Abstract
For the SnAgCu alloys, previous hardness test results suggested that high temperature thermal ageing causes a quick and significant drop in the mechanical properties. However, to date, the acceleration law of thermal ageing and the relationship between thermal ageing and fatigue mechanical behavior of SnAgCu alloys are still unknown. The aim of this paper is to understand the mechanical changes during thermal ageing of Sn3.0Ag0.5Cu alloy and their impact on solder joint reliability under mechanical stresses. In a first part, influence of thermal ageing on mechanical behavior is analyzed by means of hardness tests, reversed tensile tests on dog-bone specimens and compression test on solder balls used for electronic components. In the second part, the impact of thermal ageing on the solder joint reliability is analyzed thanks to torsion tests on assembled boards. The results show systematically a decrease of 20–60% of the mechanical properties or of the number of cycles to failure (in the case of torsion test). These results lead to enlarge tests conditions in order to define the fields where the influence of thermal ageing cannot be neglected.
Highlights
Since the RoHS directive implemented on July 2006, mass market leant towards lead-free solder joints for electronic assemblies and most of electronic manufacturers select SnAgCu alloys
The reliability of SnAgCu solder joints is still not proven in harsh environments and long mission profile applications
The aim of this paper is to understand the mechanical changes during thermal ageing of SnAgCu alloys and their impact on solder joint reliability under cyclic mechanical loadings
Summary
Since the RoHS directive implemented on July 2006, mass market leant towards lead-free solder joints for electronic assemblies and most of electronic manufacturers select SnAgCu alloys. For the SnAgCu alloys, previous hardness test results [2] suggested that high temperature thermal ageing causes a significant drop in mechanical properties. At least 400 h at 125 °C are necessary to reach a stabilization level, which represents years of storage at room temperature This ageing condition is often encountered in long lifetime electronic products but not taken into account during the reliability testing. After 400 h at 125 °C, the hardness value decreased of about 18% while the grain size increased of about 300% These previous results leaded to the analysis of the influence of thermal ageing on the mechanical and damage behavior. The aim of this paper is to understand the mechanical changes during thermal ageing of SnAgCu alloys and their impact on solder joint reliability under cyclic mechanical loadings. Impact of thermal ageing on the solder joint reliability was analyzed thanks to torsion tests on assembled boards
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