No abstract

Modern electronic devices are more and more complex and multifunctional. It could be done by producing faster and more reliable active components and increasing number of passives and interconnections' density. To form such complex devices one can embed components in substrate of printed circuit board (PCB) or build multilayer boards. The other way is to form multi-terminal passive components to spare free surface and decrease number of interconnections. Authors created three-terminal thin-film (TF) resistors embedded in PCBs and investigated their selected properties such as resistance repeatability, long term stability, pulse durability and thermal characteristics.

This paper presents systematic studies of electrical, noise and long-term stability parameters of resistors (thinfilm 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 o C to 130 o 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.

Purpose -The purpose of this paper is to present the results of thermal analysis of cermet resistors made on alumina or LTCC substrate and polymer thick-film resistors embedded in FR-4 substrate. Design/methodology/approach -The study was performed using a thermal imaging method. The research was carried out with an additional consideration of such factors as sheet resistance (which depended on the type of resistive paste), the size and topology of element and the kind of contact material (Cu, Ag or Ni/Au). A few key points on the element were specified for which a more thorough analysis was carried out. The results were approximated by physically acceptable function which allowed to determine the influence of different mechanisms of heat transfer and determine their time and thermal constants. Findings -The effectiveness of heat dissipation from resistor is determined by the type of substrate material, width of conductive paths, and contact material. The best results were observed for elements with wider conductive paths made of Cu or Ni/Au. The LTCC substrate ensures the fastest achieving of stable temperature on the component. The changes of the temperature gradient in time can be described by a formula consisting of two or three exponent parts, each one presenting different mechanism of change.Research limitations/implications -These studies do not include more detailed determination of nature of found mechanisms of change. There has not also been established what form of the formula is more accurate physically description of the results for respective structure. Originality/value -The results provide important data of the thermal properties of the chosen materials. This allows to determine their usability for specific applications where heat distribution plays an important role. The used analysis method is proven to provide reliable results and can be considered to be used for further studies in that subject.

Purpose – The purpose of this paper is to characterize electrical properties of nickel-phosphorus (Ni-P) thin-film resistors made on FR-4 laminate in a wide range of temperature (from −180 to 20°C). Design/methodology/approach – The study was performed using resistors made of Ni-P foil with two different thicknesses (0.1 or 0.05 μm) and sheet resistances (100 or 250 Ω/sq), respectively. The resistance rectangular resistors had length and width from the range between 0.59 and 5.91 mm. The resistance versus temperature characteristics and their distribution as well as resistors ' durability to low-temperature thermal shocks were investigated. Findings – The results showed almost linear temperature dependence of resistance with a negative temperature coefficient of resistance of about −95 ppm/°C for 250 Ω/sq layer and −55 ppm/°C for 100 Ω/sq layer. A very small dimensional effect was observed for sheet resistance as well as for R(T) characteristic. Thin-film resistors are also characterized by very high durability to low-temperature thermal shocks. Originality/value – The results presented in this paper can be very useful for low-temperature applications of thin-film resistors made on printed circuit boards. They suggest possibility of wide applications of these components in a wide temperature range.