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
Most are RoHS compliant thanks to non-toxic metal
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
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.
Content and images provided courtesy of TDK’s FAQ.