Characterization of the microstructure of tin-silver lead free solder

Abstract

Reliability and lifetime are the two most relevant design considerations in the production of safety critical assemblies. For example in a modern automobile dozens of electronic assemblies are integrated in which thousands of solder joints are mounting the electronic components to the printed circuit boards. There exists no standardised and universal observation method for characterising the fine microstructure of such solder joints. Previously we have developed a new method for the quantitative characterization of lead-free solder alloys and in present study the validity of the proposed method is demonstrated. Microstructure of Sn-3.5Ag lead free solder alloy was investigated by electrochemical impedance spectroscopy. Solder samples were solidified with different cooling rates in order to induce differences in the microstructure. Microstructure of the ingots was revealed by selective electrochemical etching. Electrochemical impedance spectra (EIS) were measured before and after the selective etching process. The complex impedance spectra contain information about microstructure of the solder alloys. Comparison and modelling of two EIS spectra allowed obtaining a characteristic parameter of surface structure of the etched specimens. The EIS measurements were complemented with small angle neutron scattering measurements and scanning electron microscopy, in order to correlate the EIS parameter with the magnitude of the interface of the β-Sn and Ag3Sn phases.

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

“…Their work correlated the mechanical property such as yield and ultimate tensile strengths, Young's modulus and fracture strain with microstructures to elucidate the underlying damage mechanism associated with Snmatrix microstructure and Ag 3 Sn morphology. The observed effect of cooling rate on microstructures is similar to the recent findings for the cooling rates between 1.2 • C/s and 6.6 • C/s by Hurtony et al [2016]. In addition, Ochoa et al [2004] evaluated the effect of cooling rate on the dominant mechanisms of creep behavior at the temperatures ranging from 25 • C to 120…”

BME VIK Annual Research Report on Electrical Engineering and Computer Science 2016

“…Huge tin-silver IMC plates were formed in solder samples when the liquid to solid transition occurred under longer time. In the case of samples that were rapidly solidified finer microstructure was formed [58]. The presence of tin-silver IMC plates is considered as a reliability concern, since the mechanical properties of such IMCs are known as very brittle.…”

Separating Silver from Tin Silver Alloy Residue: Effect of Agitation Rate

“…Tin lead alloys were known to be used as solder materials for packaging and interconnecting electronic components. However, due to the proved toxicity of lead and its environmental impacts, different countries have taken measures to reduce the use and release of lead into the environment with strict regulations including waste of electrical and electronic equipment (WEEE) and restriction of the use of certain hazardous substances (RoHS) [5,6]. This has resulted in the use of lead-free alloys such as tin silver copper alloy (SnAgCu), tin silver bismuth alloy (SnAgBi), tin silver zinc (SnAgZn) and tin silver alloy (SnAg) which can be applied in different areas including phosphate baths due to their physical, chemical and thermodynamic properties [7,8].…”