cracking on Ni/Au plated pad

after soldering transistors on a flex circuit (Ni/Au plated), one of the lead lift-up from the pad. under microscope (1,000 X), i find some cracks on the the pad surface. with edx analysis, the surface is mainly nickel. have you ever encounter such probelm? do you know what is the major cause of this defect. thanks for your kind concern

reply »