Effect of cleaning and non-cleaning situations on the reliability of flip-chip packages

A combined experimental and numerical study is conducted to investigate whe ther the reliability of flip-chip solder interconnects is affected by noncl eaning situations, in which underfill cannot be completely filled in the co rners of the solder balls because contamination like flux residues subsisti ng on those parts after solder reflow. The real-time moire interferometry t echnique is used to measure the warpage (deformation) for the selected "cle aning" and "noncleaning" flip chip package specimens during the test, while a nonlinear finite element technique, in which the viscoplastic material p roperties of solder balls and underfill are considered, is adapted to simul ate the corresponding "cleaning" and "noncleaning" situations to assess the impact on solder interconnect reliability. The noncleaning situation is in contrast to the cleaning situation considered by many researchers. The res ults indicate that there is no obvious difference for the warpage obtained by either the test data or the numerical work between the cleaning samples and the noncleaning samples. However, the simulation results of the stresse s (strains) reveal that the noncleaning situation decreases the mechanical stability and shortens the life time of those flip chip packages to a level well below the predictions of the cleaning simulations. The fatigue life i n some points of the outmost solder joint predicted by using the cleaning F E models is much higher than that predicted by using the noncleaning FE mod els. Since it is hard to find perfect filled layers for any real world samp les, the cleaning model yield overly conservative results. In addition, the predicted deformation values of the flip-chip package obtained from the fi nite element analysis are also compared with the test data obtained from th e laser moire interferometry technique. Good agreement is obtained. In part icular, the displacement contours of the flipchip package samples both in t he x and y directions obtained from the test show similar distribution patt erns compared with those modeled by the finite element method.