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Thread ID: 52362	2004-12-17 04:49:00	CPU temperature results	Terry Porritt (14)	Press F1

Post ID	Timestamp	Content	User
304505	2004-12-24 01:20:00	One thing which most people seem to have missed is the need for good contact between the surfaces. Extrusions are not famous for flatness. Even "powerful" springs aren't going to get good contact if you have .020" of bow. I wonder what results you could get using Wood's metal as the "gap filler". :D	Graham L (2)
304506	2004-12-24 02:29:00	This Application Note ( . intel . com/design/network/applnots/30114801 . pdf" target="_blank">www . intel . com) from Intel might interest you . The Pentium figures for Junction-Case resistance of 0 . 21 C/W and 33 C/W for Junction-Board are pretty good . (A power MOSFet I use has 1 . 19 C/W for Junction to Case, and 0 . 5 C/W for Case to Sink . If it's just mounted on a PCB, the Junction to Ambient of 62 . 5 C/W would cause problems a bit before the dissipation of 120W is reached, even though the Max Tj is 175C . ) "°" doesn't work any more to produce the degree symbol here; perhaps I should use "K/W" rather than degrees Celsius/W . That would confuse everyone . :D	Graham L (2)
304507	2004-12-28 07:09:00	First, I appologise to those whose attention span has been conditioned by 10 second sound/video bites, this is long-winded :eek: In a previous posting, I described drilling the AMD stock heatink to take a small thermocouple . Here is a photo of the copper base plate that is screwed to the aluminium heatsink . If you look carefully there is a small spot in the centre . That is the thermocouple bead lapped flush with the copper . . neoburn . net/imagef1/files/thermocouple . jpg" target="_blank">sal . neoburn . net The photo quality is not that good as I only have a very very old video camera or a webcam for pictures . Perhaps a word about laps and lapping . In general engineering cast iron laps are most commonly used . These are flat plates with grooves cut into the surface into which surplus lapping paste can go . Ideally one would have a range of plates for different grit sizes as it is difficult to remove coarser grit from the pores if fine grit is to be subsequently used . I have 2 plates, but use only 400 grit or finer . Wet & Dry silicon carbide paper on the lap or a surface plate with kerosene or turps is ok for either coarse work, or to give a polished finish after first lapping flat on the lapping plate direct . Then there are brass laps and pitch laps for optical work . Be aware that using wet & dry paper will cause the edges of the object being worked on to round off, so it is difficult to make small objects flat all over that way . Trying to lap a cpu die would be madness . There are techniques used to keep lapping plates in a flat condition . The traditional method used 3 lapping plates in correct sequence against one another to produce 3 flat surfaces . I use spot lapping and then check the lap against another known flat using engineers blue . The AMD copper base was originally grossly out of flat by up to 0 . 05mm . It had all the appearance of being hand finished on a belt linisher before plating, not the sort of tool for this job . The Volcano HSF had a good surface finish, and only required a light lap to bring the copper surface to a high state of flatness, and was then finished on 800 grit paper . The copper of the Volcano also seemed a bit softer than that from the AMD . Here is another picture showing the AMD HSF with thermocouple lead, sitting on the lap I used, and there is a set of gauge blocks behind, one of which I used to cross check a small straight edge come thermal grease spreader I made from lapping a Stanley knife blade straight to within a wavelength of light . . neoburn . net/imagef1/files/lap . jpg" target="_blank">sal . neoburn . net I would have liked to have fitted a thermocouple in the surface of the Volcano 11+ Xaser HSF, but it is in the too hard basket at this time . The thermocouple hole was drilled with a number 72 drill,ie 0 . 025in . or 0 . 635mm diameter . This is less than 0 . 5% of the area of the cpu die, so is assumed to have insignificant affect on heat transfer into the heatsink . It would be really nice to be able to measure the power going into the cpu from the power supply, and I expect this could be done possibly by using a modified power supply to enable current flows to be monitored . Failing that, the best that can be done as far as I can see, is to take the AMD quoted power values, which for an Athlon XP 2400+ is 68 watts maximum, 62 watts typical (whatever that means) . I looked around for a program that would load up the cpu, and found a package, cpuburn4 . zip from here: . dars . com . ru:8100/download/support/test/" target="_blank">www . dars . com . ru:8100 There are programs included for testing Pentiums and AMD K6 and K7 cpus, and floating point arithmetic is used to stress them . I thought the CPU Usage meter in Taskmanager would give a reasonable measure, but it seems to shoot up to 100% quite easily . So I'm not too sure that 100% usage really means what it says . For example the burnK6 . exe program for K6 cpus gave 100% usage even though the cpu temperature was lower than when using the burnK7 . exe program which also gave 100% usage but ran the cpu 5 degrees hotter . When running burnK7 . exe, opening other programs or even just opening My Computer was exceedingly and painfully slow . So I think it reasonable to assume the cpu usage was 100%, and that this would correspond approximately to 68 watts . So before giving results of measurements, lets recap . on the objects of this whole exercise, 1 . Compare some different thermal greases to see if there are significant heat transfer differences . 2 . Compare an AMD heatsink and 60mm fan supplied with a retail boxed Athlon XP 2400+ with a Volcano 11+ Xaser heatsink and 80mm fan . 3 . Compare the temperature readout from the inbuilt cpu thermal diode with the temperature at the cpu die/heatsink interface, and also with the temperature readout from a probe taped to the cpu adjacent to the die . This latter measurement should be comparable to the use of an onboard thermistor contacting the cpu from under the socket, as on somewhat older motherboards . Here is what I found: 1 . Thermal greases . I couldn't measure any difference in cpu temperatures between white Dow Corning T340 paste, Titan TTG-S101 Siver Grease, or Arctic Siver 5 silver grease . This was mentioned earlier . The most likely reason is the thinness of the applied grease film . The flatter the surfaces and the finer the finish of the surfaces then the thinner the heatsink compound can be applied . It is possible that with very flat fine surfaces that white compound would give a thinner film than something like either Arctic Silver or Arctic Ceramique, both of which have particle sizes of about 0 . 5micron . Certainly I did see when I removed the Volcano, was that where the die had been, using white compound, was almost plain copper surrounded by white compound, and a perfect imprint of a small rougher texture rectangle that AMD cpus have in one corner of the die . This was more pronounced than with using Titan or Arctic Silver Also with fine finishes, the 0 . 5 micron particle size of Arctic compounds could be too big to get into the surface surface texture to fill the valleys . Flatness of the surfaces, in the final analysis, is more important than surface finish . There is no point in polishing a heatsink with 2000 grit paper to give a mirror finish if the surface is out of flat by say 0 . 5micron or worse . The two measures should be commensurate, say aim to get 0 . 05micron for flatness by lapping, and 0 . 05micron Ra surface finish from 600/800 grit paper . 2 & 3 . Heatsinks and CPU Temperatures . It is easier to lump these two topics together . Temperature readings from a thermocouple at the fan intake, room temperature, and from the AMD heatsink have an estimated uncertainty of not more than +/- 2 deg C, with the readout being on a digital multimeter reading to 1deg C . The probe next to the die I'd also guess at +/- 2deg C The accuracy of the built in thermal diode temperature is unknown . The following readings were taken over the Christmas period 24/26 December when the ambient room temperature was remarkably constant at 21 Deg . The AMD 60mm fan speed is 3924rpm given by MSI PCAlert monitor program . I set the Volcano 80mm fan speed to 3125rpm, a speed that had a similar noise level to the AMD and just a bit faster peripheral speed . For brevity I will give the results for the heatsinks both having Titan Silver Grease as the thermal compound, but the readings for the other compounds taken a week or so earlier were virtually identicle as mentioned previously . Firstly with the cpu idling, just sitting at the Windows desktop, 0% CPU Usage from Windows Task Manager: AMD HSF TEMPERATURES . Ambient 21 deg C . Fan intake 25 deg C Heatsink surface 46-47 deg C Thermal diode 57 deg C Probe next to die 40 deg C VOLCANO 11+ XASER TEMPERATURES . Ambient 21 deg C Fan Intake 24 deg C Thermal diode 56-57 Deg C Probe next to die 39 deg C ~~~~~~~~~~~~~~ Next I ran each heatsink in turn with the cpu stressing program burnK7 . exe, and with the CPU USAGE meter reading 100% . Temperatures seemed stable within 15 minutes, and readings were taken after 30 minutes running . AMD HSF TEMPERATURES . Ambient 21 deg C Fan Intake 26 deg C Heatsink surface 64 deg C Thermal diode 69 deg C Probe next to die 52 deg C VOLCANO 11+ XASER TEMPERATURES . Ambient 21 deg C Fan Intake 25 deg C Thermal diode 67-68 deg C Probe next to die 51 deg C Then with burnK7 . exe running, 100%cpu usage, the Volcano fan speed was wound up to its maximum reported 4600rpm, these were the temperatures . Ambient 21 deg C Fan Intake 27 deg C Thermal diode 63-64 deg C Probe next to die 47 deg C ~~~~~~~~~~~~~~~~~ COMMENTS . 1 . The first thing to notice is that the difference between heatsinks is minimal . 2 . The cpu thermal diode is reported by the BIOS as hotter than the heatsink/cpu interface by about 10 Deg C when the cpu is idling, and about 5 deg C hotter when the cpu is running burnK7 . exe and cpu usage is said to be 100% . This may not be unreasonable considering that this diode is buried somewhere inside the cpu . 3 . If it is assumed that the cpu is consuming 68 watts with burnK7 . exe running, then we can estimate the thermal resistance of the AMD heatsink, as (64-26)C/68W = 0 . 56 C/W . This value seems to about what is quoted for similar looking non-exotic HSF units . We can also estimate the thermal resistance of the Volcano when it is running at top speed if we assume that the cpu interface temperature is 5 deg C less than the thermal diode, and we get about 0 . 46C/W . This can be compared with the manufacturers temperature rise curve versus watts dissipated which has a slope of about 0 . 34 C/W, not that good a match, but then increasing the speed and the noise a hell of a lot didn't do that much to the temperature . 5 . As this work involved many installs and removals of heatsinks, I placed some wood pieces between the motherboard and its mounting plate so that no bending strain would be placed on the board . The Volcano was not that easy to fit, and I had to replace a small screw that fouled against a capacitor, with a countersunk one . The PSU also had to be removed each time to fit the Volcano, but the AMD HSF was small enough not to have to do that . 4 . As a disclaimer, these results apply only to my set up, and I am open to criticism, just hope I havent made too many typos or transcribing errors . 5 . Now to finish, an appropriate tune from 1929, Turn On The Heat, the Jack Hylton Orchestra: . petefaint . co . uk/jackhylton/turnontheheat . ram" target="_blank">www . petefaint . co . uk	Terry Porritt (14)
304508	2004-12-28 08:20:00	Thanks Terry, for that very interesting info . It would be interesting to repeat these tests with some other branded coolers to see if your calculated thermal resistance is close the the claims, and if it makes a difference over the stock equipment . I wonder if it would be acceptable to speculate then, that a better method of bringing cpu temperatures down is case ventalation, to bring the ambient temperature of the cpu cooler as low as possible . Cheers, Craig .	craig.b (6571)
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