Thermal Pad vs Thermal Paste: TIM Selection & PCB Thermal Tips

Introduction

Thermal pads and thermal pastes are both essential materials for electronics. These two materials fill the gaps between components and heatsink surfaces. This article goes in-depth to compare thermal pad vs thermal paste. We are here to assist you in selecting the best TIM for your project.

What is a Thermal Pad?

A thermal pad is a solid thermal interface material that fills an air gap between a component and a heat sink interface. It provides a reliable bridge for heat transfer in your electronics.

This flexible gap filler is very easy to customize to fit your design needs. These pads are available in uniform thickness in various custom shapes. Depending on your application, you can choose a standard silicone pad, a non-silicone pad, or graphite and metal-based options to optimize thermal conductivity.

What is a Thermal Paste?

Thermal paste is a viscous liquid thermal interface material with no fixed geometry; it improves heat transfer by filling microscopic surface irregularities. The thermal grease is made of a fluid-based material with high-conductivity fillers, unlike solid pads.

You apply it directly between your electronic components and the heat sink interface. By forcing trapped air out of these tiny gaps, the paste lowers the thermal resistance, which helps in cooling the PCB assembly very effectively.

Thermal Pads as Thermal Interface Materials (TIMs)

It replaces microscopic air pockets with a highly conductive gap filler. Under pressure, the pad dissipates directly to reduce thermal resistance. This process results in a consistent and dependable heat transfer pathway.

Common Applications

Thermal pads are used in various electronics systems to cool down high-power components. They are used to reliably transmit heat in these applications.

• Cooling of the CPU, repasting of the GPU, and VRM thermal management.
• Voltage converter and power regulators.
• LED modules and commercial lighting drivers.
• Automotive control units require stable heat transfer.
• Power electronics for Telecom and Industrial.

Common Types of Thermal Pads

You can select from several pad types to enhance your specific thermal management. Every material has its own physical benefits for your PCB assembly.

• Silicone Pad: This common gap-filler offers outstanding flexibility, electrical insulation, and reliable thermal conductivity.
• Graphite Pad: These highly conductive pads require extremely flat surfaces and typically lack electrical insulation.
• Non-Silicone Pad: For optic electronics or medical sensors, use silicone-free thermal pads to strictly prevent outgassing contamination.

Key Technical Specifications for Thermal Pad

Thermal Conductivity (W/m·K)

Thermal conductivity measures the way a material transfers heat. A higher rating gives better cooling to your components. However, real-world performance depends heavily on surface flatness and contact pressure. A 10 W/m·K pad that is poorly installed won’t perform as well as a properly compressed 5 W/m·K pad. Always ensure good contact to minimize thermal resistance.

Thickness vs. Gap

If the thermal pad is too thick, the air gap will stay larger, thus increasing thermal resistance. It is best to always pick the thinnest pad you can find. Avoid the common mistake of assuming thicker pads perform better. Measure your gap tolerance accurately. Select a pad that is 10 to 20% thicker than your clearance to ensure optimal compression.

Hardness and Compressibility

The hardness of your gap filler determines how well it conforms to uneven surfaces. Softer pads adapt easily to imperfections but may deform excessively under loads. Harder pads do keep their shape; however, they require completely flat heat sink interfaces. For most general applications, you should select a medium hardness. A Shore 00 40 to 60 rating provides the best balance.

Electrical Insulation and Temperature Range

You must verify the dielectric strength when placing pads between conductive parts to prevent short circuits. This rating indicates how well the material insulates electricity. Look for a high thermal pad breakdown voltage for high voltage PCBs, typically exceeding 3 kV/mm. In addition, you should check the operational temperature limits. This is especially vital for automotive designs operating continuously around 150 °C.

Thermal Pad vs Thermal Paste: Which Is Better?

When deciding on a thermal pad vs thermal paste, the final decision will depend upon your cooling needs and mechanical restrictions. While paste has lower thermal resistance for high-power chips, pads are easier to fit. Two materials help to transfer heat but behave differently. The table below shows a simple comparison between the two.

Thermal Conductivity

The thermal conductivity rating of CPU thermal paste is often lower than that of high-end pads. However, paste usually performs better in real life due to its much lower thermal resistance. Thermal pads might advertise high numbers, but they are generally less efficient. You need to think about contact resistance. Always ensure the application meets your needs.

Application Method

A careful technique is required for the application of thermal paste as it only needs a thin layer. An even spread must be ensured to exclude all air bubbles. On the other hand, thermal pads are easy to peel and place. You don’t need any special skills to install them. This makes pads incredibly convenient for quick assembly processes.

Durability

Thermal paste generally provides great longevity for your electronic devices. However, it hardens with time and thus becomes difficult to remove. Thermal pads are somewhat less durable under extreme conditions. Repeated heating and cooling might make them brittle. You must monitor their physical condition to maintain optimal heat transfer.

Cost

Thermal paste is quite affordable and available for everyone. This can easily be bought in bulk for mass production. Thermal pads are slightly more expensive due to varied material and thickness options. The cost goes up for custom shapes and particular formulations. Consider your budget prior to making a decision.

Suitability for High-Heat Components

Thermal paste provides excellent cooling for demanding CPU and GPU configurations. It helps prevent thermal paste pump-out under cyclic thermal stress on high-power semiconductor chips. Thermal pads only offer moderate suitability for extreme temperatures. You should primarily use pads for low-to-medium heat applications. They are suitable for memory chips and general PCBs.

Ease of Reapplication

It is tough to reapply thermal paste, and it’s usually messy. Make sure to clean the hard paste thoroughly before making a precise reapplication. On the other hand, thermal pads are very easy to replace. All you have to do is peel off the old one and apply a new one. However, reused pads will experience degraded performance.

Use Cases

High-power components requiring intensive computing processes should use thermal paste. It is still the standard for GPUs and CPUs. On the other hand, thermal pads work great on low-power devices. They effectively cool RAM, NAND flash modules, laptops, and LED lighting assemblies. Knowing when to use thermal pads instead of paste optimizes cooling.

Device Suitability

Thermal paste works perfectly for desktop computers and powerful gaming workstations. Maximum high-performance cooling efficiency is needed in these demanding hardware environments. On the other hand, thermal pads work just fine in slim, portable devices like laptops. You should use them wherever convenience and electrical insulation are major priorities. They easily fit into limited mobile device spaces.

Skill Requirement

Applying thermal paste requires a moderate to high level of manual skill. A wrong application could lower the cooling effect or cause a big mess. Thermal pads require very low skill for installation. They are super intuitive to work with and fully beginner-friendly. Simply place them on top of the surface of the component.

Common Mistakes

Installing thermal interface materials can lead to mistakes if not careful. Many engineers find it hard to assess the thermal pad vs thermal paste performance comparison. Misunderstanding specifications often leads to severe overheating issues. Always assess your whole thermal system. Review these common mistakes to ensure a highly successful cooling strategy.

Focusing Only on Thermal Conductivity Numbers

You shouldn’t judge a material based purely on its thermal conductivity rating. Actual performance heavily depends on surface pressure and thermal resistance.

Using Thick Thermal Pads Where a Thin Paste Layer Is Needed

Avoid using thick pads when trying to bridge extremely microscopic gaps. At times, better results can be achieved by swapping thermal pads with copper shims and paste.

Ignoring Electrical Conductivity Risks of Some Pastes

Always weigh the risks of using non-conductive vs liquid metal thermal paste. Conductive pastes can easily short out your exposed electrical components.

IC Package Thermal Pads (Exposed Pads)

An IC exposed thermal pad is a large metal area on the bottom of surface-mount packages. It is soldered directly onto the PCB to maintain appropriate heat dissipation and mechanical strength. Connect this die pad to avoid device malfunction and failure. When assembled properly, the thermal resistance of the system drops significantly.

Why It Matters

The thermal pad efficiently transfers heat between the silicon die and copper plane. If you fail to solder it, air will get trapped inside. It causes hazardous thermal drift and lowers heat transfer. Datasheet thermal resistance values always assume you soldered this pad. A good connection avoids overheating failures.

Electrical Connection

Before routing the exposed pad, be sure to check the IC datasheet. Most thermal pads make direct contact with the system ground. However, some components leave the pad floating or tie it to another potential. You should never assume the pad function. Improper connections can easily result in major shorting or EMI issues.

PCB Design Tips

Properly soldering the exposed pad halves your junction-to-board thermal resistance. You need to use particular layout techniques for efficient cooling performance.

• Pad Size: Design your PCB land to match the size of the package pad.
• Thermal Vias: Use small vias placed underneath the pad to transfer the heat downward.
• Stencil Design: Apply a windowpane paste pattern to prevent component floating.
• Void Control: Keep solder voids below 50% to ensure excellent contact.

PCB Thermal Relief Pads

A thermal relief pad on a PCB connects a component to a large copper pour using narrow spokes. This design makes your soldering process significantly easier. Large copper planes absorb excess heat during reflow, which prevents solder from completely melting. These specialized pads solve this exact manufacturing problem.

How It Works

Thermal relief spokes reduce rapid heat conduction into the copper plane during your soldering process. It allows the pad to reach reflow temperatures much more quickly. You ensure the solder melts evenly and securely. After soldering, these spokes maintain a solid electrical connection. You can still count on them for reliable thermal transfer.

When to Use

Using thermal relief pads can help avoid cold joints or tombstoning of components during manufacturing. They prevent uneven heating during standard board assembly. Apply them in these specific situations.

• Through-hole component pads are connected to your power or ground planes.
• PCB assemblies using automated wave soldering technology.
• Any boards requiring manual hand soldering.

When Not to Use

You must avoid thermal reliefs when your design requires maximum heat dissipation or unrestricted current flow. The thin spokes introduce unnecessary electrical resistance. Avoid them in these specific applications.

• High-current or low-impedance electrical circuit paths.
• Sensitive RF circuits, which speak inductance, modify high-frequency performance.
• Power devices that use solid copper pours as main heatsinks.

FAQs

Are Thermal Pads Better Than Thermal Paste?

Thermal pads are good for consistent assembly and excellent electrical insulation. Thermal paste provides marginally superior cooling performance when the surfaces of your components are flat. You must choose based on whether you prioritize manufacturing convenience or absolute maximum heat transfer.

Can Thermal Pads Be Reused?

You can sometimes reuse thermal pads if they are in perfect condition after removal. However, we highly recommend replacing them with fresh materials. By installing a new gap filler on reassembly, you’ll ensure consistent and reliable heat transfer.

Why Is It Hard to Solder Pads Tied to a Ground Plane?

Soldering requires a higher temperature because the large copper plane draws heat away from your iron like a heat sink. Thermal relief pads should be used to fix the problem. Their narrow spokes restrict the heat flow, helping your pad maintain the proper melting temperature.

Final Thoughts

Selecting the right material in the thermal pad vs thermal paste comparison guarantees reliable cooling for your high-density boards. At PCBMay, our factory is equipped with 8 advanced SMT and THT production lines. PCBMay’s experienced team accurately applies your chosen thermal paste or thermal pads with full finished-board inspection.

If you are looking for a professional and dependable supplier, please send us your project today for a free DFM check and a quick quote.