Harsh Marine Environment - Toward Corrosion Simulation

International audienc

Dynamics of the corrosion for SAC305 solder alloy in salt environment

This study presents the corrosion dynamics of SAC305 solder alloy in two configurations (BGA solder balls components and solder material in globule) using a neutral salt spray test (NSS). SAC305 solder alloys were aged in different exposure durations ranging from 24 to 96 hours in a salt spray chamber with one salinity of 5 % NaCl at five temperatures ranging from 25°C to 45°C. Corrosion morphology, chemical composition and distribution of the elements in the corroded area and the corrosion product phases produced respectively after OM, SEM, EDX and XRD were also analyzed. The visible corrosion criterion defined on the OM and SEM results showed that the corroded areas are visible after 72h at 25°C, 60h at 30°C, 48h at 35°C, 36h at 40°C and only 24 h, at 45°C in case of BGAs solder balls components. The corroded area becomes larger at 96 hours. This indicates that temperature accelerates the corrosion mechanism. Moreover, according to the EDX result, tin (Sn), oxygen (O), and chloride ion (Cl-) were detected in the corroded area on solder balls. An activation energy (Ea) of 0.81 eV has been calculated. XRD measurements confirmed that a complex oxide chloride hydroxide (Sn3O(OH)2Cl2) was formed as a corrosion product on SAC globules. Finally, the kinetics of the failure mechanism of corrosion was investigated to refine the dynamic models of the degradation and overlay it on excessive stresses by simulations in order to predict lead-free solder alloys' lifetime

Evaluation of SAC solder joint thermomechanical fatigue in different types of components

As lead-free solder joints mechanical behavior is dependent on their microstructural characteristics, locations and geometries, developing accurate solder joint fatigue models implies correctly identifying the microstructural changes that undergo the solder alloy during thermal cycling. The present work aims at evaluating thermomechanical SAC (Sn-Ag-Cu) solder joints reliability by studying different types of components. Lifetimes data coupled to the microstructural investigation allowed us to study the microstructural process leading to SAC solder joints failure and to identify the different factors that must be considered in Finite Element Models (FEM) of electronic lead-free assemblies under thermomechanical loading. Tin recrystallization and strain-enhanced precipitate coarsening led to intergranular cracking in the solder joints, which was the first identified failure mode. A brittle interfacial crack that does not need tin grain recrystallization to propagate was the second detected cracking mode. The different behavior of one solder joint compared to another can be explained either by the presence of an unexpected microstructure highlighted during the characterization of the as-reflowed solder or by the design and the materials properties that unify each package