First, think carefully: What is this piece of graphite for?
The logic of thickness and density is completely opposite for different purposes:
| Usage | Main demand | Thickness orientation | Density orientation |
| Electronic heat dissipation (phone/chip/battery module all heat up) | Horizontal thermal conductivity, lightweight, and curved surface adhesion | Ultra thin 0.03-0.2 mm | Medium 1.0-1.4 g/cm ³ |
| Industrial sealing (flange/valve gasket) | Compression rebound, filling gaps, leak prevention | Thickening by 0.5-3.0 mm | Medium to low 0.8-1.3 g/cm ³ (pure flexible graphite) |
| Thermal management of battery pack | Uniform heating+buffering+slight insulation | 0.1–0.5 mm | 1.0–1.2 g/cm³ |
| Fuel cell bipolar plate | Conductive, airtight, and strong | 1.5-3 mm (can be as thin as 0.8mm for automotive use) | High density 1.78-1.90 g/cm ³ |
| Semiconductor thermal field/crucible holder | High temperature resistance, low impurities, and no deformation | 10-50mm or more (block/board) | Isostatic pressure 1.78-1.88 g/cm ³ |
| Military/Aerospace Thermal Shielding | Low emission, high purity, anisotropy | 0.03-0.1 mm or composite structure | 1.1–1.5 g/cm³, Ash content ppm level |
How to choose thickness: thinner is not better, nor thicker is more stable
1. Ultra thin (0.02-0.1mm)
- Scenario: Consumer electronics, chip homogenization, electromagnetic shielding, military thin layer thermal conductivity
- Advantages: Space saving, good adhesion, and full utilization of in-plane thermal conductivity
- Disadvantages: low strength, easy to break, weak vertical thermal conductivity, difficult to make thick backing adhesive
- Experience: 0.03mm is extremely difficult to achieve stable mass production; 0.05mm is a military/high-end electronic dessert; 0.1mm is the most universal
2. Thin to medium thick (0.1-0.5 mm)
- Scenario: Battery module heat pad, frequency converter LED, power module
- Advantages: Balancing thermal conductivity and certain buffering, it can be die cut with adhesive backing
- Experience: Battery packs commonly use 0.1-0.2mm; industrial heat dissipation 0.3-0.5mm
3. Thickening (0.5-3 mm)
- Scenario: Flange gasket, valve seal, heat exchanger, insulation sealing layer
- Advantages: Large compression capacity, able to fill flange unevenness, good rebound
- Experience:
Pure flexible graphite seal: 0.8-1.5mm most commonly used
High pressure flange: 1.5-3mm or composite metal toothed gasket
Adhesive backed graphite tape: Be cautious when making over 1.5mm, and it is recommended to weave/composite structures for 3mm
4. Thick plates (≥ 3 mm, even tens of mm)
- Scenario: Bipolar plate, semiconductor thermal field, EDM electrode, crucible
- It's not the concept of "graphite sheet", it's the precision machining of "graphite plate/block"
How to choose density: High density ≠ universal, low density is also useful
Flexible graphite sheet (naturally expanded and rolled)
| Density interval | Behavioral characteristics | Suitable scenarios |
| 0.7–0.9 g/cm³ | Soft, with large compression space and easy deformation | Low pressure seal, old flange, irregular joint filling |
| 1.0–1.3 g/cm³ | Universal range, flexibility+thermal conductivity balance | Sealing gasket, battery equalization, back tape |
| 1.3–1.6 g/cm³ | Tighter, higher strength, and smaller compression margin | High pressure sealing, requiring impregnation/composite reinforcement |
| >1.6 g/cm³ | Approaching artificial graphite/highly oriented film | High thermal conductivity heat dissipation film, special military thermal conductivity |
Isostatic pressure/artificial high-purity graphite board
- Conventional: 1.75-1.85 g/cm ³ (EDM, thermal field)
- Bipolar plate/semiconductor: 1.78-1.90 g/cm ³, even 1.95
- For every increase in density, the resistivity decreases and the strength increases, but the processing cost jumps
Thickness x Density Combination Decision Table
Scenario A: The battery module is uniformly heated
- Thickness: 0.1-0.2 mm (space tightness can reach 0.05mm)
- Density: 1.0-1.2 g/cm ³
- Requirements: in-plane thermal conductivity ≥ 300 W/m · K, vertical conductivity ≥ 8 W/m · K, sulfur content ≤ 50ppm, adhesive backing is acceptable
Scenario B: Flange sealing gasket
- Thickness: 1.0-1.5 mm (high pressure can be 2mm)
- Density: 1.0-1.2 g/cm ³ (pure flexibility); The overall density of the composite metal toothed pad is calculated separately
- Requirements: Compression ratio of 30-50%, rebound ≥ 15-20%, ash content ≤ 2%, low sulfur and low chlorine
Scenario C: Military thermal shielding
- Thickness: 0.05-0.1mm (multi-layer composite can reach 0.3mm)
- Density: 1.1-1.4 g/cm ³
- Requirements: High purity low exhaust gas (TML/CVCM), halogen-free RoHS, Ash content ppm level, batch traceability
Scenario D: Fuel Cell Bipolar Plate
- Thickness: 1.5-2.5 mm (vehicle thin 0.8-1.5mm)
- Density: 1.78-1.90 g/cm ³
- Requirements: resistivity ≤ 10-12 μ Ω· m, ash content ≤ 50ppm, CNC channel ± 0.02mm, helium leak detection
Scenario E: Semiconductor Thermal Field Chip/Board
- Thickness: 10-50mm (raw material before machining)
- Density: 1.80-1.88 g/cm ³
- Requirement: Ash content ≤ 5-20ppm, Fe/Ni/Cu/B single element control, CTE 3.5-4.5 × 10 ⁻⁶/K
Common selection misconceptions
❌ If the thermal conductivity is good, choose the thinnest one
→ Too thin without longitudinal heat conduction, it is also easy to break, and when the heat source is concentrated, it becomes even hotter.
❌ Once sealed, choose the highest density
→ High density sheets are hard and have poor rebound, and old/deformed flanges may leak.
❌ High density=high purity
→ Density and purity are two different things. Military/semiconductor industries look at ash content and element scanning, not just g/cm ³.
❌ The thickness is arbitrary, just stick the adhesive on the back
→ 3mm pure flexible graphite backing adhesive may collapse, roll and break edges, and must be woven/compounded.
End
Choose graphite sheet thickness:
The heat dissipation should be thin (0.05-0.2mm), the sealing should be thick (0.8-2mm), and the structure should be flat (≥ 3mm).
Select density:
Medium density for heat dissipation (1.0-1.4), medium low density for sealing (0.8-1.3), high-density for bipolar plates/semiconductors (1.78-1.90).
Always remember: first look at the working conditions, then set the parameters, and finally negotiate the price.
