A few weeks back, I happened upon a forum thread about thermal compounds asking which was best for a variety of scenarios. This got me thinking that maybe it was time to take a look at the various thermal compounds available on the market.
After a visit to Newegg.com (and spending $85), I have more syringes than Amy Winehouse. After several days of tedious testing, we'll cover every thermal compound we can find (more than 20), and explain things like thermal resistance, conductivity, and which thermal compound is the best choice for you. While the performance results may not be dramatically different (which is actually a good thing), we'll dig a little deeper and look at things a bit differently.
Many people will go the entire lifespan of their system without ever seeing the thermal compound bridging the narrow gap between their CPU and heat sink. But some people change their HSF (Heat Sink Fan) more often than their boxers; this article is for you, the folks that have Thermal Compound OCD.
(Heat is Thermal Energy)
To better understand “Thermal Conductivity” and “Thermal Resistance” as they pertain to solid objects we should first define them.
Thermal transfer or thermal conductivity takes place when energy in the form of heat is given off by one object and absorbed by another object. This transfer of energy is always from hot to cold and this process is called thermal conductivity. The more heat that is transferred per unit of time the better the heat transfer or thermal conductivity process goes along. The quicker the object on the receiving end can take and dissipate heat the better. Remember, heat is energy.
If we impede the flow of heat from object to object we would call this “Thermal Resistance” as thermal resistance opposes or impedes the flow of heat from a hot object to a cold object. If a hot object has a continuous source of heat energy and that energy experiences opposition to its path to a colder object, then thermal resistance exists. The heat energy in the hot object will continue to grow and its temperature will increase.
Let’s gain a little perspective to better understand thermal conduction and thermal resistance. I will place two one quart sauce pans on a stove. Each pan contains one quart of tap water. One pan has a metal handle and one pan has a wood handle. I will bring each pan to a boil. When at a full boil which handle would you prefer to grab less the use of a pot holder? I would choose the wooden handle because wood offers resistance or opposition to the thermal energy transfer of heat. Now in this example of thermal transfer of energy, thermal resistance is a “good thing”. Another example of thermal resistance being a good thing is on a very cold winter night when you would prefer the heat energy remain in your home rather than escape to the cold outside increasing your utility bill. So when is thermal resistance a “bad thing”?
Thermal resistance is a bad thing when we want to dissipate or remove heat from one object to another as quickly and efficiently as possible. Since conduction and resistance reciprocals when removing heat we want maximum thermal transfer or little to no resistance in the process.
Think about the walls of your dwelling again for a moment. They are insulated to keep heat (or cold) inside your dwelling. The insulation resists the flow of hot to cold or cold to hot depending on the outside temperature. Much like a Thermos Bottle it keeps the hot stuff hot and the cold stuff cold. Ever wonder how it knows the difference? The insulation lies between the two objects.
Many times heat is an undesirable product of a process and needs to be removed as quickly and efficiently as possible. To obtain a maximum transfer of heat we need a good conductor of heat between the objects. We need a medium unlike insulation to impede thermal transfer, but a medium to enhance it.
Heat is a major enemy of today’s electronic components and systems. A good example is the CPU (Central Processing Unit) or the brain of a computer. While processing data into useful information, a CPU can generate large amounts of heat energy. To function well this heat needs to be removed! It needs to be removed quickly and efficiently to prevent heat buildup. We need maximum heat transfer per unit of time. Settle for anything less and we risk damage to the processor and likely other heat sensitive components within our system.
Removal of this heat is generally accomplished through the use of a HSF (Heat Sink Fan) assembly. Between the HSF and processor we employ the use of a thermal compound designed to ensure maximum heat transfer. This compound is situated much as insulation in a wall, however, it is designed to do the opposite in that it transfers heat.
The surface of our CPU and the surface of the mating heat sink do not have a perfect micro finish. The finishes contain many “micro pores” not visible to the naked eye, and when the surfaces are pressed together, these pores allow air to become entrapped. Air is a very poor thermal conductor and offers resistance to the heat transfer or removal process. To overcome this problem we use thermal paste (sometimes called heat sink compound). The paste should work itself into those microscopic pores (nooks and crannies) eliminating air and serving to transfer the heat efficiently. A measure of how well the paste does its job would equate to a measure of the quality of the paste.