This study examines the possibility of employing an electroless-plated Ni(P) layer as a diffusion barrier between the Sn bonding layer and Cu bump for 3D integration applications. We bonded the samples at different bonding temperatures (200 similar to 350 degrees C) and probed into the bonding morphology to evaluate the effects of the addition of a Ni(P) barrier. Combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that the Ni(P) barrier effectively suppressed Cu diffusion while an interaction between Ni(P) and Sn consumed the barrier in a gradual manner. The samples with a Ni(P) barrier were found mechanically much more reliable than those without a barrier, owing to suppressed IMC reaction and Cu diffusion. In addition, the insertion of a Ni(P) barrier did not affect the resistance much in comparison with the samples without a barrier. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.007202jes] All rights reserved.