Experimental investigation of the visco-plastic mechanical properties of a Sn-based solder alloy for material modelling in Finite Element calculations of automotive electronics

Abstract

Here, we present an advanced experimental procedure for determining the properties of a SnAg3.5 solder alloy in the strain range of primary creep under cyclic load and isothermal conditions. The challenge in this experiment is the accurate high-resolution measurement of sample elongation used for a closed-loop control, as well as avoiding the influence of sensor and specimen clamping. We realized reproducible strain rate control within a total specimen elongation of 60 μm. The tensile-compression experiment comprises strain rate variation for three strain amplitudes with integrated relaxation stages followed by a measurement of cyclic fatigue. The strain rate at every strain stage was varied in the range of 1E-3 to 1E-6 per second. At the end of every strain stage a time-limited relaxation experiment is performed, where the specimen's length is kept constant, while the stress evolution is recorded. Finally, the specimen is subjected to cyclic fatigue until a drop of 50 % of the initial materials strength is reached. The total procedure is performed in a temperature range from -40 to 150 °C. We prove the capability of common creep models to map the observed cyclic stress-strain hysteresis as well as stress dependency on strain rate. The results reveal substantial limitations of common stationary creep models and strongly suggest the application of advanced visco-plastic material models for an accurate description of the solder alloy properties. The experimental data presented can be used for the calibration of unified visco-plastic constitutive models initially proposed by Chaboché et al. and further extended during the past two decades

Performance Assessment of different Machine Learning Algorithm for Life-Time Prediction of Solder Joints based on Synthetic Data

“…Here, the change in the equivalent creep strain with respect to time 𝜀̇C reep is computed by the equivalent stress 𝜎, the temperature 𝑇 and the material dependent model parameters 𝑐 1 to 𝑐 4 . These have already been characterized by Metasch et al [7] in the range between -40 °C and 150 °C. Furthermore, the highly temperature-dependent behavior of the matrix resin of the PCBs must be Evaluation: Due to a well-developed meniscus with a relatively high solder volume content, the creep strains that occur are concentrated in the small standoff with a low solder volume.…”

“…Based on these results, the evaluation of the accumulated creep strains concentrates on the elements in the standoff region of the solder contact. After each calculated half cycle, the accumulated creep strain of these elements is extracted and calculated to a volumeaveraged scalar quantity, see Equation (7):…”

Analytical stress model for tin based solder material

“…Metasch already presented in the past the advanced experimental procedure for determining the properties of a tin based solder alloy under cyclic load and isothermal conditions [5]. Hence, stress-diagrams were generated using this experimental setup.…”

Numerical study on the influence of material models for tin-based solder alloys on reliability statements

“…The solder characterisation process has been performed in the temperature range from -40 °C to 150 °C while strain rates were varied from 1e-3 1/s to 1e-6 1/s and multiple relaxation steps were applied. The detailed characterisation procedure has been presented in a previous publication [1], [2] and is shown exemplary for 25 °C in Fig. 1.…”