Enhanced Interface Adhesion of Pattern Plated Copper in Printed Wiring Boards

Trend in electronic packaging towards reduction in the dimension of conductive tracks in printed wiring boards continues, adhesion at the interface between the laminated copper and the electroplated copper becoming critical issues. In order to improve the adhesion at copper-to-copper interface, several chemical micro-etchant solutions are known to alter surface topography prior to pattern electroplating in the manufacturing of Printed Wiring board. In this paper ammonium peroxodisulphate and sulphuric acid compositions as micro-etchant was studied. Copper circuit patterns generated on glass epoxy copper laminate samples are treated in freshly prepared micro-etchant solution as well as cooled and stirred micro-etchant solution. It was observed from the experiments that sample processed in freshly prepared peroxodisulfate etchant, had random peeling of plated copper track from base copper and measured adhesion strength is very low, which is less than 0.72kg/cm. Sample processed in cooled, stirred etchant had higher peel strength of the tracks and measures more than 1.64kg/cm. This is attributed to the low exotherm of cooled and stirred etchant results in enhanced hydrophilicity of the micro-etched surface. This leads to the favorable interlocking of the copper grains at the interface during electrodeposition process. Interlocking of the grains results in the extension of base copper lattice with electroplated copper called “Epitaxial Growth” which is responsible for enhanced adhesion.