Joining At Low Temperatures with Organic Silver Complexes

Advancing miniaturisation and complexity of electronic components lead to higher power densities and therefore to elevated operating temperatures. Increasing power throughput combined with space-saving and light weighted design impede the heat management in electronic systems leading to increase in temperature of the solder materials. Excessive heating of a solder joint in the extreme can result in malfunction and even in damage of the device. For these reasons especially in solder technologies conventional processes have reached their application limits in respect of their long-term reliabilities.

From this situation fundamental interest results in advanced joining technologies. In an effort to seek for alternatives different approaches were proposed, e.g. utilizing a phenomenon known as size-dependent melting point depression of very small particles to bond materials at temperatures some hundreds degrees below the bulk materials own melting point. The bonds formed will not remelt below the melting point of the bulk material. In practice when small particles are heated those that come into contact quickly fuse together in a sintering process.

Low-temperature sintering processes are discussed particularly for silver nanoparticles formulated and applied as pastes. Silver is characterized by high electric and thermal conductivity so that heat transport through a silver layer is effective.

The silver pastes basically consist of organic silver complexes as solid material with an added fluid. They are able to generate silver nanoparticles by heat treatment. Numerous suchlike substances have already been developed. Most established are alkylcarboxylates with chain lengths of >10 carbon atoms. In recent years alkyl amines have gained increasing attention.

For further investigations various silver complexes were synthesized where the silver atoms are linked either with a carboxyl group or with an amino group. Their properties in view of their metallization applicability were investigated and compared. For characterization TG measurements were conducted.

Based on these results a method for fabricating silver layers for joining processes at low temperatures via generation of nanoparticles by heat treatment is introduced. Such yielded joints are evaluated by cross sections of SEM investigations. An organic silver complex of a novel carboxylate type was used among others that possesses by heat treatment a silver metallic molten metal like phase, which is advantageous and harnessed in the joining process.