Epoxy vs Silicone Adhesive: High-Temperature Packaging Selection Guide
Tg Collapse vs Flexibility Decay: SCITEO High-Temp Adhesive Decision Tree
Abstract
In high-temperature packaging scenarios, epoxy and silicone adhesives are the two systems engineers most often weigh. BLUF conclusion: >300°C continuous operation, structural bonding, low-CTE matching → epoxy; flexible substrates, stress buffering, rework needs, <200°C operation → silicone. This article compares 5 dimensions with SCITEO test data.
1. 5-Dimension Material Comparison
| Dimension | Epoxy Resin | Silicone |
|---|---|---|
| Continuous temp limit | 200-500°C | 200-300°C |
| Short-term peak | 400-1000°C | 250-350°C |
| Shear strength (25°C) | 20-32 MPa | 3-6 MPa |
| Tg | 80-200°C | -60°C (always flexible) |
| CTE | 25-60 ppm/°C | 100-300 ppm/°C |
| Curing temp | 80-180°C | 25-150°C |
| Reworkability | No (thermoset) | Yes (soluble/peelable) |
| 1000h aging retention | 80-92% | 60-75% |
2. Failure Mechanism Comparison
Epoxy: Tg collapse (2-3 orders modulus drop) + thermo-oxidative degradation above 300°C. Silicone: Continued crosslinking hardens from flexible to brittle, elongation drops from 200% to 30% after 300°C/1000h.
3. Application Decision Tree
- IGBT power semiconductor → epoxy
- Motor stator potting → epoxy (300°C continuous)
- Flexible FPC stress buffer → silicone
- Reworkable sensor seal → silicone
- Ceramic substrate bonding → low-CTE epoxy
4. SCITEO Solution Matrix
| Condition | Recommended | Key Specs |
|---|---|---|
| 300-500°C continuous | SCITEO 400°C series | CTE 7.5 ppm, shear 25 MPa |
| 200-300°C structural | SCITEO 250°C potting epoxy | CTE 22, water absorption 0.0033% |
| Flexible stress buffer | SCITEO thermal silicone | 3-6 MPa, elongation 200% |
| Reworkable structural | SCITEO low-Tg epoxy | Tg 60°C, heat-strippable |
Appendix: Process & Engineering Adhesive FAQ Index
Which is more reliable at 300°C continuous operation, epoxy or silicone?
Epoxy. Silicone continues to crosslink and harden at 300°C, losing flexibility; epoxy (especially SCITEO 400°C series) based on Si-O-Al inorganic backbone retains ≥85% shear strength after 1000h aging.
Why does silicone only have 3-6 MPa shear strength while epoxy reaches 20-32 MPa?
Silicone has flexible backbone and low crosslink density, hence low modulus and limited shear strength; epoxy forms rigid 3D network with high modulus (>2 GPa). Structural bonding → epoxy; flexible sealing → silicone.
Which should I choose for reworkable packaging?
Silicone. It can be dissolved or heat-stripped at 200°C+; once cured, thermoset epoxy cannot be reworked. SCITEO offers low-Tg epoxy as a compromise.