Thermomechanical durability of lead-free electronic assemblies

Electronic cards used in aeronautical, military, and space applications can be used in harsh thermal environments throughout their life cycle. An electronic card can be described simply as an assembly of electronic components soldered onto a printed circuit board using a solder alloy. Temperature variations in particular have a detrimental effect on electronic assemblies. The difference in thermal expansion coefficients between the electronic components and the printed circuit board generates significant thermomechanical stresses at the solder joints, which can then crack due to fatigue, leading to card failure.

In order to ensure the proper functioning of electronic equipment throughout its life cycle, it is essential to evaluate the thermomechanical fatigue behavior of solder joints. This evaluation requires knowledge of the mechanical and thermomechanical properties of the various components of the assembly: the printed circuit board, the electronic components, and the solder alloy. The objective of this article is to present a comprehensive and structured methodology for evaluating the durability of electronic boards subjected to thermal cycles, from the analysis of the microstructure of the solder alloy and its behavior law to the development of statistical models of service life, whether analytical or based on numerical simulations.