Andrzej Dziedzic

Stability of low ohmic thick-film resistors under pulsed operation

Abstract Durability of low ohmic thick-film resistors on pulse load with micro- and millisecond duration are described in this paper. Standard thick-film resistive compositions with sheet resistance of 10 Ohms/sq. (4311 and QS871 - DuPont; R400-10A - Heraeus) and 3 Ohms/sq. (QS870 - DuPont) were tested. Test resistors with resistance of 3 Ω were prepared on alumina substrates. Resistance changes were measured after 50 pulses at each voltage. Then the voltage was increased and the series of pulses were repeated until the resistance change exceeded 0.5%. Impact of long and short pulses was analyzed for selected pulse duration of 10 μs and 20 ms, respectively. The measurements were carried out for some selected resistors length. The resistors stressed by long pulses exhibited the highest durability, when the thermal interface between substrate and heatsink was filled by thermally conductive grease. In this case resistors made of 4311 and QS871 pastes can withstand the highest power density of about 19 W/mm2 and 18 W/mm2 for the samples with and without the overglaze, respectively. Short (microsecond) pulses had the least influence on overglazed resistors made of QS871 paste, for which the resistance change of +0.5% was observed at electric field intensity of about 85 ± 10 V/mm. Additionally, the critical electric field intensity and critical power density were determined for different pulse duration for selected resistor length of 2 mm. Pulse duration from 10 μs to 1 s with one point per decade were taken into account. The results shown, that overglazed resistors exhibit better durability for all tested resistive pastes for short pulses. However for the long pulses, the results are almost the same. This fact can be explained by limitation of heat transfer in the substrate. Repetitive pulse load was applied for selected samples. The results show that resistors exhibited very good stability after test with 0.1 million pulses with amplitude of 70% of critical electric field intensity values.

Thermal stability analysis of passive components embedded into printed circuit boards

Purpose The purpose of this paper is to investigate the behavior of embedded passives under changing temperature conditions. Influence of different temperature changes on the basic properties of embedded passives was analyzed. The main reason for these investigations was to determine functionality of passives for space application. Design/methodology/approach The investigations were based on the thin-film resistors made of Ni-P alloy, thick-film resistors made of carbon or carbon-silver inks, embedded capacitors made of FaradFlex materials and embedded inductor made in various configurations. Prepared samples were examined under the influence of a constant elevated temperature (100, 130 or 160°C) in a long period of time (minimum of 30 h), thermal cycles (from −40 to +85°C) or thermal shocks (from −40 to +105°C or from −40 to +125°C). Findings The achieved results revealed that resistance drift became bigger when the samples were treated at a higher constant temperature. At the same time, no significant difference in change in electrical properties for 50 and 100 Ω resistors was noticed. For all the tests, resistance change was below 2 per cent regardless of a value of the tested resistors. Conducted thermal shock studies indicate that thin-film resistors, coils and some thick-film resistors are characterized by minor variations in basic parameters. Some of the inks may show considerable resistance variations with temperature changes. Significant changes were also exhibited by embedded capacitors. Originality/value The knowledge about the behavior of the operating parameters of embedded components considering environmental conditions allow for development of more complex systems with integrated printed circuit boards.

Testing of the thermal model of microprocessor

The thermal, laboratory model of multi-core microprocessor was fabricated and analyzed. It consists of four separately powered thick-film resistors. Moreover, thermoelectric temperature sensor, suitable for monitoring of small and dynamic temperature changes on the microprocessor/heat sink border, was designed and tested. It consists of two separate substrates connected by nickel and silver wires. Its resolution is 113 μΥ/Κ. Static and dynamic measurements of the microprocessor model were carried out using the pyrometers or designed sensor.

Low temperature properties of thin-film resistors on laminates — A behavioral modeling

The aim of this paper was to elaborate novel two-dimensional behavioral temperature models for thin-film resistors fabricated onto FR-4 laminate. Investigated resistors were made of Ni-P alloy with two different thicknesses (0.1 μm or 0.05 μm) and the same different sheet resistances (100 ohm/sq or 250 ohm/sq). A large number of R(l, w, T) characteristics was measured automatically in cryostat system and analyzed for 10 coupons of resistors made of two types of Ni-P foil (Ni-P 100 and Ni-P 250) with very large planar differences of dimensions (both width and length from the range between 0.59 and 5.91 mm, 36 test resistors on one coupon) in the temperature range between −180°C and room temperature (+20°C). Every test coupon consisted of four subgroups of resistors — Normal, Long, Wide and Power and the elaborated model was made based on above mentioned measurements both for the whole coupon as well as every four subgroups. The mathematical model is the product of two polynomials — the first polynomial describes resistance dependence on planar resistor dimensions, while the second one approximates temperature dependence of normalized resistance. Special computational methods were developed and used for multidimensional approximation purpose. Comparison of this model with similar model for thick-film resistors was presented.

Influence of thermal treatment on electrical properties of transparent TiO 2 :Nb thin films

This study presents electrical behavior of TiO2:Nb thin films with niobium concentration up to 13 at. %. The layers were deposited on Corning 7059 glass substrates by unipolar dc pulse magnetron co-sputtering from TiO2 and Nb composite target. Manufactured films underwent thermal treatment in the ambient air up to the 873 K. Dependencies between the temperature and electrical conductivity as well as thermoelectric force were determined within the range of 300-578 K. An amorphous TiO2:Nb films with optical transparency of about 50% in the visible range and resistivity higher than 8 Ωcm were achieved directly after deposition for the target power density discharge in the range of 4.7-5.8 W/cm2. During the post process air thermal treatment a rapid resistivity decrease (over 1000×) was observed up to final value of 1.5×10-3 Qcm at 300 K. Moreover the conversion from n-type semiconductivity to metallic conductivity was observed. Simultaneously the layers exhibited the substantial increase in the transparency and decrease in Seebeck coefficient from -160 μV/K to -35 μV/K. Electrical behavior of the films where examined with the use of NiCrSi/Ag thin films contacts pads according to Kelvin method.

Ink-jet printed conductive films — Geometrical and electrical characterization

This paper presents the results of electrical and geometrical characterization of conductive films ink-jet printed on flexible substrates. Two commercially available single component nanoinks from Amepox, AX JP-6n and AX JP-60n, based on silver grains with 3-7 nm or 50-80 nm diameters were deposited onto Kapton or Mylar substrates and properly cured (sintered). Test structures, composed of a number of different patterns, allow optical inspection as well as measurement of geometrical (planar size, cross-section) and electrical (resistivity, sheet resistance) properties. Presented results show that the control of geometry of ink-jet printed films is more difficult to control than standard screen-printed ones. The cross-section of such paths has two lateral peaks (sometimes very strong) and very thin layer between them. This is related with viscosity and surface tension of the applied ink. There are also large differences in sheet resistance of layers - both kind of inks as well as substrate affects this parameter. The smallest received value, about 8 mΩ/sq (recalculated for 25 μm thick film) is larger than for high-temperature silver cermet pastes (approx. 2-3 mΩ/sq), but smaller than for polymer thick-film conductive inks (approx. 10-30 mΩ/sq).

Selected electrical properties of high ohmic thick-film resistors

Results of fabrication as well as electrical and stability characterization of thick-film high ohmic resistors are described in this paper. Five commercially available resistive compositions with sheet resistance of 1, 10, and 100 MΩ/sq were applied. The best properties were obtained for the lowest sheet resistance pastes, for which voltage coefficient of resistance (VCR) was lower than 3 ppm/V and hot temperature coefficient of resistance (HTCR) below 50 ppm/°C. Effect of resistor length on sheet resistance and impact of termination material were analyzed. High voltage pulse stress at 2 kV had negligible influence on resistors’ properties.

The Thermoelectrical Behaviour of Tantalum-Antimony-Germanium Thin Films

In this work the thermoelectrical properties of newly developed thin films materials, based on tantalum-antimony-germanium (TAG) alloys are presented. They were processed with the use of magnetron sputtering. The thermoelectric sensitivity, electrical resistivity and power factor were estimated in the temperatures range: 300 K-550 K for various proportions of tantalum in the Ge-Sb target. The target compositions were optimized with regard to the deposited layers parameters. The obtained TAG thin films withstand the temperature ca 920 K, show the thermoelectric sensitivity ca 200 muV/K and are suitable for usage in joints with thick films. They were subjected to verification in thermocouples systems where the TAG film constituted one electrode and MeSi thin film or Pd-Ag thick film the other. As thermocouples they displayed the similar electrical properties, irrespective of the substrate they were deposited on, which were made out of amorphous glass, sital or LTCC ceramic substrate.