The research objective of this award is to determine if a measurement system based on a laser ultrasonic-interferometric technique can be used for solder bump inspection in microelectronic package assemblies. The approach will be to use a concentric array of optical fibers to deliver laser energy in order to generate ultrasound in the thermo elastic regime on the surface of a chip package assembly without ablating the package. The efficiency of the system will be increased by using symmetric and asymmetric methods of signal processing to discriminate between good and bad solder bumps. For the symmetric method, a measurement metric (such as the time-domain correlation function) will be calculated using two symmetrically located points on one sample surface, and this will remove the reliance on requiring the use of a signal from a good chip as a reference in the signal processing algorithm. Wavelet and Correlation Coefficient signal analysis methods will be used to determine the presence of defects in chip packages with either symmetric or non-symmetric solder bump layouts. A finite element model, developed in earlier research for analyzing one-dimensional packages, will be improved for analyzing these packages. Three-dimensional models will be investigated to take into consideration all the layers that are present in these packages. This finite element model will be used to determine how the number and size of the solder bumps affects the detectability of defects.
If successful, this research will result in a novel and low-cost ultrasonic solder bump inspection system that can be used for evaluating the quality of a wide variety of electronic packages This system will offer the potential for rapid optimization of test programs resulting in significant decrease in new product introduction and ramp-up cycle times. It will result in cost savings in the production of electronic devices. The project will also provide educational opportunities for students.
