Conductive Epoxy

Conductive epoxy, or electrically conductive adhesives consist of an epoxy resin, or silicone filled with randomly distributed metallic or conductive carbon particles. When it is fully cured it provides an electrically conductive pathway. Simple terms its glue with metal particles that can conduct electricity. This means it can be put on many different surfaces that solder cannot. It is also great for parts that are sensitive to heat. If you change the ratio of the filler particles to the resin, you can control the performance and conductivity of an adhesive. The higher proportion of filler particles will result in higher conductivity, but can weaken the bond strength as it will displace some of the adhesive material.

Soldering can create environmental impact issues with its toxicity. Conductive epoxy can be used as a clean alternative to soldering. Epoxy alone is non-conductive, but if combined with silver filled epoxy it can become conductive. The most common is silver, but gold, nickel, copper and carbon can also be used. Another benefit is the epoxy can also be thermally conductive, meaning it can also cool the component.

List of pros:

Non-toxic metals (Lead Free)

No pre/post-clean requirements

You do not need a solder mask

Can work on many surfaces that cannot be soldered

Moisture resistant

Thermally conductive

Most are RoHS compliant thanks to non-toxic metal

No flux

List of cons:

Need to be stored correctly to keep shelf life

Epoxies cure without moving creating possible solder bridges (Because of surface tension solder will move back to the landing point)

You have to mix the epoxy correctly to get the right conductivity

Expensive

Solder generally sets faster while epoxy may need time to fully set

Built in Conductive Epoxy

Companies are starting to build in conductive epoxy into their components. Great example is TDK’s Soft termination series of MLCC’s that have this built in feature. The epoxy combined with AgPdCu termination allow for greater resistance to cracking and the low curing temperatures of the epoxy preserve heat sensitive components during manufacturing. Below shows the layout of the component.

Soft%20termination

Digi-key Conductive Epoxy Products

Content and images provided courtesy of TDK’s FAQ.

Non-toxic should really be lower toxicity because toxicity is totally dose dependent and nearly all substances, especially metals, have a limit beyond which there will be problems.

A good starting point for further study, https://en.wikipedia.org/wiki/Toxicity

A central concept of toxicology is that the effects of a toxicant are dose-dependent; even water can lead to water intoxication when taken in too high a dose, whereas for even a very toxic substance such as snake venom there is a dose below which there is no detectable toxic effect.

There actually is a reason why the USA has no federal restriction on the use of lead in many products. As long as you don’t put it in your mouth or lungs, and especially your children’s mouths or lungs, there are no well defined toxic effects. In the USA we have legislated and stopped the use of lead from the uses where it caused well defined problems. The worst was leaded gasoline, followed by paint, plumbing pipes, and plumbing solder.