Thermal Conductive Adhesive - how to cool components right?
Thermally conductive adhesives bond heat sinks and power components mechanically while carrying heat away. This guide explains selection by thermal conductivity (W/mK), electrical isolation, bondline thickness and the right cure and handling.
View thermal adhesivesWhat defines a thermal conductive adhesive?
A thermal conductive adhesive is a filled glue, usually epoxy or silicone based, that moves heat from power components into the heat sink while bonding both parts permanently. The key figure is thermal conductivity in W/mK: standard electronics adhesives sit at 0.5 to 2 W/mK, highly filled grades reach 3 to 10 W/mK.
Heat travels through ceramic fillers such as aluminium oxide, boron nitride or aluminium nitride. Metal-filled adhesives (silver) conduct best but are electrically conductive, so they only suit defined contact points.
Isolate or conduct - which type fits?
The first decision is the electrical behaviour. If the adhesive must keep both parts electrically separate, for example a transistor case against a grounded heat sink, choose an electrically isolating adhesive with a volume resistivity above 10¹² Ω·cm and adequate dielectric strength.
- Isolating (Al₂O₃, boron nitride): separates electrically, ideal for TO packages on a grounded heat sink.
- Conductive (silver filled): lowest thermal resistance, but electrically live - only where contact is wanted.
- Silicone based: flexible, good for large temperature swings and mismatched expansion coefficients.
- Epoxy based: high strength and chemical resistance, but stiffer.
How do you get a thin, void-free joint?
Even the best adhesive fails with poor handling. Clean both surfaces grease-free, apply a thin even layer and join under light pressure so the bondline stays thin and void-free. Trapped air acts as an insulator and clearly worsens cooling.
One-component adhesives (1K) cure at room temperature or under heat, are easy to dispense and suit small runs. Two-component systems (2K) reach higher strength and faster cure but need an exact mix ratio and pot-life control.
- Clean surfaces with isopropanol and let them flash off fully.
- Choose dot or bead application so the whole area wets out on joining.
- Fixture until handling strength is reached (clip, spring, jig).
- Follow the maker's data on pot life, cure time and temperature.
- Ramp heat cures gradually to avoid stress and voids.
Frequently asked questions
Thermal adhesive or thermal paste - what is the difference?
Paste only makes the thermal contact and needs a separate mechanical fixing. Adhesive also bonds the parts permanently, replacing a screw or clip, but it cannot be removed without damage.
How much W/mK do I need?
Simple applications get by with 0.5 to 1 W/mK. Power semiconductors, LED modules or power supplies benefit from 2 to 3 W/mK, more at very high losses. A thin, void-free joint matters just as much.
Must the adhesive be electrically isolating?
Only if the bonded parts must stay separated, such as a live case on a grounded heat sink. Then you need an isolating grade. Silver-filled adhesives conduct current and must not be used there.
How thick should the adhesive layer be?
As thin as possible, typically 50 to 150 µm. Every extra micron raises the thermal resistance. A thin, even, void-free joint often matters more than a high W/mK figure.
Looking for the right thermal adhesive?
We stock isolating and conductive thermal adhesives on epoxy and silicone base - from 1 to over 5 W/mK, as 1K and 2K systems.
Wide range
Adhesives from 0.5 to over 5 W/mK for any heat load.
Isolating grades
Electrically separating types for grounded heat sinks.
Datasheet checked
W/mK, CTE and temperature range clearly documented.
Expert advice
Our specialists help you choose the right grade.