Thick Film Hybrid Circuit Research Articles

Microwave Characterization of a Thick Film System for Hybrid Packaging Applications

Abstract Thick film material systems for hybrid applications have existed for many years and have provided the ability to create high density interconnects in industries such as consumer, military, telecommunications and automotive electronic devices. Despite their breadth of applications, thick film hybrid circuits are rarely utilized for microwave/millimeter-wave packaging applications. In this work, the DuPont™ QM44 thick film dielectric is characterized up to 40 GHz. Test samples to characterize this thick film system consisted of the screen-printed QM44 multilayer dielectric and QG150 gold thick film conductor and vias on top of a 96% alumina substrate. Three different fabrication methods were used in the fabrication of the test samples to illustrate the effect of processing techniques on material loss properties, with the conductor lines formed through standard screen printing, chemical etching, and laser ablation. Laser ablation is a technique recently utilized to form transmission line features in low temperature cofired ceramic (LTCC) circuits [1] to increase dimensional precision when compared to standard screen printing. S-parameter measurements of microstrip transmission lines demonstrate a system loss at 30 GHz of approximately 0.8 dB/cm for chemical etching, 0.9 dB/cm for laser ablation, and 1.0 dB/cm for screen printing. Through careful design and good processing, acceptable microwave performance of the QM44 thick film system can be achieved up to 40 GHz.

Formation of a Metastable Phase at the Interface Between Sn and Ag–Pd Substrates During Liquid-State Reaction

Ag–Pd alloys are widely used as thick-film conductors and are potential alternatives to the expensive Au bump. In this work, because Sn is the primary element in solders, we investigated Sn/Ag–Pd interfacial reactions at 250°C as a means of assessing the reliability and evaluating reflow reactions at joints between solder and Ag–Pd conductor contacts, and in the Ag bump combined with the solder cap. The experimental results showed that Sn/Ag–Pd interfacial reactions at 250°C are different from those of Sn/Ag and Sn/Pd. A metastable Sn–Ag–Pd ternary phase is formed when the amount of Pd added is 20–40 at.%. Because, in commercial applications, at least 20 wt.% Pd (~20 at.% Pd) is used in Ag–Pd alloys to eliminate the silver-migration phenomenon, assessment of the reliability of Ag bumps and the soldered joints of Ag–Pd thick film hybrid circuits must be based on Sn/Ag–Pd interfacial reactions, not those of Sn/Pd and Sn/Ag.

Reducing photoelectric response when functionally trimming with lasers

A laser processing technology has been developed that dramatically reduces, or virtually eliminates, laser-induced performance shift of a device during functional trimming. While functional laser trimming of monolithic integrated circuits and thick-film hybrid circuits has been used for over 20 years to improve yields and device performance, photoelectric response in the silicon itself to the conventional wavelengths created long delays in processing and even circuit latch-up. The answer to these problems turned out to be an alternative laser wavelength which is absorbed well by both thin-film and thick-film resistor materials but is invisible to silicon-based structures. This paper describes the results obtained by using the 1.3-/spl mu/m wavelength of a diode-pumped Nd:YLF laser for trimming deposited, thin-film-on-silicon integrated circuits and the 1.3-/spl mu/m wavelength of Nd:YAG laser for screen-printed, thick-film hybrid circuits. The trimming, or tuning of thin-film-on-silicon circuits with a low-power version of the alternative wavelength has permitted both the shrinking of resistor geometries and the expansion of the types of circuits that can be functionally tuned. Secondly, the advent of higher laser power output of the same wavelength has eliminated the photoelectric response problems associated with functionally laser trimming hybrid and multichip module circuits that incorporate silicon devices in their construction. Results are given from actual production devices.

Comparison of new no-clean fluxes on PCBs and thick film hybrid circuits

Some new no-clean fluxes were investigated by measurement of ionic contamination of flux residues and influence of flux residues on surface insulation resistance (SIR) and electromigration (EM) between soldered conductors. Also copper corrosion test in the humidity chamber was performed on samples with fluxes investigated. The results of SIR, EM and copper corrosion tests were compared on test samples prepared as printed circuits and hybrid circuits.

The design of a family of high-current switches with over-current and over-temperature protection

This paper describes the design and manufacture of a family of five high-current, high-voltage dc switches with over-current and over-temperature protection. The capacity of the switches ranged from 5 A, 163 V to 100 A, 400 V. Steps were taken to achieve stability in over-current and over-temperature trip thresholds with changes in supply voltage and ambient temperature. A small physical size was achieved, and the design of a ceramic and Kovar package is described. Difficulties arose in measuring circuit parameters while testing performance due to induced magnetic and electric noise, and solutions to these difficulties are discussed. In addition, difficulties achieving some of the design goals and subsequent solutions are described. Thick-film hybrid circuit processing was the chosen technology for circuit fabrication. Thermal management was a major area of design emphasis, and the use of aluminum nitride substrates in some of the networks offered a solution in maintaining output FET junction temperatures at a safe level. Suggestions for improvements are offered. It is clear that switching of many tens of kilowatts of power at high voltages with over-temperature and over-current protection is obtainable in a small package at a reasonable cost.

Thick-film photosensors

The use of photoconductive inks based on CdS and CdSe to form photoresistors using standard thick-film hybrid circuit techniques is described. The properties of photoconductive sensors made using these materials together with electrodes printed using standard silver-palladium conductor inks are reported. The sensors showed a wide dynamic range. Photoresistors with an area of 80 mm2 had a dark resistance of the order of 1 G Omega falling to as low as 75 Omega in bright sunlight, for a sensor formed from a mixture of CdS and CdSe. Response times varied from 2.5 ms for CdSe at high illumination to 2 s for CdS at low illumination. It is shown that the best overall performance is obtained from films formed from a 1:1 mixture of CdS and CdSe. Screen-printed photoconductive array sensors and a potentiometric position sensor are described.

CAHL — computer aided hybrid layout software

Abstract Thick film hybrid is the oldest microelectronic technology, yet it has been the last to move into using computer aided/ automated design methods. CAHL, or Computer Aided Hybrid Layout, is a simple yet powerful software package that allows experienced professional design engineers and students alike to create thick film hybrid circuits quickly. The software can handle conventional and complementary processes. Features include automatic resistor sizing, cross-over and via formation; parameter extraction; generation of SPICE simulation files; net lists, pick-and-place machine position information and component trim information files to assist with manufacture and testing.

Development of piston temperature telemetry system

The measurement of piston temperature in a reciprocating engine has historically been a very time-consuming and expensive process. Several conditions exist in an engine against which measurement equipment must be protected. Acceleration forces near 2000 G's occur at Top Dead Center (TDC) in automotive engines at rated speed. Operating temperatures inside the crankcase can range to near 150°C. To allow complete mapping of piston temperature, several measuring locations are required in the piston and data must be obtained under various engine operating conditions. Southwest Research Institute (SwRI) has developed a telemetry-based system that with stands the harsh environments mentioned above. The device is attached to the underside of a piston and temperature data is transmitted to a receiving antenna in the engine crankcase. The key element of this device is a tiny power generator which utilizes the reciprocating motion of the piston to generate electricity, thus allowing the transmitter to be self-powered. Thick-film hybrid circuit construction techniques have been used to keep the package size small. This paper covers the development of the power generator, multiplexer and transmitter circuits, and the receiver system. Sample data is included from two automotive engines.

A multilevel epoxy substrate for flip-clip hybrid multichip module applications

A multilayer organic substrate is described. The multiple multilayer is comprised of two portions: one is thicker than the other, reinforced by organic fiber in each layer; and the other is a thick film that is not reinforced by organic fiber and forms low dielectric constant layers. A sophisticated epoxy resin provides the two-dimensional support with adhesion strength between the epoxy layer, thus stabilizing the elongation, shrinking, and warpage by an order of magnitude smaller compared to the conventional FR-4 substrate with inorganic reinforcement. The resin of an aromatic-amine additive type can lower the dielectric constant suitable for high frequency circuit performance and be an excellent acceptor of both adhered copper foil and copper-plated electrodes keeping a minimum width of 25-50 mu m. This two-portion substrate enables the use of flip-chip bonding on thick-film hybrid circuits, thus providing the necessary characteristic impedance of the semiconductor circuit, while maintaining compatibility with wire bonding and reflow soldering processes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Diamond: a novel substrate for thick film technology

The increasing power density in thick film hybrid circuits requires substrate materials with a high thermal conductivity. Diamond films were tested in view of this application. In addition to the adhesion of applied conductor pads, electrical properties of the diamond such as resistivity, permittivity and electrical strength, were examined. These critical parameters enable a preliminary evaluation of the feasibility of using low-pressure diamonds as substrates for thick film technology.

A thick-film electrochemical instrument

A miniature electrochemical sensor fabricated as a printed thick-film electrode assembly has been interfaced to a thick-film hybrid circuit potentiostat and voltage ramp generator in order to produce a portable instrument for the analysis of trace elements in water. The electrode assembly consists of an array of 200 μm square gold contacts in a planar construction with a silver/silver chloride reference electrode printed and fire onto an alumina substrate. The electrode assembly is interfaced via a thick-film hybrid circuit potentiostat fabricated as a 28 pin dual in-line package (DIP). The potentiostat in turn is controlled by a thick-film hybrid circuit voltage ramp generator, also fabricated as a 28 pin DIP. The use of thick-film hybrid circuit modules in the construction of the instrument reduces the susceptibility to extraneous noise sources. The high level of integration and resulting miniaturization achieved by the electronic circuitry enables the complete instrumentation to be contained in a compact, rugged and hence highly portable housing utilizing a small battery as the power source. User-configurable parameters include the sweep rate, polarity and range of the potential applied to the electrode assembly, together with the amplification level of the potentiostat output signal. In this way it is possible to use the instrument for a variety of measurements on the oxidation and reduction of trace elements in water. The output signals of the instrument are suitable for direct connection to a chart recorder for the production of voltammograms. Initial characterization of the complete instrument has included the measurement of dissolved oxygen concentrations in water.

Copper Thick Film—A Maturing Technology

Knowledge of critical materials and process parameters necessary to fabricate quality copper thick film multilayer and hybrid circuits is being amassed and distributed throughout the industry via technical reports and presentations. Generally the information being provided in a single report deals with specific segments of the industry or only one or two specific nitrogen fireable materials. In order for hybrid manufacturers to commit themselves to the technology they need to know that sufficient flexibility exists to permit design of complex circuits and accommodate circuit design changes without imposing changes in basic process guidelines and controls. The OEM's concern, which is valid, has been that the investment required for capital equipment and establishing new processes must be fully supported by and provide reasonable return from the technology being initiated. This paper introduces new information on wire bonding in copper thick film circuits and some improvements in nitrogen fireable resistor characteristics and processing. Materials are available to produce a broad range of circuits without varying basic process parameters, and adding wirebonding as an interconnect capability further expands the circuit complexity and density achievable with copper thick films.

Laser Trim Revisited in the Light of an Excimer Laser

ABSTRACTIn the Laser Chemistry Group's program aimed at understanding the basic mechanisms involved in the fabrication and characterization of integrated circuits, we have converted an infrared laser-based, thick film trimming technique, which is over 15 years old, to UV light. It is known that excimer lasers can be used for microfabrication of semiconductors and ceramics. Much cleaner ablations than those obtainable with the infrared lasers have been demonstrated in a large variety of materials. This, together with the fact that excimers with repetition rates over 1 kHz are presently on the market, leads us to propose that better accuracies and smaller drifts, should be achievable using excimer laser-based thick film hybrid circuit trimming. Results of XeCl laser trimming of over four hundred resistors, including temperature coefficient of resistance measurements and life tests at elevated temperatures, demonstrate that UV trimming is a factor of 10 better than the presently used infrared process.

Glass Films and Interfaces in Microelectronic Applications

AbstractUse of dielectric films is integral to most microelectronic packaging, as passive components for device insulation (interlayer dielectric, passivation, diffusion layer), as thin layer capacitive structures or as insulating coatings for thin film and thick film hybrid circuits. Depending on deposition technique, film composition may include SiO2, Al2O3, Si3N4, modified silicate or phosphate glasses as insulators. Compositions as well as methodologies for film preparation on Si, glass or metal substrate by spin coating (or spraying) are discussed, including film/substrate interface characteristics and properties related to dielectric film coatings.

Preparation and Properties of a New Thick Film System

Work has been carried out to develop a new ruthenium oxide based thick film resistor whose resistance is independent of the contact area of the conductor to the resistor. Such a resistor can then be combined with a low cost silver conductor.It has been found that such a resistor can be made by doping a ruthenium oxide based thick film resistor with up to several percent of gold. With such a material it is possible to use silver or palladium silver (containing only very small amounts of palladium) as an electrode material and very few interactions have been found to occur between the resistor and electrode. Such a gold doped ruthenium oxide thick film resistor using silver electrodes has some major advantages as follows:-1. The resistor size can be made much smaller than normal.2. The design of a thick film hybrid circuit becomes easier.3. The resistor cost can be reduced.

Solid-state ion sensors. Theoretical and practical issues

Integrated ion-sensor devices may be constructed using the methods of microcircuit fabrication. The suitabilities of the silicon integrated circuit and thick-film hybrid circuit processes for this purpose are compared and it is argued that the hybrid approach will offer advantages in many cases. Theoretical questions about the operation of both the hybrid and ISFET (ion-sensitive field-effect transistor) types of device are discussed and possible origins are suggested for the output drift that is commonly observed in ISFET. Practical issues which might affect the commercial development of integrated ion-sensor devices are noted.

Electronic processing of transducer signals: hall effect as an example

The distribution of electronic processing power between the transducer, the interface electronics and the central processor is discussed. As an example, the case of a Hall effect magnetic transducer is presented. The Hall device takes the form of a split drain MOS transistor that is incorporated within a custom chip, together with some interface electronics to translate the magnetic field information ratio into a frequency difference. This form of coding provides robust information transmission with inherent structural compensation for common mode errors and suitability for microprocessor interfacing without the use of A–D converters. The sensor chip is mounted on a thick-film hybrid circuit together with a microprocessor and some minor components to yield a miniature component with full internal compensation that is capable of communicating with a host system by means of a protocol realized in clear ASCII format.

Resistor Chips for Thick Film Hybrids

Applications for thin film resistor chips in thick film hybrid circuits are discussed in relation to the different technologies involved, namely naked and encapsulated forms of mounting.

An integrated circuit silicon sensor for magnetic fields

The paper describes a differential output magnetic field sensor based on a current-splitting m.o.s.f.e.t. structure with two drain contacts. The sensor is integrated onto silicon with two n.m.o.s. voltage controlled oscillators and a temperature sensor, using the standard Southampton n.m.o.s. process. An input to the chip provides for offset compensation. The oscillators are driven by the sensor outputs, so that it is the difference in frequency which is proportional to magnetic field. Pulses from the oscillators may be counted directly into a register by a microcomputer providing a simple form of A to D conversion suitable for most applications. The microcomputer may also linearize the sensor output and provide temperature compensation using a separate input from the temperature sensor. In its simplest form the complete transducer may consist of two chips, the sensor and a single chip microcomputer, providing a serial digital output and mounted in a compact form on a thick film hybrid circuit.

Fabrication of large-area thick film hybrid circuits on RCA porcelain-coated steel substrates: A.N. Prabhu, E.J. Conlon, A.Z. Miller, J.H. McCusker and T.T. Hitch RCA Review42, 259 (June 1981)

Fabrication of large-area thick film hybrid circuits on RCA porcelain-coated steel substrates: A.N. Prabhu, E.J. Conlon, A.Z. Miller, J.H. McCusker and T.T. Hitch RCA Review42, 259 (June 1981)