Reliability modeling of soldered interconnections

The authors describe the results of work to determine the minimum solder height that would produce a satisfactory joint in an electronic assembly used in IBM disk drives. Solder pads with heights ranging from 18 to 160 μm were produced by varying the solder deposition process. After joints were made using the standard soldering process, the joint strengths were measured by pulling the wire at an angle of 45° and measuring the force required to either break the wire (wire breaks) or pull the wire out of the solder (wire peels). A figure of merit for the solder process is defined as the fraction of wire peels. A key element in this work is the use of a generalized regression model to correlate this figure of merit to solder height. This allows interpolation of the data, calculation of confidence intervals, and a check of the validity of process control plans. The model is used to determine the minimum solder height, and to establish a sampling plan to monitor production