Showing papers in "IEEE Transactions on Components, Hybrids, and Manufacturing Technology in 1982"

Accelerated Life Testing and Reliability of High K Multilayer Ceramic Capacitors

Abstract: The reliability of high K muitilayer ceramic capacitors was evaluated using accelerated life testing. The degradation in insulation resistance was characterized as a function of voltage (two to eight times rated) and temperature (85 to 170°C). The times to failure at a voltage-temperature stress conformed to a iognormai distribution with a standard deviation typically less than 0.5. A small infant mortality population was also observed for some samples. The results were least-squares fit to the following equation:

Effect of Fretting on the Contact Resistance of Palladium

Abstract: The fretting of palladium contacts was studied at conditions relevant to their use in separable electronic connectors. Wrought, clad, and electroplated palladium mated to wrought palladium develop high contact resistance due to the formation of friction polymer. This can occur in ordinary room air which contains traces of organic air pollutants. Contact resistance changes diminish as force is increased. Static contact resistance measurements were made in small steps along wear tracks during fretting tests. It was found that the contact resistance increases were greatest at or near the ends due to the accumulation of polymer, and that the numbers of fretting cycles required to produce high contact resistance diminish sharply as track length is increased from 10 to 160 #m. Thin coatings of a polyphenyl ether contact lubricant significantly improve the stability of contact resistance, and contacts flooded with this fluid showed little degradation. This is attributable to its ability to disperse the polymer which is formed. Likewise, palladium contacts immersed in toluene, a polymer precursor commonly used in laboratory studies of friction polymerization, display stable contact resistance. These findings are compared to those of previous studies of the contact resistance of palladium during fretting, and it is shown that differences in interpretation of results are due to variations in the apparatus which were used.

Development of the Spherical Silicon Solar Cell

Abstract: A unique photovoltaic/electrochemical solar energy conversion/storage system utilizing silicon spheres as the individual photovoltaic elements is being developed at Texas Instruments. A new technology has been developed to produce high-purity single-crystal silicon spheres at high throughput rates. The spherical geometry offers several advantages including high crystal growth rate, simplified in-process material flow, and excellent silicon material utilization. The silicon sphere production process is discussed and the device efficiency status and goals are presented.

Metal Migrations Outside the Package During Accelerated Life Tests

Abstract: Various large-scale integrated (LSI) ceramic and plastic packages are stressed through different accelerated life tests including temperature, humidity, hostile gases, and bias. Migration phenomena are observed after biased tests, with metal dendritic growth from the cathodic pins and large corrosion areas around the anodes. When no bias is applied only corrosion areas which could affect any pin are evidenced. The metals found to migrate are Ni, Cu, Sn, and Ag. The influence of hostile gases proves dominant through solubility control in the anodically corroded areas. The effect of residual contamination on the substrates is also described. Physical failure mechanisms are investigated through the accelerated tests results and data from defective components in service conditions. It appears that silver migration is the main concern and that the use of Ag package technology should be severely limited. The temperature-humidity bias tests are more convenient to predict package life time in service conditions in order to provide a reliable quantitative evaluation.

Silver Migration Model for Ag-Au-Pd Conductors

Abstract: An acceleration model is presented for insulation failure between biased adjacent lands of a ternary Ag-Au-Pd alloy conductor paste on alumina substrates. The failure mechanism consists of silver diffusing in the form of tree-like dendrites through borosilicate glass overlays. Accelerated life test results, maximum likelihood estimation techniques, multiple linear regression analysis, and a previously proposed physical chemical model were used to derive the acceleration model. The activation energy of "dry" silver migration which was estimated to be 1.09 ±0.16 eV was in good agreement with previous studies of this Phenomenon.A comparison of reliability is made between this ternary alloy and a binary Ag-Pd alloy. The comparison shows the enhanced reliability of the ternary alloy, which may be due to the presence of gold in its formulation.

Electrical Properties of Conductive Elastomer as Electrical Contact Material

Abstract: The conductive elastomer has both electrical and elastic properties. When the conductive elastomer is considered as an electrical contact material, it is possible to obtain conductive and elastic properties in one simple material. Therefore, the concept of metallic electrical contact can be changed to the elastomeric contact. Moreover due to excellent properties of facile shape formation, corrosion resistance, and air tight contact interface, the conductive elastomer is suitable for high density microsized connectors. However as it is very difficult to obtain as low a resistivity as in metals, the effectiveness of the elastomeric contacts is limited. The present study has been conducted to determine the electrical conduction mechanism and to find low resistivity materials. The specimen silicone rubber, in which electrical conductive particles such as carbon and metals were dispersed, was investigated. The resistivity versus conductive particle content, voltage versus current characteristics, resisitivity change in range of room temperature to liquid nitrogen temperature, and conduction mechanisms were discussed. In conclusion the conduction mechanism changes with the conductive particle content. For large content current paths were established by contact of particles, and for small content conduction electrons pass through the gap between particles by the Schottky conduction. Therefore, the resistance of the elastomer consisted of particle resistance, constriction resistance of the contact interface between particles, and the gap resistance.

Field Studies of Contact Materials: Contact Resistance Behavior of Some Base and Noble Metals

Abstract: The contact resistance of various metals was determined after exposure of from three months to four years in telephone central offices and in nonair-conditioned locations. The logarithm of median contact resistance was stable for some materials, but with most it increased on aging according to linear, parabolic, or logarithmic time relationships. The kinetics of contact resistance change depended on the intrinsic chemical reactivity of the material, the air pollutants which were present in the exposure site, and especially on the relative humidity. Contact resistance-force behaviors were affected also by the topographic and hardness characteristics of the metals. The overall ranking in central offices on the basis of stability of contact resistance from best to worst was 1) gold; 2)high gold-silver alloys, palladium, high palladium-silver alloys, 60Sn40Pb, and tin; 3) copper, high copper alloys, and nickel; and 4) silver. Where relative humidity was only slightly less well-contro11ed, as in a nonair-conditioned room in an urban central office building, except for gold the contact resistances of all materials were from one and two orders of magnitude greater after 40 months of exposure, and often displayed different kinetic behaviors. Palladium was exposed in a total of 18 sites and its contact resistance was found to be highly variable, even exceeding 1000 \Omega in less than 1 year when relative humidity was high and reactive chlorine-containing air pollutants were present. Pore corrosion of gold electrodeposits and creep of tarnish films from adjacent base metals did not occur in central offices except when the substrate was silver and the level of sulfiding pollutants was high.

A Thermophysical Criterion for the Weldability of Electric Contact Material in a Steady-State Regime

Abstract: A thermophysical criterion for the weldability of contact materials is determined as an unambiguous function of the fusion temperature and of the temperature dependences of the resistivity and thermal conductivity of these materials. The values of this criterion are calculated for most metals, a number of alloys, and some of sintered compounds usually applied in contact design. Also calculated is the dependence of the criterion on the preheating of the contact body, which is important for the estimation of weldability under conditions of circuit reclosing in the presence of a short circuit. Some limitations of the recalculation of the weldability criterion for conductors not mentioned in this paper are discussed.

Fiber Optic Rotary Joints-A Review

Abstract: The rapid increase in the use of fiber optic signal transmission has spawned a need for "optical slip rings" to transfer optical signals across a rotating interface. Performance parameters that impact the development of these fiber optic rotary joints are investigated. The designs of existing single-channel fiber optic rotary joints are discussed with the intention of identifying design features that have the greatest impact on performance. The basic design feature of several multiple-channel fiber optic rotary joints is summarized.

Debunking the Learning Curve

Abstract: The learning curve relates manufacturing cost to cumulative production. It is shown that for every well-behaved learning curve there is a corresponding relationship between unit cost and the annual rate of production. Cause and effect are assignable to this new function which is dubbed the opportunity curve. The growth in annual demand creates opportunities and provides the funds for increased mechanization and larger batch facilities in process dominated manufacture. In the absence of growth, both are seriously curtailed. The concept of the opportunity curve is developed from available data related to the U.S. integrated circuit industry. The opportunity curve in combination with the warranted growth curve permits an analysis of corporate strategies which remain obscure in interpretations of the learning curve. Reductions in cost are enhanced by growth, and a firm which holds a very significant share of the market--either across the board or in a segregated sector of the technology--will have a cost advantage. There is nothing wrong with the learning curve. But in combining annual production and time in the single variable, cumulative production, it hides more than it reveals.

The Aging Behavior of Commercial Thick-Film Resistors

Abstract: An earlier paper reported the promising prospects of accelerating thick-film resistor aging by elevated temperature and humidity stress; those early findings have now been confirmed by further results from many thousands of hours of overstress testing of commercially produced resistors from various sources--amounting to accumulated test times of some millions of resistor-hours. The normal aging trend is a steady increase in resistance at a rate influenced by various factors such as manufacturing origin, resistivity, electrical bias, environment, and encapsulation. The majority of the increases vary with the square-root of time, consistent with a diffusion-controlled degradation of the conduction processes. Some changes also conform to piezo-resistive effects and together these provide physical explanations for the aging behavior of thick-film resistors. The drift observed in the majority of resistors can be extrapolated to give a prediction of less than 0.5 percent change in 20 years operation in standard environments---a heartening prospect indeed for thick-film reliability.

Surface Topography of Printed Wiring Boards and Its Effect on Flashover

Abstract: Breakdown voltage values between conductor paths on epoxy-glass printed wiring boards (PWB's) are shown to lie on the Dakin curve relating the breakdown voltage with the dielectric constant and conductor separation on the insulator. However, the insulator surface roughness is shown to affect the breakdown voltage, the smoother the surface the lower the breakdown voltage. With a roughness (peak to valley) on the order of 10 µm or greater on epoxy-glass, the breakdown voltage approaches that of an equivalent air gap. Multiple filamentary discharges were observed per flash over similar to normal air breakdown. Erosion products from flashover include small copper spheres, from the damaged printed wiring lines, scattered around the damaged area on the PWB where, in many cases, the glass fiber supports were exposed. These effects can accelerate the degradation of the PWB insulator substrate.

Ti Compound Formation During Ti Diffusion in LiNbO 3

Abstract: Scanning electron microscopy (SEM), backscattering spectrometry, and X-ray diffraction were used to study the initial steps of Ti diffusion into both Y-cut and Z-cut LiNbO3 substrates annealed in dry 02 atmosphere. The Ti oxidation process observed at intermediate temperatures (300°C-500°C) is followed at higher temperature treatments (950°C, 30-60 min) by an epitaxial growth of the (TixNb l_x)O2 phase, which behaves as a source for Ti diffusion 'and consequently is consumed for longer annealing times (950°C, 20 h). For this compound an x value of 0.60 + 0.05 was obtained from experimental results.

Application of the Finite Element Method to Determine the Electrical Resistance, Inductance, Capacitance parameters for the Circuit Package Enviornment

Abstract: A finite-element program, Fierce, is used to obtain representative R, L, C electrical parameters for various two-dimensional conductor/dielectric packaging structures. The calculated results of Fierce are compared with an existing program C2D and correlated to hardware measurements. Specific advantages of Fierce are cited for ,modeling complex multilevel wiring packages with mixed dielectrics and several grounds. The concluding example demonstrates the capability of Fierce to characterize nine conductor--five dielectric model(s). The R, L, C outputs are inputed to a circuit analysis program, Astap, to compare the performance advantage of a ground plane located close to the conductors versus a far ground plane for a high performance application (800 ps driver switching speeds).

Bias Humidity Performance and Failure Mechanisms of Nonhermetic Aluminum SIC's in an Enviornment Contaminated with Cl 2

Abstract: The aging of aluminum-metallized silicon-integrated circuit test vehicles (bare, SiN CAPS only, room temperature vulcanizing silicone rubber (RTV) only, SiN CAPS + RTV) at 85°C, 85 percent relative humidity (RH), and 1 ppm SO2 for 4968 hours was carried out with either a + 10 V, or - 10 V, or 0 Vdc bias imposed on the samples. The leakage currents for the unencapsulated samples increased several orders of magnitude after the addition of SO2. After an induction period of several hundred hours, the leakage currents for the encapsulated samples also increased by several orders of magnitude. Most of the failures were observed in the unencapsuiated groups. The anodic corrosion rate is the highest. Subsequent to environmental stressing, the specimens were examined with a scanning electron microscope (SEM) with X-ray capability. No corrosion was observed on the encapsulated samples. The main failure mode of the unencapsulated samples showed corrosive growths containing Al and S near the Au-Al interconnect of the wire bond. This localized corrosion occured on both anodicaily and cathodicaily biased postions. There were more failures at the anodic electrode. The application of bias is not necessary for corrosion. Dow Corning QC 3-6550 RTV silicone rubber is an effective encapsulant in a moist SO2 environment inhibiting corrosive attack. It retards the occurrence of high leakage currents. A mechanism for corrosion is discussed. It involves the oxidation of sulfur dioxide in aqueous solution to sulfate ion and the acceleration of corrosion by the galvanic couple formed at the Au-Al interconnect. An estimate of the median life of the encapsulated samples under worst case use conditions was calculated to be better than 1.5 x 106 h. The results show that the failure rate is less than 1 FIT (failure in 109 device hours) after 20 years. This was obtained by assuming the same acceleration factors as obtained in previous work on encapsulated aluminum.

A Finite Element Analysis of the Thermal Behavior of Contacts

Abstract: The finite element method is applied to two basic problems in the thermal analysis of electrical contacts. The first problem studied is the welding together of contacts when a high current is flowing. The finite element method first is used to solve the electrostatic field equation in order to determine the internal heat generation due to the flowing current. The results are used then in a heat conduction model. The second problem considered is the heating of contacts by a high intensity arc. Various boundary conditions for representing the effect of the arc are considered. The model permits phase changes to occur. The particular material studied is a sintered mechanical mixture of silver and tungsten.

A Ceramic Capacitor Substrate for High Speed Switching VLSI Chips

Abstract: An integrated capacitor substrate which is proposed as an essential part in the realization of a thin film module for high speed digital computing systems is discussed Several innovative multilayer ceramic (MLC) concepts relative to the fabrication of the desired low inductance capacitor and current paths to chips are described Ceramic and metal composite material sets which may be used in the fabrication are also proposed Experimental evaluations of some of the crucial concepts were made and included in the discussions The result is an elegant approach to the fabrication of one of the key requirements in realizing the thin film high performance module

A New PTC Resistor for Power Applications

Abstract: A new positive temperature coefficient (PTC)resistor and its properties are described which utilizes the metal-insulator solid-state transition in (V,Cr) 2 0 3 . At a transition temperature of 80°C, for example, the specific resistivity of a ceramic body exhibits a · rapid increase to a value 100 times higher than that at 20°C, which is typically 1.5x 10-3 \Omega cm. Due to this low resistivity, thermistors with resistance values between at least 0.1 m \Omega and 0.1 \Omega can be manufactured which can carry rated currents substantially higher than 200 A or lower than 2 A, respectively. The construction of the new device is described, and typical properties and applications are illustrated.

Low Temperature Double-Exposed Polyimide/Oxide Dielectric for VLSI Multilevel Metal Interconnection

Abstract: By use of a double-exposed (double-etch) low temperature polyimide/oxide process, the packing density for both first and second level metal interconnection can be improved by some 35 percent and 30 percent, respectively, in the vicinity Of the via. Moreover, the complete interconnect process may be realized at temperatures below 300°C. Since polyimide can be applied in thick layers having negligible (tensile) stress, a planar surface results and also parasitic lead capacitances may be considerably reduced. This process is also amenable to either wet chemical or dry plasma processing.

Packaging Reliability-How to Define and Measure It

Abstract: Microelectronic packaging employs many combinations of materials and processes to effect the interconnection of active and passive components and to provide interfaces with system levels of equipment. Reliability of these first-level packages is a key element in user acceptance and economics of electronic equipment. Complex interactions of design, materials, and processes may significantly affect package reliability. A tutorial approach to reliability methodology for first-level packaging as practiced in one company is presented. It emphasizes the identification of physical processes of degradation, approaches for mathematical modeling to relate accelerated testing to field application, and statistical quantification of unreliability (the complement of reliability). Application of this methodology is exemplified in the evaluation of several potential failure mechanisms discovered during the introduction of a new alloy for fiip-chip interconnection to the IBM packaging technology.

Significant Features of Solder Connections to Gold-Plated Thin Films

Abstract: An investigation of 60Sn-40Pb solder connections between phosphor-bronze clip-on terminals and Ti-Pd-Cu-Ni-Au and Ti-Pd-Au thin film terminations is described. The investigation consisted of measuring joint strength and analyzing resultant fracture interfaces and metallographic cross sections by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDAX), electronmicroprobe (EMP), and X-ray diffraction, both initially and after accelerated temperature aging. Similarities and differences observed for the different terminals and termination conductors used in this, and previous investigations, are presented. Observations are explained by termination interdiffusion, intermetallic compound formation between terminal, termination, and solder constituents, and joint geometry related to the terminal design.

Some Considerations on Stability of Electrical Resistance of the TiO 2 /SnO 2 Ceramic Moisture Sensor

Abstract: Studies on the stability of the electrical resistance of the ceramic moisture sensor related to the water adsorption properties of the ceramics by using a solid disk device made of Ti0 2 /SnO 2 ceramics are reported. The relationships between the resistance increase of the device due to chemisorption of water to form hydroxyl groups and the microstructure of the ceramics by analyzing the'data of scanning electron micrograph (SEM), powder X-ray diffraction, and by the resistance variation tests of the device in vacuum with water injection were studied. Also the life-tests of the device over 3000 h were performed under the excitation of AC 100 Hz in the atmosphere. Finally the possibility of the practical use of the device without heating the moisture-sensitive element by introducing the simplified equivalent circuit of the ceramic moisture sensor was discussed.

Failure and Overheating of Aluminum-Wired Twist-On Connections

Abstract: In this investigation, twist-on connectors of the type used for branch circuit wiring in buildings have been tested with solid aluminum and copper conductors. The connector and conductor combinations tested are approved in both the United States and Canada. All of the twist-on connections were made in accordance with the connector manufacturers' instructions. Testing consisted of on-off cycling at 90 percent of rated current and 13 percent duty cycle. Failures, involving increasing connection resistance and abnormal heating, have occurred in less than a year in a substantial number of the aluminum-wired connections. The failures involve both the electrical conductor (EC) and alloy aluminum conductors. In contrast the copper-wired connections have low resistance and are stable. The temperature of many of the overheating aluminum-wired connections has been high enough to cause hazardous deterioration of the conductor insulation. The difference in performance between the copper and aluminum conductors is determined to be due to failure to achieve and sustain low resistance conductor-to-conductor contact in the aluminum-wired connections. This results in the greater portion of the current flowing through the connector spring rather than directly from conductor to conductor. The connector spring is plated steel and is not suited to be the major part of the current path. Degradation of the contacts between the aluminum wires and connector spring follows by several well-known mechanisms, leading to increasing connection resistance and the resulting heat generation and high temperatures.

Packaging Technology for Josephson Integrated Circuits

Abstract: Packaging technology used to build the first system crosssection test vehicle in Josephson technology is described. A threedimensional modular card-on-board packaging approach has been selected to fabricate the test vehicle which incorporates all the essential features of the technology required to build a high performance processor prototype. Potential viability of the described packaging technology for the fabrication of such a prototype has been demonstrated by an experiment in which a critical data path has been successfully operated with a minimum cycle time of 3.7 ns.

Fringing Field Effect in MOS Devices

Abstract: Fringing field action in metal-oxide-semiconductor (MOS) devices is discussed theoretically. Line capacitance coefficients on silicon-on-sapphire (SOS) and bulk configurations are determined from a three-dimensional model. Increase of threshold voltage of narrow-width devices due to fringing is described.

Effects of Processing Methods on the Contact Performance Parameters for Silver-Tungsten Composite Materials

Abstract: A comparative study of electrical, mechanical, and microstructural properties of silver-tungsten contact materials (49 and 64 volume percent Ag) prepared by two different processing methods, namely press-sinter (PS) and press-sinter-infiltrate (PSI), is reported Even with the same elemental composition, tungsten particle size and distribution, the two different techniques of preparation have resulted in no difference in electrical contact resistance, minor differences in microhardness, transverse rupture strength and thermal expansion, and significant differences in contact life and arc erosion properties Oxidation weight gains at 600°C and 700°C are similar but the oxide layer morphology is quite different at 700°C The oxidation rate at 700°C is more than ten times of that at 600°C Silver tungstate is found to be absent at 700°C High contact resistance is due to the formation of porous tungsten oxides and a porous tungsten layer where silver is removed by the electric arc The arc erosion is dependent on crack formation and propagation which are not fully understood

Motion of Magnetically Driven Arcs on Oxidized Electrodes

Abstract: Experiments were carried out on a number of oxidized metals such as copper, brass, aluminum, and steel. Two kinds of rectangular electrodes were investigated, narrow and wide electrodes. On the narrow oxidized electrodes the arc moved slowly and sometimes discontinuously during its first run. During subsequent runs the arcs moved continuously along the same path of the first run with speeds which were ten times faster than the first run. On the wide oxidized electrodes however no slowdown of the arc was observed during its first run. It ran right away continuously with speeds similar to the subsequent runs.

High Current Arc Movement in a Narrow Insulating Channel

Abstract: an experimental study has been performed to determine the arc speed and hesitation time of a high current arc inside a narrow insulating channel with a set of diverging copper arc runners and copper contacts. The dependence of arc speed on current, on diverging angle, and on runner width has been obtained. The results are qualitatively consistent with simple force considerations. Hesitation time (the time the arc remains immobile t H ) is influenced by current and by runner width, both of which affect the magnetic force on the arc. The dependence of t H on contact opening speed leads to the concept of minimum gap for which the arc will start to move.

Forming Feedthroughs in Laser-Drilled Holes in Semiconductor Wafers by Double-Sided Sputtering

Abstract: Electrical feedthroughs in semiconductor wafers were made by laser drilling an array of holes in a wafer and subsequently depositing a conductor on the walls of the holes by double-sided sputtering and through-hole electroplating. A maximum depth-to-diameter ratio of six for feedthrough holes through semiconductor wafers successfully implanted with a conductor by this method was determined from both experiments and theory. Two factors dictated this limit. First, the sputtered film thickness shows a very sharp decrease with distance down the hole. Second, the critical film thickness required for film coalescence and electrical continuity increases with distance down the hole because the incidence angle of sputtered material becomes more oblique with distance down the hole and increases the tendency of the film to grow as separate islands.

Laser Writing of Masks for Integrated Optical Circuits

Abstract: Masks for integrated optics applications have been fabricated using a focused Argon laser beam to expose a photoresistcoated gold-chrome plate. Curved and straight line masks were written using a combination or precision motor-driven rotational and translational stages to move the coated plate under the focused laser beam. By varying the laser power and/or writing speed, directional coupler masks have been made 3-µm wide separated by as little as 1 µm. From the results it is shown that narrow lines several centimeters long with better than 1000A edge roughness can be obtained by this fabrication technique.