The Definitive Guide to an Electronic Assembly Design Review / 21
Common Design Flaws and Recommendations (cont.)
The BOM Review is Lacking
In addition, when examining the BOM, it is important to note if any of the various
device types have known reliability issues. For example, parts like capacitors are
known to have significantly higher failure rates that the same value-part dielectrics.
Similarly, when parts are used in either a calibration or sensing circuit, we often
recommend changing resistors when resistance levels are greater than 1 megohm
per 1 or more low resistance components..
Unreliable Derating
Finally, Ansys recommends reliable derating for different device types. For example,
resistors should be aggressively derated regarding power dissipation, especially for
the higher power (1/4W, 1/8W, and 1W) components. We recommend the following:
derate to 60% of maximum applied voltage, 70% of steady state power, 80% of peak
power and 20C below peak operating temperature to maximize reliability.
