Creep Measurements of 200 μm - 400 μm Solder Joints

For the last decades, many mechanical measurements on solder alloys were carried out. As a matter of fact, the microstructure of the solder materials is affected by their compositions. In addition, external variables like the reflow cooling rate, solder volume, thermal mass of the package and pad metallization may have an influence. For those reasons the discrepancies of creep measurements on solder contact specimen are larger than on tensile samples. A motivation for the creep measurement activities is the lifetime prediction of electronic components, which have solder joints for electric-mechanical connection on their interposer or printed circuit board. Structure-mechanic simulation tools like the FEM can calculate the mechanical interactions between the assembled materials of such complete packages. Often, the solder joints are the weakest participants in the whole assembly and determine the total lifetime. Nevertheless, every simulation is highly dependent on the material laws. Therefore, the FEM needs an accurate fatigue model and a precise material model for the lifetime prediction of this solder. The paper presents a new experimental design for measuring the creep behaviour of area arrayed solder bumps in different sizes of various packages. It focuses on the feasibility of the measurement of industrial manufactured FC, CSP or BGA packages. First measurements were accomplished on solder bumps with 200 μm and 400 μm diameter. The test setup works by cyclic reversible shear force initiation into solder joints. It operates in the temperature range between T = [20...125]°C. High-resolution force adjustment and displacement measurement enables a steady state strain rate measurement range of [10^-2...10^-8] 1/sec. Industrial demands for introducing the new SnAgCu base solders required a concentration on various high Sn-based alloys.