Effects of Bath Composition on the Adhesion Characteristics of Electroless Cu Layers on Epoxy-Based Polymer Substrates

Abstract

We investigated the effects of bath composition on the adhesion characteristics of electroless Cu on epoxy-based polymer substrates. The Cu layer was electroless-plated on the epoxy-based polymer substrate via four electroless-plating baths. A Cu layer was electroplated, which was then cured at 150°C for 1 h. The adhesion was evaluated using a 90° peel test. The size of the nodules and grains found in the electroless Cu layers decreased with increasing electrolyte concentration in the plating bath, resulting in increased hardness. At the highest electrolyte concentration, the electroless Cu layer exhibited high porosity in conjunction with the least coverage. The porosity of the electroless Cu layer decreased and the coverage improved with decreasing electrolyte concentration; however, a non-uniform layer formed at the lowest electrolyte concentration. The peel strength increased initially with the bath concentration, and then decreased upon further increase in bath concentration. The variation of the peel strength was related to the coverage and the hardness of the electroless Cu layer. We utilized a two-step electroless-plating method (the first layer with better coverage and second layer with larger ductility). The peel strength of the optimized double-layered electroless Cu layer was higher than that of the single-layered electroless Cu layer.