How to Replace Thermal Pads with Thermal Paste

Thermal pads and thermal pastes are commonly used in electronics, power modules and high-performance computing devices to facilitate heat transfer. However, swapping pads for paste presents a thermal and manufacturing challenge to electrical manufacturers, designers and sourcing teams.

This guide covers the compatibility considerations, process, and factors to consider when making the switch.

Thermal Pad vs Thermal Paste: Quick Comparison

Step 1: Decide If Thermal Paste Is an Appropriate Replacement

· Measure the Gap Between the Chip and Heatsink

The clearance between the semiconductor package and heatsink should be measured after assembly when changing a thermal pad for paste. This gap determines whether a sufficient amount of heat may be able to pass through the thermal paste, or whether a gap filling material will be required to complete the thermal path.

Measure the distance using feeler gauges, pressure sensitive films, laser displacement sensors or coordinate measuring machines (CMMs).

· Check the Original Thermal Pad Thickness

The original thickness of the thermal pad is often the reason for a pad being used instead of paste. The thickness of standard silicone thermal pads are 0.5 mm-5 mm, and custom-made can be more than 10 mm for special applications.

For example, if a 2 mm thermal pad is replaced with paste without redesigning the mounting system there will be a gap that cannot be filled with thermal paste. Although the paste may be good for conductivity, the thermal resistance will be much greater because of the thicker bond line.

· Verify Mounting Pressure

Mount pressure determines how effective the spreading of the thermal paste is on the surfaces. Too little pressure would result in a paste that is too thick, while too much pressure would break the ceramic packaging, or bend the PCBs or create defects in solder joints.

· Evaluate Component Power Density

Power density is the heat produced over the surface area of a component. For higher power devices such as AI processors, IGBTs and power modules, heat transfer must be handled effectively to guarantee safe junction temperatures above 50-100 W/cm².

High power devices that have direct heatsink contact use the thermal paste to reduce the thermal resistance as it forms a thin bond line.

· Determine the Heat Load

Calculate the maximum heat generated in normal and peak operating condition. The heat load is measured in watts (W) and is the indicator that checks if the current thermal interface material is adequate to dissipate the heat. As a rule, products having high heat loads require low interface thermal resistance.

· Check if the Heatsink is Directly in Contact

Once heatsink is installed, verify that there is complete contact. During prototype testing, contact can be verified by using pressure indicating film, contact imprint analysis or thermal imaging.

Step 2: Tools and Materials You Need

These tools and materials are used for accurate dispensing, consistent assembly and accurate inspection processes resulting in a higher first pass yield, less material wastage and a consistent thermal performance for each production batch.

· Dispensing Equipment

Automatically dispenses paste volumes, with precision of ±3 to ±5%, suitable for minimizing material waste, assisting automated production lines and ensuring uniform bond line thickness.

· Thickness Gauge

Checks assembly tolerances and measures gaps between interfaces before production to help ensure that thermal paste fits mechanical design and to prevent costly assembly mistakes.

· Torque Screwdriver

Delivers a controlled tightening torque for uniform pressure during mounting.

· ESD Workstation

Protects electrostatic sensitive components during assembly, helping to reduce latent component failures, improve manufacturing yield and ensure reliable high volume electronic production.

Step 3: Power Down and Disassemble the Device

Before touching the assembly, unplug power sources and remove stored power before removing the thermal interface material. Move the product to an ESD protected workstation to prevent electrostatic damage. When disassembling, loosen the heatsink screws in a cross pattern. This evenly distributes clamping force and reduces mechanical stress on the PCB.

Step 4: Remove the Existing Thermal Pad

Remove the thermal pad carefully so as not to damage the semiconductor package or scratch the heatsink. Look for uneven compression, tearing, hardening or residue in the removed pad. These signs may relate to defects in the thickness of the pad, the pressure applied and issues with the surface which should be addressed prior to using the thermal paste.

Step 5: Clean the Contact Surfaces

Surface preparation has an impact on heat transfer. Even good thermal paste will lose its efficiency if there is old thermal compound, silicone residue, oil or oxidation on the contact surfaces. Use 99% isopropyl alcohol (IPA) and lint free wipes to clean both the heatsink and semiconductor package.

Step 6: Apply Thermal Paste Correctly

· How much Paste to Use

Use sufficient amount of paste for a bond line thickness of 20-100 μm after compression. Too much of paste contributes to high thermal resistance and contaminates adjacent parts.

· Common Application Methods

Pea size

Ideal for square processors and small packages. The pressure exerted on mounting distributes the paste uniformly with minimal trapped air and complex dispensing.

Small Line

Suitable for rectangular processors or for elongated power modules. The line is located along the longest dimension and enhances distribution of paste during heatsink installation.

X-pattern

It is recommended for High Power and Larger processors. The pattern provides better surface coverage and minimises the chances of incomplete contact around the corners.

Step 7: Reinstall the Heatsink

Carefully place the heatsink on the component but be careful not to move it too much over the thermal paste. Too much movement can cause air bubbles and create irregular bond line. Once assembled, check the alignment of the heatsink and check the mounting hardware position.

Step 8: Test Whether Replacing the Thermal Pad with Thermal Paste Worked

· Thermal Cycling

Perform multiple heating and cooling cycles within the operating temperature ranges, for example from −40°C to 125°C to assess the stability of the paste.

· Benchmark Loads

Run under controlled loads and measure the junction and heatsink temperatures.

· Infrared Inspection

With infrared thermal imaging, locate localized hot spots, unequal heat distribution, or insufficient heatsink contact, which a standard temperature sensor might not be able to detect.

Compare Temperatures Before and After Replacement

Determine the junction temperature, case temperature and heatsink temperature under the same ambient condition. An effective replacement should achieve uniform temperature reductions and not create assembly or reliability problems.

FAQs

Can thermal paste completely replace a thermal pad?

The thermal paste is only effective when heatsink makes almost direct contact with the component. For designs that need gap filling above 0.2 mm, the thermal pad is the optimal option.

What will happen if the gap is too wide?

A big gap results in air pockets because thermal paste cannot keep sufficient thickness. This will increase the thermal resistance, raise the junction temperature, and can also lower the long term product reliability and service life.

Are thermal pastes better than thermal pads?

Not always. Typically, thermal paste conducts heat more effectively due to a thinner bond line. Thermal pads are more effective when components are not of consistent height, there is more space between components or there is limited mounting force.

When should the thermal paste be changed?

The lifespan of most industrial thermal pastes ranges from 3 to 10 years, depending on the thermal cycling, operating temperature and environment.

When is replacing a thermal pad with thermal paste not recommended?

Do not replace if gaps between parts exceeds 0.2 mm, parts height is uneven, mounting pressure is low, vibration prone environment, or the design needs the pad to compensate for the mechanical tolerance.

What are the common mistakes when replacing thermal pads with paste?

Typical errors involve neglecting the gap, applying too much paste, applying the wrong amount of torque, not cleaning the surface, and replacing thermal pads without checking the mechanical design.

What are the advantages of replacing thermal pads with thermal paste?

Thermal paste can, when the design allows for direct contact, decrease interface thermal resistance, enhance heat dissipation, lower operating temperature and assist high-power components in achieving better long-term operation stability.

Final Thoughts

Deciding to replace thermal pads with thermal paste requires careful analysis of heat dissipation characteristics of a system. Therefore, it is a decision that must be arrived at by specialists.

At Gallop, our engineers will carefully evaluate and then recommend a perfect heat management strategy. For all thermal interface materials, Gallop is a partner you can trust in China – Get a quote now.