NPL invites participation in CAF project

14 January 2010

Dr. Chris Hunt
Dr. Chris Hunt

UK-based National Physical Laboratory is seeking partners interested to participate in a three-year project.

Part funded by the UK government, and partly by the industry, the project is designed to further the understanding of conductive anodic filament (CAF) phenomena in printed circuit boards and to develop predictive tools for characterising the susceptibility of PCBs to CAF formation.

CAF was first reported in the 1980s, and it is an electrochemical effect, occurring within the weave of epoxy-glass printed circuit substrates, which can cause assemblies to fail through short circuits. It is known that CAF depends on three principal factors; the electrical field strength, the aggressiveness of chemical environment, and the solubility of corrosion products. In a context of reducing component pitch and cost-down demands, CAF becomes a serious reliability issue, necessitating difficult design decisions and careful material selection.

This NPL project aims to develop a clear understanding of the factors controlling CAF formation, particularly the influence of laminates characteristics and PCB manufacturing processes, and to devise detection techniques with improved sensitivity. Model systems will be built to study the CAF phenomenon in detail, and impedance techniques will be explored. Sensitivity to environmental factors will also be measured. Current PCBs materials with representative CAF designs from partners will be tested, too.

The project is headed-up by Dr. Chris Hunt, recognised for his work on the development of IPC-9201A, Surface Insulation Resistance Handbook and his contribution to the development of IPC-9691A, User Guide for the IPC-TM-650, Method 2.6.25, Conductive Anodic Filament (CAF) Resistance Test (Electrochemical Migration Testing)

A meeting will be held at NPL on 26 January at 10:30 in Birmingham at Aeo Engine Controls, to discuss the project in detail, how it will develop, and ways in which partners can influence its direction and benefit from its outcome.

An outline of the project programme and objectives can be found here.


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