Extensive data on 62Sn36Pb2Ag, 60Sn40Pb, 96.5Sn3.5Ag, 97.5Pb2.5Sn, and 95Pb5Sn solder are presented. All of the data were collected on soldered assemblies to properly account for the effects of grain size and intermetallic compound distribution. Tensile and shear loading were employed in the strain rate range between 10/sup -8/ and 10/sup -1/ s/sup -1/ and the temperature range between 25 and 135 degrees C. It is remarkable to note that all of the data can be fit to the same general form of constitutive relations; i.e., only the constants depend on the solder alloy. The derived constitutive relations are used to predict solder joint response under thermal cycling. Based on the calculated hysteresis loops, it is apparent that each solder will have a different acceleration factor between field use cycling and accelerated test cycling. >

Constitutive relations for tin-based-solder joints

The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitivity at intermediate strain rates (region II) where the material exhibits optimal superplasticity This relationship is examined in detail, with reference both to the conflicting results reported for the Zn-22 pct Al eutectoid alloy and to the significance of the three regions of flow

The mechanical properties of superplastic materials

A unified viscoplastic constitutive law, the Anand model, was applied to represent the inelastic deformation behavior for solders used in electronic packaging. The material parameters of the constitutive relations for 62Sn36Pb2Ag, 60Sn40Pb, 96.5Sn3.5Ag, and 97.5Pb2.5Sn solders were determined from separated constitutive relations and experimental results. The achieved unified Anand model for solders were tested for constant strain rate testing, steady-state plastic flow and stress/strain responses under cyclic loading. It is concluded that the Anand model can be applied for representing the inelastic deformation behavior of solders at high homologous temperature and can be recommended for finite element simulation of the stress/strain responses of solder joints in service. @DOI: 10.1115/1.1371781#

Applying Anand Model to Represent the Viscoplastic Deformation Behavior of Solder Alloys

A constitutive equation for a typical SnPb eutectic or near-eutectic solder joint is developed, based on empirical data in shear and generalized to three dimensions. Three strain components are considered: elastic, time independent plastic, and steady-state creep. A continuum mechanics rather than a metallurgical approach is taken with emphasis on the formulation of an equation useful for predicting solder behavior under a variety of conditions. Solutions of the constitutive equation predict the experimental hysteresis data for the loading histories available. Solutions of the equation for the test conditions of three independent sets of solder fatigue data show that the equation, together with the matrix creep failure indicator, can give an estimate of fatigue life. >

Constitutive relation and creep-fatigue life model for eutectic tin-lead solder

Both high Pb-Sn and eutectic 63Sn-37Pb have been the suitable materials for the interconnection of electronic components because of their low cost and appropriate physical properties. Due to environmental awareness, and the health hazards caused by the lead in the solders, large efforts have been made to develop a lead-free soldering technology. Among the large variety of lead-free solders the Sn-Ag alloys are expected to be the best candidates. Furthermore, from a reliability point of view, there has been interest in the improved thermal fatigue resistance of solder interconnects. Therefore, in this study two lead-free solder alloys (Sn96.5Ag3.5, Sn95.5Ag3.8Cu0.7) and two lead-containing solder alloys(Sn63Pb37 Sn59Pb40Agl) were investigated and compared with each other in order to give an estimation of the reliability enhancement of the new lead-free soldering technology. These investigations were focused on mechanical and physical properties (coefficient of thermal expansion, stress-strain curves at different strain-rates, ultimate strength) as well as on the microstructural appearance of the solders.

G.S. Murty

Papers

Experimental constitutive relations for the high temperature deformation of a PbSn eutectic alloy

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