Introduction
Thermal interface materials (TIMs) play a critical role in thermal management by reducing contact thermal resistance between heat-generating components and heatsinks. Among the various TIM options, thermal greases have been widely used for many years due to their low cost and ease of application.
However, thermal greases also present well-known reliability and maintenance challenges—particularly in high-power applications. This article introduces a real-world problem-solving example in power conversion equipment, such as inverters, where replacing conventional thermal grease with graphite-based TIM (Graphite TIM) effectively addresses these issues.
Thermal Management with Thermal Grease—and Its Limitations
Power modules generate significant heat and are typically mounted to heatsinks to dissipate that heat efficiently. In practice, when a heatsink is attached directly to a power module, microscopic gaps inevitably form between the module base plate and the heatsink surface due to slight distortion or unevenness of the base plate.
These gaps increase contact thermal resistance, preventing the heatsink from delivering its full cooling potential.
To address this, thermal grease is commonly applied between the base plate and the heatsink as a TIM. The grease fills surface irregularities, improving thermal contact and reducing thermal resistance.
[Figure 1 – Filling gaps between base plate and heatsink using thermal grease]
Despite its widespread use, thermal grease has several inherent drawbacks.
Key Issues with Thermal Grease
1. Thermal Resistance Variations Due to Voids
Achieving consistent performance with thermal grease depends heavily on application amount and uniformity. Incomplete filling or uneven spreading can leave voids, leading to localized increases in contact thermal resistance and inconsistent heat dissipation.
2. Increased Thermal Resistance Due to Dryout
Thermal grease is susceptible to the dryout phenomenon, where exposure to elevated temperatures causes volatile components to evaporate. Over time, oil and filler separate, the grease hardens, and cracks may form. As a result, contact thermal resistance increases.
[Figure 2 – Dryout phenomenon illustration]
3. Increased Thermal Resistance Due to Pump-Out
During long-term operation, repeated thermal expansion and contraction of the base plate can cause pump-out, in which thermal grease is gradually pushed out from the interface. As the grease layer thins, gaps reappear and thermal resistance rises.
[Figure 3 – Pump-out phenomenon illustration]
4. Higher Total Cost of Ownership
Although thermal grease itself is inexpensive, mitigating dryout and pump-out requires periodic maintenance. This typically involves disassembly, cleaning, reapplication, and reassembly—adding labor, downtime, and long-term cost.
Solving These Issues with Graphite TIM
Replacing thermal grease with Graphite TIM, a graphite-based thermal conduction sheet, addresses these challenges effectively.
Graphite TIM is a sheet-type TIM with excellent thermal conductivity, designed to be sandwiched between heat-generating components and heatsinks. Panasonic’s Graphite TIM offers high reliability, simple handling, and stable long-term performance. While adequate clamping pressure is required to achieve optimal thermal characteristics, installation is straightforward and repeatable.
[Figure 4 – Graphite TIM product image]
Performance Comparison: Thermal Grease vs. Graphite TIM
The table below summarizes how Graphite TIM resolves the common issues associated with thermal grease.
| Thermal grease issues | Thermal conduction sheet Graphite TIM |
|---|---|
| ① Thermal resistance variation due to voids | Absorbs differences in level through its high compressibility, achieving a stable thermal resistance equivalent to that of thermal greases. |
| ② Increase in thermal resistance due to the dryout phenomenon | Heat-resistant to temperatures over 400ºC; no degradation due to heat |
| ③ Increase in thermal resistance due to the pump-out phenomenon | Physical properties remain unchanged semi-permanently. |
| ④ Increase in total costs | Easy installation that only requires placement and simple maintenance ⇒ Low total costs |
[Table 1 – Comparison of thermal grease issues and Graphite TIM features]
-
Void-related thermal resistance variation
Graphite TIM’s high compressibility allows it to absorb surface unevenness, providing stable thermal resistance comparable to thermal grease. -
Dryout-related degradation
With heat resistance exceeding 400 °C, Graphite TIM does not degrade due to heat and is unaffected by dryout. -
Pump-out phenomenon
As a solid sheet material, Graphite TIM maintains its physical properties semi-permanently, eliminating pump-out concerns. -
Total cost
Easy installation and minimal maintenance requirements contribute to significantly lower total cost of ownership.
Thermal Resistance vs. Pressure Characteristics
The graph below shows how the thermal resistance of Graphite TIM changes with applied pressure.
[Figure 5 – Thermal resistance vs. pressure graph]
As pressure increases, thermal resistance decreases. In high-compression regions, Graphite TIM achieves thermal resistance levels equivalent to thermal grease. This demonstrates that Graphite TIM can be used as a direct replacement without compromising thermal performance.
Heat Resistance and Long-Term Reliability
An accelerated heat-aging test was conducted to evaluate resistance to dryout. Samples were placed on a 150 °C hot plate for 30 minutes, simulating approximately 10 years of operation.
[Figure 6 – Before/after heat aging photos]
Unlike thermal grease, Graphite TIM showed no visible degradation or performance loss after the test, confirming its ability to resolve dryout-related reliability issues.
Graphite TIM applications
Summary
Thermal greases have a long history and remain widely used as TIMs, but their susceptibility to dryout, pump-out, and maintenance-driven cost increases presents clear limitations—especially in power electronics.
Graphite TIM, as a graphite-based thermal conduction sheet, offers a reliable, maintenance-friendly alternative with stable thermal performance and excellent heat resistance. For power modules and other high-heat applications, it provides a practical solution to the longstanding challenges associated with thermal grease.
8. Panasonic Product Page
Explore Panasonic Graphite TIM Solutions
Learn more about Panasonic’s graphite-based thermal interface materials and how they can improve thermal reliability in your power electronics designs.
→ Visit the Panasonic Graphite TIM product page
Learn more about Panasonic’s graphite-based thermal interface materials and how they can improve thermal reliability in your power electronics designs.
→ Visit the Panasonic Graphite TIM product page
