Effect of mechanical properties of the ceramic substrate on the thermal fatigue of Cu metallized ceramic substrates

The effects of temperature cycling from -40°C to 250°C on the active metal brazing (AMB) substrates were investigated using silicon nitride ceramics or aluminum nitride ceramics with different fracture toughness and strength. Visual inspection of the substrates after 1000 cycles hardly detected failure in the Si
₃
N
₄
-AMB substrates with the high fracture toughness of 8.0 MPa·m
^1/2
. By contrast, the Si
₃
N
₄
-AMB substrates with the lower fracture toughness of ca. 5 MPa·m
^1/2
exhibited delamination of the Cu layer at only 20 or 50 thermal cycles. Detachment of the Cu layer occurred at seven cycles when the AlN-AMB substrates with fracture toughness of 3.2 MPa·m
^1/2
were employed. It was found that the endurance to thermal fatigue of AMB substrates was controlled by the fracture toughness of ceramic substrates rather than the fracture strength.