Abstract: A connective medium is provided for use in ball grid assemblies for detachable connections between electronic devices and circuit boards. The medium includes novel, discrete spheres defining an inner metallic, spherical core and one or more outer, electrically conductive concentric, hard and non-deformable metallic layers of nickel, copper or alloys thereof and a coating of silver or gold thereon.

Abstract: An improved process for the manufacture of uniformly and accurately sized metal spheres, particularly copper spheres, which comprises the steps of classifying a starting lot of spheres into closely sized fractions; separately electroplating each size fraction to a desired final mean diameter and size distribution; and then combining the plated fractions to give a metal sphere product having the requisite mean particles size and size distribution. The electroplating build-up step is characterized by a high level of precision. Additional benefits derive from the high hardness of copper electroplate on relatively soft copper starting particles which facilitates grinding or polishing irregularly shaped plated particles down to the desired sphericity and mean diameter, from the ability of metal such as copper electroplate to cover and envelop contaminated surfaces of starting particles, and from the ability to produce spheres having a unique combination of bulk and surface properties.