Synthesis and characterization of nanoscaled solder material

Abstract

A new concept based on the usage of ultra thin films as solder material will be presented here. For this purpose nanoscaled solder films of pure tin with the maximal thickness 100 nm were synthesized through physical vapor deposition method and then characterized with high resolution methods of scanning electron microscopy and atomic force microscopy. For the protection from oxidation during phase change analysis and also during storage and soldering process silicon nitride and carbon were sputtered in the same process chamber. The function of these coatings was tested through x-ray diffraction. The crystalline film under protective layer after cooling down is a sign for impermeability of oxygen. The thermodynamic properties like melting point and undercooling were researched with the sophisticated method of chip calorimetry that allows the measurements at very fast heating and cooling rates and therefore very small amounts of material can be studied. In the first soldering experiments passivation coatings were also tested on their convenience to produce a stable solder joint. Very promising solution for the production of stable solder joints was seen on the system consisting of alternating nanoscaled metal layers, which react during soldering process by building of an alloy. One of the components of such reactive solder systems has to serve for passivation at the same time. Carrier foil with the sputtered solder structures on its both sides can noticeably improve the stability of solder joint. After assembling at low temperature the solder structures transform into diffusion zone and the main physical properties like electrical and thermal conductivity and mechanical strength of the final solder joint are determined by the properties of the carrier foil. In this work such system consisting of silver carrier foil with nanoscaled solder layers of tin and gold was successfully tested.