Mechanical Stresses Induced by Thermal Gradients During Reflow Soldering in Repair and Resuse of Multilayer Ceramic Capacitors (Mlcc): Experiments and Simulation

Thermo-mechanical assessments of desoldering MLCC components from a PCB were undertaken, in order to estimate the possible damage to the component for its potential reuse on a new PCB. For that purpose Computational Fluid Dynamics (CFD) models were developed. In a second step the results of the CFD simulation were used as boundary conditions for FEM simulations, in order to compute the resulting mechanical stresses inside the component. The CFD simulations were supported by experimental studies. To experimentally analyze the temperature distributions during the desoldering process, thermocouples and PT-100 SMT sensors were placed on representative locations on the PCB. Experiments were carried out on a soldering repair station. The employed temperature sensing elements are able to record the dynamic changes in temperature during the reflow process, because they have a small thermal mass and correspondingly short response times. In order study the metallurgical reactions at the MLCC terminations during the desoldering process, a number of subsequent reflow experiments were conducted using a eutectic SnAgCu-solder. The solder joints of the MLCC components were microstructurally analyzed (metallography, SEM, EDX) after different numbers of reflows.