Placement for reliability and routability of convectively cooled PWBs

A coupled reliability and routability placement procedure for arranging electronic components on a convectively cooled two-dimensional workspace, printed wiring boards (PWBs), is developed. The objective is to improve the total reliability of all the components on the PWB by minimizing the sum of the individual component failure rates (i.e. minimizing the total failure rate) while also minimizing the total wire length. The placement procedures for reliability are based on a priority metric derived from a temperature-dependent failure rate equation and heat transfer equations for a single row of convectively cooled components. After a brief discussion of the force-directed methodology in terms of placement for routability and its relation to placement for reliability, a theory of placement for reliability on convectively cooled PWBs is discussed, and placement procedures for reliability along a row and an entire PWB are presented. A force-directed placement technique for reliability is developed, and the coupled placement procedure for reliability and routability is introduced. Examples of each procedure are presented and discussed.>