Conductive epoxy is a polymer matrix with flakes of silver mixed into it. These silver flakes span a distance of about 40 microns or less. The silver acts as a conductive guide to channel both heat and electricity through a relatively insulative polymer matrix. There are some misconceptions about the conductivity of these materials, since they are often branded as “high thermal conductivity” epoxies.
The thermal conductivity of these epoxies are around to 2W/m-K. In the world of solder this is pathetically low, as solder is generally 30-87 W/m-K. The silver in the mixture has a thermal conductivity of >400W/m-K, but it is only part of the mixture – which explains the low overall conductivity.
It’s not all bad though, epoxy is great in certain circumstances. It provides a low voiding bond at lower temperature with quicker profiles than solder. It definitely has a place in certain packaging applications. I wouldn’t advise using a conductive epoxy to attach a high-power device, but it is suited for some lower power die attachment and solar applications. Considering ‘time is money’, this can be a way to reduce the cost of your assembly through process optimization.