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.