TABLE OF CONTENTS The effects of lead-free solders, underfills, and microvia build-up PCBs/ substrates on the solder joint reliability of WLCSP and DCA are discussed in this chapter. Also, three new empirical equations for predicting the thermal fatigue life of WLCSP solder joints on PCB are presented.
The solder joint reliability of solder-bumped WLCSP on microvia build-up PCB subjected to thermal cycling conditions is investigated in this section. The Sn62-Pb36-Ag2 solder joints are assumed to be (1) an elastic material; (2) an elastoplastic material; and (3) a creep material that obeys the Garofalo-Arrhenius creep constitutive law. The stress and strain in the corner solder joint of the WLCSP assembly are presented and compared for these three material models. Also, the results presented here are compared with those from creep analysis of the WLCSP on PCB without the microvia build-up layer.
Since the research of Tsukada et al.1 3 in 1992, the electronic packaging industry has witnessed an explosive growth in the research and development efforts devoted to solder-bumped flip chips on low-cost PCB or organic substrate in a PBGA package (see for example Refs. 4 to 10). Because of the thermal expansion mismatch between the silicon chip and the epoxy substrate, underfill encapsulant is usually needed for solder joint reliability. However, due to the underfill operation, the manufacturing cost is increased and the manufacturing throughput is reduced. In addition, the rework of an underfilled flip chip on PCB...
