Thermal Interface Materials (TIMs) for Heatsinks
Types · Capabilities · Benefits · Applications
5
Why TIMs matter (quick reality check)
No matter how flat a heatsink and device look, microscopic air gaps exist. Air is a terrible thermal conductor.
TIMs replace trapped air with a material that conducts heat efficiently from:
- IC / power device → heatsink
- Cold plate → power module
- PCB component → chassis
1. Thermal Grease / Thermal Paste
(Silicone or non-silicone based)
Capabilities
- Thermal conductivity: ~3 to 12 W/m·K (some higher-end pastes exceed this)
- Very thin bond line (excellent contact)
- Handles surface roughness well
Benefits
- Best all-around thermal performance for the cost
- Low thermal resistance
- Easy to apply (manual or automated)
Limitations
- Can pump out over thermal cycling
- Messy, not structural
- Not ideal for vertical or high-shock environments
Typical Applications
- CPUs, GPUs
- Power transistors (TO-247, TO-220)
- Prototyping and lab validation
Verdict
👉 Best performance, lowest cost, lowest mechanical stability.
2. Thermal Pads (Gap Pads / Elastomer Pads)
Capabilities
- Thermal conductivity: ~1 to 8 W/m·K (advanced pads up to ~12)
- Thickness: 0.25 mm to 5+ mm
- Compressible (fills gaps)
Benefits
- Clean, consistent, reworkable
- Electrically insulating
- Absorbs tolerance stack-ups
Limitations
- Higher thermal resistance than grease
- Compression force matters
- Can age/harden over time
Typical Applications
- Power electronics
- LED modules
- Telecom and industrial electronics
- High-volume manufacturing
Verdict
👉 Best balance of performance, manufacturability, and reliability.
3. Phase Change Materials (PCM)
Capabilities
- Solid at room temperature, flows at ~50–65 °C
- Thermal conductivity: ~2 to 6 W/m·K
- Thin bond line after phase change
Benefits
- Clean handling (no mess during assembly)
- Low pump-out compared to grease
- Consistent performance over time
Limitations
- Requires operating temperature to activate
- Not ideal for low-power devices
- Slightly higher cost than grease
Typical Applications
- CPUs in OEM systems
- Automotive electronics
- Long-life industrial products
Verdict
👉 Grease-like performance with better long-term stability.
4. Thermally Conductive Adhesives (Epoxy / Acrylic / Silicone)
Capabilities
- Thermal conductivity: ~1 to 4 W/m·K
- Structural bonding + heat transfer
- Permanent attachment
Benefits
- Eliminates clips, screws, fasteners
- Vibration-resistant
- Good for compact designs
Limitations
- Permanent (no rework)
- Lower thermal performance than grease/pads
- Cure time affects manufacturing flow
Typical Applications
- LED lighting
- Small electronics
- Cost-sensitive consumer devices
Verdict
👉 When mechanical attachment matters more than peak thermal performance.
5. Liquid Metal TIMs (Advanced / Niche)
Capabilities
- Thermal conductivity: 20–70+ W/m·K
- Ultra-low thermal resistance
Benefits
- Best thermal performance available
- Ideal for extreme heat flux
Limitations
- Electrically conductive (risk!)
- Corrosive to aluminum
- Hard to handle, not production-friendly
Typical Applications
- Enthusiast CPUs
- Aerospace / specialty R&D
- Not recommended for standard heatsinks
Verdict
👉 Amazing performance, terrible manufacturability.
Quick Selection Guide
| Application | Best TIM Choice |
| CPU / GPU | Thermal grease or PCM |
| Power electronics | Thermal pads |
| LEDs | Adhesive or pads |
| Automotive | PCM or high-reliability pads |
| Prototyping | Thermal grease |
| High vibration | Pads or adhesive |
Practical Engineering Advice (real-world)
- Flat surfaces + controlled pressure → grease or PCM
- Tolerance stack-ups → pads
- High volume manufacturing → pads or PCM
- Field reliability > peak performance → avoid grease
