Acoustic Surface Flatness Measurement; An Alternative For SMT Warpage Analysis
Authors: J. Richtsmeier and S. Martell Company: Sonoscan, Inc. Date Published: 5/17/2010
ICSR (Soldering and Reliability)
Abstract: As new SMT devices are being designed, developed and manufactured they have become thinner and smaller with the demand for greater reliability and less tolerance for defects. Differences in the expansion or shrinkage characteristics of a device and substrate can produce stresses that eventually cause deformation such as bowing and warping. One example is the development of Package on Package (POP) type devices that rely on the relative flatness of both packages for proper assembly. The same scenario holds true for both BGA as well as flip chip style packaging. Acoustic Micro Imaging (AMI) has long been associated with evaluating SMT devices and PCBs for physical defects, such as delaminations, cracks, voids, etc. however the acoustic data, which includes time, depth and velocity information, can also be processed simultaneously to obtain surface profile and contour measurements. With the advancement of Acoustic Surface Flatness (ASF) measurement capabilities it is now possible to simultaneously determine the surface profile to +/- 1 micron at the same time the device is being inspected for internal defects. The ASF measurement technique can be used for a variety of applications including wafers, singulated devices, substrates and PCBs (bare and/or populated).