Automated Twisted-Pair Wire Bonding

A need for highly dense and reworkable external interconnections with controlled characteristic impedance on high-performance printed-circuit boards led to the development of the process and equipment described in this paper. These interconnections are required to implement engineering changes, to install precise circuit delays, to repair printed-circuit defects, and to complete interconnections not possible with printed circuitry alone. As an economical way to meet the characteristic impedance requirement of 80 ± 10 Ω and the density requirement for terminations on a 2.5-mm “staggered” grid (twice as dense as a 2.5-mm-square grid), 39-gauge twisted-pair wire is used. A solder-reflow process bonds the wires to the printed circuitry and meets the need for reworkability. Computer-controlled equipment, developed to install twisted-pair wires at production rates, is now being used in several IBM plants worldwide.