Reliability of Sn3wt%Ag0.5wt%Cu0.019wt%Ce (SACC) solder joints

Abstract

The impacts of a very low level (0.019wt%) of doping of Ce (cerium) on the SnAgCu lead-free solder joints of lead-free PQFP (plastic quad flat pack), PBGA (plastic ball grid array), BCC (bumped chip carrier), and wafer-level chip scale package (WLCSP) using immersion-Ag (ImAg) lead-free PCB (printed circuit board) are investigated in this study. Emphasis is placed on the estimation of the life distribution, reliability, characteristic life, and mean time to fail (MTTF) of the SACC (Sn3wt%Ag0.5wt%Cu0.019wtCe) solder joints of these lead-free components through thermal cycling (−40 to +125°C, one-hour cycle @ 15-minute dwells and 15-minute ramps) test (4,628 cycles). In addition, another set of samples with Sn3wt%Ag0.5wt%Cu (SAC) is tested (side-by-side with the SACC samples in the same thermal cycling chamber, under the same test condition & data acquisition, and with the same failure criterion), which serves as a comparison, and their mean lives (quality) are compared with those of the SACC. The confidence levels of the comparisons are also estimated. It is found that the MTTF of the PQFP, BCC, and PBGA solder joints (with SACC solder paste) are better than those with SAC solder paste with reasonable confidence levels. On the other hand, the MTTF of the SAC WLCSP solder joints (with SAC solder paste) are superior than those of the SAC WLCSP with SACC solder paste with very high confidence. Finite element modeling and analysis are performed to understand why.