Cooling and Annealing Effect on Indentation Response of Lead-Free Solder

Abstract

With the development of lead-free solders in the electronic packing industry, Sn-Ag-Cu solders are one of the most promising lead-free alloys to be applied due to their outstanding mechanical property and wettability. By performing indentation experiments, the effect of cooling rate on the mechanical properties of Sn-3.0Ag-0.5Cu (SAC305) solder is investigated in typical cooling conditions (i.e., furnace cooled and water quenched) and compared with the as-machined samples of bulk solder bars from the industry. Based on continuous stiffness measurement technique, Young's modulus and hardness are reduced by 2.3-3.9 GPa and 0.053-0.085 GPa, respectively, after annealing treatment for the indentation depth between 1000 nm and 1100 nm in samples after cooling, however, the value of hardness is independent of cooling condition. By defining the contact stiffness to represent residual stress in solder samples after cooling and annealing process, an exponential-based Oliver-Pharr model is employed to fit the unloading responses of indentation. It is found that the smaller cooling rate induces less contact stiffness and thus less residual stress. Despite different cooling conditions, the contact stiffness of unannealed and annealed solder samples are 711.8-842.5 µN/nm and 655.2-673.4 µN/nm, respectively. Thus, annealing treatment of 210 • C for 6 h can effectively alleviate residual stress to a similar level for SAC305 solder samples with different cooling conditions. This conclusion is supported by the alleviation of pile-up deformation in the residual indentation after annealing treatment.

Correlation of microstructure and constitutive behaviour of sintered silver particles via nanoindentation

“…There are a few numerical and analytical approaches available to extract the constitutive behaviour in the form of stress-strain relationship from the nanoindentation responses subjected to different indenters such as conical and spherical indenters [7,[25][26][27][28][29][30] . By overcoming the difficulty of solution uniqueness, the analytical approach proposed by Ogasawara et al [31] and recently improved by Long et al [32] is utilized to measure the plastic properties of a power-law constitutive model in Eq.…”

A finite element model to study the effect of porosity location on the elastic modulus of a cantilever beam

“…As such, structures may be affected in various locations, and in differing intensities, depending on the exposure to the environment. Conversely, it was shown in Long et al (2017) through experiments that the process of annealing SAC305 solder healed microdefects to reduce the reduction in elastic modulus caused by porosity. As such, while a proper heat treatment can reduce the effect of porosity prior to environmental effects, it is still critical to quantify the effect of porosity and its location on a structure as evident from the results of Morrissey et al (2019).…”

Calibration of a Constitutive Model from Tension and Nanoindentation for Lead-Free Solder

“…Humphrey and Jankowski [ 15 ] measured and compared the strain-rate dependence of the tensile strength on the grain size in crystalline nickel foils, using both tensile and micro-scratch methods. However, it is controversial to correlate the constitutive behaviour measured by tensile tests with the material behaviour measured by nanoindentations, despite the intensive investigations of mechanical properties measured using the instrumented nanoindentation approach [ 16 , 17 , 18 , 19 , 20 ]. In terms of the equivalence of measured material constitutive relationships, it is rare to further quantitatively investigate the constitutive behaviour obtained from tension and indentation methods.…”