Fuji Electric Co Ltd introduced directly-water-cooled IGBT power modules for electric vehicles including hybrid cars at PCIM Europe 2014.
This time, the company announced (1) the technologies used for a module employed for a commercially-available vehicle and (2) a next-generation module that is smaller and lighter than it.
Module employed for commercially-available vehicle
The most distinguished feature of the module employed for the commercially-available vehicle is that aluminum (Al) is used for its heat sink. Al is lighter, cheaper and easier to process than copper (Cu), which is usually used.
Though the Al-based heat sink has many advantages, it also causes a problem. Specifically, the difference in thermal expansion coefficient between Al and the ceramic substrate (Si3N4) on which a power semiconductor device is mounted becomes larger, compared with Cu. As a result, the stress applied at the time of thermal cycling becomes stronger, causing cracks in the solder used for connecting the ceramic substrate and heat sink.
Therefore, Fuji Electric developed a new solder material. This time, the company used an "improved" SnSb-based solder material in place of a SnAg-based material. With the new solder material, it ensured a reliability high enough for automotive applications while using an Al heat sink.
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