The Basics of Conductive Epoxy
It’s been said before that epoxies are perhaps the most versatile adhesive available. Conductive epoxy is just one of the many types of epoxy adhesives available.
Typically, on its own without additives, epoxy is a nonconductive adhesive. However, because of the unique attributes it possesses, adhesive manufacturers can change the mixing ratios and impregnate the compound with additives that allow epoxy to be conductive.
The most common conductive adhesives are silver-filled thermosetting epoxies. The most common use for these glues is for electrically interconnecting and mechanically bonding components to circuits.
This type of epoxy has been in use for decades, although it has changed over the years. Electrically conductive epoxy was first developed in the 1950’s and has been widely used in semiconductor and electronic packaging industries since the 1960s, as a reliable connection method instead of soldering or eutectic joining of metals.
After about 2000, the majority of the electronic component manufacturers began using pure tin or tin-rich alloys. This change has resulted in increased reflow temperature, less ductility and the likelihood of “tin-whisker” forming. These needle-like metal crystals cause electrical and have been known to knock out guided missiles and communication satellites, caused heart pacemakers to fail and watches to stop ticking. Obviously this is an inherent problem with tin that can cause catastrophic failures.
These concerns have catapulted the use of silver epoxy in all kinds of applications. Silver is by far the most popular conductive filler, although gold, nickel, copper and carbon are also used.
While silver alleviates the electrical short, there is the potential for galvanic corrosion and non-conductive oxides if not used with incompatible metal component. Silver will oxidize under the right conditions. However, even if the silver is oxidized, its oxides are conductive. Unlike lead or tin, which have free electrons that will readily form non-conductive oxides and can cause serious conductivity issues. Since these oxides form on the surface of the metal, they can also significantly reduce the shear strength of an industrial adhesive bond. The shear strength of an industrial adhesive like epoxy is of the utmost importance.
Essentially here are the advantages of using a conductive silver epoxy:
- Compatibility with a wide range of surfaces, which includes substrates that you cannot solder.
- Displays low thermal stress during processing
- Provides a lot of process latitude
- Exhibits excellent temperature cycle performance
- Solder mask not required
- No pre-clean or post-clean requirements
- Non-toxic metal
- Finer pitch capability
Conductive adhesives are still in the infancy stage of development in the electronic component assembly area. There are issues that must be overcome but there is every reason to believe that adhesive manufacturers can adequately address all of these issues. The high “tailorability” of epoxy can be expected to produce superior electric conducting epoxies as conductive adhesives for the future.
For more information about Adhesive System’s epoxy adhesives or any other adhesives please contact us at 877.740.1250 x20. You can also send us an email at firstname.lastname@example.org If you don’t find exactly what you’re looking for, tell us about your application and we’ll help you find something that will work, or customize something specific for you.