Partenaires et organisations internationales
(Anglais)
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AT, BE, BG, CZ, FI, FR, DE, EL, HU, IE, IT, NL, PL, PT, RO, CS, SK, SI, ES, SE, CH, UK
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Résumé des résultats (Abstract)
(Anglais)
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Particle reinforcement of lead free solders for superior mechanical /thermomechanical properties were successfully demonstrated. Lead free solder composites were prepared by mechanical dispersion of commercial Ni (3-7µm), Cu (3-20 µm) or custom made nanometer sized poly (vinyl pyridine) PVP coated copper oxide Cu2O/PVP (~150 nm) particles. The base matrix alloy was Sn4Ag0.5Cu and the amount of particle addition was varied from (2-10vol.%). Composite solder joints produced with Cu substrate were tested both in shear and tension. An increase of ultimate tensile strength ~25% for composite Ni(4vol.%) reinforced solder joints were achieved over non reinforced joints. Solid state isothermal aging experiments at 150 °C upto 144 hrs were performed on Cu substrate. The effect of reinforcement particle on the interfacial intermetallic (IM) layer growth were analysed based on the growth exponents. Intermetallic layer growth exponent (n) for the composite solders produced by adding Cu(micron or nanosized-1.5vol.%) were estimated to be in the range of 0.3 which is indicative of a grain boundary dominant diffusion mechanism. The aging study exploits the fact that the nanosized reinforcements due to its reduced diffusion distances are capable of quicker transformation into intermetallics. Such a quick transformation aids in achieving an earlier onset of steady-state growth exponent. Microstructural refinement for composite prepared with nano additives exhibit fine AgSn needle like network surrounding the ?-Sn islands comparable to a non reinforced Sn-4.0Ag-0.5Cu alloy was achieved. For the composite prepared with micron sized Cu particles huge AgSn platelets were observed. Such AgSn platelets are unfavoured to ensure good joint reliability. Mechanical tests of the aged composite specimens indicate a stability of the mechanical response (ultimate stress) for the composite reinforced with nano Cu additives. Current investigations supports that addition of suitable particles into the solder is a promising solution to simultaneously resolve the problem of thick IM layer growth and improving the thermomechanical reliability of the joints.
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