The adhesion strength between electroless copper and acrylonitrile-butadiene-styrene (ABS) resin can be improved significantly by an environmentally friendly etching system containing H2SO4-MnO2 colloid as a replacement for conventional chromic acid etching solutions. In this paper, the effects of the H2SO4 concentration and ultrasound-assisted treatment (UAT) on the surface roughness and adhesion strength were investigated. When the H2SO4 concentration was 11.8 similar to 12.7 M, good etching was obtained. With UAT, many uniform cavities formed on the ABS surface with the average surface roughness (R-a) and maximum roughness (R-max) of ABS substrates decreasing from 386 and 397 nm to 278 and 285 nm, respectively, which were much lower than that etched by CrO3-H2SO4 colloid (420 and 510 nm, respectively). The average adhesion strength increased from 1.29 to 1.39 kN/m, which was close to that obtained with chromic acid etching treatment (1.42 kN/m). The surface contact angle measurement indicated that the density of the polar groups on the ABS surface increased with increasing time of UAT. The results indicated that surface etching with UAT not only improved the uniformity of cavities, but also enhanced the oxidation rate of ABS resin, which in turn resulted in greater adhesion strength and a lower surface roughness. (C) Koninklijke Brill NV, Leiden, 2011