One. The working principle of vinyl-terminated silicone oil in thermal conductive potting adhesive
Vinyl-terminated silicone oil is the base polymer of silicone thermal conductive potting compound. Both ends of its molecular chain contain vinyl functional groups (-CH=CH₂). This special structure determines the key performance of the potting compound.
1. Cross-linking Reaction Principle
Vinyl-terminated silicone oil cross-links with hydrogen-containing silicone oil via a hydrosilylation reaction:
Reaction formula:
Vi-PDMS-Vi + H-PDMS-H → Three-dimensional cross-linked network (Vi: vinyl group, PDMS: polydimethylsiloxane, H: hydrogen group)
Under the action of platinum catalyst, vinyl reacts with silicon-hydrogen bonds to form stable Si-C bonds and construct a three-dimensional network structure, which is the chemical basis for the curing of potting compound.
2. Principle of Heat Resistance
The Si-C bonds and Si-O-Si backbone formed by vinyl-terminated silicone oil have very high bond energies:
Si-O bond energy: 451 kJ/mol, significantly higher than the C-C bond (347 kJ/mol).
Si-C bond energy: 318 kJ/mol, resulting in excellent thermal stability.
The flexible molecular chain and low thermal expansion coefficient ensure stable performance over a wide temperature range of -50°C to 250°C.
3. Achieving Thermal Conductivity
Vinyl-terminated silicone oil itself has poor thermal conductivity, but it can serve as a "molecular backbone" to support a high proportion of thermally conductive fillers.
Key Point: Vinyl-terminated silicone oil has excellent compatibility with thermally conductive fillers (such as alumina and boron nitride), forming a composite system with low interfacial thermal resistance, achieving efficient heat transfer.
By optimizing the vinyl content and molecular weight distribution, the filler loading capacity can be increased, forming a continuous thermally conductive network.
TWO. Viscosity Selection Guide for Di-Terminated Vinyl Silicone Oil
The viscosity of vinyl-terminated silicone oil directly affects the construction performance and final performance of the potting compound, so choosing the appropriate viscosity is crucial.
| Viscosity Range (mPa·s) | Features | Applications | Precautions |
| 100-1,000 | Excellent fluidity and strong permeability | Delicate electronic components, narrow gap filling | Filler prone to settling, requiring controlled curing time |
| 1,000-5,000 | Good fluidity and easy handling | General electronic modules, sensor packaging | Balanced fluidity and anti-settling properties |
| 5,000-20,000 | Medium viscosity, highly versatile | Power modules, automotive electronics | Suitable for most potting applications |
| 20,000-50,000 | High viscosity, excellent sag resistance | Vertical potting, partial filling | May require specialized potting equipment |
| 50,000 and above |
Paste-like, excellent shape retention | Thermal gasket replacement, dispensing applications | Poor fluidity, unsuitable for complex structures |
Key selection parameters for vinyl-terminated silicone oil
1. Vinyl content affects crosslink density and cured hardness. A high vinyl content provides a higher crosslink density but may result in brittle material.
2. A narrow molecular weight distribution provides more consistent properties, while a wide distribution may improve processability but affect performance stability.
3. Low volatile content reduces cure shrinkage and air bubbles, improving product reliability.
4. Purity and Impurities: High-purity products ensure complete cure, avoiding catalyst poisoning and performance degradation.
Three. Application Scenarios and Selection Recommendations
1. High-Power Electronic Devices
Applications: High-power LEDs, power modules, and new energy vehicle electronic control systems
Selection Recommendation: Choose a product with a medium viscosity (5,000-20,000 mPa·s) and a moderate vinyl content to ensure good thermal conductivity and flowability.
2. Precision Electronic Components
Applications: Sensors, microelectronic modules, precision circuits
Selection Recommendation: Choose a product with low viscosity (1,000-5,000 mPa·s) and low volatility to ensure complete penetration and stress-free encapsulation.
3. High-Temperature Applications
Applications: Engine controllers, industrial heating equipment
Selection Recommendation: Choose products with high vinyl content and high molecular weight to improve crosslink density and thermal stability.
4. Rapid Production Applications
Applications: Consumer electronics, high-volume production products
Selection Recommendation: Choose products with moderate reactivity and long working time to balance production efficiency and cure speed.
