Heat sinking large pads that are connected to high voltage - Page 1
Forum section: electronics / projects

author: eerocketman
author_rank: Contributor
timestamp: August 26, 2017, 05:25:24 am
content: Hi everyone,I have a D2PAK IGBT where the pad is connected to up to 600V how would I heat sink this component? I'm worried about having a high voltage heat sink. The copper plain that it is connected to is very large but I'd also like to use a heat sink. Is there a way to do this without connecting the heatsink to the 600V.Thanks!

author: Ian.M
author_rank: Super Contributor
timestamp: August 26, 2017, 06:07:56 am
content: That's reasonably simple. Lots of thermal vias to transfer the heat to a large plane on the other side of the board, and a reinforced silicone heat transfer pad rated for 1KV insulation to a grounded heatsink would be one option. If you want the heatsink above the board, you'd want a thick copper L bracket, with a cutout so it fits round the edge of the D2PAK thermal pad footprint, and put the silicone pad between the copper bracket and the heatsink. However at that point it would be easier to use a vertically mounted TO220 through hole part.

author: jbb
author_rank: Super Contributor
timestamp: August 26, 2017, 06:28:15 am
content: There is a temptation to put a heat sink on top of the DPAK. Unfortunately that won't work; the thermal resistance on the top side is really high.You can get small solder-on heat sinks from Aavid Thermalloy (and others), but they will be live.

author: eerocketman
author_rank: Contributor
timestamp: August 26, 2017, 07:20:29 am
content: Thank you for your responses. Would it be considered bad practice to have a 600V live heatsink?

author: Ian.M
author_rank: Super Contributor
timestamp: August 26, 2017, 07:50:33 am
content: Quote from: eerocketman on August 26, 2017, 07:20:29 amIMHO, in an enclosure that's not either permanently sealed, or protected by an anti-tamper switch to cut the power, then YES its bad practice. 340V peak half wave rectified 240V on the primary side of a direct from line SMPSU is bad enough, I don't even want to *think* about working on a board with a live heatsink at 600V unless it has an insulating cage or guard over said heatsink.Others opinions may differ.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 26, 2017, 08:08:47 am
content: If the heatsink is very small (think about a small piece of soldered-in copper, which looks like a component, or a reinforced copper trace, not like a traditional aluminium heatsink), it can be acceptable to have it live, but even then you need to add warning labeling / stickers / at least a silk screen warning.If it's large (and looks like a mechanical part), then the repair guy / reverse engineer guywilltouch it accidentally, even if properly labeled, so don't do it.Ian had the right answer in his first post. +1.

author: jbb
author_rank: Super Contributor
timestamp: August 29, 2017, 07:39:57 pm
content: Quote from: Ian.M on August 26, 2017, 07:50:33 amI think the Aavid solder-down types go up to around 30 * 50mm, which is probably big enough to have the rest-your-hand-heretrap. I burnt myself (it was tiny and I went to the hospital and I was fine!) in a similar manner a few years ago.A guard could be an earthed aluminium sheet, or a floating polymer sheet (make sure it won't sag at operating temperature + margin) etc. and could form an airflow guide.Alternatively, you could try to avoid this problem by a) doing the double sided cooling thing (it works!) or b) finding packages which are intended for double sided cooling. The advantage of option a is that it's quite standard. The advantage of option b is you don't need to punch in a stupendous number of vias, but you are setting yourself up for a single-supplier problem.I think Infineon and Toshiba do some double-sided SMT packages. IRF (now Infineon) do the DirectFET devices, which look interesting but only go up to 250V rating...