Takuji Kobayashi

Experimental Observation of Correlation Between Creep and Uniaxial Ratchetting of Sn∕37Pb and Sn∕3Ag∕0.5Cu Solder Alloys

Time-dependent deformations such as creep and ratchetting of solder alloys are significant deformation phenomena that need to be understood to ensure the safety and reliability of solder joints in electronic packaging. There is much research on creep deformation of solder alloys, but ratchetting deformation, especially the correlation between creep and ratchetting deformation of solder alloys has not been investigated. This paper discusses the correlation between creep and uniaxial ratchetting deformation to establish the differences in the time-dependent deformation of lead-free and lead-containing solder alloys. Uniaxial ratchetting tests were conducted by cyclic tension-compression tests or cyclic tension-unloading tests at several ratios of the maximum to minimum stresses. Additional creep tests following the uniaxial ratchetting were also conducted to observe the effect of the uniaxial ratchetting on creep deformation. An empirical method to select an optimal lead-free solder alloy is discussed by defining a uniaxial ratchetting strain rate. The additional creep tests also show that the uniaxial ratchetting deformation has a strong correlation to the creep deformation and that the correlation is different for lead-free and lead-containing solder alloys.

Experimental and Theoretical Investigation of Viscoplastic Deformation of Solder Alloys for Electronic Packaging

This paper discusses ratchetting deformation of lead-free solder Sn/3Ag/0.5Cu and lead-containing solder alloy Sn/37Pb with several stress amplitudes and stress ratios of the maximum stress to the minimum stress. First the uniaxial ratchetting testsare conducted with three maximum stresses and five stress ratios. The all tests are conducted using cylindrical bulk specimens of the solder alloys at 313 K. The test results show that there is the difference in the viscoplastic deformation behavior between two solder alloys. The relationship between ratchetting strain and time is estimated by Biley-Norton law to explain that the uniaxial ratchetting deformation is strongly dominated by the viscous deformation. Finally, the ratchetting deformation is simulated by the dislocation based constitutive model proposed by Estrin [1]. The simulations show that there is a possibility to simulate the uniaxial ratchetting by clarifying the dislocation mechanism of the solder alloys.

Microstructural Change of Sn/37Pb and Sn/3Ag/0.5Cu Solder Alloys Subjected to Uniaxial Ratchetting Deformation

Ratchetting deformations of solder alloys are significant deformations for the safety and reliability of solder joints of electronic packaging. In this paper, the microstructural change of the solder alloys due to the uniaxial ratchetting deformation is evaluated to clarify the effect of the microstructure on the viscous deformation of solder alloys. The microstructures are observed after the specimens are subjected to the uniaxial ratchetting deformation during several cycle numbers. The change of the size of grains or lamella structures is used to evaluate the uniaxial ratchetting deformation of solder alloys. The observation clarifies that the differences in the microstructural change due to the uniaxial ratchetting deformation between the lead-free and lead-containing solder alloys. The uniaxial ratchetting deformation and the additional creep deformation after the ratchetting deformation is also simulated by the dislocation based constitutive model. The simulation suggests that the material parameters used in the constitutive model may be correlated to the microstructural change of the solder alloys.Copyright

Correlation Between Creep and Uniaxial Ratchetting of Sn/37Pb and Sn/3Ag/0.5Cu Solder Alloys

Ratchetting deformations of solder alloys are significant deformations for the safety and reliability of solder joints of electronic packaging. This paper discusses a correlation between creep and uniaxial ratchetting deformations to clarify the difference in the time-dependent deformations between lead-free and lead-containing solder alloys. Uniaxial ratchetting tests are conducted by cyclic tension-compression and cyclic tension-unloading with the several ratios of maximum to minimum stresses. Additional creep tests are also conducted after the uniaxial ratchetting tests to clarify the effect of the uniaxial ratchetting on the creep deformation. A method to evaluate the uniaxial ratchetting deformation is discussed using the creep curves. The results show that the uniaxial ratchetting deformation correlates to the creep deformation and that the correlation is different between the lead-free and lead-containing solder alloys.Copyright