Epoxies are being used as a solder replacement and for some time now. Some products just cannot take the heat of soldering example LED’s.

Epoxy conductive chemistry however has some issues with long term reliability and for now an intermetallic bond is the most reliable.

Epoxy use raises many issues with component and board cleanliness, the surfaces must be very clean but also free of out-gassed chemicals so solder and flux seem to do better here.

Also these conductive epoxies cost much more than solder. Also they are next to impossible to rework.

Conductive epoxies where going to revolutionize the electronic assembly industries in the late 70’s when they were first introduced to the industry. Unfortunately nothing conducts like metal. Epoxies have issues with X, Y,Z conductivity. They may conduct one way better than another. Additionally epoxies are not totally hermetic. Moisture can penetrate them causing corrosion on the base contact, leading to resistance failure and eventual failure. This can be corrected by using board and component finish design. In spite of these issues epoxies have found a section of the market to be used in but for standard electronics they have not been able to compete with the reliability and conductivity of solder.

Regarding the use of adhesives to replace solder, this concept has been discussed and tested for years. The most recent work I have seen on it is from the 2006 Pan Pacific Microelectronics Symposium in Hawaii, where Fritz Byle and Jin Liu, of Kester, made a nifty presentation on the use of epoxies for soldering. The problem historically has been that the less metal in the epoxy the weaker the electrical flow; fixing that problem with more metal then reduced the structural strength of the glue. They were able to surmount these problems by embedding carbon fibers into the epoxy. For more info see:  Electrically Conductive Adhesive.