SMT007 Magazine

SMT-Nov2016

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48 SMT Magazine • November 2016 FEATURE by Patrick McGoff MENTOR GRAPHICS CORP. If you research electronics reliability for the automotive industry, for example, you will find they all address only the electronic components mounted on a PCB. One of the more referenced reliability studies for the industry was conduct - ed by Telcordia Technologies, titled, "Reliability, Prediction Procedure for Electronic Equipment (SR-332)." Like most other electronics reliability studies, it excludes the PCB. Automotive manufacturers need to have stringent reliability requirements, and thus they have set goals for reducing component defect rates [1] . For example, a defect rate of less than 10 ppm for an engine control unit (ECU) or less than 1 ppm for a component within the ECU. The end game is "zero defect, zero failure." The automotive industry has quantified the reliability rate for all the various component packages today and report defect rates as follows: • ASIC—0.2 ppm • Microprocessors—0.5 ppm • Inductors—0.2 ppm • Resistors—0.0 ppm How to Improve PCB Reliability Component failure rates have steadily de- clined over the years to the point where non- component failure sources have become the dominant cause of failures for a PCB [2] . The problem with automotive-electronics reliability studies is they do not consider the PCB. If the reliability of the components is be- coming a non-issue, then the only way to im- prove automotive electronics further is to look at the non-component aspects of the electron- ics, and a significant one is the PCB. Each PCB design is a custom component, with its own unique, complex recipe: • Material types and stackup • Copper features • Mechanical processes • Chemical processes • Electronic components • Component mounting methodologies • Impedance and capacitance concerns All of the above form dependencies and con- straints to every aspect of the PCB. How do you assess reliability for a "component" you have never used before? You measure the elements that make up the component, that is, the struc-

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