Matching Material and Method for Efficient Thermal Transfer

When designing equipment or semi-conductor packaging, it is essential that you identify sources of excess heat and make engineering decisions about how to handle it. This often means deciding what type of material is best suited to the particular need at each physical interface.

The class of materials often used for these transitions are called Thermal Interface Materials, or TIMs, and a great deal of engineering goes into their design and specification. It is critical to have accurate thermal measurements when designing these materials, especially with the ability to measure small differences in performance between candidates. A device such as the ThermalSure TEPT X1 is an ideal companion in the exploration of materials suitable for TIMs.

Key Properties

Thermal properties:

• Thermal conductivity: The TIM should have high thermal conductivity to efficiently transfer heat from the semiconductor devices (IGBT or SiC MOSFET) to the heat sink
• Low thermal resistance (Rth): A low Rth ensures minimal temperature rise across the TIM, allowing effective dissipation of heat
• Thermal stability: The material should remain stable over a wide temperature range without degradation

Chemical properties:

• Compatibility: The TIM must be chemically compatible with the semiconductor materials (IGBT or SiC MOSFET), the heat sink, and any other adjacent components
• Non-corrosive: It should not corrode or react with the surfaces it contacts
• Non-contaminating: The TIM should not introduce impurities that could affect device performance

Physical properties:

• Consistency and uniformity: The TIM should be easy to apply uniformly across the contact surfaces
• Compliance: It should conform well to irregular surfaces, ensuring efficient heat transfer
• Thickness: The optimal thickness depends on the specific application and the pressure applied during assembly
• Ease of application: Consider ease of handling, dispensing, and curing

Electrical properties:

• Insulating: The TIM should electrically insulate the semiconductor devices from the heat sink to prevent electrical shorts
• Dielectric strength: It must withstand high voltage differences without breakdown
• Low capacitance: Minimize any impact on switching performance

Commonly Used TIM Materials

• Thermal greases/pastes: Thermal greases or pastes are widely used for their good thermal conductivity. These materials serve as a bridge between mating surfaces, filling microscopic gaps, and improving heat transfer. When applied, they ensure efficient conduction of heat from components like CPUs, GPUs, and other electronic devices. The advantages of thermal pastes include high thermal conductivity and ease of application. However, they may require reapplication over time due to drying out. Therefore, they are ideal for applications where reworkability is essential.
• Thermal pads: Thermal pads come pre-cut and offer consistent thickness. They are straightforward to use, making them popular for various scenarios. These pads provide a thermal bridge between components, ensuring effective heat transfer. Thermal pads are suitable for applications where simplicity and uniformity matter. Common uses include laptops, smartphones, and other consumer electronics.
• Phase change materials (PCMs): Phase change materials (PCMs) are intriguing materials that adapt to temperature variations. During operation, they transition from a solid to a liquid state, effectively managing heat. PCMs are excellent for applications where dynamic temperature changes occur. For instance, they find use in automotive components, battery packs, and LED lighting systems. Their self-adjusting nature makes them valuable in scenarios where maintaining consistent temperatures is critical.
• Thermal adhesives: Thermal adhesives serve a dual purpose as thermal and mechanical bonding. These materials provide both secure attachment and efficient heat transfer. When applied, they create a strong mechanical bond between components. Thermal adhesives are suitable for permanent installations, such as power modules, industrial equipment, and power electronics. However, removing them can be challenging, and their thermal conductivity is moderate.
• Graphite sheets: Graphite sheets combine high thermal conductivity with flexibility. They bridge gaps between mating surfaces, ensuring effective heat dissipation. These sheets conform to irregular surfaces, making them suitable for specific applications. However, they can be expensive and have limited availability. Graphite sheets find use in high-power LEDs, automotive control units, and aerospace electronics.