Reliability assessment of discrete passive components embedded into PCB core

Abstract

This paper will present the research results for reliability of two embedding technologies in comparison to the current standard - surface mount technology. The chosen embedding approaches utilize a cavity to place the necessary components into the PCB core. The difference is found in the way the component is connected to the PCB routing. For the first approach the circuit is first assembled on a carrier substrate using conventional surface mount technology (SMT). The solder paste is printed, the components are placed and the substrate board is soldered afterwards. The base substrate is then put together with prepared additional layers holding preformed cavities at the component locations. After another top layer has been added, the stack is finally laminated and the components are placed in the PCB core. The second approach is based on placing the components, then putting together the stack-up as described earlier and followed also with the laminating process. However the components have not been soldered. Instead an opening to the component's terminals is created through laservias. Then galvanic deposition is utilized to establish the connection to the PCB routing. For a comparison of the technologies samples with embedded resistors and ceramic capacitors in various sizes for the technologies as well as standard SMT have been prepared. To assess the reliability potential the samples have undergone temperature cycling tests. The testing is supported with FEM simulations which aided in the detection of critical design parameters and assess the residual manufacturing stress/strain states. The results of the investigations have shown that the damage mechanisms and predominant failure sites of the SMT & Cavity embedding variant is significantly different from conventional SMT. Here the resin material should be adopted to increase lifetimes even more. In the case of Microvia & Cavity the geometry of the microvia is essential towards the achievable reliability. Overall the results indicate the increased reliability potential of the novel approaches.