High Performance Gold Coated Nickel Powders for Packaging Applications in Electronics

Metal-based powders are used as fillers to make polymers conductive for various devices in electronics packaging technologies. Many applications require the fillers to have high conductivity and robust electrical stability that can only be achieved through using composite gold-coated powders. Packaging components such as keypads, microphone holders, z-axis connectors and specialty conductive adhesives, tapes, inks and polymer thick films depend on gold-based fillers for electrical interconnection. The increasing material cost of gold is a primary motivating factor to reduce, or minimize the gold content of these fillers.

This work shows how electrical conductivity and stability are related to the amount of gold that is applied to nickel and nickel graphite powders with particle sizes ranging from 10 to 100 microns. It is shown that these powders attain their maximum conductivity values at surprisingly low gold weight percentages. The very thin layers of gold also provide electrical stability as shown in tests where they are exposed to C) and humidity (95% RH). Addition of 1%°conditions of elevated temperature (80 gold by weight in the form of a coating increased the measured conductivity of a 30 micron Ni powder from 0.00005 (ohm-cm)^-1to 640 (ohm-cm)^-1, a factor of over ten C, 95% RH for 143°million. The same filler was stable when exposure to 80 hours.

The amount of gold that is required to produce a maximum saturation level of conductivity is a function of the surface area of the particles. As particle size increases, the amount of gold by weight percent required to coat the particle surface with a thin film decreases. Each type of base powder has a characteristic saturation point where further addition of gold does not increase conductivity.