Effects of Extreme Temperature Swings ( $-\hbox{55}\ ^{\circ}\hbox{C}$ to 250 $^{\circ}\hbox{C}$) on Silicon Nitride Active Metal Brazing Substrates

Reliability of power electronic substrates has been one of the main issues of high-temperature packaging technologies. Widely used direct bonded copper (DBC) substrates, if subjected to wide temperature swings, suffer from copper layers peeling off from a ceramic because of the large thermal stresses resulting from the difference in coefficient of thermal expansion (CTE) between the copper and the ceramic (e.g., Al
₂
O
₃
or AlN). Recently, silicon nitride active metal brazing (Si
₃
N
₄
-AMB) substrate has been developed with the aim to utilize power electronic substrates for extreme environmental conditions. Si
₃
N
₄
-AMB has superior reliability because of the high mechanical strength of Si
₃
N
₄
. In this paper, the effects of extreme temperature swings (-55 °C to 250 °C) on Si
₃
N
₄
-AMB substrates were investigated to evaluate their applicability to harsh environment. Their high resistance to the peeling off of copper layers was confirmed. However, the surface-roughening phenomenon was observed on the surface of copper layers after the temperature cycling test. The mechanism of surface roughening was analyzed. It was found that the out-of-plane displacement of single grains, which is called the orange-peel phenomenon, occurred on the surface of the copper layers.