Investigating voltage effects in Conductive Anodic Filament (CAF) failures

Investigating voltage effects in Conductive Anodic Filament (CAF) failures - Using Insulation Resistance (IR) techniques to evaluate electrochemical failure phenomena at higher voltages

Presenters: Ling Zou and Martin Wickham

Achieving high reliability in service is a key issue for today’s electronic circuits. Electrochemical reliability becomes more critical, as electronic circuits move to increased packaging densities, and also operated at high voltages and in harsher environments (hotter/damper/ condensation). Electrochemical reliability failures are mainly caused by contaminants and bias under damper conditions, facilitating the electrochemical corrosion process that results in a loss of continuity/short circuits.

For CAF failure, voltage bias is one of the main driving forces. Increasing voltage bias significantly increases CAF failures. With the electrification of transport and corresponding increases in the voltages at which electric vehicles operate, CAF testing needs to be conducted at higher voltages. NPL has developed CAF testing to extended test voltages from 100V to 1000V. The webinar will introduce 1000V CAF testing in NPL and discuss the issues associated with earlier than predicted failures at higher voltages. We will also discuss our current programme to increase SIR and CAF testing to 3000V.

The most important failure model caused by metal corrosion is the CAF formation inside the printed circuit board (PCB). CAF failure and electrochemical reliability can be identified and evaluated using the Insulation Resistance (SIR) technique. In this webinar we will focus on using the IR technique to evaluate electrochemical reliability of electronic circuits. The principle of IR measurement technique will be described. IR measurement is a direct measure of circuit reliability and is the only method which attempts to correlate contamination, bias, and climatic conditions with circuit reliability. IR measurement can be used to detect the localised failure down to CAF structures with different pitches and orientations. Some examples from NPL research works will be given to illustrate the effect of PCB materials, PCB manufacture processes, reflow processes and test voltages on CAF results. The webinar will also guide you on how to design CAF test boards and test matrixes to qualify or evaluate electronic materials and processes to improve the reliability of electronic products. Some test standards and test boards will also be introduced.

To watch previous webinars in this series and find out more information, please go to: https://www.npl.co.uk/electronic-magnetic-materials/reliability-webinars