Copper microcircuit repair of opens using thermally driven exchange plating

Abstract

A two-step method for the repair of circuit board defects consisting of complete opens is described. First, a small copper bridge is grown in unacidified copper sulfate solution by passing a few milliamperes of ac current at a frequency of 2-2000 kHz through the break. Local Joule heating results in copper deposition and bridging of the open via thermally driven exchange plating. For the second step, the cross section of the repair is increased by exchange plating in acid copper, using up to ∼1 A of ac current at a frequency on the order of 60 Hz or greater.