Microstructure evolution of innovative thermal bridge composite (i-TBC) for power electronics during elaboration

- A new substrate, innovative Thermal Bridge Composite (i-TBC), for high temperature electronic systems was developed.
- i-TBC was characterized through all elaborations steps: first cold rolling, heat treatment and second cold rolling.
- Ultra-fine and coarse grained areas can be formed during the cold rolling due to heterogeneous plastic deformation.
- Interface adherence and strain hardening were found to be dependent on rolling direction.

To improve the reliability of the power electronic modules for the high temperature applications, an innovative Thermal Bridge Composite (i-TBC) was designed. It has the architectured structure consisting of perforated FeNi36 sheet inserted between two Cu sheets. Due to simultaneous use of Cu and FeNi36, i-TBC possesses both a good thermal transverse conductivity and a limited longitudinal coefficient of thermal expansion. Different characterisations of i-TBC are required to understand the formation of its microstructure leading to the final properties. Therefore, the aim of this study was to analyse the integrity of Cu-Cu and Cu-FeNi36 interfaces as well as copper microstructure evolution throughout all elaboration steps: (i) first cold rolling, (ii) heat treatment and (iii) second cold rolling. First cold rolling did not lead to a bonding of Cu-Cu interfaces in the thermal bridge. Moreover, heterogeneity of Cu grain microstructure was observed with formation of ultra-fine grained structure close to junctions of Cu and FeNi36. The heat treatment led to a degradation of different interfaces adherence and to a complete copper recrystallization. Finally, the second cold rolling ensured an efficient solid welding of Cu-Cu interfaces and led to a heterogeneity of strain hardening of copper.

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