Deformation and Oxidation of Copper Metallization on Ceramic Substrate During Thermal Cycling From −40 °C to 250 °C

The active-metal-brazed copper (AMC) on Si₃N₄ ceramic substrate was used to fabricate the all-silicon carbide (SiC) high-temperature power modules. Its reliability was evaluated under the conditions of high-temperature storage (HTS) at 250 °C and thermal cycling test (TCT) from -40 °C to 250 °C. During HTS, the AMC substrate was stable without deformation of the Cu layer. The shear strength of the Au-Ge eutectic-bonded SiC power devices slowly decreased with storage time, from the original 83 to 60 MPa after 3000 h. During TCT, no detachment of the Cu layer was observed even after 3000 cycles. However, severe plastic deformation of the Cu layer, which was induced by the cyclic thermal stresses, was observed. The plastic deformation progressed as the number of the thermal cycles increased. The deformation of the Cu layer was described by the peak-valley distance Rz of the Cu layer. Rz increased with thermal cycles. The plastic deformation of the Cu layer fractured its Ni(P) top layer, resulting in oxidation wherein. The Cu deformation degraded the bonding interface of the device with the Au-Ge solder, leading to sharp decrease of the shear strength. Another type of degradation of the AMC substrate was proposed.