Does anyone have any experience (good or bad) with MOSFET heatsinks that come with peel-and-stick thermal tape? (whether it's on the heatsink to begin with...or comes on a separate piece of paper like the "enzotech" MOS-C1 heatsinks)
I recently bought a nice overclockable motherboard that does not provide heatsinks on the power regulator MOSFETs and PLL controller chips.
Originally I planned to use heatsinks I have on hand, but decided I want something that will look nicer.
I was also originally planning to use Arctic Silver thermal compound and pressure mounting to get optimum heat transfer, but I think as long as my goal is simply to substantially improve the heat dissipation (which even tape-mounted heatsinks will do), these will work fine.
Here are some of the MOSFET and small support chip heatsinks I've found so far. My preference is to use heatsinks I can mount on and bridge between at least two chips at once. This will provide perhaps 20-30% more heatsinking as compared to a heatsink that just mounts on a single chip. Thus, anything smaller than 10x10mm would not be my first choice...but it would still make a difference.
One concern I always have with the epoxies is that if you accidentally bump a heatsink bonded with that, you can pull the entire chip off the board.
Not as big a risk (but still there) with the large chips because they have stronger bonds to the motherboard, but with the small chips they just pop right off.
I'm not sure if that's any different when using the tape, but that's why I prefer to use a pressure-mount non-adhesive thermal bond system. But even with non-adhesive bonding agent it can still stick to the chips well enough to pop chips after it has aged when you bump the heatsink (or try to remove it).
What I had planned to do was:
1) tack (using superglue) a couple plastic spacers to the motherboard at each end of the MOSFET row (2x9 MOSFETS in a row about 1/2" W x 3" L). The spacers are just a bit less thick than the MOSFETs (step 3 explains)
2) apply non-adhesive thermal bond to the top of the MOSFETs
3) tack a strip heatsink* over the top of the MOSFETs. This strip is almost 4" long and the ends sit on the tops of the spacers. A bit of superglue on the top of the 2 spacers holds the strip heatsink in place and because they are very slightly lower than the tops of the MOSFETs, also ensures pressure is applied between the strip and the MOSFETs.
Sometimes, depending on the consistency of the thermal bonding agent, I've left spacers the same thickness as the chips. The thin film of thermal bonding agent on the chips is enough in some instances to ensure some pressure is maintained.
With multiple mosfet chips on the board, i found that you had to use thermal tape as the difference from chip to chip varied by quite a bit. Thus a compound wouldn't make up the difference.
I found this out while lapping my coolers on my board. Even after lapping the mosfet heat sink flat,it couldn't contact all of the chips.
(With stock cooler being all in one piece)
I know your going with individual coolers. I am just adding this in case someone has a question in the future and googles for this info.
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With multiple mosfet chips on the board, i found that you had to use thermal tape as the difference from chip to chip varied by quite a bit. Thus a compound wouldn't make up the difference....
I should have pointed this out as something to look-out for...thank you for doing so.
In my case, I checked before-hand and a single heatsink would have worked well on this particular motherboard. As I pointed out in my "first impressions" review of the Gigabyte mATX motherboard... http://www.hardwareanalysis.com/content/topic/77207/
...it has extremely high quality manufacturing, esp w/r component placement. The MOSFETs are all the same height (even though there are 2 different types, 4921N and 4935N) and they are all absolutely flat...no significant mis-oriented mounting of the MOSFETs on the PCB at all.
There are however some pretty thick non-adhesive thermal transfer strip that might work even on some motherboards where there is some variation in the heights of the chips. They definitely wouldn't transfer heat as well as they are after all, thicker, and their heat transfer coefficients aren't nearly as high as with pretty much any Arctic Silver compound, but thermal strips could still be useful in such situations.
I've seen the non-adhesive thermal bonding strips come in thicknesses anywhere from 0.5mm to 1.5mm. There are probably thicker versions (2mm+) out there as well...but I wouldn't even consider using those.
Now I'm wondering even more if heatsinks with their (usually) pre-applied tape adhesive will be a reliable bond...or will they be falling off after a short period of time?
Here's something I didn't expect regarding the T405 adhesive used on a lot of the heatsinks sold...
Apparently it isn't considered suitable for use on plastic cases...which of course means a lot of components these days.
So, I have to wonder why they are using this on parts they KNOW are going to be mounted on parts that usually have a plastic case.
In addition to the plastic case issue, though I bet this is a less significant issue with these MOSFETs except under extreme OCing, T405 adhesive tape is apparently advised for use only on parts that dissipate LESS than 25 Watts (even though the temperature rating is -30C to +125C)
(note: use the short link) http://bit.ly/hhyKPP
HWA won't parse the entire link properly for some reason (the "$" ?) and it would take you to the wrong web page. But I like to keep the original link info where possible so here's the entire link... http://vendor.parker.com/Groups/Seal/Divisions/Chomerics/
John, in my experience, using a good silver or ceramic based thermal adhesive is far better than thermal tape.
Sure, you must ensure that you handle the board with care should you knock a heatsink, but sometimes thermal tape does not adhere as well as it should, and the heatsinks may become either semi-adhered (such as in a verticle mounted scenario, like most tower cases) or fall off totally due to the weight of the sink pulling laterally to the direction of adhesion..
Utilising a thermal adhesive can solve this issue, and provide better thermal transfer than tape can.
It is a semi-permanent / permanent solution, but I don;t imagine you'll be swapping the heatsinks on MOSFET's all that often!
Ensure to measure the height of your heatsinks, so you can be certain they will not obstruct any other compnents you may install in the direct vacinity - like your CPU heatsink. You can always modify the MOSFET sink if needs be.
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