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 reliability is the size of the gap between the die and the substrate, i.e. standoff height. A nondestructive technique using Scanning Acoustic Microscopy (SAM) for 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 and water interface and water and substrate surface interface from the A-scan image can be found. Then, the corresponding standoff height can be calculated. When compared with the traditional destructive measurement method (SEM analysis on sectioned samples), the results suggest that the present method yields reliable results.