A linear motor-driven mini fatigue tester has been developed at Wayne State University and reported in this paper with its application to mechanical fatigue testing of mini solder joint specimen. The tester, as the second generation of our DC motor-driven mini tester, is backlash free. Another advantage of the tester is its capability of high speed and long travel distance, making it powerful to the wide range of frequencies for mechanical fatigue testing, which is ideally suitable for accelerated fatigue testing. Several fatigue tests of solder joints have been performed by this mini fatigue tester. It is found that the kinematical hardening coexists with cyclic softening of solder joints, indicating early damage stage of solder fatigue. The testing results of a solder joint specimen designed by authors can also indicate both macro crack initiation and its propagation The voiding on failure surface of a solder ball specimen after fatigue is observed to support ductile damage characterization of solder joints.