Updated: March 3rd, 2014

Porosity – The (w)Hole Story is all about the defects

Sorry about the title, but I couldn’t resist.

Porosity consists of small (microscopic) defects in a plated coating. In connectors, a typical plated coating thickness for noble metals (gold and palladium alloys) is in the range of 0.1 to 1.25 microns (4 to 50 microinches). As Max Peel noted in his article in the last issue, porosity depends on plating thickness and is not generally a problem at thicknesses greater than 1.25 microns. Let’s consider this thickness dependence from a physical point of view.

The following description is somewhat simplistic but illustrates the essential concerns at issue: The plating deposits on the substrate appear in a discontinuous manner, nucleating at numerous sites on the substrate. The plating spreads out over the surface as it increases in thickness and the growing islands of plating eventually coalesce to completely cover the surface. Early in this coalescence process, the issue is surface coverage and towards the end, it becomes porosity. In connector-speak, thin gold, or flash, platings, of the order of 0.1 microns, are in the surface coverage regime. This is a different issue than porosity in that it is intrinsic to the plating process. Surface coverage will always be an issue in flash gold platings. Porosity, in contrast, is process-dependent.

A typical noble metal plating includes a nickel underplate over the contact spring base metal, usually a copper alloy. The nickel underplate provides many performance benefits, as described in previous articles. One of the benefits is that nickel plating (typically 1.25 to 2.5 microns) can bring the porosity down to low levels; it, too, is process-dependent. In the ideal case this means that when the gold plating is applied, any gold porosity will generally be to the n