Thermal dissipation
Thermally-conductive paste for high heat transfer coefficient

Effective heat dissipation can only occur between materials with a high conductivity coefficient. A poorly-designed heat-transfer chain can cause energy and efficiency losses or even an interruption to the dissipative effect with a corresponding loss of functionality of the mechanical device. 

The most frequent cases in which it is necessary to rapidly transfer heat from one element to another can be traced back to:

• Heat exchangers 
• Frictional overheating of mechanical components such as motors or gearboxes
• Processor components in electronic equipment

The methodologies available on the market are varied, effective and require a precise analysis of the thermal and environmental operating conditions for:

• • Fans 
  • Aluminium sheeting
  • Radiators 
  • Heatsinks
  • Conductive rubbers

  In some cases, however, the use of a "rigid" solution may not be adequate for the application context, due for example to the lack of flatness and the consequent interposition of insulating air pockets between the conductive foils, the presence of which would compromise the dissipative effect since air is a mixture of gases with a low conductivity coefficient when compared to metals or other conductive materials.

  In such cases, the use of a thermal-conductive paste can help.

A thermal conductive paste is a plastic compound with high thermal conductivity that accommodates the geometric imperfections of the coupling. A good heat-conducting paste must be carefully selected, taking into consideration:

• Conductive filler
• Base oil
• Additives
• Thixotropic agents

The selection of the conductive filler and its heat transfer coefficient both condition the dissipation efficiency, whilst the base oil, additives and thixotropic agents determine other key properties, such as:

• Permanence against gravity in the applied position
• Evaporation and drying by thermal effect
• Tendency of the oil to separate from the filler
• Compatibility with contact surface materials
• Tendency towards carbonisation
• Incorporation of air and reduced conductivity
• Easy dosing and film deposition 

A thermal paste is classified on the basis of its specific thermal conductivity, the value of which is primarily conditioned by the type of filler and its concentration. 

The production of a thermal paste requires a process that must be constantly controlled. An often-overlooked problem is the potential incorporation of air into the finished product, the presence of which would lead to a drastic reduction in the heat exchange coefficient and consequent heat dissipation.

Another fundamental aspect concerns the choice of base oil, which significantly influences stability at different operating temperatures. In particular at:

• High temperatures, between 150° and 200° C, almost all carrier base oils undergo profound structural changes, evaporation loss and subsequent oxidisation, leading to rapid carbonisation with consequent losses in efficiency, being why it is recommended to evaluate fluorinated-based high thermo-oxidative solutions where temperatures could exceed 200° C for prolonged thermal cycles
• Low temperatures, being an equally critical condition of potential crystallisation of the base oil, with crack formation, loss of conductive film continuity and reduced effectiveness of the heat transfer

Adhesion to the friction zones and the potential loss of material by gravity from the heat transfer zones represent one possible threat to the proper functioning of the device.  For this reason, it is possible to perform a specific adhesion test by checking the rheological and visco-dynamic properties of the product in use in the thermal operating range provided by the application context.