The process of mixing thermal paste and the importance of pressure, vacuum and temperature
The production of thermal compound, in particular the mixing of components in a vacuum, is a specialized process aimed at optimizing the quality and performance of the final product. This process uses the principles of pressure, negative pressure (vacuum) and temperature to achieve a homogeneous mixture, remove air bubbles and improve the thermal properties of the paste. I will describe the exact process and the importance of these factors in detail here, without digressing too much into theory that is incomprehensible to the general public. I’m sure the manufacturers will forgive me. But it has to be done.
Step 1: Preparing the components
First, the basic components of the thermal paste, such as the base material (e.g. silicone, polyurethane or another polymer base), thermally conductive fillers (e.g. aluminum oxide, boron nitride, copper or silver particles) and any additives are prepared. The choice of components depends on the desired thermal, electrical and mechanical properties of the finished paste.
Step 2: Mixing under atmospheric pressure
The components are first roughly mixed at atmospheric pressure. This first step serves to combine the various components and create a preliminary, still incomplete mixture.
Step 3: Vacuum mixing
This is where the introduction of the vacuum begins. The preliminary mixture is transferred to a special mixing container that can be evacuated. By applying a vacuum, the air pressure in the container is lowered. The vacuum helps to remove air bubbles and other trapped gases from the mixture, which could otherwise cause thermal resistance within the paste. The negative pressure (vacuum) plays a crucial role in minimizing air pockets and improving the homogeneity of the mixture. Air bubbles can significantly reduce the thermal conductivity of the thermal paste as air is a poor conductor of heat. Removing these bubbles ensures that the paste provides maximum contact area between the heat sources and the heat sinks. During mixing under vacuum, the components are thoroughly blended to ensure an even distribution of the fillers in the base material. This is critical to achieving optimum thermal conductivity.
Step 4: Temperature control
Temperature control is important during the mixing process. The temperature can influence the viscosity of the mixture and therefore the efficiency of the mixing process as well as the distribution of the fillers in the polymer. A moderate increase in temperature can reduce the viscosity of the paste, making mixing easier and allowing a finer distribution of the filler particles. However, care must be taken to ensure that the temperature is not so high that it changes the chemical structure of the components. After the mixing process, however, controlled cooling may be necessary to ensure the desired consistency of the paste for filling and packaging.
The process of mixing thermal paste under careful control of pressure, vacuum and temperature is critical to producing a product that can efficiently transfer heat between surfaces. By optimizing these conditions, manufacturers can produce pastes with superior thermal properties, reduced air bubbles and improved reliability, which is essential for use in electronics cooling and other heat-intensive applications. If something goes wrong here, you might even find water in the paste:
Incidentally, the manufacturer confirmed my analysis at the time, which ultimately led to an outdated and defective filling system. You can read more about this here, because in addition to the unwanted water, there was a lot missing in return.
Thermal paste comparison with laser-induced plasma spectroscopy: We discover a violet surprise!
- 1 - The three big P's - introduction to pastes, pads and putty
- 2 - The purpose of thermal pastes
- 3 - The big debate between cheap and expensive
- 4 - The matrix as the basis for all pastes and pads
- 5 - Silicone-based pastes: optimization, durability, decomposition
- 6 - Thermally conductive fillers are important
- 7 - How the degree of grinding influences performance
- 8 - Silicone modification for low temperatures and LN2 overclocking
- 9 - The paste production process and possible hurdles
- 10 - Special case liquid metal (LM)
- 11 - Special case of graphite pads and phase changers
- 12 - Temperature window, expansion behavior, application
- 13 - Ageing and decomposition of pastes and pads
- 14 - Manufacturer vs. bottler, misleading marketing and conclusion
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