probably be difficult to slide it in with the board (they tend to stick to surfaces, for good reason). I think the term you are looking for is "gap filler" or "gap pad".Maybe you could only thermally couple the case to the devices producing heat instead of the whole PCB?

author: ebclr
author_rank: Super Contributor
timestamp: June 02, 2016, 12:36:48 pm
content: This may workhttp://www.aliexpress.com/item/DIY-laptop-notebook-brass-cooler-heat-exchanger-tube-fins-efficient-copper-pipe-80mm-300mm-Thermal-conductivity/32291675053.html?spm=2114.30010308.3.40.a70nbp&ws_ab_test=searchweb201556_8,searchweb201602_4_10037_10017_10021_507_10033_10022_10032_401_10020_10018_10019_101,searchweb201603_3&btsid=73f4589c-187b-4fad-9602-68110819cbda

author: zlymex
author_rank: Frequent Contributor
timestamp: June 02, 2016, 02:15:02 pm
content: I use this kind of thing, insulation is very good(tested >10^12 ohms), and feel very cool(as opposit to hot) indicating it's very heat conductive.There are different sizes and different thicknesses available.http://www.aliexpress.com/item/1Pieces-100-x-100-x-2mm-Green-Thermal-Pad-Silicon-Heatsink-Cooling-Conductive-GPU-CPU/32413596132.html

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 02, 2016, 02:34:57 pm
content: An extreme solution, but one that would work is to seal the enclosure and fill with Fluorinert.

author: nfmax
author_rank: Super Contributor
timestamp: June 02, 2016, 03:08:36 pm
content: A long time ago, I was involved with designing an avionics system. The boards were conduction cooled. A thick inner copper layer acted as both a ground plane and a heat spreader, and at the two side edges of the board the layer stack to one side of this layer was cut back, so the copper was exposed. The card slid into guides attached to the housing, and when fully home, wedge-locks pushed the exposed copper against a heat transfer surface in the guide. In turn, this conducted heat to a heat exchanger where air from the plenum was blown through (the main enclosure remaining sealed, except for a pressure equalising vent).A bit overkill for your application, but you do have metal card guide slots, and you could use a surface copper layer and expose the board edges from the soldermask (gold plating might be advisable though to minimise galvanic corrosion issues). You then just need a way of holding the board against the slot...

author: CJay
author_rank: Super Contributor
timestamp: June 02, 2016, 03:15:15 pm
content: Rivet or somehow weld to the case or packages leaf springs that contact the package of the devices that are dissipating the powerIf it doesn't have to be serviced then pot it in epoxy, if it does have to be then pot it in silicone (Dow Corning make some excellent two part silicone potting compounds)Measure the temperature of the board and once you're sure it has no deleterious effect on operation just accept it's going to get hotIf the board has hotspots then you could use a heat spreader on the board to even it outRedesign the board to have huge copper pour regions to spread the heat.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 02, 2016, 03:26:53 pm
content: Search digikey for "thermal pad"I've used ones like this:http://www.digikey.com/product-detail/en/t-global-technology/TG2030-25-25-5/1168-1557-ND/3042370for similar applications with good results, but it is tacky, so that may cause problems with sliding in/out of the enclosure.

author: nctnico
author_rank: Super Contributor
timestamp: June 02, 2016, 05:34:19 pm
content: If the lid can slide out it could (on some of these cases that is possible) the PCB can be mounted so that the lid becomes a heatsink. Thermal conductive rubber or a thermal conductive spacer will be required though. The lid + PCB slide into the housing as one assembly.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 02, 2016, 06:04:57 pm
content: Thanks all. I think the best option is to use one of these heat pads:http://www.walmart.com/ip/6mm-Thick-Adhesive-Thermal-Pad-8-x-4-for-Notebook-IC-Chipset-Chip-CPU/46934305However, I need to find one that is much cheaper. Approximately a few dollars for 100mmx100mmx6mm. The distance between the PCB and bottom of enclosure is 6mm. So far no luck on Ali express, Ebay, Amazon etc...

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 02, 2016, 06:51:25 pm
content: Quote from: John_ITIC on June 02, 2016, 06:04:57 pmI doubt that 8W of power dissipation is spread evenly across an entire 100mm x 100mm area. You probably just have 1-2 high power devices that are drawing the bulk of it, right? Focus on them, not the entire board. You can pick up one of these for about $2/ea in quantity, $3/ea in singles:http://www.digikey.com/product-detail/en/t-global-technology/H48-6-25-25-9/1168-1703-ND/330036125x25mm should be enough to center it over the part with the highest power dissipation, take care of that part and the rest of the board should take care of itself. 9mm thickness gives you some room to compress it to improve the thermal conductivity.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 02, 2016, 10:14:54 pm
content: Thanks all. My board is a 10-layer PCB with lots of power and ground planes so the heat is indeed spread quite evenly. When used on the lab bench, the hottest IC is about 55 degrees C. But since no opening in the box, the temperature will rise above that so the heat pad should couple to the case more effectively. I actually have an older product that uses exactly the same PCB and enclosure but it doesn't get quite as hot. I simply measured the power going into the board from the power supply and it is about 8W (of which all gets converted into heat).I may have to use multiple smaller heat pads and experiment...

author: Aodhan145
author_rank: Frequent Contributor
timestamp: June 02, 2016, 10:25:46 pm
content: Dave made a video about this, may not be the best resource of information though.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 02, 2016, 10:36:01 pm
content: Quote from: John_ITIC on June 02, 2016, 10:14:54 pmIf you haven't done so before, I suggest picking up a thermal camera, eg:http://www.amazon.com/FLIR-ONE-Thermal-Imager-Android/dp/B00W5PRY52/ref=sr_1_2?ie=UTF8&qid=1464906784&sr=8-2&keywords=flironeAnd check out where the hot spots on the board are. Watch it when booting up cold so the steady-state thermal transfer through the board doesn't fool you, if you look at it in steady-state it may appear as though the entire board needs to be heatsinked, when it might just be 1-2 key ICs doing all of the heating. It should be pretty obvious under IR.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 03, 2016, 12:57:03 am
content: Quote from: suicidaleggroll on June 02, 2016, 10:36:01 pmThanks, I may pick up at some point. For now, I already know where most of the heat is dissipated from. The PCB acts well as a heat-sink but I need to get the heat out of the enclosure better. I'll pick up some thermal pad (6mm thickness) from Walmart.com to see how well it works. If efficient, I can try to find a cheaper source for production.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 03, 2016, 01:15:02 am
content: You should go thicker than 6mm. Those silicone pads are very compressible, if you get one that's the exact thickness as your spacing it'll barely be making contact.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 03, 2016, 02:37:46 am
content: Quote from: suicidaleggroll on June 03, 2016, 01:15:02 amCopy that

author: Flenser
author_rank: Regular Contributor
timestamp: June 09, 2016, 02:20:50 pm
content: This teardown of the Gopher CPS-3205C power supply by Voltlog has high-res photo's that show you how they bolted their power devices to the aluminium enclosure to get good thermal contact for both their original version and it's 2016 revision:http://www.voltlog.com/voltlog-48-new-2016-gopher-cps-3205c-review-teardown/

author: TiN
author_rank: Super Contributor
timestamp: June 09, 2016, 02:33:13 pm
content: Other option is to expose copper on ground via-perforated areas of PCB if you have such possibility and have copper block coupling thermally to both PCBA and enclosure finned walls.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: June 09, 2016, 05:49:45 pm
content: Thanks.