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|Intermetallic connections for high temperature applications|
|Keywords: intermetallic connection, interdiffusion soldering, remelting temperature|
|The trend for power electronics based on DCB application with mounted IGBT components will result in increasing of temperature above 200°C for the next 10 years. For soft soldering technology there are no suitable alloys in form of solder paste for operation temperature of more than 250°C. The operation temperature based on the homolog temperature should have a factor to the melting temperature not greater than 0.8 . For using soft solder alloys based on solder paste there would be a possibility with a combination of thermal solidification and isothermal solidification. Such technologies are known under the names solid liquid interdiffusion (SLID) and transient liquid phase soldering (TLP) . Both of them are limited by the stand-off of solder joint that has to be very small for realization of such intermetallic connection. Through this limitation the electroplated solder layer or a thin solder preform is normally used. Smaller stand-off results in higher thermomechanical stress and can be a reason for earlier failure of the connection. As part of German founded project for new technology in the automotive market together with high power modules for e-mobility (HPC) a new technology based on mixing of standard alloy SnCu in form of solder paste with copper powder or rather copper paste was developed . This technology enables the production of intermetallic interconnections with standard parameters of soldering of SnCu. The produced solder joints consist of homogenously distributed copper particles surrounded by grown together SnCu intermetallic phases. The resulting solder joint can withstand much higher temperatures up to 300°C that was proven by remelting temperature measurement . Another possibility for acceleration of the interdiffusion is the usage of low melting alloys. They can be processed in form of standard solder paste and processed at the temperatures typical for standard lead-free solders like SnAgCu or SnCu. During one alloying components will be transformed to high melting intermetallic phase another one (with higher melting point) will remain in the solder joint. That would lead to an increase in the melting temperature of the finished soldered joint and its higher thermal stability.|
University of Rostock