Standoff height measurement of flip chip assemblies by Scanning Acoustic Microscopy

Flip chip technology is the emerging interconnect technology for the next generation of high performance electronics. One of the important criteria for the reliability issue is the size of the gap between the die and the substrate i.e. standoff height. A nondestructive technique using the Scanning Acoustic Microscopy (SAM) for the standoff height measurement of flip chip assemblies is demonstrated. The method, by means of the implementation of the pulse separation technique, time difference of the representative signals of the die bottom & water interface and water & substrate surface interface from the A-scan image can be found. Then, the corresponding standoff height can be calculated. When comparing this method with the traditional destructive measurement method (SEM analysis on sectioned sample), the results compromise with each other, which suggests that this method yields reliable results.