Reliability study on SMD components on an organic substrate with a thick copper core for power electronics applications

In this work we present the results on a reliability study on SMD components mounted on an organic power electronics substrate. The substrate technology has been developed to meet the needs of high ampacity and thermal conductivity with an organic substrate material. Therefore a thick structured copper core was introduced throughout the entire substrate size (see fig. 1). On top of the copper core common FR4 multilayer structures are realised to create a typical SMD PCB surface. The bottom of the copper core was covered with one prepreg with a high thermal conductivity and one copper layer to be able to connect to a heat sink. The copper core becomes structured to enable the use as the layer for conducting high currents. Therefore insulation trenches were manufactured and plugged with a polymer. Introducing a copper core as described changes the thermo-mechanical behaviour of the substrate. Hence, due to the higher stiffness of the copper core PCB, the thermo-mechanical reliability of SMD components can be affected as well. Thermal cycling and shock tests were conducted to reveal the life time of ceramic chip resistors with a size of 0603, 0805 and 1206 in the case of mounting position entirely over the copper core or FR4, over the copper core/FR4 interface or over the copper core insulation trenches (see fig. 2). A specific test board was designed and manufactured (see fig. 3). The achieved results indicate some differences in the reliability of the components depending on the mounting position. In case of component mounting over the copper much higher failure counts have been seen compared to components mounted over FR4 (see fig. 4). Mounting the components on top of the copper core/FR4 interface or insulation trenches changes the reliability in dependence of the component size.