Epoxy polymer adhesives are inherently electrically insulating. Below are some samples of materials that adhesive formulators commonly use to lower the electrical resistance of their epoxy systems and create electrically conductive epoxy adhesives.
Nickel displays electrical resistivity in the low range of 7x10^-8 ohm ⋅m at 20°C. Conductive epoxies filled with nickel can have resistivity of approximately 3x10^-2 ohm ⋅cm. Specialty adhesive formulators use Nickel as an electrically conductive filler alternative to silver at a more affordable price point.
2. Silver Coated Glass Sphere
Similar to nickel in terms of being a cost-effective soultion, silver coated glass spheres take advantage of the high electrical conductivity of silver. The process of coating affordable glass spheres allows a smaller amount of silver to go further by increasing its relative volume. Although silver coated fillers do not have the same low resistivity as pure silver, they do however yield a solid alternative to pure silver systems.
Depite being slight more expensive, silver is an excellent heat, transfer and electrical material. As a pure substance, silver exhibits about 400-420 W/mK thermal conductivity and electrical resistivity of approximately 1.6x10^-8 ohm ⋅m at 20°C. Silver filled epoxies can have thermal conductivities as high as 7 W/mk with electrical resistances potentially as low as 1x10^-4 ohm⋅cm.
4. Carbon and Graphite
Carbon fillers can be used both as a black pigment and they can also be used to increase electrical conductivity. Graphite in a pure substance form has electrical resistivity of about 2.5x10^-6 ohm ⋅m along the basal plane at 20°C. A graphite filled epoxy can exhibit resistivity in a range of 40 ohm ⋅cm, and is therefore best used in applications where extremely low resistivity is not necessary such as RFI and EMI applications.
Selecting An Electrically Conductive Epoxy
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