Showing papers in "IEEE Transactions on Components, Hybrids, and Manufacturing Technology in 1980"

Thick-film Technology: An Introduction to the Materials

Abstract: The use of thick-film technology to manufacture electronic circuits and discrete passive components continues to grow at a rapid rate worldwide. When applied to hybrid microcircuits, it can be viewed as a means of packaging active devices, spanning the gap between monolithic integrated circuit chips and printed circuit boards with attached active and passive components. The strength of the thick-film approach is a consequence of function, size, and unit cost trade-offs; advances in materials have played a major role relative to each of these factors. Thick-film materials are developed to meet needs defined by electronic circuit design and process engineers. A general understanding of thick films is provided from a materials standpoint, particularly for the new engineer. Background is developed for a basic, yet simple, understanding of the components that make up resistor, conductor, and dielectric compositions, of processing, and of the properties of the final thick-film composite structures.

A Multilayer Ceramic Multichip Module

Abstract: The increased performance and circuit/bit densities of today's semiconductor chips require corresponding technological advancements in chip packaging. More interconnections and increased heat dissipation must be accommodated in a package compatible with the higher performance of these chips. In the packaging approach described, increased package performance and reliability were achieved by the use of a multilayered ceramic substrate upon which nine chips can be mounted. Conductors for ground, signal, and power lines are interlayered in the ceramic with connections to the top surfaces and to pins at the bottom surface for connection to external circuitry. This multilayer multichip module significantly advances the state of the art; it provides higher circuit density and performance with a ten-fold increase in circuit density over previous logic systems hardware.

Ceramic Humidity Sensors

Abstract: A novel humidity sensor using a MgCr 2 0 4 -TiO2 porous ceramic has been developed for an automatic microwave oven. Physical properties of the MgCr 2 0 4 -TiO2 ceramic, construction and humidity characteristics of the sensors, and outlines of the control of the automatic microwave oven by humidity sensing are described. The MgCr 2 0 4 -TiO2 ceramic exhibits a typical porous structure and semiconduction. The porous ceramic easily absorbs water vapor throughout the pores. The ceramic grain surfaces behave like electrolytes. The ceramic humidity sensor utilizing its humidity sensitive effects and rejuvenating response to heat treatment exhibits high humidity and long term stability. The novel humidity sensor has been applied in many processes such as microwave ovens, air conditioners, dryers, etc.

IBM Multichip Multilayer Ceramic Modules for LSI Chips-Design for Performance and Density

Abstract: The design objectives and features of two modules are outlined which, with their LSI chips, give significant advantages of performance, power reduction, logic gate density, and reliability in their IBM 4300 processor applications. In these applications an average module gate density of 196 gates/cm2is achieved. This is 30 times the density achieved in IBM's monolithic systems technology (MST). Even larger density improvements are realized at the card level.

Strain Sensivity of Thick-Film Resistors

Abstract: The strain sensitivity measurements of Dupont 1400Biroxr thick-film resistor materials in untrimmed and laser trimmed conditions are described. This was studied to better understand the post-laser trim drift phenomenon and evaluate the effect of packaging/assembly induced stresses on the resistors. The strain coefficient of resistance or the strain sensitivity of the untrimmed 102_ 106 \Omega / \Box$^b$ resistor materials is small, reversible, and independent of resistor geometry or fired thickness (t f ). This strain sensitivity (?i) is an intrinsic material property which is determined by the conduction mechanism in the material. The strain sensitivity of the laser trimmed · resistors is a sum of the intrinsic sensitivity (?i) and an additional term called the extrinsic strain sensitivity (\gamma ex ). The additional extrinsic contribution can be large and irreversible and depends strongly on the fired thickness (t f of the resistor. A mechanism is proposed to explain these observations. The mismatch of the thermal expansion coefficients of the resistor material and the substrate leads to high internal stresses in the thick resistor. Hence crack formation and propagation is easier which leads to increased strain sensitivity (extrinsic) and post-trim drift. It was experimentally determined that Al 2 O 3 from the substrate dissolved 6-8 µm into the thick-film resistor during resistor firing. For thin resistors the relatively higher amount of dissolved Al 2 O 3 from the substrate in the resistor glass reduces the thermal expansion mismatch between the fired resistor and substrate. Thus its strain sensitivity and drift are much smaller than a thicker fired resistor.

Metallic Brushes for Extreme High-Current Applications

Abstract: Recent studies of homopolar machines and electric vehicles have generated a renewed interest in sliding contacts which can carry a very high-current density. Simple metallic brushes were shown to be capable of the efficient transfer of very high currents under proper conditions of mechanical load and with control of the surrounding atmosphere. In stable operation under a carbon dioxide cover gas, copper fibers have transferred 12.4 MA/m2(8000 A/in2) with contact drops less than 50 mV. During a 240-h test, the dimensionless wear rate was found to be 5 x 10-11. Current densities as high as 23.2 MA/m2were demonstrated in short-term tests. To evaluate the feasibility of practical application a larger copper fiber brush was assembled and tested in a standard holder with a conventional spring loading system. The observed contact voltage drop was quite similar to that found for the smaller brushes. The test results conformed to elastic contact theory and indicated that the controlling resistive component was due to film rather than constriction. The ability to use metallic contacts under a controlled atmosphere provides an opportunity for the investigation of sliding electrical contacts without the complexity introduced by excessive oxide formation and without the added parameters that would be introduced by graphite or other lubricant films.

Modeling of Two-Dimensional Spiral Inductors

Abstract: The trend toward size reduction of power-conditioning circuitry is increasing the use of higher switching frequencies (in the megahertz range) for dc-to-dc conversion. For power magnetic components this is requiring novel designs of energy-storage inductors. An investigation is reported of two-dimensional spiral wound air-core inductors. These inductors have the potential advantages of being printable as a thick- or thin-film circuit element and, therefore, inexpensive to manufacture. Via a simplifying approximation, one can reduce a formidable mathematical problem to one in which closedform expressions can be written for the total inductance and the resistance. Our approximate expression for the resistance is meant to account for the skin effect exactly and for the proximity effect in an average way. A comparison is presented between the predicted and measured value of impedance as a function of frequency. Implications of these results and of modeling the effects of parasitic capacitance are discussed in the context of determining an optimized geometry and operating frequency.

Bonding Wire Microelectronic Interconnections

Abstract: Fine-wire bonding is an important technology used for making electrical connections inside microelectronic device packages. In this method of interconnection, wire leads carry power and signals between semiconductor active circuits and leadframe or substrate metallization. Wire bonding technology is reviewed from a practical point of view. The thermocompression (T/C), thermosonic (T/S), and ultrasonic (U/S) bonding methods are briefly explained, and the advantages of each are considered. Proven practices for enhancing bond reliability are discussed. Suggestions are given for developing effective break strength and the elongation specifications for bonding wire. Wire inspection and quality assurance procedures are also reviewed. A major section deals with Al + 1% Si wire for U/S bonding, including Si dispersion, wire microstructure, mechanical properties, and bond heel cracking. Also discussed is Au wire for T/C and T/S bonding, including controlled metal doping, spooling, and the future trends in Au wire development. The advantages of Al/Mg wire for U/S bonding and the possible materials for Au-wire substitutes are additional subjects that are briefly addressed. This review is intended to serve as an up-to-date guide to wire bonding technology. It also points out areas in which additional material development work is required to maximize the utility of the new high-speed automated wire bonding equipment.

Performance of Digital Integrated Circuit Technologies at Very High Temperatures

Abstract: Results of detailed investigations of the performance and reliability of digital bipolar and complementary metal-oxide-semiconductor (CMOS) integrated circuits over the 25-340°C range are reported. Included in these results are both parametric variation information and analysis of the functional failure mechanisms. Although most of the work was done using commercially available circuits (TTL and CMOS) and test chips from commercially compatible processes, some results from experimental simulations of dielectrically isolated CMOS are also discussed. In general, it was found that commercial Schottky-clamped transistor-transistor logic (TTL) and dielectrically isolated, low power Schottky-clamped TTL functioned to junction temperatures in excess of 325°C. Standard gold-doped TTL functioned only to 250°C, while commercial isolated integrated injection logic (l2L) functioned to the range of 250-275°C. Commercial junction-isolated CMOS, buffered and unbuffered, functioned to the range of 280-310+°C, depending on the manufacturer. Experimental simulations of simple dielectrically isolated CMOS integrated circuits, fabricated with heavier doping levels than normal, functioned to temperatures in excess of 340°C. High temperature life testing of experimental, silicone-encapsulated simple TTL and CMOS integrated circuits have shown no obvious lifelimiting problems to date. No barrier to reliable functionality of TTL bipolar or CMOS integrated circuits at temperatures in excess of 300°C has been found.

Thick-Film Thermistor and Its Applications

Abstract: The electrical properties, reliability, and several successful applications of a thick-film thermistor are described. The thick-film thermistor is composed of a semiconducting oxide, precious metal (RuO 2 ), and glass. The resistivity and thermistor constant are affected to a great extent by the electrical properties of the semiconducting oxide, the particle size of RuO 2 , and the characteristics of the glass. The thermal expansion coefficient of the semiconducting oxide is required to be less than 105 x 10-7K-1in order to prevent the cracks in as-fired film. A resistivity ranging from I \Omega 2.cm to 10 M \Omega .cm together with a thermistor constant from 100 to 4500 K can be obtained by controlling these factors. These glass coated thick-film thermistors exhibit extremely high stability. An accelerated life test shows the drift rate as less than 0.02 percent/year in the resistance of a thick-film thermistor with a crystallized glass coating. A thick-film thermistor can be used widely as an accurate and stable temperature sensor and as an exact temperature compensating element in a thick-film hybrid circuit.

Strain Sensitivity in Thick-Film Resistors

Abstract: Piezoresistive properties of Dupont 1400 series thick-film resistors have been investigated by measuring longitudinal and transverse gauge factors as a function of applied strain between 0 and _+ 1000 microstrain in the temperature range from -70 to + 140°C. The relative change in resistance of thick-film resistors is linear, reproducible, and hysteresis free for the full range of applied strain. They appear more sensitive than metal resistors and have a low temperature coefficient of resistance (TCR) and gauge factor.

Heat Transfer of Modified Silicon Surfaces

Abstract: The heat transfer between silicon surfaces and perfluorohexane has been measured for fluxes ranging from 0 to 2.2 W/cm2. Data are presented for ten different surface treatments designed to encourage thermal nucleation.

Some Fundamental Properties of Aluminum-Aluminum Electrical Contacts

Abstract: The results of a fundamental Investigation of the properties of stationary aluminum-aluminum (AA1350) electrical contacts at room temperature both in an ultrahigh vacuum and in an oxygen atmosphere are reported. The contact couples consist of two polished spherical surfaces held together under constant load over a small area; the work was carried out in an environmental chamber which allows manipulation of the contact samples and external adjustment of contact loads. The loads required to rupture the oxide films on the contact surfaces have been measured and yield estimates of fracture strain for aluminum oxide films in compression. Once the insulating oxide films are ruptured, the area of metallic contact is generally found to grow with time. In a vacuum the growth rate is consistent with the rates predicted from sintering theory; the experimental evidence suggests that sintering is driven by capillarity forces and controlled largely by dislocation creep. Growth in oxygen is slower but can be also understood qualitatively in terms of creep-controlled sintering. Although growth in electrical contacts has been observed by earlier investigators, this is the first time that the phenomenon has been correlated with sintering. These results suggest that stationary aluminum-aluminum electrical contacts are characterized by "self-heal" properties which should be conducive to exceptionally stable performance in a vacuum or in an Inert gas environment.

Progress in and Technology of Low-Cost Silver Containing Thick-Film Conductors

Abstract: Thick-film materials have been proved to possess economic, processing, and functional advantages over other technologies in the high-volume production of miniaturized circuits. Inherent in the adoption of thick-film technology for increasingly diverse applications has been the ability of thick-film materials suppliers to provide progressive performance improvements at lower cost concurrent with circuit manufacturer's needs. Since the first major commercial thick-film adoption in the early sixties when IBM adopted platinum-gold conductors and palladium-silver resistors in their 360 computers, rapid technological advances over the last decade have produced an increasing variety of hybrid circuits and networks. The wide adoption of thick-film technology in all segments of the electronic industry has placed increasing demands on performance and processing latitude. The development of low-cost silverbearing conductors is outlined and the evolution of technology improvements to present day systems is described. Initially the deficiencies of early Pd/Ag conductors are reviewed, particularly solder leach resistance and degradation of soldered adhesion following hightemperature storage, and focus is placed on the first Pd/Ag system which overcame these problems. Extension of this technology and subsequent improvements in both binders and vehicles to fulfill adhesion requirements to AI 2 O 3 substrates of Varying chemistries and to meet demands for high-speed printing are described also. In the second segment an overview of the present understanding of thickfilm conductor composites from a mechanistic point of view is given. The various types of binder systems commonly employed in conductors are discussed in terms of how they effect a bond between the sintered metal and the substrate, and the advantages and disadvantages of each type. Metallurgical aspects of conductor/solder connections are considered and their effects on bond reliability following exposure to high temperature are discussed. Rbeological considerations of paste design are presented and related to printing performance. In the final segment newer low-cost high-performance materials systems that have evolved over the past two years are considered. The technologies of each system are reviewed in terms of metallurgy, binder, and vehicle. Important functional properties are presented to illustrate cost/performance trade-offs. Special emphasis is given to a recently developed Ag conductor which has outstanding soldered adhesion even after 1000 h of storage at 150°C.

Influence of the Substrate on the Electrical Properties of Thick-Film Resistors

Abstract: The thick-film technology is widely used for hybrid circuit manufacturing and there is a definite trend to use it in other applications. However, the understanding of the electrical, mechanical, and chemical characteristics of thick-film materials has been approached essentially on an empirical basis, even if many hypotheses have been formulated on their conduction mechanisms. In fact, thick-film resistors present a temperature coefficient of resistance that is negative at lower temperatures and positive at higher temperatures with a TCR vanishing in the range of the room temperature. Recent papers attribute the conduction mechanism to percolation tunneling of electrons through conductive grains embedded in the glassy matrix of the resistor layer. The model assumes that the resistance of the percolation paths dominates the resistance of a network electrically equivalent to the thick-film resistor. With this model a good fitting of the experimental data is obtained. However only data concerning Ru-based resistors screened and fired on 96 percent alumina substrates were considered. In order to better understand the influence of the ceramic substrates on thc electrical and thermal characteristics of thick-film resistors, zirconia, beryllia, and alumina (with different purity) were employed in the present study. The results indicate that the "substrate effect" plays an important role in ruthenium-based resistors, so that, in order to understand the thick-film conduction mechanisms, it is necessary to take into consideration the "substrate resistor system" and not to limit the analysis to the film in itself. Of particular interest is the fact that the minimum of the resistance-versus-temperature curve varies for different substrate materials, even if the resistors under test are made with the same resistor series and are characterized by the same sheet resistivity. An equation is proposed that correlates the resistor gauge factor to thermal expansion coefficient of the ceramic substrate. By assuming the validity of a recently proposed model of conduction mechanism in thick film, a new set of equations is proposed that fits the experimental results obtained on resistors screened and fired on substrates of different compositions or with a different content of impurities.

Influence of Some Geometric Factors on Contact Resistance Probe Measurements

Abstract: The effect of variations in the geometry and preparation of gold probe tips for contact resistance measurements has been evaluated. Tips prepared by melting and by machining and possessing shapes ranging from a point to hemispheres with radii from 0.9 mm to 3.2 mm were used. The contact resistance values are nearly independent of probe geometry on gold and on very lightly filmed (<5 to 10 A) copper targets. On more heavily filmed copper and nickel targets, the contact resistance varies as much as 2½ orders of magnitude at a fixed contact force. The only known variable is the apparent contact area of the various tips, determined by examination in a scanning electron microscope (SEM) after use. It appears that contact pressure predicts contact resistance more reliably than does contact force.

Thermal Resistance: A Reliability Consideration

Abstract: The importance of the mean operating temperature of a monolithic integrated circuit encapsulated in a molded plastic package and its relation to the reliability of that component is reviewed. A thermal model of a plastic package is described and experimentally verified. The model is applied to measure chip or junction temperature under operating conditions, and errors which can be introduced are discussed.

Membrane Touch switches: Thick-Film Materials Systems and Processing Options

Abstract: Thick-film materials and processing parameters critical to the production of membrane touch switches are reviewed. The primary emphasis is on polymer-bonded silver conductor systems; electrical conductivity versus silver content, conduction mechanisms, techniques to determine adhesion, materials for screen printing, choice of Mylarr polyester film, and appropriate drying conditions are discussed. Also described is the performance of a new series of polymeric resistors on various substrates (including Mylarr polyester), under different curing and storage conditions. Future trends in the development of materials systems for membrane switches and associated circuitry are also briefly reviewed.

High-Current Brushes, Part IV: Machine Environment Tests

Abstract: Brush performance has been investigated with a view to establish whether or not continuous very high-current density operation is feasible for many parallel brushes running under machine environment conditions. The ultimate objective is the development of sliding-brush contact systems for advanced powerful electrical machines that require large currents in order to achieve high efficiencies and small volumes. Using a homopolar generator designed for that purpose, the performance of a full complement of 92 brushes (46 in parallel per polarity) was evaluated under conditions that included electrical loads to 9500 A (1.6 MA/m2) and a slip ring speed of 42 m/s. Based on test data presented, asymmetry in the anode and cathode brush electrical contact resistances and wear rates of about 2:1 were found. Under the maximum imposed load conditions, the anode and cathode brush interface contact voltage drops are 0.17 and 0.08 V, respectively. Typically, the highest dimensionless linear wear rate (anode brush) is 1.7 x 10-11. This wear rate is about one-sixth that of diesel-electric locomotive motor brushes, which slide on contact surfaces of similar peripheral speed but with less than one-tenth the electrical load imposed here. The high feasibility demonstrated for multiple-brush high-current operation is attributed to the use of silvergraphite brushes (0.75 mass fraction silver), a nonair (e.g. humidified carbon dioxide) environment, and cooling of the brush holders and slip rings.

Thermal Transients in Electronic Packages

Abstract: The use of a transient analysis to accurately characterize the operating temperature of electronic modules should result in lower temperature estimates. This will reflect increases in both the reliability estimates and the performance specifications. An accurate cooling analysis would also enhance the projected product life or reduce the system cooling requirements. Simplified expressions have been obtained for the calculation of chip and module thermal transients which, when superimposed, characterize the total package time/temperature response. Empirical data demonstrate the validity of the assumptions used to obtain these expressions. The thermal time constants are also presented in graphical form using parameters easily obtainable by the design engineer (e.g., cooling air velocity, steadystate temperature differences, and module location) so that order of magnitude assessments can be made.

High-Current Density Carbon Fiber Brush Experiments in Humidified Air and Helium

Abstract: Metallized carbon fiber brushes capable of operating at up to 4.65 MA/m2(3000 A/in2) in an air environment have been developed, fabricated, and tested. Experiments in humidified air and helium gas atmospheres containing 50 to approximately 5000 ppm of water vapor have been undertaken. The results show that the total brush losses (electrical plus mechanical) are not substantially changed by the water vapor level, but the distribution of frictional and electrical losses is altered.

Connector Finishes: Tin in Place of Gold

Abstract: Gold has been the natural choice as a contact material for low-voltage circuits (dry circuits) because of its properties and characteristics. In addition to having low electrical resistivity, it is not attacked by most chemicals and does not form surface oxides and sulphides so that good electrical contact is made with minimal force, even at low voltages. The rapidly escalating price of gold has motivated the investigation of less costly connector finishes. Some of these developments are reviewed. In particular, tin and its alloys form thin oxide films which may be easily broken, so that low-resistance metal-to-metal contact can be established with the underlying tin base. Changes in connector design are aiding the development of new contact materials.

Interactions of Efficiency and Material Requirements for Terrestrial Silicon Solar Cells

Abstract: Recent recognition of the influence of "heavy doping effects" on solar cell performance and the evaluation of new design options such as the "three-layer structure" including a high/low junction, front surface texturizing, and the formation of optically reflective back surfaces has led to a rethinking of approaches to the design of silicon solar cells. This rethinking has been facilitated by the application of the transport velocity transformation method which eases the analysis of muitilayer devices. Many solar cell design variations have been analyzed using this technique in order to determine optimum cell structures. The key results of the analyses are that: low resistivity material should be used, up to the point of onset of Auger recombination; the highest lifetime material available should be used; a properly designed three-layer structure permits base regions approaching in performance the ideal device, even if the back surface is completely covered by an ohmic contact; the surface recombination velocity in the front region must be controlled by passivation or similar means, but the front region itself may be thicker than in current cells; higher resistivity front regions will require more sophisticated grid metallization structures than those that are usually applied now; cells with limited minority carrier lifetimes should be very thin, requiring surface texturizing and back surface reflectors in order to achieve optimum performance. With these design features, the idealized silicon solar cell structures analyzed yield airmass 1 efflciencies between 24 percent and 26.5 percent, so that real cell efflciencies near 22 percent should be achievable.

High-Current Brushes Part VI: Evaluation of Slip Ring Surface Films

Abstract: The thin film that is formed on the surface of an oxygen-free high-conductivity (OFHC) Copper slip ring sliding against monolithic silver-graphite brushes in a humidified carbon dioxide atmosphere has been investigated experimentally. The object was to study the nature and method of formation of the film since the films play a major role in the electrical, frictional, and wear performance of sliding electrical contacts. The techniques used included optical and electron microscopy and Auger electron spectroscopy. With the latter, two techniques were employed, both of which involved placing complete (83-mm diameter) slip rings within an Auger high vacuum chamber. In the first case externally operated slip rings were transferred into the Auger chamber for film analysis. In the second case a complete rotatable slip ring assembly, including brushes, was mounted within the Auger chamber. Low-speed rotational operation of this ring then permitted brush/slip ring sliding to take place so that film build-up could be analyzed in situ. The nature of the film formed on a copper slip ring was found to be dependent on the surface preparation and the ambient atmosphere, but it was found that the thin films of adsorbed gases did not form an oxide of appreciable thickness. Water vapor was identified and is known to play a critical role in the successful operation of brushes containing graphite. The adsorbed thin films were also found to contain significant quantities of sulfur and chlorine. In the presence of water vapor the adsorbed film on copper surfaces appears to have a special character. A hypothesis is suggested to explain the nature of this adsorbed film and the way in which it is bonded to the slip ring surface.

Connectorized Optical Link Package Incorporating a Microlens

Abstract: An inexpensive connectorized optical data-link package for light-emitting diode (LED) sources, or p-i-n or avalanche photodiode (APD) photodetectors is described. This package uses a 1-mm diameter sapphire spherical lens to couple the light directly from the LED to the connectorized data-link fiber. For an LED with a 35-µm diameter light-emitting spat and a graded index, 0.23 numerical aperture (NA), 55-µm diameter core fiber, a coupling efficiency approximately equal to that for butt coupling is obtained. At the same time, the lateral and axial LED-fiber alignment tolerances are relaxed by factors of at least two and five, respectively. Preliminary thermal cycling measurements show no lass in coupled power after 230 cycles from -55°C to +150°C.

Wear of Silver-Graphite Brushes Against Various Ring Materials at High-Current Densities

Abstract: A study has been carried out to evaluate noble metals for potential use as ring materials for high-speed high-current applications. A pin-on-disk friction apparatus was constructed so as to allow sliding tests to be carried out at high speeds and high-current densities in controlled environments. The pin material was a silver-graphite brush composite while the flat material was one of the elemental metals nickel, copper, silver, gold, platinum, palladium, rhodium, ruthenium, rhenium, or iridium. The pressure was 0.2 N/mm2, the current density was 0.8 A/mm2, and the sliding speed was 4 m/s. The friction, wear, and electrical resistance were determined in wet CO2 and dry air. In general, and surprisingly, materials which give high friction give low wear although, in fact, both the friction and the electrical resistance values covered a narrow range. The wear results are not in agreement with earlier data obtained during tests of silver pins sliding against the same metals at much lower loads, speeds, and electrical current densities, in which case the low wear metals were those with low metallurgical compatibility against silver, or else metals with a hexagonal crystal structure. In these new tests, the wear behavior at high speeds and high-current densities with silver-graphite brushes obeys essentially the same compatibility relationships, but referred to the graphite. The best performance in terms of low wear was provided by the metals rhodium, palladium, and platinum.

A Computer-Aided Design System for Hybrid Circuits

Abstract: A software system used to aid hybrid circuit design, layout, and documentation is described. The intent of the programs is to address the design needs of a company that requires a considerable number of new custom hybrids each year. The system, called HCAD, resides on a mainframe engineering computer and is available to designers on a time-share basis via interactive graphics terminals. The system acts as a design aid for the user by handling difficult computations and by storing large amounts of data while leaving most of the creative tasks to the user.

Heat Transfer Correlatins for Use in Naturally Cooled Enclosures with High-Power Integrated Circuits

Abstract: Heat transfer rates were experimentally measured in an air-filled two-dimensional simplified model of a naturally cooled rectangular enclosure with a concentrated energy source representing a high-power integrated circuit (IC). The aspect ratio of the enclosure and the size and location of the source were parametrically varied. Correlations are presented such that a component temperature rise can be estimated if the energy dissipation rate is known in a specified design.

A Printed-Circuit-Board Connector Family with up to Forty-Eight Contacts per Inch of Board Height

Abstract: A new family of circuit-board-to-backplane connectors has been developed for general-use packaging of electronic telecommunications equipment. They provide a range of interconnect densities between the circuit board and the backplane of from 16 to 48 connections per inch of printed-circuit-board height, up to a total of 324 connections. The family consists of four connector styles which provide two, three, four, or six columns of contacts which mate with selectively gold-plated pins inserted into a backplane on a 0.125-in grid. Each socket-type contact in the circuit-board portion provides two gold-plated contact points with a minimum end-of-life normal force of 100 g. The maximum connector insertion force is 140 g] contact. The two- and three.column connectors are attached to the printed circuit board by the heat staking of integrally molded bosses, and the terminals are connected by wave soldering. The four- and six-column connectors are riveted to their printed circuit boards and the contact tails are reflow soldered to the circuit-board conductors. A variety of environmental tests and connector characterization tests indicate that this connector family will perform reliably in telecommunications equipment.

Effects of Surface Films on the Performance of Silver-Graphite (75 wt% Ag, 25 wt% C) Electric Brushes

Abstract: The brush resistance of silver graphite (Stackpole SG142, 75 wt% Ag, 25 wt% C) has been investigated over a range of speeds up to 35 m/s and a range of current densities up to 46.5 x 105A/m2. The data show conclusive evidence for the buildup and breakdown of surface films due to the graphite lubrication and also for a persistent surface film of about 10-12\Omegam2film resistivity. Film breakdown appears to be triggered at some critical combination of current density and speed. In the absence of the lubricating film the brushes run at much lower electrical loss and with a reduced coefficient of friction. This result suggests that the optimum performance of the brush is at high speeds and current densities.