Thermal Adhesive: Bond Heat Sinks Without Screws

Thermal adhesive bonds heat sinks to components permanently without screws, clips, or mechanical fasteners. It combines the heat transfer of thermal paste with the bonding strength of an adhesive — ideal for small heat sinks on SMD components, LED modules, and Raspberry Pi chips. This guide covers types, application, and when to use thermal adhesive vs other thermal interface materials.

What Is Thermal Adhesive?

Thermal adhesive is a two-part or single-part compound that cures to form a permanent bond between two surfaces while providing a thermal path. Unlike thermal paste (which is non-curing and requires mechanical clamping), thermal adhesive holds the heat sink in place without any additional hardware.

Thermal conductivity: 1-3 W/m·K for standard epoxy adhesives. This is lower than thermal paste (4-8 W/m·K) because the adhesive must be thicker to provide bonding strength. However, for small heat sinks on low-power components, this is more than adequate.

Types of Thermal Adhesive

• Two-part epoxy (thermal epoxy): Mix resin and hardener, apply, and cure in 2-24 hours. Permanent bond. Thermal conductivity: 1-3 W/m·K. Best for permanent installations.
• Thermal adhesive tape (pre-cut): Double-sided adhesive with thermally conductive filler. Peel and stick. The most common — found on Raspberry Pi heat sinks and LED star PCBs. Thermal conductivity: 0.8-2 W/m·K.
• Silicone-based thermal adhesive: Flexible, vibration-resistant. Lower strength than epoxy but can be peeled off for replacement. Good for automotive and vibration-prone applications.
• Cyanoacrylate (thermal super glue): Fast cure (seconds). Brittle. Not recommended for thermal applications above 80°C as it degrades.

When to Use Thermal Adhesive

• Small heat sinks on SMD components: No room for screws or clips. Adhesive tape or epoxy is the only practical mounting method.
• Raspberry Pi heat sinks: Pre-applied thermal tape is standard. Quick, clean, and adequate for the Pi’s power levels.
• LED star PCBs: Bond the star PCB to the heat sink with thermal epoxy for a permanent, reliable thermal path.
• TO-220 packages in vibration environments: When screws might loosen, supplement with thermal adhesive.
• Prototype assemblies: Quick heat sink attachment during testing and prototyping.

Application Technique

For thermal tape:

1. Clean both surfaces with IPA (isopropyl alcohol)
2. Peel protective film from one side of the tape
3. Apply to the heat sink base
4. Peel the other protective film
5. Press the heat sink firmly onto the component for 10-15 seconds

For thermal epoxy:

1. Clean both surfaces with IPA
2. Mix equal parts of resin and hardener on a disposable surface
3. Apply a thin layer to both surfaces
4. Press together firmly, align, and hold or clamp for cure time
5. Cure time: typically 5 minutes for initial set, 24 hours for full strength

Important: Less is more. A thinner adhesive layer has lower thermal resistance. Apply just enough to wet both surfaces completely.

Thermal Adhesive vs Thermal Paste vs Tape

Removing Thermal Adhesive

Removing cured thermal epoxy is difficult:

• Heat method: Apply 150-200°C with a heat gun for 1-2 minutes. The adhesive softens enough to pry the heat sink off with a plastic tool. Be careful not to damage the component.
• Solvent method: Acetone (nail polish remover) softens many epoxy adhesives over several hours. Soak and pry gently.
• Mechanical method: Twist gently while pulling. The bond may break at the weaker interface. Clean residue with IPA.

Thermal tape is easier to remove: gently pry with a plastic spudger. Clean residue with IPA.

Recommended Products

Best Practices

• Use thermal adhesive only when mechanical mounting is impractical
• For power above 3W, prefer thermal paste with mechanical mounting for better thermal performance
• Clean surfaces thoroughly before bonding — contamination weakens the bond and increases thermal resistance
• Apply minimum thickness for best thermal performance
• Allow full cure time before powering on the circuit