Showing papers in "IEEE Transactions on Parts, Hybrids, and Packaging in 1977"

The Ultrasonic Welding Mechanism as Applied to Aluminum-and Gold-Wire Bonding in Microelectronics

Abstract: This paper represents a review as well as an extension of previous work concerned with the mechanism of microelectronic ultrasonic welding for both aluminum and gold wires. A series of experiments was carried out to determine the mechanism of gold-to-gold ultrasonic bonding. These experiments, including lift-off pattern studies, clamped-wire studies, and bond deformation versus ultrasonic vibration amplitude studies, indicate that gold ultrasonic bonding takes place primarily by means of a deformation mechanism as opposed to a heating or sliding mechanism. This is substantially the same result previously obtained from studies on the aluminum ultrasonic bonding mechanism. Further, it is shown that a deformation mechanism also holds for other forms of solid phase microelectronic bonding. Specific examples are taken from electric discharge "tweezer welds" and from thermocompression bonds. The role of contaminant removal and certain reliability aspects of ultrasonic bonding are also discussed.

Nonhermeticity of Polymeric Lid Sealants

Abstract: Organic adhesives are useful lid sealants because they are processed at low temperatures, are inexpensive, and are easy to rework. However, there has been concern about the degree of protection organics can provide moisture-sensitive components. Data presented in this paper show that organic adhesives can seal packages which pass gross and fine leak tests but allow water vapor to permeate rapidly. Permeation measurements on hybrid microcircuit packages gave seal permeabilities of 3-7 x 10-11g/cm-s-torr; these permeabilities agree with those listed for epoxies in the literature. With this permeability range and the package configuration used in this study, the interior humidity of a package will reach 50 percent of the exterior humidity in 6-10 h.

ZnO Varistors for Transient Protection

Abstract: ZnO varistors are novel ceramic semiconductor devices used for protection of electronic equipment against transient overvoltages due to switching surges or lightning. This article describes the microstructure, circuit behavior, and operation of ZnO varistors. ZnO varistors have highly nonlinear current-voltage characteristics similar to back-to-back Zener diodes but with much greater current, voltage, and energy handling capability. These devices are capable of protecting circuits with operating voltages from ten to thousands of volts while passing surge currents in the kiloamp range. Varistor response time is too small to measure (less than 500 ps). ZnO varisters are comprised of an array of conducting ( \Omega ·cm) ZnO grains, each grain being surrounded by an insulating oxide barrier 106V/cm) across the insulating barriers promote the tunneling of electrons through these intergranular barriers. The details of the varistor conduction mechanism are complex and a discussion is given of our present understanding of this process.

Computerized Thermal Analysis of Hybrid Circuits

Abstract: A computer program was written to perform steady-state analysis for hybrid circuits. The output of the program gives the temperature of each power dissipating element in the hybrid. The program is based upon solution of Laplace's equation in three dimensions using Fourier techniques. The assumptions made are: no convection or radiation, constant and isotropic thermal conductivity for any single material, and constant temperature at the bottom of the hybrid package. Bessel's inequality allows one to input the desired accuracy and to determine where the infinite series should be truncated. Theoretically, the program will attain any desired accuracy less than 100 percent, but practical considerations of computer run times limit accuracies to the 90- to 95-percent region. The program has been tested by comparing computer results to known theoretical exact solutions and to actual measurements on sample hybrids. When compared to known theoretical exact solutions, the computer result accuracy is between 95 and 100 percent. When compared to actual measurements on sample hybrids, the computer result accuracy is between 90 and 95 percent. This program has been used successfully on over twenty circuit designs. It has also been used to evaluate simpler types of thermal anal- yses.

Kinetics of Thermocompression Bonding to Organic Contaminated Gold Surfaces

Abstract: The kinetics of thermocompression gold ball bonding were studied for gold metallization contaminated with organic films. The contaminants studied were residual photoresist and atmospheric contamination. For gold metallization contaminated with organic films, thermo-compression gold bonding is a two-stage process. The first stage occurs within a fraction of a second and results from the mechanical disruption of barrier films by shear displacements at the faying surface. Bonding during this initial stage is a strong function of the interface temperature, the bonding force, and the contaminant films. The second stage involves growth of the metal-metal interfaces by a sintering phenomenon. Growth of bonds by sintering also occurs in the absence of external loads though at a decreased rate. Analysis of the rate data leads to the conclusion that the growth mechanism follows a parabolic rate law and, in the absence of external loads, exhibits an activation energy of approximately 11 kcal/mole. Under high external loads, the rate of second-stage growth exhibited little temperature dependence, indicative of a stress-assisted process. Bond growth rates for the atmospherically contaminated metallization were an order of magnitude higher than that for the photoresist contaminated samples.

Lead-Indium for Controlled-Collapse Chip Joining

Abstract: Lead-indium for flip-chip solder ("controlled-collapse") connections has been investigated as a possible alternative to the commonly used 5-95 tin-lead. In thermal cycle tests, lead-indium was substantially mote resistant than tin-lead to fatigue resulting from chipsubstrate mismatch. The lead-indium that has been studied most extensively, 50-50 by weight, gives a 3:1 improvement in lifetime over 595 and is compatible with standard chip and substrate processing. Evaporated above a Cr-Cu-Au pad on the chip surface, the solder is eventually joined to tinned Cr--Cu lands on the ceramic substate. Because of its lower melting point, lead-indium can be joined at a lower temperature than 5-95 tin-lead. In its reactions with copper and gold, which are present in chip and/or substrate metallizations, indium resembles tin. Gold, present only as the protective top film of the chip metallization, dissolves completely during chip joining, whereas copper is present in sufficient quantity to exceed its solubility limit, and thus forms copper-indium intermetallic layers at both interfaces. To ensure terminal strength and reliability, these layers should be stable and adherent both to the solder and to the underlying metnllizations. Lead-indium has been found to be more susceptible than lead-tin to corrosion in high-humidity and hostile environments. This susceptibility must be borne in mind when lead-indium is considered for nonhermetic applications.

The Effect of Solid-State Reactions Upon Solder Lap Shear Strength

Abstract: The effect of solid-state reactions between gold plating and the eutectic solders 88Au:12Ge, 80Au:20Sn, 90SN:10Au, and 85Pb: 15Au and the off eutectic solder 60SN:36Pb:4Ag upon the solder lap shear strength has been investigated at four aging temperatures ranging from 75 to 150°C. Failure analysis of the lap shear samples has shown that Au-Ge and Au-Sn solders failed cohesively whereas Sn-Au, Pb-Au, and Sn-Pb-Ag solders failed adhesively. Scanning electron micrographs and microprobe analysis of gold-solder metallographic sampies aged at 125°C revealed the presence of AuSn, AuSn 2 , AuSn 4 , and voids at the plating-solder interface of Sn-Au solder. AuSn 2 and AuSn 4 intermetallic compounds were detected at the interface of SnPb-Ag solder, and AuPb 2 was detected at the interface of Pb-Au solder. The zeta phase of the Au-Sn binary system was detected at the plating-solder interface of the Au-Sn solder. The plating-solder interface of the Au-Ge solder was devoid of any intermediate phases or intermetallic compounds. The results of the lap shear measurements have shown that all five solders can be expected to exhibit adequate strength for microelectronic purposes for >105h at a sustained temperature of <100°C when the mating materials have similar coefficients of thermal expansion. However, with dissimilar thermal expansion coefficients, the SnAu and Sn-Pb-Ag solders both failed catastrophically within 103h at 100°C

Thermal Fatigue Failure of Soft-Soldered Contacts to Silicon Power Transistors

Abstract: Scanning electron microscopy was employed to characterize the structure of the soft-soldered joints in Si power transistors (type 2N3055), which failed electrically during thermal cycling. Cracks were observed in the soldered joint of many failed devices. Crack propagation seems to be accelerated by the presence of voids in the joint region. The importance of the reactions between the Ni layers and Sn of the .solder also affects the long-term reliability of the devices. Fractographs obtained from the failed devices reveal ductile fracture of the soft solder as well as creep or fatigue failure of the solder at the elevated temperature. Based on the structural studies of both failed and uncycled devices, some possibilities for improving device performance are discussed.

Lubricants for Separable Connectors

Abstract: About two dozen lubricating fluids were tested for use on electrical contacts on card edge or pin-and-socket connectors. The lubricants selected for screening represented a cross section of thewide variety of natural and synthetic materials available on the market. Among them were polyphenyl ethers, natural and synthetic hydrocarbons, several types of esters, polygiycols, some fluorinated materials, a few silicones, and some proprietary formulations. Lubricants were evaluated on the basis of volatility and their ability to prevent fretting corrosion on tin-to-solder contacts. Limited tests were also done on their spreading characteristics, their thermal degradation properties, and their effect on contact resistance. The objective of the work was to develop guidelines in the selection of contact lubricants for field testing. The lubricants were ranked on the basis of weight loss from thin deposits of the samples on solder foil coupons at 65°C. Fretting experiments were done by forcibly moving a printed circuit card finger between a pair of spring contacts cut from actual cards and connectors. The time required for contact resistance to increase from a few milliohms to 2 \Omeg was determined as a function of the amount of lubricant present.

Reliability Study of Wire Bonds to Silver Plated Surfaces

Abstract: The influence of temperature and environment on bond integrity was investigated for both aluminum ultrasonic and gold thermocompression wire bonds made to silver plate. Storage of aluminum-silver bonds at 85°C-8S-percent relative humidity (85/85) (no bias) resulted in progressive bond strength degradation and a shift in the primary failure mode from wire breaks to bond lifts. Degradation was attributed to massive aluminum corrosion. Bond degradation was not observed for the gold-silver system during storage at 85/85 (no bias) for 1500 h. In addition to humidity testing, gold-silver bonds were isothermally aged at 150, 250, 350, 450, and 540°C for a minimum of 10 min at each temperature to a maximum of 2000 h at 150°C, 1500 h at 250 and 350°C, 1000 h at 450°C, and 500 h at 540°C. Although rapid silver diffusion was observed in samples aged above 150°C, the system was determined to be mechanically reliable. An effective silver diffusion coefficient for the wire bond system was calculated from destructive wire pull data and was found to obey the equation

Hybrid Microcircuitry for 300&#176;C Operation

Abstract: Microelectronic instrumentation for geothermal well logging must operate in ambient temperatures up to 300°C for several hundred hours. This study involved an extensive survey of 25 to 300°C operation of resistors, capacitors, conductors, interconnections, and active devices. Three major selection criteria were: 1) part lifetime of at least 1000 h at 300°C; 2) minimum change in electrical parameters from 25 to 300°C; 3) availability to the common circuit builder (no one of a kind). Certain thick film resistors, capacitors, and conductors were found compatible with such high-temperature operation. In addition, reconstituted mica and aluminum solid electrolytic capacitors were found useful up to 300°C. Simple circuits for a geothermal temperature logging tool have been fabricated using these hybrid materials, components, and Si MOS and JFET devices. Oven tests show satisfactory stability from 25 to 300°C and at least 100-h circuit operation at 300°C.

Low Loss Surface-Acoustic-Wave Filters

Abstract: For several years surface-acoustic-wave (SAW) devices have looked promising as future components for receiver front-end and intermediate frequency filters. However, high insertion loss and a time domain triple transit signal have limited the utilization of these devices. The low loss SAW filter overcomes both previous problems and is a milestone in electronic component development. Filters with loss as low as -0.6 dB at 35 MHz, -2.3 dB at 320 MHz, and -50 dB sidelobes are routinely constructed. This paper discusses surface-wave filters in general, and then specifically the design of low loss SAW filters.

A Production Parylene Coating Process for Hybrid Microcircuits

Abstract: Application of Parylene for protecting microelectronic circuits from loose particles and external environment has been visualized for many years. With a joint effort by NASA and TMD, a process has now been qualified to perform Parylene deposition on hybrid circuits on a production basis, for the Centaur inertial guidance computer. The Parylene coating process developed during this program consists of a) obtaining a hybrid cover with a hole in it, b) sealing of the circuit with a hole in the cover, c) Parylene coating through the hole with the external leads protected from Parylene by appropriate fixturing, and d) sealing of the hole by soldering a pretinned Kovax tab. Development of the above process required optimization of the Parylene coater parameters to obtain a uniform consistent coating which could offer adequate protection to the circuits, fixture design for packages of various types, determination of the size of the deposition hole, the amount of dimer charge per run, a process to hermetically seal the deposition holes and establishment of quality control techniques or acceptance criteria for the deposited film. Several experimental runs were made on test circuits as well as actual production circuits to determine the effect of Parylene coating on active components, thin film resistors, and wire bonds under various conditions. Tests were also made to determine if Parylene indeed protected circuits from loose particles and external environment. After these experiments, Parylene coating acceptance standards were established and a long and rigorous qualification program was completed in order to prove the feasibility of this process. The results of the qualification program will be reported in a future publication. It is concluded that Parylene offers excellent protection against loose particles and a degree of protection from some environmental conditions. It is expected that the fraction of hybrids being coated with Parylene will continue to increase in the microelectronic industry.

The Erosion Characteristics of Ag Contacts and the Effect of Adding a Small Percentage of W

Abstract: Silver and Ag-W (10 weight percent W) were operated in a 5.I-A (peak) 308-V (peak) full-wave rectified dc circuit. The experimental switching system was operated 1.5 times per minute; the opening and closing velocities were 4 x 10-2 and 3 x 10-4 cm/s, respectively; the fully open contact spacing was 200 µm; and the contacts were closed for 3 s. The opening and closing of the contacts were controlled by a heater-bimetal combination attached to the moving contact. The following contact pairs were used: Ag versus Ag, Ag-W versus Ag-W and Ag versus Ag-W. All combinations of contact material and contact polarity were used. The experimental results showed that there was always a net transfer of contact material from the cathode to the anode. The volume of material transferred was strongly dependent upon whether the anode was the moving (hotter) or the fixed (cooler) contact: the greater erosion occurring when the anode was the hotter contact. For Ag versus Ag contacts thc erosion pattern resulted inone pip on the anode and one crater on the cathode. For Ag-W versus AgW contacts the presence of the small percentage of W resulted in multiple pip and crater formations. The experiments with the Ag versus Ag-W showed that the cathode electrode material determined the erosion pattern observed, i.e., when the Ag-W was the cathode, multiple pip and crater'formations occurred, but when Ag was the cathode, only a single pip and crater structure was observed. The presence of the W either in the cathode or in the anode decreased the observed erosion. These experimental results are discussed in terms of how the presence of W affects the emission characteristics of the cathode region and also affects the movement of the arc roots.

Studies of Second Breakdown in Silicon Diodes

Abstract: First and second breakdown in silicon diodes are studied with a one-dimensional computer program that includes both electronic and thermal processes. Extensive calculations of both static and dynamic current density-voltage characteristics are shown for temperatures from 300 to 600 K. The variations of first and second breakdown voltages with doping density and diode width are presented. Second breakdown voltages are shown to increase initially with temperature due to the decrease in avalanche coefficients and saturation velocities with increased temperature, and then to decrease as thermal injection from the high doping boundary regions drastically reduces the multiplication factor required to reach the breakdown current. It is shown how the temporal rate of temperature increase, as a function of current density, can be used to calculate both current-versus-time and voltage-versus-time curves from static characteristics at several temperatures. A limited comparison is made with experimental data and with other computations.

Electric and Spectroscopic Characterization of Arcing in Electrical Contacts: A Study of Erosion

Abstract: Arcing in electrical contacts of telephone switching relays and the subsequent erosion have been the subject of a great deal of work. Nevertheless the problem depends on many parameters (the electrical circuit, environment, relay type, etc.) and knowledge is incomplete. The AgCu 90/10 contact used in the French CP 400 telephone switching system and, more particularly, the consequence of arcing in the current range 1-500 mA are the subject of this paper. Two methods are used to study arcing: measurement of the arc duration and analysis of the emission spectrum from the arc. The first results show that these two arc characterizations are related to erosion and that the variations with current are similar.

Reduced Gold-Plating on Copper Leads for Thermocompression Bonding-Part I: Initial Characterization

Abstract: In this two part series, Au-plated Cu leads with reduced Au thicknesses are evaluated for thermocompression (TC) bonding. Part I is concerned with initial characterization, which makes use of recent measurements of grain boundary diffusion coefficients (D') of Cu through Au. Part II considers the problem of predicting the long term reliability (40 years at 50°C) of these TC bonds, using recent measurements of the volume interdiffusion coefficients (D). Oxygen-free Cu leads plated with as little as 0.7 µm Au were compared to the more typical plating thickness of about 2.5 µm. The properties evaluated in Part I are: 1) initial TC bondability; and 2) prebond shelf life, i.e., TC bondability after storage of the Au-plated leads. Results of these evaluations are the following. 1) Leads plated with as little as 0.7 µm Au can have acceptable initial TC bond strengths especially when bonded at 30 to 50 percent deformation. 2) High-temperature storage of the leads followed by TC bonding indicates a shelf life of greater than two years at 50°C. This is in agreement with predictions based on grain boundary diffusion of Cu through Au: D' = 8 x 10-5exp (-0.91 eV/kT) [cm2/s]. Thus the initial characterization was successful for Au thicknesses down to 0.7 µm.

Performance of New Copper Based Metallization Systems in an 85&#176;C 80-Percent RH Cl 2 Contaminated Environment

Abstract: The performance of TPCNA (Ti-Pd-Cu-Ni-Au) and TCN+A (Ti-CuoNi+Au in selected areas only) meta!lizations in 85°C, 80-percent RH, with 0.5 to 1.8 ppm Cl 2 was compared with that of the standard TPA (Ti-Pd-Au) metallization. Encapsulated (RTV silicone rubber) and unencapsulated triple track conductor test specimens were used. Electrolytic corrosion was studied by biasing the specimens in the high humidity corrosive environment and measuring in situ leakage currents as a function of time. For the unencapsulated specimens, leakage currents increased and all samples failed by 600 h. The failure rates for TPCNA and TCN+A samples due to the formation of Cu and Ni dendrites between oppositely biased conductors were the same as for TPA which had Au and Pd dentrites. None of the encapsulated samples showed dendrite growth after ~ 1000 h. Unencapsulated TPCNA and TCN+A were less resistant to galvanic corrosion in the moist Cl 2 contaminated environment than were the TPA specimens. TCN+A failed first by Ti-Cu delamination and later by delamination of the Au due to corrosive oxidation of the underlying Ni. This latter failure mode was predominant for TPCNA. TPA conductors eventually failed at Ti-Pd interfaces. At 85°C, 80-percent RH, 1.6 ppm C!2, unencapsulated TCN+A degraded at the Ti-Cu interface ~10 times faster than unencapsulated TPA at the Ti-Pd interface. The corrosion product found on unencapsulated TPCNA and TCN+A and on Cu-NiAu external leads was identified as Cu, NiCl 2 . 3 [Cu, Ni(OH) 2 ]. The encapsulant was extremely effective in retarding galvanic corrosion. For encapsulated TCN+A and TPCNA, eventual bond failures were the result of penetration of the corrosive environment under the edges of the encapsulant. For TCN+A, encapsulation retarded the time to failure by a factor of >10. The relative resistance to galvanic corrosion in moist Cl 2 may be ranked TPA > TPCNA > TCN+A.

Reduced Gold-Plating on Copper Leads for Thermocompression Bonding--Part II: Long Term Reliability

Abstract: This two-part series is an evaluation of the acceptability for thermocompression (TC) bonding of Cu leads having reduced thicknesses of Au-plating at the bond sites. Part I was concerned with initial characterization which made use of recent grain boundary diffusion work in the Cu-Au system. In this second part, long term reliability is considered where use is made of recent work in volume interdiffusion in the Cu-Au system. Three properties are evaluated: 1) Long term reliability based on accelerated aging of bonded leads; 2) temperature cycling; and 3) cyclic 45° bend fatigue. Results of these evaluations are the following. 1) A lifetime of greater than 40 years at 50° C is predicted for Cu leads with as little as 0.7 µm Au-plating. This conclusion was reached using volume interdiffusion as the rate controlling mechanism for the observed decrease in strengths. The same conclusion was reached from a statistical analysis of the lifetime data without making recourse to a physical model for the degradation. 2) No degradation in bond strength was observed for up through 300 temperature cycles between -40 and +150°C. 3) Cyclic 45° bend fatigue of the bonded leads was not affected by the Au-plating thicknesses studied. In summary, when the results of both parts are combined, the overall conclusion is that oxygen-free Cu leads plated with as little as 0.7 µm Au are judged acceptable for TC bonding.

Hybrid Microcircuit Tape Chip Carrier Materials/Processing Trade-Offs

Abstract: This paper surveys and compares several metallurgical structures and compositions used in the various reel-to-reel gang bonding processes now being implemented by high-volume semiconductor manufacturers. Various gang bonding techniques are reviewed briefly as background. Thermocompression (TC), hard solder, and soft solder inner lead bonding processes are compared, as well as TC, welding, and solder processes for outer lead bonding to lead frames or alumina-based networks. The characteristics, advantages and disadvantages of 1, 2, 3 layer interconnect metallizations, different bump structures, TC and solder bonding processes, and various carrier materials are discussed and compared.

Impact of the Contact on Electrical Systems

Abstract: Many electrical systems, for example, telephone systems or computer systems, use great numbers of contacts. This paper will indicate how such extensive contact usage must in turn influence the architecture of the system as a whole, to a degree that is not commonly realized. One illustration relates especially to the case of electromechanical switching, using relays and connectors; and a second example refers to applications using electronic technology, where connector use continues to expand. This paper reviews those variables that control the physical design of contacting units, with emphasis on relays and connectors. Consideration is given to the influence of contact material and contact force; to the related effects of these on spring materials and shapes; and the consequences of these on magnet design if relay action is needed. The interplay of these relationships determines the structural design of the contacting unit-and this in its turn must influence the system as a whole.

Oxygen Embrittlement of Copper Leads

Abstract: Electrolytic tough pitch copper (known as ETP, CDA110, or copper alloy no. 110) is a material used in the manufacture of external leads for hybrid integrated circuits. Cracking during the formation of 90° bends and the relatively poor cyclic fatigue behavior of this material are identified as due to embrittlement caused by second-phase oxide inclusions. Optical and SEM examinations of failures led to the following model for embrittlement. Under the applied loads, voids nucleate at the second-phase inclusions; continued loading causes the voids to grow and coalesce, resulting in a fracture. This model is consistent with the published literature. Cyclic fatigue behavior, i.e., the median number of cycles to failure (MCTF), was found to vary inversely with the oxygen concentration. Over the range 10-650 ppm oxygen (by weight), the fatigue results could be represented by [100/MCTF] = 0.0228 [ppm oxygen] + 8.32. For both CDA110 and oxygen-free copper (CDA102 or copper alloy no. 102) the MCTF was found to vary inversely with the percent of bond deformation over the 10-60-percent range. Therefore, all cyclic fatigue comparisons among the various CDA110 and CDA102 specimens were made at a common bond deformation, chosen to be 35 percent. Oxygen-free copper with ~10 ppm oxygen was found to have about twice the MCTF as CDA110 with ~400 ppm oxygen.

Effect of Foil Edge Modifications and Configurational Changes on Energy Storage Capacitor Weight

Abstract: Corona failure at foil edges is the principal failure mechanism in well-designed and manufactured high energy-density pulse-discharge capacitors. By forming the foil edge with laser cutting or spark discharge machining, a 25-percent increase in corona inception voltage (CIV) over untreated edges is obtained. Folded foil produces a larger increase. Weight minimization using peak edge field as the limiting factor suggests that a configuration where the foil and dielectric are of equal thickness produces the lightest capacitor. Typical designs are presented.

IOAP-A Novel Process for the Manufacture of Long-Life Silver-Cadmium Oxide AC Contact Material

Abstract: This paper describes a new more versatile internal oxidation technique for the manufacture of silver-cadmium oxide contact tips. The process allows precise control in producing a fine homogeneous microstrueture, it avoids the occurrence of a central denuded core in contacts and uses oxidation times which are several orders of magnitude less than in the conventional method. This novel technique essentially combines internal oxidation and powder metallurgical methods of compaction and densification. By correct control of the processing of the powder into high-density contact parts, a wide range of microstructures may be obtained from a single powder. The first stage of the process is the formation of a silvercadmium alloy powder of fine particle size by the low-temperature reduction and alloying of a silver and cadmium oxide powders mixture. This powder is produced in spherical aggregates in preparation for the second internal oxidation step. Internal oxidation of the fine alloy powder is then carried out at relatively low temperatures in times typically 103 times shorter than are required in conventional internal oxidation. This results in powder which contains extremely fine cadmium oxide particles in a simple orientation relationship with the matrix within and on the surface of each powder particle. This internally oxidized alloy powder (IOAP) is then compacted to provide green compacts for sintering and coining to provide high-density contact tips. During the sintering stage of the IOAP process, the ultrafine cadmium oxide particles within each powder particle grow by an Ostwald ripening process. The extent of this coarsening is governed by the time and temperature of the sintering operation and the oxygen potential of the furnace atmosphere: these parameters can be controlled to provide a specific final material selectable from a very wide range of possible microstructures. The coining operation increases the density to a value approaching the theoretical. The IOAP process also allows the addition of selected elements or compounds to the basic material at several stages in the process and retains the ability to control the microstructure independently from the chemical composition. This feature of the IOAP process is in sharp contrast to more common internal oxidation techniques.

The Effect of Surface Segregation of Mg on the Contact Resistance of Al-0.5-Percent Mg

Abstract: Silver and Ag-W (10 weight percent W) were operated in a 5.I-A (peak) 308-V (peak) full-wave rectified dc circuit. The experimental switching system was operated 1.5 times per minute; the opening and closing velocities were 4 x 10-2 and 3 x 10-4 cm/s, respectively; the fully open contact spacing was 200 µm; and the contacts were closed for 3 s. The opening and closing of the contacts were controlled by a heater-bimetal combination attached to the moving contact. The following contact pairs were used: Ag versus Ag, Ag-W versus Ag-W and Ag versus Ag-W. All combinations of contact material and contact polarity were used. The experimental results showed that there was always a net transfer of contact material from the cathode to the anode. The volume of material transferred was strongly dependent upon whether the anode was the moving (hotter) or the fixed (cooler) contact: the greater erosion occurring when the anode was the hotter contact. For Ag versus Ag contacts thc erosion pattern resulted inone pip on the anode and one crater on the cathode. For Ag-W versus AgW contacts the presence of the small percentage of W resulted in multiple pip and crater formations. The experiments with the Ag versus Ag-W showed that the cathode electrode material determined the erosion pattern observed, i.e., when the Ag-W was the cathode, multiple pip and crater'formations occurred, but when Ag was the cathode, only a single pip and crater structure was observed. The presence of the W either in the cathode or in the anode decreased the observed erosion. These experimental results are discussed in terms of how the presence of W affects the emission characteristics of the cathode region and also affects the movement of the arc roots.

Analysis of Mobility, Volatility, Morphology, Physical States, and Oxidation Stability of Selected Contact Lubricants

Abstract: The increasingly strenuous and variable thermal environments in which static gold-plated contacts must operate has generated a need for expanded information on the physical properties of traditional and new lubricant materials. This work investigated the mobilities, volatilities, oxidation stabilities, morphologies, and physical states of microcrystalline waxes, synthesized hydrocarbons, polyphenyl ether, di-2-ethylhexylsebacate, and polyethylene glycol over a wide temperature range. The mobilities of the microcrystalline waxes, high viscosity synthesized hydrocarbons, polyphenyl ether, and polyethylene glycol were all very low. The relative volatilities were: di-2-ethylhexylsebacate > low viscosity synthesized hydrocarbon > polyethylene glycol > polyphenyl ether > microcrystalline wax> high viscosity synthesized hydrocarbon. Oxidation tests indicated that the microcrystalline waxes and synthesized hydrocarbons were mildly sensitive to oxidation. Morphologies of thin films, determined up to 150°C with scanning electron microscope, were variable. The microcrystalline waxes and high viscosity synthesized hydrocarbons existed as generally uniform films with some clustering. The di-2-ethylhexylsebacate produced a very uniform film, and the polyphenyl ether distributed itself in a beaded nonwetting manner.

High Temperature Thermal Characteristics of Microelectronic Packages

Abstract: This paper describes results of the computer-analysis pottion of a research program which was conducted to study the thermal characteristics of microcircuits in high temperature environments. A special IC chip, bonded to an alumina chip carrier, was modeled for these simulations. It was found that thermal resistance values and thermal time constants nearly double when the chip carrier temperature is increased from 70 to 257°C. For a chip power dissipation of 1.5 W, the peak junction temperature increased from 138 to 385°C, an increase of 247°C, while the chip carrier only increased by 187°C. The thermal time constant of the junction peak temperature rise, measured relative to the chip carrier, increased from 15 to 26 µs over the same temperature range.

High-Energy Solid-State Electrical Surge Arrestor

Abstract: In this paper an engineering model of a high-energy (20 ~ 40 C of charge, 15 ~ 35 kJ) solid-state electrical surge arrestor (ESA) is presented. The basic elements are commercial or custom-made metal oxide varistors (MOV). The approach to achieve a high-coulomb ESA is to use paralleled MOV's with efforts concentrated on ensuring uniform current partition by matching the MOV's conduction characteristics and using ballast resistors. The unit with custom-made large area MOV's survived consecutive 40-C surges of 5-ms exponential decay. The peak current was 6.5 kA at a clamping voltage of 1.1 kV. Design consideration, screening techniques, packaging, and test results are reported. A brief review of the MOV physics is also included.

Reliability of Clad Metal Inlays for Electrical Connectors

Abstract: Following the prior publication [ 1 ], we tested more connector hardware of clad metal inlays the quality of which is quite close to the production level. In other words, the spring base material was all made of beryllium copper fully heat-treated after forming. The springs were punched and formed with a production the spring gaps were more uniform and all within the specified range, though in the high end. The inlay materials used in this extended test were: a) 18K Au (75Au25Ag), b) pure palladium (100 Pd), c) Alloy 69Au25Ag6Pt, d) 60Pd40Ag alloy, and e) alloy-55(55Au39Ag3Cd31n). These materials were reported to have relatively better performance among the many candidates we initially studied. The sample size used in these tests was much larger than the previous one; as a result, the experimental data are more reliable and meaningful. Two groups of connector hardware representing today's highdensity miniature electronic packaging were used. One group was the cylinder-cylinder contact, the other was the cylinder-flat contact. Also some discussion was devoted to the dimple-flat contact system. The contact-resistance data were collected over a period of 6 months to 1 year from three kinds of environmental tests. Both porosity and formability were acceptable for all the inlay springs. No wear-through contacts were found after 50 insertions with lubricant applied on the Au or Pd plated pins. All five inlay materials tested behaved almost equally well in their contact-resistance measurements. Previously the 69Au25Ag6Pt was chosen as the best, and the palladium stood as the second best at that time. However, in this paper we have shown that the Pd is clearly the winner in many aspects of the tests. The 69Au25Ag6Pt is equivalent to the 75Au25Ag alloy as the second best choice.

Energy Storage Capacitors of Very High Energy Density

Abstract: A detailed discussion of the design and manufacture of reliable high-energy-density pulse-discharge capacitors is presented. Electrical design and thermal analysis of single sections are described and illustrated with actual test data. The physics of failure of high voltage capacitors is explored, and its application to the design and manufacturing process displayed. A unique winding method allowing the direct fabrication of fiat sections without mechanical flattening is described. Modified drying and impregnation cycles that produce wrinkle-free sections with oil resistivity above 2 X 1015 \Omega ·cm are given. Life and energy density data from full pulse-forming network (PFN) pulse tests and from simulated PFN tests show 550 J/kg (250 J/lb) at 250 pps.