High thermal resistance in any thermal interface material (TIM) can be catastrophic – from overheating and shortening component life to product failure due to inefficient cooling.
Therefore, this is not something you can ignore when choosing thermal pad material. So, how do you choose a material with the lowest thermal resistance for your electrical component assembly?
Why Thermal Resistance is Critical in TIM
Thermal resistance is bad for any electrical system that dissipates heat. At some point, the heat will be excessive to the extent that it can cause damage.
Ideally, the thermal pad resistance should be low. Below is a quick reference you may consider.
| Recommended Application for Thermal Pad | Units of Measurement (W/m.k) |
| General purpose or low power applications like DRMA chips, router processors, low-power LED drivers | · 1.0 to 3.0 |
| Mid-range to high-performance applications like CPU/GPU heatsinks, automotive electronics (ECU) or motor controllers | · 3.0 to 8.0 |
| Extreme or elite performance applications like high-end graphics card memory (GDDR6X VRAM), enterprise servers, or high-frequency telecommunication systems | · 8.0 to 15.0+ |
Therefore, you must choose a material with appropriate thermal resistance to achieve stable system performance. Higher thermal conductivity with the ability to compress by about 20% to 30%, which also helps to eliminate air gaps.
When you factor in price, this can at times be a difficult tradeoff; that’s why Gallop Innotek engineers are here to help you get the best material.
Know How to Calculate the Thermal Pad Resistance
By calculating the thermal resistance of materials in the early design stage, your engineering team can compare different thermal interface materials to choose the right options before production begins. This is to prevent the possibility of parts being rejected or not conforming to the required thermal transfer specifications.
The thermal resistance formula is:
Rθ =t/(k*At)
In the formula
- Rθ: represents thermal resistance and uses either ∘C/W or K/W.
- t is the thickness of the pad, given in meters.
- k: stands for thermal conductivity, given in W/(m⋅K)
- A: represents the contact area, given in m2
When calculating the thermal pad resistance, it is critical to note that:
- The lower the thermal resistance, the better the heat conduction
- Elevated thickness, in turn, elevates resistance.
- Increased conductivity minimizes resistance.
- Larger surface area reduces resistance.
For example:
- Thickness t=0.15 mm =0.00015 m
- Thermal conductivity k = 0.9 W/(m.K)
- Contact area A=0001 m2
Thermal resistance will be 0.00015 (0.9×0.00010), bringing it to 1.670C/W
Key Factors That Affect Thermal Pad Resistance
Thermal interface materials have varying thermal resistance that is influenced by a wide range of factors. By evaluating each parameter with your design team, it will be easier to develop an electronic system with stable performance.
· Pad Material Thermal Conductivity
Thermal conductivity of a pad gauges how easily heat is transferred through the thermal pad material. The more conductive the pad material is, the less thermal resistance it will experience. It is important to note that other properties of the material, such as thickness, among others, can also influence conductivity, which in turn influences resistance.
Thermal pads with elevated conductivity are designed compactly and can reduce component temperature as well as elevate durability. However, given their superior feature, which enhances functionality, pads designed with super-conductive materials tend to cost more.
· Thickness and Compression Ratio
One of the most direct influences on thermal resistance is the thickness of the pad. A thicker thermal pad increases the heat path length, increasing thermal resistance. However, pads that are too thin may not always function as required. Therefore, the pad must have the required thickness as per the application requirements.
Instead of reducing thickness by removing material, you can compress it to shorten the heat path of the pad. The ratio of compression varies depending on the manufacturer as well as the pads’ intended application, ranging between 20% and 30%. With correct thickness and compression, the risk of overstressing components as well as inconsistent production is minimized.
· Surface Roughness of Mating Parts
The type of pad that can provide the required resistance can vary depending on the roughness of the surface of the mating parts. If the surface is rough, then the pad’s contact area to be covered increases because of the rises and falls. On the other hand, if the surface of the mating parts is smooth, then the contact area will be well covered.
Having a smooth surface finish is therefore integral to maximizing the thermal resistance effects of the pad. Rough surfaces will require functionally enhanced pads to afford the same resistance, but typically cost more.
· Contact Pressure and Clamp Force
Contact pressure gauges ensure that the pad is well pressed against both surfaces. How pressure is properly applied elevates conformity by minimizing the air trapped between the two surfaces. If excessive pressure is applied, then the pad can be damaged; if it’s not enough, then air gaps may be present, which reduce thermal reliability.
The clamping force applied should also be sufficient to keep the pads in place. Correct contact pressure and clamp force are required for stable and even thermal resistance. Incorrect mounting increases the risk of failure, leading to wear of parts and pads.
· Air Gaps
Pads are typically used as a method of eliminating air gaps found between surfaces, given that air has limited thermal conductivity. The more air gaps that are left between the surfaces, the more the insulation effect, which in turn elevates thermal resistance. These pads are, therefore, like a bridge allowing for solid heat transfer.
For example, air conductivity is about 0.026 W/Mk while a typical thermal pad is about 3 to 13 W/Mk.
By eliminating air gaps using thermal pads, your electronic parts will have improved heat transfer to the heat sink. As a result, they minimize the risk of overheating and possible component failure.
· Voids
Such air gaps are internal empty spaces between the mating surfaces, as well as in the pad, and have insulating effects, increasing thermal resistance. Voids are typically a result of materials that are defective or of poor quality, poor placement, and not enough compression. The higher the number of voids present, the greater the thermal resistance.
Pads that are of good quality have very few voids present, as it offers the best resistance, making them more reliable. These pads will not only have reduced warranty exposure but will also have better customer feedback.
· Assembly Quality
Properly assembled high-quality pads are especially vital for proper installation, which aids in minimal thermal resistance. Assembly affects factors like uniform compression, proper placement, and contamination-free pads. If not properly assembled, numerous errors are likely to occur, which will greatly minimize the thermal pad resistance.
Assembly not only ensures the quality of the thermal pad produced, but also ensures a thermal pad with elevated functionality. It also reduces the number of pads to be scraped, increasing supplier qualification as well as user satisfaction.
· Material Aging and Long-term Stability
The longer the pads are used, the more they deform by hardening, creeping, and even oil migration, which in turn elevates thermal resistance as it does not properly conform. Continuous pressure during operations impacts the thickness of the pad and the area of contact. Quality pads designed with long-term stability offer a long service life and enhanced functionality.
· Operating Temperature Range
Pads used are great heat conductors, but should be used within an optimal temperature range to ensure that it remains usable for longer. Drastic temperature variations may result in softness, compression, and stiffness, among other issues. Choosing pads with the right temperature range that meets your application requirements ensures durability and maintained functionality.
FAQs
What is the difference between thermal pad resistance and thermal conductivity?
Thermal pad resistance quantifies the pad’s resistance to heat flow, while thermal conductivity determines the ease with which the material can transmit heat.
What thermal pad material provides the best heat transfer?
The most suitable material will vary depending on the exact application’s requirements
Are silicone thermal pads suitable for high-power electronics?
Yes, this pad variation is highly suitable for electronics that are high-powered.
Can thermal pads be reused?
You can reuse thermal pads; however, the longer it is used the less effective it will be.
Is there a difference between thermal resistance and thermal impedance in thermal interface materials?
Thermal resistance gauges the extent to which a material can resist heat flow.
Thermal impedance helps you track the behavior of the material when subjected to heating during operations.
Looking for Efficient Thermal Pads for Electronic Component Assembly
At Gallop Innotek, we help you choose thermal pads based on your unique application requirements. Our engineers will help you choose the right material, tolerance, or any other customization option for optimal heat transfer.
Contact us today for custom thermal pad solutions.
Thermal Pad Resistance & Impedance Planner
Compare a simple through-thickness resistance estimate and normalize a tested thermal impedance value to a selected contact area.
Planning/reference estimate: The idealized value excludes contact resistance, compression, surface finish and test-method effects. Use supplier test data and assembly validation for final design.
