The traditional ball shear test is not suitable for evaluating joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. The present study expands recently reported research by investigating the effect of thermal aging on the joint strength and fracture mode of Sn-3.0Ag-0.5Cu ball grid arrays during high-speed shear testing, with a shear height of 50 lm and a shear speed ranging from 0.01 m/s to 3 m/s. The test specimens were aged at 393 K for 1000 h. After reflow, a (Ni,Cu) 3 Sn 4 intermetallic compound (IMC) layer was observed at the solder/Ni-P interface and the thickness of the IMC layer was increased through the aging process. The shear strength increased with increasing shear speed. The fracture surface of the solder joints showed three different fracture modes according to the shear speed and aging time. The fracture mode changed from ductile fracture to brittle fracture with increasing shear speed.
The hygrothermal and mechanical reliability of board-level packages with various underfills under sequential temperature and humidity (TH) testing and drop testing were investigated. Board-level packages with underfill had greater resistance to drop shock than that without underfill, indicating that underfill protects the package from failure by absorption of the applied drop shock. The underfill, which was composed of polypropylene glycol epoxy resin and silane, exhibited good reliability for drop shock because of the improved adhesion of the underfill compared with that without the polypropylene glycol epoxy resin and silane. In addition, the drop reliability of board-level packages with underfill decreased with increasing TH test duration. Adhesion between the substrate and underfill or between the solder and underfill was decreased by moisture absorption. Components positioned at the board center were more susceptible to failure by drop shock than were corner components.
The electromigration of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu (in wt.%) solder bumps was investigated with a high current density of 2.5 9 10 4 A/cm 2 at 423 K using flip-chip specimens comprised of an upper Si chip and a lower bismaleimide triazine (BT) substrate. Electromigration failure of the Sn-37Pb and Sn-3.0Ag-0.5Cu solder bumps occurred with complete consumption of electroless Ni immersion Au (ENIG) underbump metallization (UBM) and void formation at the cathode side of the solder bump. Finite element analysis and computational simulations indicated high current crowding of electrons in the patterned Cu on the Si chip side, whereas the solder bumps and Cu line of the BT substrate had a relatively low density of flowing electrons. These findings were confirmed by the experimental results. The electromigration reliability of the Sn-3.0Ag-0.5Cu solder joint was superior to that of Sn-37Pb.
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