What is a low expansion epoxy?

Eb 315


A common issue facing many engineers is the expansion rate of epoxy adhesives. This property is called the coefficient of thermal expansion (CTE). Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. This can be an issue if a chosen epoxy has a different CTE than its substrates. During temperature cycles if substrates expand and contrast at different rates than the epoxy, then the epoxy can crack or de-bond from the substrate leading to a parts failure. Many factors affect the CTE of an epoxy including glass transition temperature (Tg), rigidity, and chemistry. Most unfilled epoxy systems have a CTE of over 100 in/in/°C at temperatures of above 100°C. Adding low expansion fillers to epoxy decreases the CTE and stabilizes the epoxy for high temperature applications.

EB-315 is a low expansion, high temperature epoxy adhesive. Specially designed to have an extremely low CTE at high temperatures, EB-315 is used in many aerospace and semiconductor applications. With a CTE of 25 in/in/°C at temperatures below 175°C, EB-315 maintains integrity at extremely high temperatures. EB-315 passes NASA outgassing standard with proper cure. In aerospace guidance systems, EB-315 creates near hermetic gasket seals as well as high temperature wire bonds. It is also used to join SMDs to PCB, for staking applications replacing soldering.

Product Specifications

No.of Components 2
Mix Ratio by Weight 100/5.5
Mixed Viscosity @RT(cps) 70,000 - 100,000
Pot Life @25°C(100 gram) 90 min
Recommended Cure 2 hrs @ 100°C + 2 hrs @ 175°C
Alternate Cure 3-4 hrs @ 150°C
Color Beige or Black
Specific Gravity 1.8
Hardness(Shore) D-92
Refractive Index NA
Lap Shear Strength @25°C(psi) 2000
Tg(°C) 182
CTE(Below Tg)10-6/°C 25
Service Temp.Range -55°C to 230°C
Thermal Conductivity(W/m°K) 0.6
Volume Resistivity(500 V) 2.0 x 10^15

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