One of the most critical specifications when buying thermal pads for any project is the thermal conductivity. But here is where the problem comes in – should you choose high or low thermal conductivity?
That is exactly what we will answer in this article.
Remember, many variables affect thermal pad conductivity like thermal resistance, operating conditions, surface contact, compression and thickness.
So, we want to kill this narrative of just buying thermal pads with the highest conductivity available and focus on optimal thermal management.
What is Thermal Pad Thermal Conductivity?
This is the ability of the thermal interface material to conduct heat. Usually, we express this in watts per meter-kelvin (W/m.k). Higher conductivity generally means lower resistance to heat flow through the pad, assuming other conditions remain comparable.
But there’s an important qualification.
Thermally conductive electrical insulation materials are often heterogeneous materials containing polymers, fillers, reinforcements, or other layers. ASTM D5470 uses the term apparent thermal conductivity when characterizing these materials. The method measures steady-state thermal impedance and can be used to calculate apparent thermal conductivity under defined test conditions
Compare Thermal Conductivity of Different Thermal Pad Materials
| Thermal Pad Material | Thermal Pad Conductivity in W/m.k | Characteristics and Uses |
| Standard silicone | · 1 to 5 | · Cost-effective and highly compressible · Suitable for lower power delivery components like LED arrays and general consumer electronics |
| High-performance silicone | · 8 to 15 | · Best for GPU memory (VRAM), high-end motherboard VRAMs and NVMe SSDs · It is usually packed with ceramic fillers such as aluminum oxide or zinc oxide |
| Non-silicone thermal pads such as acrylic or polyurethane | · 1 to 4 | · Do not release silicone oil · Suitable for optical devices and aerospace applications |
| Phase change materials (PCM) | · 5 to 8.5 | · Common in laptops and high-density chips · They are solid at room temperature but melt into a grease-like state at their operating temperature to eliminate microscopic air gaps |
| Graphite sheets | · 15 to 35+ | · Less compressible but highly thermally conductive and electrically conductive |
| Indium/metal foil | · 80+ | · Restricted to specialized industrial applications · Offers massive thermal transfer but requires extremely high mounting pressure |
Factors to Consider when Choosing Thermal Pad Thermal Conductivity
1. Start With the Heat You Need to Remove
The first question isn’t: “What is the highest thermal conductivity available?” It should be: “How much heat does the thermal interface need to transfer?”
Identify the approximate heat generated by the component and where that heat needs to go.
Typical applications include:
- Power semiconductors
- MOSFETs and IGBTs
- CPUs and GPUs, LED modules, automotive electronics, battery systems, power supplies, telecom equipment, and industrial control electronics.
Higher heat loads generally justify a higher-performance thermal interface material. But that doesn’t mean every high-power application needs the highest conductivity pad available.
If another part of that path creates the dominant thermal resistance, upgrading only the pad may deliver little improvement.
A practical starting point: estimate component heat generation, maximum allowable component temperature, heatsink or spreader temperature, available thermal path, and expected operating environment.
2. Understand What the W/m·K Rating Actually Tells You
Thermal conductivity is normally expressed in W/m·K. It describes a material’s ability to conduct heat through its thickness under specified test conditions.
In simple terms: Higher W/m·K means greater theoretical ability to conduct heat.
But the number alone doesn’t tell you how the pad will perform in your assembly. A 12 W/m·K pad isn’t automatically better than a 6 W/m·K pad if it is too hard to conform or must be installed at the wrong thickness.
Don’t buy the highest conductivity number. Buy the conductivity that works with the rest of the assembly.
3. Match Thermal Conductivity to Thermal Resistance
A simplified relationship is R = t / (k × A), where R is thermal resistance, t is thermal pad thickness, k is thermal conductivity, and A is effective contact area.
If you double the pad thickness while keeping conductivity and area constant, theoretical thermal resistance also increases. That’s why a thin, appropriately selected pad with moderate conductivity can sometimes outperform a much higher-conductivity material used at excessive thickness.
Your specification should address required thickness, thermal resistance, contact area, compression, hardness, operating temperature, electrical insulation, and environmental conditions. The target should be thermal performance at the required interface thickness, not simply the conductivity number.
4. Select Hardness Based on the Interface
Hardness is closely connected to compression and conformability. A softer thermal pad generally conforms more easily to uneven surfaces. That can help when surface flatness is poor, gap variation is significant, components are mechanically sensitive, or low assembly force is required.
A harder material may be more suitable where dimensional stability is important, higher mechanical support is required, the interface is relatively flat, or controlled compression is available.
The correct choice depends on the assembly. Evaluate thermal conductivity, thickness, and hardness together.
5. Consider Electrical Insulation Requirements
Many electronics applications require the thermal interface to provide electrical isolation as well as heat transfer. If the pad sits between an electrically active component and a conductive heatsink, check dielectric strength, volume resistivity, breakdown voltage, and required insulation thickness.
Don’t assume every thermally conductive pad is electrically insulating. Don’t select an insulating material without checking whether its thermal performance meets the requirement.
6. Check the Operating Temperature
Your thermal pad must remain stable across the actual operating temperature range. Check minimum and maximum operating temperature, continuous operating temperature, short-term exposure, and thermal cycling requirements.
A material can perform well initially but change mechanically after repeated thermal cycles. Depending on the application, also evaluate compression set, hardness change, oil bleeding, outgassing, aging, and pump-out or material movement.
For demanding electronics, long-term thermal stability matters as much as initial thermal conductivity.
7. Confirm the Pad Conductivity Testing Method
Thermal conductivity values depend on how the material is tested. ASTM D5470 is commonly used to evaluate thermal transmission properties of thermally conductive electrical insulation materials. The method measures steady-state thermal impedance under defined test conditions and can be used to determine apparent thermal conductivity. However, test conditions don’t perfectly reproduce every real-world assembly.
If Supplier A reports 8 W/m·K and Supplier B reports 10 W/m·K, don’t immediately assume Supplier B has the better product. Ask what test method was used, at what thickness and pressure, what the test configuration was, whether the value is nominal or guaranteed, and whether it is typical or minimum.
At Gallop, we will give you a complete data sheet that shows all our testing methods and techniques.
8. Higher Thermal Conductivity Isn’t Always the Best Value
Suppose two thermal pads can both keep your component within its required temperature range. One costs significantly more because it uses a higher-conductivity filler system. If the lower-cost pad already provides sufficient thermal performance, paying for additional conductivity doesn’t necessarily improve your product.
The better specification is the one that meets the required performance margin without unnecessary material cost.
FAQs
Why does thermal conductivity matter in electronics thermal pads materials?
Thermal conductivity determines the rate at which the thermal interface material can remove heat from a system to maintain optimal working temperature. Therefore, it will determine components performance, system stability, component lifetime, thermal protection and the overall system stability.
Does higher thermal conductivity mean better performance in thermal pads?
No. You should focus on the specific system requirements to attain the needed thermal interface material.
What is the difference between thermal conductivity and thermal resistance in thermal pad materials?
Thermal conductivity refers the materials ability to transfer heat, while thermal resistance determines how a specific material can actually restrict heat flow.
What this means is that, even a highly conductive material can still have a substantial thermal resistance if it is too thick.
Is higher thermal conductivity better for thermal pads?
In most cases, a material with higher conductivity will reduce thermal resistance is other parameters are carefully selected. However, this does not always guarantee better system performance. Always seek advice from professionals.
Is there a standard that determines thermal pad thermal conductivity?
In most cases, ASTM D5470 acts as a reference standard when determining the thermal pad performance.
Final Thoughts
Don’t buy thermal interface material based on the thermal conductivity. It is important to verify all the critical parameters, including thickness, compression, hardness, temperature range and electrical insulation.
At Gallop, we customize every thermal interface material to match your unique and specific application needs – Get a custom quote now.
