Effects of solder joint shape and height on thermal fatigue lifetime

Solder joint thermal fatigue failure is a major concern for area array technologies such as flip chip and ball grid array technologies. Solder joint geometry is an important factor influencing thermal fatigue lifetime. In this paper, the effects of solder joint shape and height on thermal fatigue lifetime are studied. Solder joint fatigue lifetime was evaluated using accelerated temperate cycling and adhesion test. Scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), scanning acoustic microscopy (nondestructive evaluation) and optical microscopy were utilized to examine the integrity of the joint and to detect cracks and other defects before and during accelerated fatigue tests. Our accelerated temperature cycling test clearly shows that solder joint fatigue failure process consists of three phases: crack initiation, crack propagation and catastrophic failure. Experimental results indicated that both hourglass shape and great standoff height could improve solder joint fatigue lifetime, with standoff height being the more effective factor. Experimental data suggested that shape is the dominant factor affecting crack initiation time while standoff height is the major factor influencing crack propagation time.