Current-carrying capacity of PWB internal conductors in space environments

The current-carrying capacity of printed wiring board (PWB) electrical conductors in a space environment (i.e. vacuum with radiation) has previously not been quantified. The results from this paper help to characterize the temperature response of PWB conductors as a function of current and cross-sectional area. This paper documents PWB internal conductor temperatures as a function of current and cross-sectional area in vacuum/space environments. It also shows the influence of an internal 2-ounce copper plane on internal conductor temperatures. A series of tests were performed to collect PWB conductor temperatures as a function of current in vacuum environments. Tests were performed following ANSI standard ANSI C83.59-1971, Reference 1. This standard describes a methodology for testing PWB conductors. Additional configuration tests were done to show the influence on conductor temperatures from the presence of an internal copper plane within the PWB. The results are for electrical circuit conductors in printed wiring boards constructed with a space applicable polyimide board material. Results are shown for internal conductors of varying conductor widths and thickness. The conductor temperature rise for various current levels is presented with respect to conductor cross-sectional area. The tests were performed in vacuum to simulate a space environment. IPC-2221, Reference 2, contains design standards for sizing electrical conductors in printed wiring boards. Test results are presented and compared with the IPC standard. These results show as much as 60% margin exists in the current-carrying capacity of internal conductors in a bare (no internal copper plane) polyimide board with only traces. Then, margins as high as 200% are observed in a board with a 2 ounce internal copper plane