The use of conductive epoxies in the electronic industry is becoming more and more common as the number of new epoxy systems on the market increases. Epoxies filled with nickel, carbon and silver are used for chip bonding, die attachment and many other applications. Silver filled epoxy presents best conductivity but is also most expensive.

In 1966, Epoxy Technology was the first company to promote silver-filled epoxy resins as die-attach materials. Prior to this time, all dice were bonded to metal or ceramic substrates by means of eutectic alloys.

Most (more than 90%) of the electrically conductive adhesives for die bonding are isotropic materials that conduct electricity in the in-plane and out-of-plane directions. Electrically and thermally conductive adhesives are available in the form of thixotropic plates or films.

Paste silver-filled epoxies are available either as two-part materials that have to be mixed, or as one-part compositions premixed, degassed, and frozen in small syringes. Both are designed to have optimum flow properties when dispensed by screen printing, stamping, or with automatic dispensing machines.

>> Applications and Advantages

Most common two part electrically conductive epoxies are used for component attachment, termination and other applications in hybrid circuits, membrane keypads and other electromechanical assemblies.

The thixotropic properties and non-stringing characteristics make them ideal materials for high-speed, dot dispense processes where low temperature curing is required. They allow automated dot dispense processes to run up to 70% faster. This is attributed to their low viscosity and non-stringing characteristics.

They exhibit very good adhesion to most metal and plastic substrates, have good temperature resistance, toughness, and allow for differences in coefficients of thermal expansion between two bonded substrates.

Convenient mix ratios and packaging in pre-weighed amounts allow for ease of use in fast paced production environments. Most are also available in due, pre-weighed and sealed plastic pouches, or pre-mixed and frozen in syringes. Some silver-filled electrically conductive epoxy can be modified on the cure speed, working time, or rheology which makes them more compatible with many unique manufacturing process.