Measurement of the standoff height between a flip-mounted IC chip and its substrate

A technique for measuring the standoff height for flip-chip solder bonding is described. In the technique the assembly is viewed at an oblique angle by using a specially modified microscope that has its optical axis tipped relative to the direction of focus. It is a fast, nondestructive optical technique that requires no special sample preparation or unusual equipment. Its results agree well with those obtained by using the previous time-consuming method of preparing a cross section of the sample. This measurement technique is now being used extensively to characterize the flip-chip solder attachment process for new solder materials and new product codes. It can also be used to measure the standoff height between a surface mounted integrated circuit (IC) package and the underlying printed wiring board (PWB). The author gives a detailed analysis of the effects of different types of microscope lenses and the effects of errors caused by inaccurate sample orientation, and compares results obtained using this technique to those obtained from cross sections