Electroless copper deposits were plated on epoxy substrates in various plating solutions at either a high operating temperature (60 degrees C) or a low one (45 degrees C). Cross section samples were made using epoxy resin cured in room temperature, and then ground, polished and over-etched. The scanning electron microscopy (SEM) images of the over-etched cross section samples show voids in low temperature deposits and solid structure in high temperature ones. The surface morphology images also indicated such structures in low temperature samples. The SEM image of the cross section of a stand-alone deposit prepared on stainless steel substrate shows similar voids observed on etched cross section samples on epoxy board substrates. An image processing program was written using MATLAB to identify the voids in the over-etched cross sections of the deposits from low temperature solutions and thus the void fraction can be directly measured and compared with the previously published simulation results. (C) 2008 Elsevier B.V. All rights reserved.