The National Physical Laboratory (www.npl.co.uk) has announced the launch of a new report, "Susceptibility of Glass-Reinforced Epoxy Laminate to Conductive Anodic Filamentation," written by Alan Brewin, Ling Zou and Christopher Hunt.

Conductive anodic filamentation (CAF) is a subsurface failure mode for woven glass-reinforced laminate (FR4) materials, in which a copper salt filament grows and results in a consequential electrical short between plated through hole walls or adjacent copper planes. In the study, FR4 laminates in the form of high PTH density multi-layer test circuits were exposed to different manufacturing conditions and studied for resistance to CAF initiation and growth.

CAF performance was assessed using high temperature and humidity conditions to promote failures, with a voltage applied across adjacent vias. By applying a range of voltages and via geometries, the basis for a performance map for laminates was obtained for use in materials comparison. The changes due to exposure of laminates to lead-free temperatures and other processing steps were then examined using the technique and a number of important recommendations were made to minimize the possibility of CAF initiation and growth.

All reports released by the Electronics Group at NPL can be searched and downloaded free from: www.npl.co.uk/ei/publications.

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