Study of micro-BGA solder joint reliability

A new reflow parameter, heating factor (Q(n)), which is defined as the inte gral of the measured temperature over the dwell time above liquidus, has be en proposed in this report. It can suitably represent the combined effect o f both temperature and time in usual reflow process. Relationship between r eliability of the micro-ball grid array (micro-BGA) package and heating fac tor has been discussed. The fatigue failure of micro-EGA solder joints refl owed with different heating factor in nitrogen ambient has been investigate d using the bending cycle test. The fatigue lifetime of the micro-BGA assem blies firstly increases and then decreases with increasing heating factor. The greatest lifetime happens at Q(n) near 500 s degreesC. The optimal Q(n) range is between 300 and 750 s degreesC. In this range, the lifetime of th e micro-EGA assemblies is greater than 4500 cycles. SEM micrographs reveal that cracks always initiate at the point of the acute angle where the solde r joint joins the PCB pad. (C) 2001 Elsevier Science Ltd. All rights reserv ed.