Paweł Winiarski

Analysis of steady-state and transient thermal properties of cermet, polymer and LTCC thick-film resistors

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 wi...

Analysis of long-term stability of capacitors embedded in printed circuit boards

This paper presents studies of long-term stability of capacitors embedded in printed circuit boards. Planar capacitors fabricated from FaradFlex dielectric foil with copper plates laminated to FR-4 substrate served as test structures. The dielectric was BaTiO3 ceramic/polymer composition with various fillers and consequently various dielectric constants. Moreover test samples differed in composition thickness and surface size. The investigated capacitors were covered with LDP 2×106 (Laser Drillable Prepreg) protective layers to achieve embedded structures. The behaviour of capacitance as well as dissipation factor was investigated for two values of frequency (1 and 10 kHz) in order to determine their long-term stability. The in-situ accelerated ageing process (capacitance and dissipation factor of test samples performed directly at the ageing conditions) was carried out to perform long-term behaviour analysis. Temperature characteristics both before and after aging process were performed for determination of influence of environmental exposure. Additionally insulation resistance under voltage and temperature stress was monitored and analyzed.

Reactance components embedded in printed circuit boards

Purpose – This paper aims to report the investigations of capacitors and inductors embedded into printed circuit boards (PCBs) designed in various layouts. Design/methodology/approach – The research were focused on the components embedded into four-layer PCBs with different structures of the inner layers. Three special capacitive laminates for manufacturing of thin-film embedded capacitors and several types of coils in the form of a spiral, meander and solenoid are described. In addition, a part of the spiral-type coils was formed with an aperture in the center in which the magnetic core, made of soft magnetic composites’ material was placed to increase the coil inductance. Findings – Various constructions of embedded capacitors and coils were designed and manufactured. Capacitance and loss tangent of capacitors to determine the repeatability of the production process were determined. Capacitor’s long-term stability analysis was performed by exposing test samples to elevated temperatures (70, 100 or 130°C...

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

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.

Selected properties of multi-terminal resistors embedded in printed circuit boards

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.

AC properties of low-pass RC filters embedded in printed circuit boards

Impedance Spectroscopy (IS) is a widely used measurement technique for determining the characteristics of a variety of materials and systems. Analysis of object’s AC-response can allow determine of different electrical properties due to its structure. IS can also be used to study electronic components such as gas and humidity sensors, thermistors, varistors, capacitors or resistors. The resulting impedance spectrum can be approximated by electrical equivalent circuit. However, It is difficult to find papers dedicated to the electronic systems investigated by IS method. For this reason authors analyzed properties of RC low-pass filters embedded in printed circuit boards using IS technique. These four-contact structures were made of special Ohmega/FaradFlex® composite material. It consists of a resistive/capacitive core containing OhmegaPly RCM layer (resistive NiP alloy) laminated to FaradFlex dielectric of Oak-Mitsui company. Analysis of the measurements results using impedance spectroscopy allowed a more precise determination of the filter parameters than an analysis using standard method based on ideal components. Additionally selected filters were subjected to one of the aging process (thermal aging or thermal-humidity exposure), and found that this results in a frequency shift of the filter.

Stability of thin-film resistors embedded in printed circuit boards

Long-term stability of embedded passives is very important issue. To determine this matter an aging process can be used, where test samples are exposed to environmental conditions. Objective of this research was analyzing reliability of thin-film resistors based on Ohmega-Ply® technology. Resistive material was a nickel-phosphorus (Ni-P) alloy (with sheet resistance 25 ¿/sq or 100 ¿/sq) on FR-4 substrate. A number of variables were considered in this study (sheet resistance, geometry of resistor, type of cladding, laser trimming, pulse stress and environmental conditions). Two different accelerated ageing processes ¿ Ex-Situ (samples exposed to elevated temperature and/or relative humidity but resistance measurements made at room temperature) and In-Situ (resistance of test samples performed directly at the ageing conditions) were carried out to perform long-term behavior analysis. The results revealed a significant influence of thickness of resistor, type of cladding and temperature on stability of investigated structures. Signification of other factors was negligible.

Low-temperature properties of capacitors embedded into Printed Circuit Boards

This paper presents low-temperature properties of capacitors embedded in Printed Circuit Boards. Planar capacitors, differed in composition thickness and surface size, were fabricated from FaradFlex dielectric foil with copper plates laminated to FR-4 substrate. The dielectric tapes were polymer or BaTiO3/polymer compositions with various dielectric constants. The investigated capacitors were covered with LDP 2×106 (Laser Drillable Prepreg) protective layers to achieve embedded structures. The temperature dependences of capacitance as well as dissipation factor (i.e. C(T) and tgδ(T) characteristics) were investigated for two values of frequency (1 and 10 kHz) in a wide temperature range between -180 °C and room temperature. Moreover durability of capacitors to low-temperature thermal shocks (between liquid nitrogen and room temperature) are reported and analyzed.

Pulse durability of thin-film resistors embedded in printed circuit boards

The passives (resistors, capacitors, inductors) embedded in printed circuit boards (PCBs) can improve electrical properties and reliability of electronic systems. Pulse durability is an important parameter of passive components and active devices. In the case of resistors it allows to determine many properties including maximum power dissipation, resistance change or phenomena occurring in resistor structures after pulse surging. Furthermore pulse durability defines utility for pulse circuits. Thus this work presents pulse durability of thin-film resistors made on the surface or embedded in Printed Circuit Boards. Investigated test structures were made of nickel-phosphorus (Ni-P) alloy on FR-4 laminate with sheet resistance 25 Ω/sq or 100 Ω/sq. Pulse durability was determined by calculating the maximum nondestructive electric field, maximum nondestructive surface power density or maximum nondestructive volume power density. These parameters were determined in dependence on pulse duration, resistor geometry (length, width, aspect ratio), type of cladding, laser trimming and accelerated aging process.

Long-term stability of resistors embedded in printed circuit board

This paper presents principle of manufacturing process of thin-film resistors embedded in printed circuit boards (PCB) as well as their chosen electrical and stability properties. Test structures were fabricated on FR-4 laminate with Ohmega-Ply® technique basing on nickel-phosphorus alloy (NiP). The thickness of resistive foil was 0.4 µm and 0.1 µm with sheet resistance 25 Ω/sq. and 100 Ω/sq., respectively. Moreover, part of the samples was covered with two different types of cladding - Resin Coated Copper (RCC) or Laser Drillable Prepreg (LDP). The long-term stability of components was determined basing on resistance changes during ageing tests. The resistance was measured in two cases: at room temperature after keeping of samples at elevated temperature and/or humidity or directly during heating of resistors on hot plate. The measurements were carried out for structures after fabrication process as well as for resistors trimmed with Nd-YAG laser or treated with voltage pulses.