A practical mtbf estimate for pcb design considering component and non-component failures

Accurate reliability prediction for MTBF (mean-time-between-failures) is always desirable and anticipated before the new product is ramped up for customer shipment. In reality it is often difficult to obtain the accurate MTBF estimate for a new product due to the lack of the testing time in pilot line and limited field failure data. In this paper, a practical reliability prediction model is presented for predicting the MTBF of PCB (printed-circuit-board) in the design phase. Unlike conventional reliability prediction models, which usually focus on parts failure rates, the method presented here not only incorporates component failures but also non-component failures which include design, software, manufacturing and process issues. Component failure rates are computed using either historical data or the nominal failure rates together with operating conditions such as temperature and electrical derating. Triangular distributions are used to model non-component failure rates due to design errors, software bugs, manufacturing and handling problems. Finally, the confidence intervals for the new product MTBF are obtained based on six-sigma criteria. The method was applied to the design of a DC/analog instrument board that is used in the semiconductor testing equipment