Heat sink for SMD TO-268? - Page 1
Forum section: electronics / projects

author: iXod
author_rank: Frequent Contributor
timestamp: June 20, 2020, 11:12:02 pm
content: I want to use these SMD IGBTs and isolate the collectors from each other. These devices can each dissipate 160W according to the datasheet:https://www.mouser.com/ProductDetail/IXYS/IXBT12N300HV?qs=gQEZvVdd8Gu6zNE3ZZzUfg%3D%3DBut how to get rid of that heat? The recommended SMD sinkshttps://www.mouser.com/Thermal-Management/Heat-Sinks/_/N-5gg0Z1yzvvqx?P=1z0z7ptZ1y8egdpZ1y9fv1vZ1yzvkz7Z1yztn61don't look like they're going to handle that.How does one design to dissipate huge heat from such a small package?Thanks.

author: TimNJ
author_rank: Super Contributor
timestamp: June 21, 2020, 12:42:43 am
content: I would use some sort of spring-loaded heatsink assembly, sort of how CPUs or GPUs are often cooled. Or, use your chassis as a heatsink, with a similar mounting strategy.

author: TimNJ
author_rank: Super Contributor
timestamp: June 21, 2020, 12:46:35 am
content: Although, I do wonder how effective heatsinking to the plastic part of the chip really is.

author: wraper
author_rank: Unknown
timestamp: June 21, 2020, 12:59:32 am
content: Quote from: iXod on June 20, 2020, 11:12:02 pmDream about that, not even close under realistic conditions. Even if they could be mounted directly on a heatsink, it still would be wildly unrealistic. Look at the conditions when they can dissipate this much.Quote

author: Phoenix
author_rank: Frequent Contributor
timestamp: June 21, 2020, 02:41:07 am
content: What you can do with smd like this is heavily via stitch through the pcb and mount a heatsink on the other side with silpad. Good luck getting anywhere near 160W though.For a more expensive option mount it on an alumina substrate and put that on a heatsink.If you want to dissipate serious power for some reason it's easier to look at to247 or even modules.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 21, 2020, 03:03:42 am
content: Liquid nitrogen, anyone?Now seriously. These are also 3 kV IGBTs, and I suppose that your application will run at a high voltage.Unfortunately good thermal coupling and electrical insulation are many times at odds.

author: David Hess
author_rank: Super Contributor
timestamp: June 21, 2020, 07:26:20 pm
content: Also, do not consider heat pipes without a heat spreader because that power density exceeds their capability be several times. This is why you do not find heat pipes directly attached to CPUs except in the lowest power applications.

author: iXod
author_rank: Frequent Contributor
timestamp: June 22, 2020, 09:27:24 pm
content: Would there be any insurmountable issues with paralleling several of these devices to lessen the heat load on each of them?Thanks.

author: David Hess
author_rank: Super Contributor
timestamp: June 23, 2020, 02:44:19 pm
content: Quote from: iXod on June 22, 2020, 09:27:24 pmNo, and I would even recommend it just to decrease the thermal resistance.

author: wraper
author_rank: Unknown
timestamp: June 23, 2020, 04:13:35 pm
content: https://www.onsemi.com/pub/Collateral/AND9100-D.PDF

author: H713
author_rank: Regular Contributor
timestamp: June 27, 2020, 08:11:57 am
content: I've thought about this for a completely different application. In this case, it's low-voltage FETs (sub 100V) switching hundreds of amps each. The topic of cooling has been considered, as better heatsinking allows for fewer devices- keep in mind this application would have used many modules and tens of thousands of these devices- each module supplying about 10 kA at about 50 volts for short pulses, with perhaps up to 100 modules running in parallel.One idea involves soldering them directly to a liquid-cooled copper bar. In this case, because it would be pulsed, the liquid cooling would mostly be used to cool the bar down between pulses (very low duty cycle). The bar would also double as the electrical connection, so obviously this won't work where the tab needs to be insulated.In order to solder them, the heatsink bar would be uniformly heated to some temperature above the melting point of solder (leaded in this case). It would be tinned, then the many devices get applied all at once. The bar could then be cooled, hopefully before damage to the devices occurs. This would not be a trivial task, and it would require a lot of careful preparation and control over the process. It has never been tried, but could conceivably work. Smaller heatsinks would be easier to solder to.The project above is unlikely to come to fruition at this point, but the cooling concept could still work.My suggestion? Unless you have very good reason not to do so, just add some more devices. Minimizing thermal resistance is often a very tricky task. There are situations where it is necessary, but it's best to avoid needing to do so if possible.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 27, 2020, 08:55:38 am
content: Quote from: H713 on June 27, 2020, 08:11:57 amHave done this, it's not too bad. Note that leaded solder melts at about 170 degC, you don't need to heat the bar much above that. AFAIK, and IME, FETs are just fine at soldering temperatures even for a prolonged time. Assuming the copper block is thick to transfer heat properly, it also heats up fairly slowly and evenly, allowing you to monitor the temperature. Put visible blobs of solder paste along the bar to see when it melts. Stop applying heat when it happens.I would recommend polishing the copper surface to get rid of oxidation, then use a small amount of solder paste for each device.