Chosen electrical, noise and stability characteristics of passive components embedded in printed circuit boards

Abstract

This paper presents systematic studies of electrical, noise and long-term stability parameters of resistors (thin-film or polymer thick-film) and capacitors embedded in Printed Circuit Boards (PCBs). The temperature dependence of resistance or capacitance were determined in a wide temperature range (from -180°C to 130°C) and analyzed as a function of geometry of passives and cladding process. The in-situ accelerated ageing process (basic properties of passives measured directly at ageing conditions) was carried out to perform long-term behavior analysis. Low frequency noise measurements were made in room temperature using noise spectra measurements in dc bridge configuration. The R(T) characteristics are linear with almost constant, negative value of differential TCR (of about -60 ppm/K for 100 Ω/sq Ni-P resistors). Both groups of investigated resistors revealed similar range of relative resistance changes after ageing processes but the results showed the quite different behavior of both groups versus time. It means that the dynamics of ageing changes was different. Only positive resistance changes were observed for Ni-P resistors, whereas the shape of characteristics for polymer ones were much more complex, exhibited increase as well as decrease in resistance under environmental exposure. 1/f noise generated by resistance fluctuations was found as the main noise component but the significant difference of noise level was observed for both groups of investigated resistors. The C(T) characteristics are nonlinear with larger capacitance changes at higher temperature. Capacitors exposed to elevated temperature exhibited capacitance and dissipation factor decrease. The relative changes were from the range from -12% to -2% for capacitance and up to -60% for dissipation factor. The value of relative drift of parameters was dependent strongly on dielectric composition and size. Moreover the results revealed nonlinear characteristics in temperature domain as well.