Current-Carrying Capacity of Fine-Line Printed Conductors

Printed wiring technology presently provides the physical designer with fine-line copper conductors to interconnect integrated circuits and other components at the circuit-pack (CP) level. These fine-line conductors now have a nominal width of 7 mil, and a nominal thickness of 1.4 mil. For such relatively small conductor sizes, (~AWG39), the current-carrying capacity of the conductors becomes an important matter of concern. Can such fine-line conductors carry the required current to operate the various components on a CP without causing an excessive temperature rise? What is the temperature rise during normal current flow? If a fault occurs and a current of 10 A flows for 100 ms, will the CP be damaged? Questions of this nature are becoming very important as printed wiring technology provides finer conductors for the electrical interconnections. Also, as large-scale integrated (LSI) circuits are introduced, the assembled CPs are becoming more expensive. Therefore, there is more incentive to protect the CP from possible damage as a result of an over current. Some early work by W. Aung and A. J. Colucci1 has shown that a 7.5-A current flowing through a fine-line printed conductor inside a 1375