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Transient Liquid Phase Soldering for Lead-Free Joining of Power Electronic Modules in High Temperature Applications
Keywords: high temperature application, transient liquid phase bonding/ soldering, power electronic
The study focuses on a new variant of transient liquid phase soldering on tin based solder with copper powder as an alternative for lead free joining of high power electronics. The current used lead-free joining technics like gold-rich solders and silver sintering are well suited for high temperature applications due to the high metal price they have a limited acceptance. Through a specific process we have succeeded to produce an almost pore-free joint gap, based on a paste of SAC405 solder powder, copper powder and a solvent with a weak effect in reduction. The resulting interconnection is characterized by an almost complete transformation into intermetallic phases of Cu6Sn5 and Cu3Sn. Infect of these the melting point of the transformed joining could be raised up to the decomposition temperature of the Cu6Sn5 intermetallic phase which is 415 °C. A two-step process is developed which allows us to eliminate the typical framework structure that forms as a result of the immediate reaction of the liquid SAC405 solder with the higher melted copper powder to form the Cu6Sn5 and Cu3Sn intermetallic phases. We will show chips assembled using the new transient liquid solder paste for power modules. Early reliability results will be shown.
Christian Ehrhardt, Engineer for Material Science
Fraunhofer IZM
Berlin,
Germany


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