Thermo-mechanical investigation of the reliability of embedded components in PCBs during processing and under bending loading

Abstract

FE models were developed to investigate the effect of processing and 3PB on the mechanical reliability of the embedded components. The results focus on the central region of resistor and capacitor. Local effects around the vias or copper layers are not considered. During processing, after processing and after bending compressive stresses are observed on both the embedded capacitor and the resistor. These results indicate that the risk of cracking on the components is low; however, the compressive stresses should be compared to the critical compressive stress limits of these materials. Similar results were obtained for the capacitor and the resistor. Due to the difference in the material properties (mainly CTE) higher compressive stresses are observed in the Alumina (resistor) compared to the Ceramic (capacitor). During processing, cooling causes the horizontal compressive stresses to increase, and heating causes them to decrease. Before the PCB is subjected to 3PB, the components possess compressive stresses which are caused by the lamination process. This is an advantage of the embedded components over a surface mounted component, where tensile stresses occur on the components. The 1mm bending loading causes the horizontal compressive stresses to reduce slightly. Bending the strip to 20 mm still does not cause the horizontal compressive stresses to diminish. The overall conclusion is that embedding the components is favorable to mounting a component on the surface of a PCB with respect to risk for component cracks. A high stiffness region was included in the model to represent the fiber glass around the components. This model was subjected to lamination process. The results show that the compressive stresses occurring on the components due to lamination is slightly affected by this region. Overall conclusions do not change with existence of a stiffer area above the components.