|80-way Thermal Interface Material Performance Test|
|Reviews - Featured Reviews: Cooling|
|Written by Olin Coles|
|Sunday, 14 June 2009|
Page 8 of 14
Let's start this section by defining Newton's law of cooling: which asserts that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings, or environment. Science (and fact) has a strange way of eluding the average enthusiast, so if you didn't understand that definition Benchmark Reviews will summarize Newton's law and apply it to computer processors: the cooling rate of a heatsink is equal to the difference in temperature between that heatsink and the ambient surrounding temperature. Therefore, a heatsink with a 60°C temperature will cool faster (and with better performance) in a 20°C room than a heatsink of the same temperature in a 30°C room.
One of the toughest parts of our benchmarking process was maintaining a temperature-controlled test environment, which is critical to comparing results according to Newton's Law of Cooling. To establish a stable and consistent ambient room temperature, all of the testing hardware was partitioned off and the room was sealed. While we did our best to operate at exactly the same testing temperature for each product, there were very small fluctuations which resulted in fractional differences inside of one degree. As we progressed into the later stages of testing, the ambient temperatures were much tighter and more controlled because testing could be completed in one day instead of weeks or months.
Probably the most critical step in the testing process was the preparation. Thanks to the team at Arctic Silver, we were able to clean and prepare the surface of our test heatsinks and Intel Q9450 Core 2 Quad IHS (Integrated Heat Spreader) to a pristine state with their ArctiClean products. While these products are praised by product analysts like myself, they can be equally as useful for anyone who frequently separates the cooler from the CPU or frequently applies TIM material such as extreme overclockers and hardware enthusiasts.
The Gigabyte GA-EP45T-EXTREME offers a waterblock cooler on the P45 Northbridge, which we connected into a water-cooling radiator through the ZOTAC GeForce 9800 GTX+ Zone Edition video card. This enabled our tests to isolate CPU temperatures, and yield results without residual heat interference from other hardware components. The video card and motherboard Northbridge consistently operated at or near ambient room temperature, which dramatically reduces the temperature a CPU would report under normal circumstances.
Benchmark Reviews would rate the contact pressure between the Intel Q9550 quad-core processor's integrated heat spreader (IHS) and the Intel push-pin thermal management system to have been moderately firm. The surface condition of the processor's nickel-plated copper IHS was smooth with light texture visible, while the CPU cooler featured a polished copper surface. The use of a standard-performance cooler with mounting clip system and unpolished IHS finish was intentional, as improvements would narrow the range of thermal performance. By testing with a mild yet fundamentally sound configuration, recorded temperatures were not as closely staged between products.
Several stock Intel thermal cooling units were availble during our test period, which were discarded whenever a material appeared to permanently contaminate the surface (such as CooLaboratory's liquid metal products). While using the exact same unit throughout all tests would help reduce potential test result differences, Benchmark Reviews stands by our decision to rotate these parts out of the test configuration whenever necessary.
Benchmark Reviews used the following hardware parameters for all of our test equipment:
It is the position of this author that when Benchmark Reviews compares products, they should be tested using identical methods. However, there are a few Thermal Interface Material products which recommend special application or added cure time. Although only a couple of the items we tested suggest or mention special application needs (either on the product or at the manufacturer website), we understand that certain interface products will exhibit improved thermal conductivity if they are allowed several temperate cycles to expand and contract the material.
For this article, each and every single product tested received the curing time recommended (see below), or approximately one hour of thermal cycling prior to testing when no cure time was specified.
(0) No Curing Time or Special Application Suggested
(1) Antec Formula 5 Application Instructions (no curing time recommended)
(2) Arctic Silver II Application Instructions(48-hours minimum curing time recommended)
(3) Arctic Silver 3 Application Instructions (up to 200-hours recommended curing time)
(4) Arctic Silver 5 Application Instructions (up to 200-hours recommended curing time)
(5) Arctic Silver Ceramique Application Instructions (25-hours minimum recommended curing time)
(6) IC Seven Carat Diamond Application Instructions (10-minute evaporation time, 2-hour curing recommended)
(7) CooLaboratory Liquid Pro Application Instructions (no curing time recommended)
At the start of each test, the ambient room temperature was measured to track any fluctuation throughout the testing period. Lavalys EVEREST Ultimate Edition was utilized to create maximum processor loading and measure each individual CPU core temperature. It's important to note that software-based temperature readings reflect the core temperature output as reported by the processor through the motherboards BIOS. For this reason, it is critically important (for testers) to use the exact same software and BIOS versions throughout the entire test cycle, or the results will be incomparable. All of the units compared in our results were tested on the same motherboard using the same BIOS and software, with only the product itself changing in each test. These readings are neither absolute nor calibrated, since every BIOS is programmed differently. Nevertheless, all results are still comparable and relative to each products in our test bed.
One unfortunate problem is that CPU's report temperatures as a whole number and not in fractions. This in turn causes the motherboard BIOS and subsequent software applications such as EVEREST to also receive whole-number reports from the processors thermal diode. Thankfully, EVEREST also does offer averages in the statistics panel, which gives us more precise readings. To further compensate for this, our tests were conducted between five and nine times after complete power down thermal cycles. Conversely, the ambient room temperature levels were all recorded and accurate to one-tenth of a degree Celsius at the time of data collection.
When each cooler is tested, Benchmark Reviews makes certain to keep the hardware settings identical across the test platform. This enables us to clearly compare the performance of each product under identical conditions. While the ambient room temperature did fluctuate between 20~21°C, this would not be enough to cause a noticeable impact on our test results since only the thermal difference is reflected in the charts.
The Accuracy Myth
All modern processors incorporate an internal thermal diode that can be read by the motherboards' BIOS. While this diode and the motherboard are not calibrated and therefore may not display the actual true temperature, the error is constant. This means that if the diode reports 40°C when it is actually 43°C, then it will also report 60°C when it is truly 63°C. Since the design goal of a thermal solution is to keep the CPU core within allowable temperatures, a processor's internal diode is the most valid means of comparison between different heatsinks, or thermal compounds. The diode and motherboard may be incorrect by a small margin in relation to an actual calibrated temperature sensor, but they will be consistent in their margin of error every time.