Forschungsprogramme
(Englisch)
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COST-Action MP0602 - Advanced Solder Materials for High Temperature Application- their nature, design, process and control in a multiscale domain
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Kurzbeschreibung
(Englisch)
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The main objective of the project is to develop nanostructured lead free solder with application-oriented properties and to enable a low temperature, short duration bonding method for fabrication of high-temperature (260-320°C), high performance joints. Integration into a group project of COST MP0602 and a close cooperation with the LMAF-EPFL (Prof. Botsis) is envisaged.
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, BG, CH, CZ, DE, DK, FI, FR, HU, IE, IT, NL, PL, PT, RO, RS, SE, SI, SK, TR, UK
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Abstract
(Englisch)
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The scope of the project was to obtain alternative advanced soldering process fulfilling the requirements of thermal stability of electronic devices. The two novel nanotechnological approaches were investigated: the solder modification by nanoparticles and the application of nanolayers within Transient Liquid Phase Bonding (TLP) Process. By the modification of the SnAgCu (SAC) solder with Cu nanoparticles the growth of the intermetallics layer at the solder-base material interface at the service temperatures was limited and the thermomechnical performance and reliability of the solder joints were strongly improved. It was shown that the Cu nanoparticles are fully transformed into stable Cu6Sn5 intermetallics after the initial reflow and thus their further growth is improbable. In co-operation with LMAF/EPFL the effect of the particles on the shear response and the creep strain rate of composite lead-free solder joints was studied with a combined experimental-theoretical approach. Shear tests indicated a 23% strength increase for Cu nanoparticle reinforced SAC solder when compared to the non-reinforced solder material. It was also shown that such modified solder provides improved creep properties at low applied stresses. Very good correlation was observed between model and experimental results. The nano-layer assembly for the TLP process allows for shortening the process duration time into minutes. According to the thermodynamic data study the high-melting point intermetallic phases Cu6Sn5 and Cu3Sn were achieved as the final phases for the Cu-Sn-Cu joints. A model describing the mass transport and reaction processes during solder joint formation and service life was developed in collaboration with AGH/Poland and used to simulate the simultaneous isothermal growth of IMCs in the Cu-Sn system. The model is based on Darken method (bi-velocity), involving the different molar volumes in the system and Wagner boundary conditions. It combines the interdiffusion, reactive diffusion and the effective flux constraints to couple processes occurring at different time scales. The isothermal solidification during the TLP process was assumed to occur simultanously at both advancing solid/liquid interfaces as a consequence of continued diffusion of solute from the liquid phase into the adjacent solid phases, i.e. bilateral counter-flow movement of the solid/liquid interfaces.
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