Abstract:

The placement of electronic components on a printed wiring board (PWB) is a complex problem which requires tradeoffs between several goals.  Traditionally, placement techniques have focused on improving routability based on minimizing the total wire length between interconnected components.  However, electronic card assembly (ECA) reliability, which is measured in terms of time to failure, cycles to failure, or the hazard rates of the individual components, the interconnections, and the PWB, is also affected by component placement.  The reliability of an ECA is a function of the design, manufacture, assembly, environmental conditions, and stresses which include humidity, vibration, shock, and temperature.  The temperature dependent failure of an ECA can generally be described by functions of component junction or case temperatures, threshold temperatures, temperature changes, temperature gradients, and/or temperature histories.  This paper examines the problem of component placement of reliability based on a failure model which incorporates component temperature, a base operating temperature, a threshold temperature, and change in temperature of an individual component.  Placement procedures are developed so as to minimize the time to failure or the total hazard rate of the components on a PWB based on a forced convection cooling technology.

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