TO-263 (D2PAK) junction to case thermal resistance - Page 1
Forum section: electronics / projects

author: Asim
author_rank: Regular Contributor
timestamp: January 22, 2017, 07:50:08 pm
content: Hello people of earth,normally in datasheets, you will find the following two parameters in regards to thermal resistance:1. thermal resistance from junction to mounting base ( exposed pad)2. thermal resistance from junction to ambientmy question is as follows, what is the thermal resistance from junction to case from the top ( NOT the exposed pad side) if I want to stick my heat sink on it ?meaning the heat sink is mechanically isolated from the exposed pad.Regards,Asim

author: Miyuki
author_rank: Frequent Contributor
timestamp: January 23, 2017, 10:19:47 am
content: Thermal resistance will be hugeyou can use at least 20 °C/Wfullpak will be better solution if is available

author: Asim
author_rank: Regular Contributor
timestamp: January 23, 2017, 06:37:51 pm
content: Quote from: Miyuki on January 23, 2017, 10:19:47 amthat's A LOT of C/W, I will probably order To-220 fullpak if my current solution is not sufficientThanks

author: Benta
author_rank: Super Contributor
timestamp: January 23, 2017, 08:41:59 pm
content: Fullpak makes no sense, that just an isolated TO-220.Look at Powerpak instead.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 27, 2017, 11:51:34 am
content: Thermal resistance of D2PAK to the top plastic is not given because it's too big for it to be useful for cooling; there is too much plastic inbetween. Heatsinking the top works only in corner cases where it would work even without, and only minor extra cooling is needed. It's usually only seen in poorly designed Ebay modules or hobbyist designs. A much better design choice is to use a lot of vias to the bottom side of the board, then couple the bottom side to a heatsink using an insulating thermal pad.

author: Asim
author_rank: Regular Contributor
timestamp: January 27, 2017, 12:41:20 pm
content: Quote from: Siwastaja on January 27, 2017, 11:51:34 amI see, my mistake was I assumed connecting the heat sink on top is a good idea because I saw it in ebay modulesgood thing is the PCB I designed will be able to take the heat sink at the bottom as all the components are SMD and in the top side .Thanks,

author: David Hess
author_rank: Super Contributor
timestamp: January 27, 2017, 03:41:49 pm
content: When faced with this kind of question, I usually setup a test circuit to produce a constant power in the device and then measure the case temperature with different heat sink configurations allowing a calculation of the thermal resistance.

author: Asim
author_rank: Regular Contributor
timestamp: January 27, 2017, 04:23:39 pm
content: Quote from: David Hess on January 27, 2017, 03:41:49 pmI will do that upon receiving the pcb.I don't even mind putting heatsinks on top & bottom if thermal proformance wasn't good enough

author: apblog
author_rank: Regular Contributor
timestamp: February 18, 2018, 12:00:40 pm
content: I am resurrecting this old thread just to say that it is useful to include a Junction-to-top thermal resistance figure in the datasheet.It's very useful for measuring the junction temperature indirectly with a thermal camera. Once you know the junction temperature and the power dissipation, you can then calculate the actual junction-to-ambient of your entire system... Part & PCB.I wish more manufacturers would include this number.

author: Benta
author_rank: Super Contributor
timestamp: February 18, 2018, 12:44:20 pm
content: QuoteDo you mean PolarPak?

author: amspire
author_rank: Super Contributor
timestamp: February 18, 2018, 12:59:59 pm
content: You may be choose a device designed for a top heatsink like the irf7749l2pbf. I am not sure what kind of semiconductor you are after.https://www.infineon.com/dgdl/irf7749l2pbf.pdf?fileId=5546d462533600a40153560445e71ca2

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 18, 2018, 07:52:59 pm
content: RthJC is from junction to case.The whole case.It's soaked in refrigerant and tested that way.That's how they claim preposterous figures like 350W into a D2PAK, and 100A+ out the leads.Almost all of that heat exits the heatsink tab, but some leaves through the front side (of the tab, and leads, and case) too.Anyway, what you want is this:a. If you have space on the backside for a heatsink, put it there. Load the heatsink pad with vias to a pour on the backside. Fill them with solder, if possible. This can get you to about 10 C/W.b. Otherwise, for topside access only, there are SMT heatsinks made to straddle a D2PAK. Pour solid copper between the tab and heatsink pads. This won't do quite as well but doesn't require anything special -- it works with conventional pick and place and reflow assembly.Tim

author: jbb
author_rank: Super Contributor
timestamp: February 18, 2018, 08:39:25 pm
content: I frickin’ hate those b******* claims about power dissipation and current rating. They are useless. We do need to know Rth j-c, but we’re not going to bolt the device to a heat sink the size of Antartica.Strangely, the data sheets become much more honest once you move up to an industrial module style.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 18, 2018, 09:45:21 pm
content: Quote from: jbb on February 18, 2018, 08:39:25 pmWell, flooding them with freon wouldn't do much good anyway, the dies are hidden under silicone goo -- a terrible conductor to begin with, and would probably swell from the solvent!They do show more concern about proper mounting; a flat, smooth heatsink, proper paste application (even including a recommended mask pattern!), and cooling.Like how there's those Aavid cold plates, that are just copper pipes glued into an aluminum heatsink, spaced so they just happen to coincide with the dies in most modules.Tim