Ph.D. Thesis Defense by Sheng Liu
Wednesday, March 21, 2001

(Dr. Charles Ume, advisor)

"System Implementation, Modeling and Defects Pattern Recognition for Flip Chip Solder Joint Inspection Using Laser Techniques"


Solder bump technology has been proven to be a reliable interconnection in flip chip and other surface mount components.  However, because of the physical configuration of these integrated circuit packages, traditional solder joints inspection methods are either not suitable for solder bump inspection, or not efficient for automated on-line inspection.  New techniques for inspecting the solder bump defects in a reliable, fast and non-destructive means are highly desired in today's electronic packaging industry.

The objective of this research is to develop a non-contact, non-destructive, low cost, fast, accurate, high resolution, and automated system for monitoring the quality of solder bumps in flip chips and other surface mount components.  This novel approach for solder bump quality inspection has been developed by using laser ultrasonic and interferometric techniques.  Experimental results indicate that this system offers great promise for solder bump inspection in a fast and efficient manner.  A fully developed system could be used in an assembly line for quality assurance, or off-line during process development for process optimization.

A finite element model, based on vibration modal analysis, has been constructed to model the chip vibration phenomenon.  The modeling and experimental results indicate that defects in a solder joint change chipís vibration transient response and its natural frequencies. Measurement of these properties can be used to detect solder joint defects.  In order to automate this system, a defects pattern recognition method was also developed to automatically classify chips into different clusters, so that good chips can be distinguished from chips with defects.  The defects pattern recognition method can find differences between good and bad chips, as well as classifying the type of defect.