Jean-Michel Morelle

Creep behavior of Innolot solder alloy using small lap-shear specimens

The paper is concerned with the development of a micro testing machine for solder joint specimens. The micro tester has been developed for testing a new solder alloy, namely Innolot (Sn-Ag3.7Cu0.65Bi3.0Sb1.43Ni0.15), under various cross-beam speeds and temperatures. In addition, the procedure for fabricating lap-shear solder joints, which will be tested under monotonic and creep loadings, is given. The effect of temperature is accounted for in all the tests. The results show that the properties of the Innolot solder alloy are strongly dependent on both the strain rate and the temperature. In addition, a creep constitutive model was derived to describe the creep behavior of Innolot lap-shear solder joints. The results suggest that the derived creep constitutive model is a good approximation of the real behavior of the solder alloy under different loading conditions (stress level, temperature).

A design of a new miniature device for solder joints’ mechanical properties evaluation

This paper makes a focus on the design of a micro-testing machine used for evaluating the mechanical properties of solder alloys. The different parts of the testing device have been developed and assembled in a manner that will facilitate the study of miniature solder joints as used in electronic packaging. A specific procedure for fabricating miniature lap-shear joint specimens is proposed in this work. The tests carried out with the newly developed machine serve to determine the material behavior of solder joints under different controlled loading and temperature conditions. Two new solder alloys, namely SACBiNi and Innolot, are characterized in the study, showing the influence of strain rate and temperature parameters on their respective mechanical responses. In addition, the as-cast and fracture surfaces of the solder joints are observed with a scanning electron microscope to reveal the degradation mechanisms. The SACBiNi solder alloy, which contains less Ni and Sb elements, is found to have smaller shear strength than the Innolot alloy, while its elongation to rupture is significantly improved at the same strain rate level and testing temperature. The highest shear strength is 58.9 MPa and 61.1 MPa under the shear strain rate of 2.0 × 10−2 s−1 and room temperature for the SACBiNi and Innolot solder joints, respectively. In contrast, the lowest shear strength values, 26.6 MPa and 29.5 MPa for SACBiNi and Innolot, respectively, were recorded for the strain rate value of 2.0 × 10−4 s−1 and at temperature of 125℃.

Reliability in Mechatronics Systems from TEM, SEM and SE Material Analysis

Mechatronic systems designed to comply to new EU directives are studied through interconnections by electronic or photonic probes, SEM, TEM, SE or 3D Tomography. Leaded and lead free modules assembled by standard interconnection technologies are studied for robustness relative to thermal accelerated life tests. Results obtained from JEOL 6060LV SEM and Optical Microscopy show that although slow growth rate of inter-metallics (IMC) is consistent with expected reliability, they are responsible for propagation of cracks especially in the presence of gold on PCB side. Innovative Low Temperature Joining (LTJ) technology applied to nano or micro silver pastes which should reduce IMC effects are tested on mechatronic systems. Results obtained from SEM, TEM and 3D Tomography will be shown as well as non destructive Spectroscopic Ellipsometry studies of samples. Pressureless LTJ technology is unsuitable for robust interconnection.