Reliability of SnAgCu Interconnections with Minor Additions of Ni or Bi under Mechanical Shock Loading at Different Temperatures

Abstract

Novel portable devices will be equipped with increasing number of new and more powerful functions. Therefore dissipated heat from components can cause significant rises of local temperatures inside the products. Since products are likely to be dropped when their components are running hot, it is important to drop test component boards also at different temperatures. The drop reliability of component boards with different interconnection compositions (Sn3.1Ag0.52Cu, Sn3.0Ag 0.52Cu0.24Bi, and Sn1.1Ag0.52Cu0.1Ni) was studied under mechanical shock loadings at ambient as well as at elevated temperatures (room temperature, 70degC and 110degC). The drop tests were carried out according to the JESD22-B 111 drop test standard. The component type used was a 12 mm x 12 mm CSP/BGA with 144 bumps of 0.5 mm diameter and 0.8 mm pitch. The statistical analysis pointed out that (1) the drop reliability decreased significantly with increasing temperature, (2) the interconnections on the Cu-OSP printed wiring board (PWB) coating were more reliable than those on the Ni(P)Au over the temperature range studied, and (3) at room temperature the SnAgCuNi assemblies were the most reliable on Cu-OSP-coated PWBs, while SnAgCu assemblies were the most reliable on the Ni(P)Au coating. However, at elevated temperatures the SnAgCu assemblies were the most reliable while the SnAgCuNi assemblies were the least reliable regardless of the PWB coating material. The failure modes of the SnAgCu and SnAgCuBi interconnections changed with increasing temperature from the cracking of interfacial regions of the solder interconnections to the cracking of the copper traces of the PWB soldering pads. SnAgCuNi interconnections exhibited the same failure mode, the cracking of the copper traces, at each temperature and with both PWB protective coatings. The increased bending of the printed wiring board and decreased strength of solder interconnections at elevated temperatures changed the failure modes and decreased the drop reliability as compared to the room temperature test results.