Effect of Intermetallic Compound Bridging on the Cracking Resistance of Sn2.3Ag Microbumps with Different UBM Structures under Thermal Cycling

In this study, the effect of intermetallic compound (IMC) bridging on the cracking resistance of microbumps with two different under bump metallization (UBM) systems, Cu/solder/Cu and Cu/solder/Ni, under a thermal cycling test (TCT) is investigated. The height of the Sn2.3Ag solders was ~10 µm, which resembles that of the most commonly used microbumps. We adjusted the reflow time to control the IMC bridging level. The samples with different bridging levels were tested under a TCT (−55–125 °C). After 1000 and 2000 TCT cycles (30 min/cycle), the samples were then polished and characterized using a scanning electron microscope (SEM). Before IMC bridging, various cracks in both systems were observed at the IMC/solder interfaces after the 1000-cycle tests. The cracks propagated as cyclic shapes from the sides to the center and became more severe as the thermal cycle was increased. With IMC bridging, we could not observe any further failure in all the samples even when the thermal cycle was up to 2000. We discovered that IMC bridging effectively suppressed crack formation in microbumps under TCTs.

Thermal Cycling Test and Simulation of Fan-Out Chip-Last Panel-Level Packaging for Heterogeneous Integration

In this study, the reliability of the solder joints of a heterogeneous integration of one large chip (10 × 10 mm) and two smaller chips (7 × 5 mm) by a fan-out method with a redistribution layer-first substrate fabricated on a 515 × 510-mm panel is investigated. Emphasis is placed on the thermal cycling test (−55°C Δ 125°C, 50-min cycle) of the heterogeneous integration package on a printed circuit board (PCB). The thermal cycling test results are plotted into a Weibull distribution. The Weibull slope and characteristic life at median rank are presented. At 90% confidence, the true Weibull slope and the true 10% life interval are also provided. A linear acceleration factor is adopted to map the solder joint reliability at the test condition to the solder joint reliability at an operating condition. The failure location and failure mode of the PCB assembly of the heterogeneous integration package are provided and discussed. A nonlinear, time- and temperature-dependent 3-D finite element simulation is performed for the heterogeneous integration PCB assembly and correlated with the thermal cycling test results.

Thermal Cycling Test and Simulation of Six-Side Molded Panel-Level Chip-Scale Packages (PLCSPs)

In this study, the reliability of the solder joints of a six-side molded panel-level chip-scale package (PLCSP) is investigated. Emphasis is placed on the thermal cycling test (−55°C Δ 125°C, 50-min cycle) of the six-side molded PLCSP on a printed circuit board. For comparison purpose, the one without six-side molded (ordinary) PLCSP is also subjected to the same test. The thermal cycling test results are plotted into a Weibull distribution, and the true Weibull slope and true characteristic life at 90% confidence are presented. The solder joint mean life ratio of these two cases and its confidence level are also determined. Furthermore, their solder joint failure location and failure mode are provided. Finally, a nonlinear, time- and temperature-dependent 3-D finite element simulation is performed for these two cases and correlated with the thermal cycling test results.