Development of Miniature Creep Testing for Environment Friendly Solders

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Quality assurance of solder connections is an important subject for guaranteeing the reliability of the connections. This study determined the creep characteristics of lead and lead free solders by making extensive creep experiments.Creep deformation and creep rupture characteristics were presented for Sn-37Pa and Sn-95Pb solders. These lead solders were most commonly used. The effects of Sn content and temperature on creep and creep rupture were studied. The prediction method for creep deformation and rupture time was proposed as a function of stress, time and temperature.Creep deformation and rupture characteristics of Sn-3.5Ag was studied. The solder is the most potential lead free solder and is expected to be used in major electronics connections. The superior creep deformation resistance and rupture strength were experimentally found compared with Sn-37Pb and Sn-95Pb lead solders. From the viewpoint of creep performance, Sn-3.5Ag solder was verified to be available in actual solder connections.Size effect in solder creep was investigated. A new miniature creep tester was developed for making creep tests for miniature specimens. There was almost no size effect in solder creep to the specimen diameter down to 1 mm but there was a clear size effect below that diameter. A large scatter in creep rate and rupture time was found in specimens with diameters of 0.3 and 0.5 mm whereas almost no scatter was confirmed in bulk specimens. The creep rupture times of miniature specimens were predictably from those of bulk specimens by considering a factor of two allowable band with Sn-37Pb solder.