A heat sink only works if heat can get into it. Thermally conductive epoxy bonds the component to the sink and carries heat across the joint at the same time, replacing both a fastener and a separate thermal interface material with one cured layer.
What Thermally Conductive Epoxy Is
Thermally conductive epoxy is a two-part or one-part epoxy loaded with a conductive filler. The epoxy provides structural adhesion and chemical resistance; the filler moves heat. Filler choice sets the two properties that matter most:
- Alumina and aluminum: moderate thermal conductivity, roughly 0.6 to 1.5 W/mK for alumina-filled grades, at reasonable cost.
- Aluminum nitride and boron nitride: higher conductivity while staying electrically insulating.
- Silver: the highest conductivity, but electrically conductive, so it is used only where the joint should also carry current or ground.
Real Incure Grades
The Incure Epo-Weld thermally conductive epoxy line covers the common cases:
- TC-9033 and TC-9042: aluminum-filled grades for efficient heat transfer in structural bonding. They are formulated for thermal conduction; they do not carry an electrical-insulation rating, so keep them off exposed conductors.
- TC-9051: aluminum-nitride-filled, thermally conductive and electrically insulating, for bonding a component directly to a sink where dielectric isolation is required.
Email Us with your device, heat sink material, and whether the joint must be electrically isolated, and our team will point to a grade.
Why Use It Instead of Grease or a Pad
- Structural: the cured bond holds the component in place, so no clip, screw, or spring is needed.
- Thin, stable bond line: cure locks the geometry; there is no pump-out over thermal cycles the way there is with grease.
- Gap filling: fills uneven or non-flat interfaces that a rigid pad bridges over.
- Permanent: the trade-off is that a cured epoxy joint is not reworkable, so grease or a pad is the better choice where the component may be replaced.
Design Considerations
Keep the bond line as thin as the surface flatness allows; a thicker glue line adds thermal resistance no matter how conductive the epoxy is. Control it with spacer beads or a fixture. Because the component, the epoxy, and the sink expand at different rates, thermal cycling shears the bond edge, which is the failure path described in how CTE mismatch causes adhesive bond failure; a slightly more flexible grade or a filleted edge reduces the stress. Follow the specified cure schedule, since an under-cured epoxy has lower conductivity and strength than the datasheet value.
Cure Schedule and Its Effect on Properties
An epoxy’s thermal conductivity, strength, and glass transition temperature are all reported for a fully cured sample. Cut the cure short and every one of those numbers drops. A room-temperature cure reaches usable strength in hours but may take a week to fully crosslink, and the conductivity in the meantime is lower than spec. A heat cure, for example 80 to 150°C for 30 to 120 minutes, completes the network quickly and often yields a higher glass transition temperature and better retention of properties at elevated service temperature. Confirm the entire bond line, including the center of a large area, reaches and holds cure temperature; a fixture that heats only the perimeter leaves an under-cured core.
Dispensing and Bond-Line Control
Filled epoxies are abrasive and often thixotropic, so use wear-resistant dispensing tips and size the needle for the filler particle size to avoid clogging. For repeatable bond-line thickness, mix in a small fraction of glass or polymer spacer beads of the target diameter, or design a mechanical stop into the parts. Degas the mixed adhesive or use a static-mixed cartridge system to keep entrained air, which is an insulator, out of the joint. A single trapped void a millimeter across under a small die can raise its temperature by several degrees, so voiding is worth checking with an acoustic scan or a cross-section during process qualification.
Applications
Thermally conductive epoxy bonds heat sinks to power transistors, IGBTs, and MOSFETs in motor drives and inverters; attaches LED arrays to metal-core boards and extrusions; mounts sensors and control electronics in automotive and rail modules; and stakes components in consumer electronics where space rules out a mechanical clip. For high-temperature surface protection on metal or ceramic parts, an Epo-Weld HECC high-emissive ceramic coating addresses a different need. Where the joint is structural first and thermal second, UV glue versus epoxy for heavy-duty repairs compares the options.
Closing
Thermally conductive epoxy combines a structural bond with a defined heat path, which simplifies the assembly and removes the pump-out risk of grease. Match the filler to the electrical requirement, keep the bond line thin, and cure it fully. Contact Our Team to select a grade for your thermal design.
Visit www.incurelab.com for more information.