Qualification of AgPd thick films using Atomic Force Microscopy

This paper introduces a method using contact mode Atomic Force Microscopy (AFM) for qualification of AgPd thick films. The described measurement technique is capable of detecting very small concentration of surface contaminants, which can be crucial if the thick film conductor is directly bonded by ultrasonic welding. During this welding process an aluminum wire is pressed vertically onto the thick film surface; an applied horizontal vibration forms the Al_wire-AgPd_film bonded interface. The introduced method is based on a known artifact of AFM, which is a well-defined image distortion in contact mode height data and AFM deflection signal. In our case, an image distortion carries information about sample-tip interaction, this attractive/repulsive force changes if the tip moves on a contaminated surface. We suggest a short, moderate temperature annealing in order to clean the surface from previously observed contaminations. During the experiments, the optimal parameters of annealing were also determined; these parameters have been validated by pull tests.