If you are seeking the appropriate thermal interface material for your electronic products and find it a problem to choose between thermal putty and thermal pads, this article will provide more comprehensive information on their characteristics, application methods, and uses. This will assist you in identifying the most suitable thermal management solution for your product.
What is the Thermal Putty？
Thermal putty is a soft, semi-liquid, thixotropic thermal interface material. It can be applied and compressed to achieve a thin layer of TIM between heating elements and heat sinks to fill gaps and displace air, thereby enhancing thermal conductivity for improved heat dissipation. Compared with thermal grease, it has lower fluidity, reducing the need for curing steps while better preventing pump-out issues in thermal cycling aging tests.
What is the Thermal Pad？
Thermal pads are also used between heating elements and heat sinks to increase thermal contact area, thereby enhancing heat dissipation in electronic devices. Unlike thermal putty, however, they are pre-formed into solid sheet materials. These can be freely die-cut to sizes according to application requirements and applied to fill gaps, making their use considerably simpler.
Thermal Putty vs Thermal Pads: How to Apply？
Thermal putty and thermal pads are both applied to fill the gaps between heating elements and their casings, or between heating elements and heat sinks. However, due to their differing physical forms, their methods of application are different.
How to Apply Thermal Putty？
Clean the Component and Heat Sink Surfaces
Contaminants such as dust, moisture, or grease can impair the thermal putty’s contact and adhesion properties. Therefore, you should thoroughly clean the surface of the heat-generating component requiring application. Additionally, if there are some maintenance jobs to be done, please remove all the TIMs carefully, such as thermal putty or thermal pads.
Applying Thermal Putty
Calibrate the application area and gap distances based on your 3D drawings. Please consider about the factors as follows.
- Mechanical tolerances
- Adequate compression ratio (typically suggested ratio at 20-30% compared to the gap distances)
Dispense an appropriate or minimal amount of thermal putty to better control usage and allow for top-up as needed. Make it cover surfaces while remaining as thin as possible. You can use a syringe or spatula, spread the thermal putty evenly across the surface, and fill in any irregularities or depressions.
Installing the Heat Sink
Align the heat sink with the surface of the heat-generating component and press down evenly, ensuring the thermal putty is uniformly distributed and minimizing the formation of air bubbles or slippage.
Inspection
After installation, you must check whether the thickness of the thermal putty is appropriate. Avoid insufficient coverage due to excessive thinness or increased thermal resistance from excessive thickness. Promptly remove any excess thermal putty and vertically place it for 24 hours to check if there’s any fall-off distance exceeding 1.0mm, which can be defined as non-conformity in surface adhesion & reliability when it comes to the condition of vertical assembly at the end products. Should the application prove unsatisfactory, it is advisable for you to remove and reapply an adequate amount of gel and repeat the validation test. This test is recommended to be conducted during PV/DV periods before mass production.
How to Apply Thermal Pads?
Switch off the Power Supply and Clean the Surface
As with thermal putty, you must switch off the power supply completely and wear protective equipment before using thermal pads to safeguard both yourself and the electronic components. Similarly, remove any dust and old thermal material from the surfaces of the heat-generating components and heat sinks to enable the thermal pads to function properly.
Selecting the Thermal Pad
Unlike thermal putty, which you control the application amount yourself, thermal pads are pre-formed. Therefore, you must select the right thermal pad for your application. As thermal pads have a fixed thickness and cannot be layered, you must choose one that is sufficiently thin yet of adequate thickness to cover uneven surfaces.
Cutting Thermal Pads
The shape and size of thermal pads can be tailored to suit your components and heat sinks. You should measure when cutting to avoid material wastage or performance degradation caused by ill-fitting dimensions.
Adhesion and Pressing
Thermal pads typically are double or single sided adhesive layers. After removing the release liner, align the thermal pad and press it on the component surface. It is advisable to press the thermal pad multiple times to ensure full surface contact, expel any trapped air, and maximize thermal transfer efficiency.
Installing the Heat Sink
Remove the release paper from the other side and press the heat sink firmly onto the thermal pad to ensure secure attachment. The adhesive layer of the thermal pad provides a long-lasting bond, allowing you to secure it without additional screws. This reduces the number of steps required, making it more convenient to use. Should you require use in applications involving vibration and shock, you may also opt for additional screw fastening.
Thermal Putty vs Thermal Pads: Comparative Analysis of Plasticity and Bond Strength
Plasticity and Bonding Strength of Thermal Putty
The paste-like consistency of thermal putty affords it a degree of fluidity, making it a superior filling and conforming to irregularities on the surface of heat-generating components. This permits you to use it on highly uneven surfaces and allows for more flexible adjustment of application volume according to requirements, achieving maximum filling effectiveness. The adhesive incorporated into the thermal putty can be tailored to your needs, though it does not provide high-strength fixation.
Plasticity and Adhesive Strength of Thermal Pad
Compared to thermal putty, thermal pads lack fluidity and thus offer inferior filling performance. However, their exceptional softness enables tight surface coverage under uniform pressure, making them more effective on relatively flat surfaces. Their adhesive layer typically provides superior bonding strength, eliminating the need for additional screw fastening in some of your applications. However, compared to thermal tapes, the viscosity of thermal pads is lower.
Thermal Putty vs Thermal Pads: Installation Difficulty and Repeatability
Installation Difficulty and Reusability of Thermal Putty
Applying thermal putty requires you to control over quantity and spreading, making installation more complex than using thermal pads. You must also remove any spillage or excess thermal putty. Furthermore, once used, the thermal putty’s shape becomes altered and its adhesive properties diminish. You’d better not reuse it.
Installation Difficulty and Reusability of Thermal Pads
Thanks to their solid-state and pre-moulded form, thermal pads eliminate the need for laborious processes, making installation significantly simpler. In some instances, screw fastening may not even be required. Furthermore, unlike thermal putty, they do not exhibit issues such as oozing during installation, resulting in a cleaner component interior and reducing the need for cleanup steps. Provided their thermal conductivity and shape remain unaffected, thermal pads can be reused.
Thermal Putty vs Thermal Pads: Thermal Conductivity Comparison
Thermal Conductivity of Thermal Pads
The working principle of thermal pads is achieved through contact and filling. Therefore, thermal pads demonstrate high heat dissipation performance on more flat surfaces. Thermal pads can be made with varying thermal conductivities to suit different applications, allowing you to select the appropriate option for your requirements. They typically have lower thermal conductivity (1–12W/mK), though certain high-performance variants may achieve higher values, such as the graphene thermal pad.
Thermal Conductivity of Thermal Putty
On the one hand, thermal putty typically offers lower thermal conductivity (1-14W/m.K), but due to its lower BLT(Bond-line Thickness) and outstanding wettability, it will exhibit low thermal impedance for some high-power applications. On the other hand, thermal putty offer exceptional conformability, enabling satisfactory thermal contact area and minimizing thermal resistance for complex shapes and surfaces. So, this brings better heat dissipation performance compared to thermal pads in some cases.
Thermal Putty vs Thermal Pads: Application Comparison
Application of Thermal Putty
Firstly, thermal putty’s higher thermal conductivity makes it well-suited for use in high-performance heating devices such as LED lighting equipment, automotive battery systems, and computers handling heavier workloads. It delivers satisfactory heat dissipation, thereby extending the lifespan of your equipment. Secondly, you can also use it on the surfaces of rough and complex-shaped components to better fill gaps. Additionally, should there be a significant gap (0.1 to 4.0 millimetres) between your heating element and heat sink, thermal putty will better fill this void and deliver superior heat transfer performance.
Applications of Thermal Pads
If you are seeking suitable thermal interface materials for electronic devices such as laptops, mobile phones, and tablets, thermal pads are an ideal choice. Not only are they straightforward to install and offer advantages in high-volume manufacturing, but they are also well-suited to the small-to-medium-sized thermal management requirements of portable devices. Furthermore, their lower cost allows you to operate within a tighter budget. However, you are best to use them in projects where component surfaces are flat.
Thermal Putty vs Thermal Pads: Operating Temperature Comparison
Thermal pads and thermal putty both work effectively at high temperatures to transfer heat between heat-generating components. Thermal pads can be used reliably within a temperature range of -60 to 200 degrees Celsius, whilst thermal putty operates best between -50 and 150 degrees Celsius. Consequently, thermal putty has lower resistance to both high and low temperatures compared to thermal pads. Furthermore, thermal pads and thermal putty both possess enhanced safety credentials, having passed the UL94-VO fire rating test. Should you require thermal materials for environments with more extreme temperature conditions, they all have a high level of safety.
Thermal Putty vs Thermal Pads: Cost
In terms of cost basis, it’s not easy to define which one is the best cost-effective solution for you, as it’s more closely related to the project volumes. If you’re evaluating for a high-volume project, thermal putty is the best option for your application. If there are many spots to be applied with TIMs, thermal putty can also demonstrate its unparalleled benefits by simplifying programming to complete everything quickly and accurately. Here is a general summarized comparison chart for you to easily follow the key points between these two materials.
Thermal Putty vs Thermal Pads
| Item | Thermal putty | Thermal pads |
| Form | Semi-solid mud-like material | Preformed solid sheet material |
| Ease of use | Complex (Requires dispensing robot or manual dispenser) | Easy |
| Repeated workability | N/A | OK (if no adhesive laminated) |
| Thermal conductivity | 1-15W/m.K | 1-20W/m.K (Available in higher performance options) |
| Lifespan | 2-8 years | 2-10 years |
| Typical Operating temperature | -50 ~ 150deg. C | -60 ~ 200deg. C |
| cost | Lower | Higher |
| Application | Larger gaps, rough surfaces, and high-performance applications | Fit in rough & Smooth surface, can fill up to 20mm gaps |
How to Choose between Thermal Putty and Thermal Pads？
Determining Thermal Conductivity Requirements
Thermal pads and putty with higher thermal conductivity offer superior heat dissipation performance. You should establish your thermal conductivity requirements based on your product type, power rating, and other specifications. Should your product demand enhanced heat dissipation, opt for thermal putty featuring a higher thermal conductivity rating.
Consider Component Characteristics
You must also select based on the gap size and surface flatness of your components and heat sinks. Thermal pads are more suitable for products with consistent gap thickness and flat surfaces. Should your gaps be larger or component shapes more complex, thermal putty would be the right choice.
Select based on Ease of Use
Using thermal pads allows you to reduce certain operational steps and minimizes the need for cleaning. Moreover, they are better suited for high-volume production, enhancing processing efficiency. In contrast, thermal putty requires more complex application and tidying procedures.
Consider Budget
Thermal pads offer a lower initial cost, making them suitable for your projects with tighter budgets. For projects with greater budgetary flexibility, thermal putty provides a more cost-effective solution.
FAQs
Can I Stack Thermal Pads?
Stacking multiple thermal pads may create gaps, leading to increased thermal resistance and reduced thermal conductivity. Therefore, you should select thermal pads of a more appropriate thickness based on the size of the gap distance between the chips and the heatsink/metal housing.
Are Thermal Putty and Thermal Pads Conductive?
To ensure greater safety in electronic devices, thermal putty and thermal pads are typically insulated to prevent hazards such as short circuits. Should you require conductive variants, certain models are also available.
What is the Difference between Thermal Grease and Thermal Putty?
Thermal grease offers superior fluidity, making it more suitable for products with narrower gaps, typically lower than 0.15mm. Thermal putty, however, can fill larger voids and prevent drying during prolonged use owing to its partially cross-linked structure, which helps exhibit outstanding thixotropic performance over time.
Does Thermal Putty Require Curing?
No. Thermal putty is viscous and will not flow after application. This makes it easier to work with and allows it to remain moist for longer use.
How to Remove Thermal Pads？
Begin by peeling off the old thermal pad. If any residue remains, wipe it away using a cotton swab or soft cloth. You may also select a cleaning agent recommended in the instruction manual that will not damage your components.
How to Store Thermal Pads and Thermal Putty？
Thermal pads and thermal putty should be stored in a dry location, protected from ultraviolet light, at temperatures between 8℃ and 28℃. Furthermore, they must be used before their expiry date (approximately 6 to 24 months).
Final Thoughts
Having understood the respective characteristics and uses of thermal pads and thermal putty, you should now be able to make an informed choice. GALLOP INNOTEK supplies high-quality thermal interface materials (TIMs), with products certified to ISO 9001:2008, ISO 14001, IATF 16949, and ISO 45001. Contact us for a bespoke solution
