Mitsubishi Materials Corp developed the "DBA (direct bonded aluminum) substrate with thick Cu," an insulated circuit board made by directly attaching copper (Cu) to aluminum (Al), for inverters that control the power supplies of hybrid electric vehicles' (HEVs') high-power motors.
The heat resistances of insulated circuit boards used for inverters that control the power supplies of HEVs need to be reduced by using a thick plate of Cu, which has a high thermal conductivity, as a circuit material in order to cope with increases in heat generation density caused by increases in device power.
However, when silicon nitride, a high-strength ceramic, is used as an insulated substrate, the thickness of a Cu circuit material can be up to 0.8mm. When the thickness is further increased, the substrate becomes more likely to break, making commercialization difficult.
The DBA (direct bonded aluminum) substrate with thick Cu has a structure in which a Cu circuit material is directly joined to one or both of Al plates attached to both sides of a ceramic substrate. It allows to join a Cu circuit material having a thickness of about 3.0mm, which is four times thicker than before.
The high-purity Al layer located between the Cu plate and ceramic substrate reduces thermal stress and prevents the ceramic from cracking even under a temperature cycling condition of -40 to 125°C x 3,000 cycles or higher. Also, it is possible to use not only silicon nitride but aluminum nitride, which has a high thermal conductivity, as a ceramic substrate, enabling to realize various structures including one having a Cu plate on both sides of a substrate and one integrated with an Al heat sink.