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Help cooling Mosfets

H

homerjr43

Gawd
Joined
Nov 12, 2004
Messages
763
I need some expertise here from the masters... I am planning on doing some minor OC'ing

I have a i7 860 and a GIGABYTE GA-P55M-UD2 and 4 (2x2gb) of 1866 ram.

I Just ordered a Thermaltake Contac 29 120mm HSF (had mixed reviews but it was the cheapest 120mm hsf with heatpipes and 1156 support)

I plan to run the Machine at 3.7 ghz with a fsb of 176 with a 21x multiplier.

So my main question is can someone locate all the essential mosfets that need additional cooling on my board...

I have Ram sinks from an old video card or I can modify an old aluminum CPU heatsink and use adhesive to apply the extra cooling. I know that most of the essential cooling space is to the top and back of the CPU. Is there any other areas that would require extra cooling??? Also I have a old small north bridge fan from an old MB would it be wise to mount that on the small heatsink that is labeled gigabyte?

P55M.jpg
 
OK lets go on a tour.

Around the cpu socket towards the top and right side of the socket.
The little round silvery things are the filtering capacitors.
Next moving slighty outward from the cpu socket, again from the top and the right, just behind the capacitors you find 6 inductors, three along the top and three along the right side. These are dark cubes slighlty larger than sugar cubes and are much higher in height than an IC or other chip on the board.

Directly above and directly to the right of the inductors we have the power Mosfets along with some kind of (guessing) control chip etc. These are in groups of 3 and a control chip (so group of four) as you go left to right along the top and then "turn the corner" and look down. The last two groups of mosfets on the bottom right of our "string" does not have the extra chip. Those last two groups are arranged in a triangular pattern. Looking closely at those will allow you to better see in the other groups of four, which three are the mosfets. In the groups of 4, each group right behind an inductor, you can readily tell the "odd" chip. The "odd' chip is not a mosfet. It would not hurt anything to cool it as well if you can make a cooler/heatsink that works well, otherwise you run the risk of the heatsink actually transferring heat from the mosfets to this "odd" chip. If you can read the part number off of the odd chip and google it you could determine if it is a power handling chip (np with heatsink) or a logic/control chip (likely best not to heatsink it).

Between the ATX main power connector and the memory slots is the memory power, 2 inductors and one very obvious FET near the upper right corner of the ATX power connector (using your picture) with 3 leads on one side, middle shorter than outer, and the other side completely soldered to board. There are likely some others in the area but I cannot read part numbers and these others likely would not be a cooling issue.

Keeping in mind this 3 legged on one side, full solder on the opposite, we see another one of these devices imedately to the left of the cpu socket with a capacitor, the two parts all by their lonesome. No clue what this is power for but thats a mosfet or some other voltage regulation/supply.

Looking below the blue southbridge heatsink you will see 2 groups of 2 of these devices. Likely USB power and who knows what else.


Thats all the ones I can see from pictures. The power mosfets around the cpu socket is what you want.

Just keep in mind a heatsink in dead air is no better than no heatsink at all. Anything you can do/rig up to get even a little air washing over the area around the cpu will do wonders for component life. Those are solid caps and last longer than the old electrolytics but they still degrade due to high temp.

Hope this answers at least part of your question.


The Gigabyte heatsink in the lower left is for the southbridge. As your processor has the northbridge/MCH built in (which was the thing we loved to cool on our old boards with an extra fan) it is not critical to put a fan on the southbridge. The southbridge is mainly used for I/O stuff, like your SATA ports etc. So one is not really needed for OCing. However, electronics loves to be cool, and it cannot hurt and if you have a nice quiet little fan you can stick on there with some RTV or a couple of screws/whatever it certainly will not hurt a thing, But I recommend avoiding anything "whiny" 1800 rpm or less you dont need much air at all and again, if you can place/mount/rig any kind of fan to wash air over the board it will do wonders. Most of us just rely on "airflow" the normal air movement of air in the case as it enters the bottom front and exits the top rear (most cases are designed this way, of course there are exceptions) and maybe a side fan blowing in. This leaves hot spots on the board where cards block air movement etc. Side fans are great as they tend to stir up the air at the bottom of the case. blah blah blah.
Just trying to say active airflow over the surface of the board helps with long life and component stability under stress which helps in OCing.

The next chip you will want to find is the clock. ICS 9LPRS914EKLF look for ICS and a portion of that part number. A little heatsink on that would be neat.

It is absolutely critical you not get heatsink compound on the leads of these devices. I suggest mixing 50% AS5 with 50% Artic epoxy in small batches and apply paper thin to the heatsink and stick on. Do not press hard to "squish" out any extra. It should be applied so thin there is no "extra". You might have one fall off because of the thin application. I would test glue a heatsink onto a chip on a dead board etc. for a dry run to see/practice how thin I could apply the "glue" and still get it to stick and not fall off when hit with a medium flick of the finger. Make sure to leave it undisturbed for enough time for the epoxy to set up all the way.

Lap (just rub on a piece of 400 grit sandpaper which is laying on a flat surface like a piece of glass) the heatsinks as cuttin them out will distort them. Rub until the scratch marks on the bottom are uniform.

Wipe the chips and the heatsink with an alchoal pad to remove oils before applying TIM/glue/whatever.
 
Thanks for the indepth repsonse...

I have a p180 Case. I have 120mm fan on the top and a 120mm fan in the rear and I will have another 120 mounted on the opposite side of my processor. None of them face down and my case does not allow for a side fan. with 3 120mm fans moving air in the area of the cpu I dont believe air flow should be a problem. Right now the small heatsinks i have can be easily pryed off an old geforce 3 the have thermal tape on the back of each heatsink that is still adhesive and can be easily reapplied to the mosfets. This would eliminate the risk of getting as5 into the solder points. Should this thermal tape be reused or should i remove it lap and reapply with epoxy as5 mix?? Below is a pic of the ram sinks that I am planning on using..

gainward_geforce3_ti_200_video_card.jpg


My CPU HSF should be here tomorrow and I plan on finishing this up this week or over the weekend...

I really appreciate you help and expertise...
 
Another Question...

Should I even bother worrying about mosfet cooling?? Should I just make sure my cpu temps are 70 or below under full load??

According to Anandtech

"We have absolutely no concerns about recommending this board for 24/7 overclocking use. This board overclocks Core i7 processors just as easily as it does the Core i5 offerings, which is a feat several of the upcoming budget/mid-range P55 boards cannot accomplish. To be honest here, overclocking a Lynnfield processor is extremely easy; really, you only need to worry about VCore, VDimm, VTT, and occasionally PLL settings. If you get a really good CPU, such as our current i7/860 sample, it makes overclocking really easy, even if you just woke up from a coma and your last memory was playing pong at a disco club. What made our overclocking experience enjoyable was the fact that this board is so easy to operate with up to its limits. It simply is a great motherboard to own for quick and stable overclocks.

In regards to voltage regulation, we think the GA-P55M-UD2 has very good voltage output. We checked all the major voltages with a DMM and found very little variance between what you select in the BIOS and what the board actually outputs. The VTT, PLL, DIMM, and other voltages are accurate and stable across the spectrum until you hit the upper limits of current draw. As a side bonus, S3 resume worked perfectly with Bclks up to 215.


This is not a board to have for extreme clocking as I would not run CPU voltages higher than 1.45V on it without expecting something to fail, rather quickly I might add. It is perfectly suited for air-cooling and typical water cooling setups and one should not expect more. I was initially concerned about the lack of passive MOSFET cooling. With our voltage settings and stated goal of practical overclocking for the majority of users, it is not a problem, even with the Core i7/860 at 4.3GHz under full load. We typically measured MOSFET temps around 61C at 4.3GHz and around 58C at 4.2GHz without any direct airflow over the board. I would still recommend a well ventilated case for these types of overclocks. "
 
Based on the "red" in your last post and what would be good case airflow, I will go against my common advice and say, no you do not need to put heatsinks on them.

Reading that and looking again at the voltage regulation design I can see why. It was bothering me, the "set of three" as that is an odd number and the layour was not the classic x2 . What is happening is each phase of the cpu power supply (it apparently has 6 "real" phases as there are 6 inductors, has 3 mosfets instead of the normal two. Each mosfet is on for only 1/3 of the time that particular phase is providing current. This splits the work and the heat up between 3 instead of the more typical 2. Thus each mosfet runs cooler.

Sorry I got so into answering your question I didnt see the forest for the trees. However I would have still recommended it just for long life and "coolness" until I saw that anandtech had actually measured it under a pretty heavy OC. Thats the final word. 60C is nothing, I bet the mosfets are rated for 100C or more likely 120C as they are designed as power devices.

So with all the facts in, frankly not worth the trouble IMO.

That said, if I, me, myself had complete confidence I could make it look nice and it was raining outside and I was out of beer, and I had everything I needed and nothing was on TV, I might put them on anyway. But only maybe. And if I did I would not use the sticky tape. Its crap.
 
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