Why can graphite sheets dissipate heat?
Graphite is an anisotropic material:
- In plane thermal conductivity (XY direction): 300-1950 W/m · K (natural graphite 300-600, synthetic graphite 700-1950)
- Vertical thermal conductivity (through plane, Z direction): only 5-15 W/m · K
Core logic: Graphite sheets do not "take away" heat, but "spread out" hot spots - allowing the heat from the heat source to quickly spread horizontally, and then evenly dissipate it with the radiator or chassis.
Two main types of graphite sheets: natural vs synthetic
| Parameter | Natural graphite sheet | Synthetic graphite sheet |
| Raw material | Natural flake graphite expansion and rolling | Polyimide (PI) high-temperature carbonization |
| In-plane thermal conductivity | 300–600 W/m·K | 700–1950 W/m·K |
| Thickness range | 0.03–0.5 mm | 0.012–0.1 mm |
| Density | 1.0–1.8 g/cm³ | 1.5–2.0 g/cm³ |
| Flexibility | Good, bendable | More brittle, requiring a large bending radius |
| Cost | low | High |
| Typical scenario | Electric heating bed LED, Industrial uniform heat | Mobile phones, ultra-thin laptops, 5G modules |
Key parameters
1. In-plane Thermal Conductivity
- Determine the heat dissipation capacity, unit W/m · K
- Testing standard: ASTM D5470/ISO 22007-2
2. Through-plane
- Determine whether heat can pass through the graphite sheet and reach the radiator
- Natural graphite is typically 5-8 W/m · K, while synthetic graphite is 10-15 W/m · K
- Attention: Graphite sheets are not thermal pads and cannot be used to fill gaps
3. Thickness
- Thinner is more suitable for narrow spaces, but with smaller heat capacity
- 0.05 mm is suitable for mobile phones; 0.1-0.2 mm is suitable for LED/power modules; Suitable for industrial uniform heating above 0.5 mm
4. Density
- Natural graphite 1.0-1.8 g/cm ³
- The higher the density, the better the thermal conductivity, toughness, and temperature resistance
- Recommended sealing condition: 1.2-1.4 g/cm ³; Recommendation for electronic heat dissipation: 1.5-1.8 g/cm ³
5. Electrical insulation
- Pure graphite is conductive and cannot be directly attached to PCB wiring
- Insulation is required → Choose PI/PET coated graphite sheet or add insulation isolation layer
- Dielectric strength: PI coating can reach 100 kV/mm
Quick investigation of application scenarios
| Application | Recommended thickness | Recommended thermal conductivity | Do you need insulation | Adhesive backing |
| Mobile SoC is uniformly hot | 0.03–0.05mm | ≥1000 W/m·K(synthesis) | Yes (PI coated) | Acrylic acid PSA |
| LED luminaire | 0.1–0.2mm | 400–600 W/m·K(natural) | View layout | Acrylic/Silicone |
| 5G base station/module | 0.05–0.1mm | ≥700 W/m·K | Yes | Silicone PSA |
| IGBT/power module | 0.2–0.5mm | 400–600 W/m·K | Yes | Silicone PSA |
| Electric bed/tatami | 0.1–0.2mm | 300–500 W/m·K | No | Silicone PSA |
| Notebook/Tablet | 0.012–0.05mm | ≥1500 W/m·K(synthesis) | Yes | Acrylic acid PSA |
Summary
Graphite sheet is a "heat spreader" for electronic heat dissipation, not a "heat sink".
The selection first depends on the thermal conductivity requirements (natural ≤ 600/synthetic ≥ 700), then determines the thickness, insulation, and backing adhesive, and finally concludes with die-cutting accuracy and reliability testing.
Remember: Only when the hot spot temperature drops can it be considered truly useful.
