Low-temperature assembling process with nanoscaled solder layers

Further development of electronics with higher requirements to integration density and reliability needs new technological solutions for the production of extremely small interconnections with less material and power consumption. This problem can be solved with the usage of nanoscaled solder materials, which have in comparison with bulk materials a reduced melting temperature due to another surface-to-volume ratio. A new concept based on the usage of ultra thin films as solder material and its combination with carrier foil was investigated. For this purpose the main solder material tin was sputtered with the thickness between 5 and 100 nm and then characterized by high resolution methods of scanning and transmission electron microscopy (SEM/TEM) and atomic force microscopy (AFM). The oxidation of nanoscaled layers was studied by X-ray and electron diffraction methods. The melting behavior of such nanoscaled foils was investigated by the method of fast chip DSC. In the first soldering experiments different passivation coatings and separation interlayers were studied on their convenience to produce a stable solder joint. For the improvement of the stability of a solder joint thin carrier metal foils can be used. During soldering process nanoscaled solder layers are melting at lower temperature and going into the intermetallic reaction. Whereas the carrier foil dominates the mechanical, electrical and thermal properties of the final solder joint.