Research On Size Effect Of Creep Damage About Lead-free Solder Joint Under Shear Tension

As the electronic devices develop instantly on the frivolous miniaturization direction, the space between the lead-free solder joints own size and solder joint is becoming smaller and smaller, the reliability of the size effect caused by the solder joint also caused much concern. As the creep damage caused by failure of lead-free solder joints is an important factor, the research on the damaged size effect solder joints creep is of great importance. Taking a single rectangular lead-free solder joint as the research object, this paper applied the method of combining the theoretical deduction, the experiment and the simulation together to do research in detecting the damage caused by the pull force to shear solder creep under the size effect. To establish a model of equivalent crack propagation of solder joint damage with the foundation of damage mechanics and conductive metal theory, and to deduct the relationships between the resistance strain and the creep damage. With the combination of the definition of the resistance strain and crack growth rate formula, there comes the relationship between the shear creep resistance strains and solder joints under the condition of the geometry size equation. As the online measurement and test method is cheap, at the experimental stage, the experiment of the resistance strain as characterization of solder joint creep damage would be taken as effective parameter. By using the independent development of four probe solder characteristics tester, a series of measurement of solder resistance strain will be done by Sn3.0Ag0.5Cu solder production of different thickness and sectional area, then the solder creep damage size effect will be reflected from the resistance strain. Putting different sizes solder joints under the same tension and then testing them by Origin software fitting to the analysis. The experimental results show that the rectangular solder joints, whose thickness is0.23mm, sectional area is1.00mm2, becomes small under shear pull force resistance strain, which explains that this size solder creep damage under small, high reliability. On the other hand, when analyzed by using the finite element simulation software ANSYS simulation under shear pull force of individual rectangular lead-free solder joints, the shear creep of solder joint in the process of stress and strain distribution results as follows:under the same action of shear stress, the solder with the thickness of0.23mm, sectional area of1.00mm2, whose critical damage, Mises equivalent stress and Mises equivalent creep strain are small, which shows that creep damage is small. Since the simulation and experimental results match, it can be considered that when the thickness is0.23mm and the cross-sectional area is1.00mm2, the creep damage is smaller and reliability of the solder joints is better.