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Cova Scientific By Cova Scientific • March 6, 2017

Resistance of Conductive Epoxies

Depending on the filler material conductive epoxies can range from 40 to 1x10^-4 ohm ⋅cm, however most electrically conductive epoxies are silver filled and exhibit around 1x10^-4 ohm ⋅cm.

Neat (unfilled) epoxy polymers are actually highly insulating materials, and are commonly used to help protect and insulate electrical circuits. Dielectric epoxies can have volume resistivity of 1.0x10^12 ohm ⋅ cm and have a dielectric strength (breakdown voltage) of 420-480 volts/mil for a .125 inch thick specimen.

However, when these same epoxy resins are filled with electrically conductive particles (typically precious metals) the tables completely turn. What was an excellent insulator becomes a electrically conductive binder that can compete with solder in many electronics applications. By far the most effective electrically conductive epoxies are silver filled, but some other metal systems do exist.

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  • Silver (1x10^-4 ohm ⋅cm) - Silver is an excellent electrical transfer material. Silver filled epoxies can exhibit resistances as low as 1x10^-4 ohm ⋅cm. Silver filled epoxies also tend to have the best flow and cure properties in comparison to the other metal systems due to silver particle typical shape, size, and chemical interactions while in suspension.
  • Silver Coated Glass Spheres (1x10^-1 ohm ⋅cm) - silver coated glass spheres take advantage of the high electrical conductivity of silver at a bargain price. 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 find use in many EMI/ RFI shielding applications with an electrical resistance of around 1x10^-1 ohm ⋅cm.
  • Nickel (3x10^-2 ohm ⋅cm) - Conductive epoxies filled with nickel can have resistivity of approximately 3x10^-2 ohm ⋅cm. Unfortunately nickel systems are very rarely used due to poor flow and material properties of nickel filled epoxies.
  • Carbon and Graphite (40 ohm ⋅cm) - 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.