Investigations on interconnection technologies for CPV systems

Long lifetime of concentrator photovoltaic systems strongly depends on the reliability of the interconnection technologies. In this paper the result of experiments to investigate the long term stability of a lead free Sn95.5Ag4Cu0.5 solder alloy and two isotropic conductive adhesives are presented. Samples were subjected to accelerated aging consisting of high temperature storage at 150 °C and temperature cycles between -30 and 125 °C. The samples were characterised after various aging steps by x-ray imaging, scanning electron microscope and energy dispersive x-ray. The experiments showed a degradation of the soldered samples through the formation of cracks in the joint. Also a growth of brittle intermetallic phases was determined which can promote the generation of cracks. One of the tested adhesives shows a positive post curing and no degradation after aging. The second adhesive shows some cracks after the hard tests.