Thermal Conductivity- An Enigma for Everyone
Posted: Mar 17, 2014
Thermal Conductivity – A Challenge for Customers and Mereco Alike
Over my 35 year career, many customers, both current and potential, have asked me to recommend thermally conductive compounds for use as a heat transfer medium in their electronic or heat sink applications. Thermally conductive applications pose one of the most challenging applications for Mereco to address, for the following reasons..
- Customers rarely know what value of thermal conductivity is the best performing and most cost effective in their application
- There are many different values for thermal conductivity. In SI units, it is commonly expressed as Watts/(meter • Kelvin) , and in US units, it is commonly given in BTU/(hr • feet • °F).
- There has been (in the resin formulating industry) no standardized technique for the measurement of thermal conductivity. Listed values can vary wildly from technique to technique.
- Supplier product data bulletins used as a reference point for thermal conductivity values often list values that are incorrect, inaccurate, or even impossible to achieve. No test procedure is indicated.
So, here are a few rules of thumb to help Mereco determine the best thermally conductive compound for your application.
- Try to determine what value of thermal conductivity will work in your application. Over specifying on a value can increase product cost and cost of qualification. Make sure that you get Mereco involved very early in the product design process (concurrent engineering). Try to remember that higher thermal conductivity values require higher viscosity values. Also realize that most compounds require the use of highly abrasive ceramic like fillers to achieve high thermal conductivity. These fillers can shorten the life seals, valves, and dispensing heads in automated dispensing units.
- Use a commonly accepted and practiced unit of thermal conductivity. We prefer Watts/(meter • Kelvin), which is often written as W/mK.
- If trying to replace or qualify a second source for product that you are currently using, contact the current vendor to ascertain the measurement technique that was used and when the test was conducted. You will often find that you may not get a satisfactory answer.
In closing, Mereco has been formulating and manufacturing thermally conductive compounds for almost every one of the 54 years of our existence. We currently use a Netzsch 447 NanoFlash™ testing instrument. Conforming to ASTM E1461, the Xenon flash lamp based NanoFlash™ uses optical coupling to heat and read the sample surfaces, eliminating potential interface thermal resistance, and making accurate measurement of thin samples, coatings on a substrate and materials in a thin film or sandwich possible. The NanoFlash™ can test samples both through and in the sample plane over a diffusivity range covering materials from neat and filled polymers to diamond. The thermal conductivity can be measured over a temperature range of 25°C to 300°C.
The NanoFlash™ is fully automated: powerful Windows based software controls the test temperature, flash lamp firing, and data analysis. The available automatic sample changer allows the instrument to measure multiple samples in one test. Each data point normally takes less than five minutes from the time the furnace reaches the test temperature. The instrument independently sets the flash power level, pulse width and temperature for each sample.
Contact Mereco for all of your thermally conductive resin requirements.