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Numerical study of thermomechanical fatigue influence of intermetallic compounds in a lead free solder joint

Pin, Samuel and Frémont, Hélène and Gracia, Alexandra Numerical study of thermomechanical fatigue influence of intermetallic compounds in a lead free solder joint. (2016) In: ESTC 2016 (6th Electronics System-Integration Technology Conference), 13 September 2016 - 16 September 2016 (Grenoble, France).

(Document in English)

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Official URL: http://dx.doi.org/10.1109/ESTC.2016.7764674


As electronics is increasingly present the reliability of automotive and aircraft equipment is linked to the reliability of electronic boards. Solder bumps are subjected to multiple stresses (e.g. mechanical, thermal, thermo-mechanical, coupled electro-thermal) due to usage conditions. In the scope of RoHS directive, solder joints are made of lead-free alloys. Very promising candidates to replacing standard SnPb solders in electronic assemblies are based on Tin-Silver-Copper alloys, commonly referred to as SAC. The intermetallic compounds (IMC) located at the interfaces of a lead free solder joint form a layer with usually different mechanical properties from the rest of the volume. They depend on the type of finishes and the solder alloy reacting together. The resulting compound is stiffer and more fragile than the solder itself. The IMC are of great concern when it comes to the thermomechanical fatigue characterization of a solder. Indeed, the thickness of the IMC layer increases in function of the exposure duration to high temperature due to atomic diffusion. The whole rigidity of the assembly increases and can lead to some changes in the solder behavior in the vicinity of the interfaces. Fatigue characterization requires to correlate the relevant failure mechanisms of a model in order to be predictive in different conditions. For that purpose, finite element analyses (FEA) must be accurate and representative. Therefore, it has been decided to evaluate the influence of IMC prone to be implemented in simulations. The drifting stiffness, the concentration of stress or the accumulation of viscoplastic strain near the interfaces are the main aspects investigated in this study using two different FE models made in ABAQUS. First, the simulation of a shear test performed on “grooved” single lap shear specimens 1 is used to quantify the error made on the shear modulus with different thicknesses of IMC. This model is also necessary to determine the creep behavior of the lead free solder in another study by fitting the response of such a stack to the experimental curves. A second model composed of a solder ball with its interfacial IMC has been made (cf. Figure 1). It is used to calculate the increasing in global stiffness due to IMC. The final purpose is to highlight the weaknesses to take into account in fatigue life design for which IMC could be responsible. In a final study this model is to be implemented with a proper nonlinear solder material behavior to correlate with thermomechanical fatigue tests of BGA components.

Item Type:Conference or Workshop Item (Paper)
Additional Information:Thanks to IEEE. The original document is available on IEEE Xplore :http://ieeexplore.ieee.org/document/7764674/.© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works
HAL Id:hal-01688091
Audience (conference):International conference proceedings
Uncontrolled Keywords:
Institution:Other partners > Bordeaux INP - BINP (FRANCE)
French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Other partners > IRT Saint Exupéry - Institut de Recherche Technologique (FRANCE)
Other partners > Université de Bordeaux (FRANCE)
Laboratory name:
Air bus Group Innovations - Continental Automotive France - Hirex Engineering - Labinal Power Systems - Nexio - Thales Alenia Space France - French National Agency for Research
Deposited On:19 Jan 2018 09:11

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