Mixed mode fracture toughness of lead–tin and tin–silver solder joints with nickel-plated substrate

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2005-09, Vol.404 (1), p.244-250
• Main Authors: Siow, K.S., Manoharan, M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Brazing. Soldering; Exact sciences and technology; Fracture toughness; Fractures; Joining, thermal cutting: metallurgical aspects; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Mixed mode; Sn–3.5Ag; Sn–37Pb; Solder joint
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2005.05.086

This study uses modified compact tension specimens to evaluate the fracture toughness of solder joints under a combination of tensile and shear loads. Copper substrates were coated with electroless nickel plating before they were soldered together. The samples were reflowed to peak temperatures of 215 and 240 °C for Sn–37Pb and Sn–3.5Ag, respectively, with appropriate preheating temperatures, holding time and cooling rates. Fracture toughness tests were conducted as per ASTM E399-90. Cross-sectional microstructural and fractography studies were carried out on the tested samples. Earlier fracture studies which were based on J integral as per ASTM E813-89 did not produce valid results because of brittleness of the solder joints. The current results showed that the fracture of the solder joints follows the general principles of a mixed mode fracture mechanism map and shear is the preferred mode of failure regardless of different mode of loadings, type of solders and substrate coatings.