Reliable Multiwire Circuits with Small Gauge Wires

Reliable Multiwire circuits have been developed. The objective of this development was to reduce design and assembly cost of backwiring boards in an electronic switching system. To realize high holeto-wire connection reliability, various factors were investigated and the following results have been obtained. 1) The use of Pyre-ML as a wire insulating material is the most effective for obtaining high connection reliability because of its solubility in alkaline type plating solution. 2) In manufacturing processes, cleaning of resin smear is the most important process. 3) Pads around plated through-holes are effective for reduction in thermal expansion around plated through-holes and failure rate is reduced to 2 percent with pads. By using these technologies, Multiwire circuits with a wire thicker than 0.09 mm have obtained equal or higher connection reliability, compared with multilayer printed circuits.