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Examples of corrosion failures in electronics: summary of case studies
Abstract
This chapter presents a collection of the case studies related to corrosion of electronics, which are a manifestation of the failure modes and mechanisms described theoretically in earlier chapters 1–5chapter 1chapter 2chapter 3chapter 4chapter 5. A variety of field returns and testing results have been described in the literature, and the exemplary cases are now selected and reported here in the respective manner depending on the root cause of the observed failure modes. Each of the subchapters represents a different main root cause of the failures, which are generally related to the PCBA cleanliness, presence of the corrosive atmospheric gases, mismatch of the thermodynamic activity of the makeup materials, and harsh operational and environmental conditions.
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Reliability characterization of SiC devices is an ongoing activity. For this work, 650 V SiC JBS diodes in TO247 housings were tested in H³TRB. After a test period of 4000 hours none of the devices had failed during the test and only two out of sixteen devices had failed during blocking curve measurements performed at intermediate time steps. This is significantly better performance than many silicon devices offer today. The failure spots of the failed devices were detected at the edge of the main junction appearing as semi-circular cavities in the aluminum metallization. All other devices did not even show deviations from their original blocking curves.
In traction applications HV-IGBTs are subjected to changing and particularly demanding climatic conditions. A new methodology is proposed to derive the chips mission profiles from realistic mission profiles of the railway vehicle and to more accurately assess the status of degradation or health of the IGBT modules. This will help to more precisely predict the remaining useful lifetime or schedule preventive maintenance of the railway traction converters.
Corrosion-induced failures remain frequent in electronics products used in industrial environments. The International Society for Automation (ISA) Standard 71.04-1985 provides a classification system using corrosion (or reactivity) monitoring to determine the corrosive potential of an environment towards electronic equipment. Changes to electronic equipment mandated by the European Union directive 2002/95/EC "on the Restriction of the use of certain Hazardous Substances in electrical and electronic equipment" (RoHS) required the elimination of lead in electronic equipment. Recent research has shown that printed circuit boards made using lead-free materials can be more susceptible to corrosion than their tin/lead counterparts. Now even environments previously considered relatively benign concerning electronics corrosion are experiencing serious problems as a direct result of RoHS compliance. With the passage of a number of RoHS regulations and the switch to lead-free finishes on printed circuit boards, many are now questioning whether this type of environmental monitoring is adequate. Reactivity monitoring now needs to provide a more complete environmental assessment than the monitoring techniques described in ISA Standard 71.04. This standard is long overdue for a major revision to address issues described for and since the implementation of RoHS. This paper will discuss changes that have been proposed for the current vision and what changes may be anticipated in future revisions.
The temperature-humidity-bias (THB) test is the standard for accelerated stress testing with respect to corrosion and other humidity driven degradation mechanisms. Usually, 1000 h tests at 85°C and 85% relative humidity are used to predict up to 25 years of operation. The bias is usually limited to 80 V in order to fulfil the respective standards. Nevertheless, THB tests on 1700 V insulated-gate bipolar transistor (IGBT)-modules have shown that higher bias is a more severe test condition. The failure analysis confirmed Cu- and Ag-dendrites and corrosion of the aluminium (Al)-chip-metallisation as the relevant failure mechanisms. To determine the acceleration factor due to voltage, 1200 V IGBT modules were tested in THB at 780 V (65% of VCES) and 1080 V (90% of VCES). A characteristic degradation consisting of three phases has been identified. The second phase seems to be determined by Al corrosion and an acceleration factor of about two has been estimated from 780 to 1080 V. Within the third phase, the devices stabilised probably due to localised self-heating. Thus, this degradation mechanism is kind of self-limiting, but the higher leakage also increases the risk of thermal runaway especially when biased close to the rated collector-emitter voltage.
The temperature-humidity-bias (THB) test is the standard for accelerated stress testing with respect to corrosion and other humidity driven degradation mechanisms. Usually, 1000 hrs tests at 85 degree Celsius and 85 percent relative humidity (85/85) are used to predict up to 25 years of operation. With regard to the respective standards asking for limited self-heating, the bias was commonly limited to 80 V. Nevertheless, recent THB tests on 1.7 kV IGBT modules have shown that higher bias is a more severe test condition. Failure analysis confirmed corrosion of the Al chip-metallization as well as Cu-and Ag-dendrites as the relevant failure mechanisms. In order to determine the acceleration due to bias, 1.2 kV IGBT-modules were tested in THB at 65 percent and 90 percent of their nominal voltage Vnom, respectively. A characteristic degradation consisting of three phases has been identified. The 2nd phase seems to be determined by Al corrosion and a factor of about two has been estimated for the acceleration between the aforementioned test-voltages. Within the 3rd phase, the devices stabilized probably due to localized self-heating. Thus, this degradation mechanism is kind of self-limiting, but the higher leakage increases the risk of thermal runaway, i.e. catastrophic breakdown especially when biased close to Vnom.
Introduction: Comparison of the performance of hearing instrument batteries from various manufacturers can enable otologists, audiologists, or final consumers to select the best products, maximizing the use of these materials.
Aim: To analyze the performance of ten brands of batteries for hearing aids available in the Brazilian marketplace.
Methods: Hearing aid batteries in four sizes were acquired from ten manufacturers and subjected to the same test conditions in an acoustic laboratory.
Results: The results obtained in the laboratory contrasted with the values reported by manufacturers highlighted significant discrepancies, besides the fact that certain brands in certain sizes perform better on some tests, but does not indicate which brand is the best in all sizes.
Conclusions: It was possible to investigate the performance of ten brands of hearing aid batteries and describe the procedures to be followed for leakage, accidental intake, and disposal.
Failures due to conductive anodic filament (CAF) formation in copper-plated through-vias have been a concern in printed wiring boards since the 1970s. With the continuous reduction in through-via pitch to meet high circuit density demands in organic packages, the magnitude of CAF failures is expected to be significantly higher. In this study, an accelerated test condition [130°C, 85% relative humidity (RH), and 100 V direct current (DC)] was used to investigate CAF in two organic package substrates: (1) cyclo-olefin polymer–glass fiber composite (XR3) and (2) epoxy–glass fiber composite (FR4). Test coupons with through-via spacing of 100 μm and 200 μm were investigated in this study. CAF failures were not observed in either substrate type with spacing of 200 μm. With spacing of 100 μm, insulation failures were observed in FR4, while XR3 exhibited stable insulation resistance during the test. The substrates were characterized using gravimetric measurement, and XR3 was found to exhibit significantly lower moisture absorption compared with FR4. The CAF failures in FR4 were characterized using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The results suggest a strong effect of moisture sorption of organic resins on CAF failure at smaller through-via spacing in package substrates.
Under certain environmental conditions, printed wiring boards (PWB) respond to applied voltages by developing subsurface deposits of copper salts extending from anode to cathode along separated fiber / epoxy interfaces. The formation of these deposits, termed conductive anodic filaments (CAF) require high humidity (80%RH) and high voltage gradient (5V/mil). The humidity exposure during the storage environment may cause the failure in the use environment. CAF formation is enhanced by the use of certain hot air solder leveling (HASL) fluids and / or water soluble flux constituents.
In this work, two catastrophic field failures were analyzed. Both failures were related to boards produced in a manufacturing process, which included HASL. One CAF failure occurred between a component through-hole and power plane held at a potential difference of 40V with a 0.005″ nominal spacing. The other occurred on an inner layer of a multi-layer board (MLB) between a via and ground plane held at a potential difference of 320V with 0.015” nominal spacing. The nature of the CAF was analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Ion chromatography (IC) was used to identify residue extracted from a failed board. The failure phenomena known as CAF poses serious longterm reliability concerns in electronic products exposed to adverse and hostile environments, especially those with closely spaced conductors.
Odor emission rates and characteristics were evaluated at two commercial swine nurseries in Indiana during the months of March, April, and May. The nurseries, housing 94 to 250 pigs, were mechanically ventilated with long-term manure storage pits under wire floors. Incoming ventilation air at one of the nurseries was tempered in a heated hallway. An eight-member odor panel evaluated odor concentration with a dynamic olfactometer and odor intensity and hedonic tone at full strength. The odor concentration of incoming ventilation air ranged from 7 to 85 odor units per cubic meter (OU m-3) and averaged 18 OU m-3. It ranged from 94 to 635 OU m-3 and averaged 199 OU m-3 in the ventilation exhaust air. The mean odor emission rates of the two nurseries were 18.3 and 62.5 OU s-1 AU-1 (1.1 and 2.7 OU s-1 m-2), respectively. The overall mean odor emission rate was 34 OU s-1 AU-1 (1.8 OU s-1 m-2). The measured emission rates are expected to be lower than those that follow stringent panel sensitivity requirements not currently required by olfactometry standards in the U.S. Keywords. Odor evaluation, Manure management, Ventilation system, Air flow rate, Air quality. dor nuisance continues to be a major issue for the swine industry, which is an important sector of the agricultural economy in the United States. Therefore, a significant amount of research has been initiated to better understand the nature and control of
Reliable measurements of air quality and emissions at large livestock buildings with inherently large spatial and temporal variations of pollutant concentrations are relatively difficult and expensive. Appropriate methodologies for such measurements are not readily apparent and techniques and strategies vary widely. Several important technical issues need to be addressed by an air pollutant emission measurement plan. This article describes comprehensive field measurements of indoor air quality and air pollutant emissions at eight commercial swine finishing buildings. The objective of the field test was to evaluate the effect of a manure additive on concentration and emission of ammonia, hydrogen sulfide, and odor. Continuous measurements of gases, ventilation rate, building static pressure, inside and outside temperature and humidity, and wind speed and direction were conducted at four naturally–ventilated buildings and four mechanically–ventilated buildings. Air was pumped continuously from inside each building into air–sampling manifolds. One air stream was drawn from beneath the floor to assess pit headspace air concentrations. Another air stream was drawn from ventilation exhaust points to assess inside gas concentrations and building emission rates. Gas analyzers were switched between sampling manifolds on 10– to 15–min sampling intervals. Ammonia was measured with chemiluminescence NO x analyzers after conversion to nitric oxide. Hydrogen sulfide was converted to sulfur dioxide and measured with pulsed–fluorescence, sulfur dioxide analyzers. Odor samples were collected in bags and evaluated using olfactometry. Gas and odor emission rates were determined by multiplying mean gas concentrations in the exhaust air by ventilation airflow rates. Ventilation rates of naturally–ventilated buildings were estimated using sensible heat and carbon dioxide balances. Ventilation rates of mechanically–ventilated buildings were determined by monitoring wall fan operation and directly measuring airflow of some variable–speed pit fans with full–size impeller anemometers. Labor and equipment requirements, pitfalls, problems, and solutions to problems of field studies are discussed. Several recommendations for future studies of this type were developed based on experience gained during this measurement campaign. Keywords. Air quality, Pig house, Environment, Pollution, Instrumentation. odern livestock production facilities have in-creased in size resulting in a greater geographi-cal concentration of animals, increased public scrutiny, stricter government regulation, and more nuisance odor complaints. Increased public acceptance of pork production operations may be achieved by reducing odor, gas and particulate matter emissions. Commercial manure additives reportedly mitigate odor production, reduce ammonia (NH 3) and hydrogen sulfide (H 2 S) emis-Article was submitted for review in October 1999; approved for publication by the Structures & Environment Division of ASAE in July 2001.
Accelerated corrosion leading to system failure has been observed on printed circuit boards present in industrial environments that contain abnormal levels of reduced sulfur gasses, such as hydrogen sulfide (H2S) and elemental sulfur. The problem is compounded by the fact that elemental sulfur is regulated by OSHA as a nuisance dust, and is allowed in a human working environment at the parts per thousand levels. Anecdotal data shows clearly that elemental sulfur gas present at the parts per million level can cause computer systems to fail within 2 months of use. Newer technologies such as immersion silver plating are especially susceptible to this type of corrosion. With the rapid growth of organically coated copper (OCC) and immersion silver platings, the number of failures due to reduced sulfur gasses in the environment has risen substantially.
A technique is described to measure a surface self-diffusion coefficient (D) of a metal (gold) by scanning tunneling microscopy. Micro-hills formed on a gold face show a shape evolution by a diffusion transport of kink site atoms. D is determined via a measurement of the hill apex radius as a function of time and includes corrections of image errors. The technique shows that STM can be used to study diffusion and it opens the possibility of measuring diffusion at lower temperatures where D could not be measured previously.
Precision thick chip resistors are used in a variety of different industries, from telecommunications to automotive electronics, and as such can be exposed to mild and aggressive corrosive environments. This paper investigates the corrosion performance of two generic precision thick chip resistors in a controlled corrosive atmosphere consisting of 60degC, 4 ppm H<sub>2</sub>S and water vapor in purified air. The resistors were exposed in an environmental chamber for periods of 5, 10, 15, 30, and 60 days. Following exposure, the samples were cross sectioned and subjected to surface analysis using microscopy and microanalysis. After the initial stages of exposure, corrosion was observed on only one of the two types of resistors. The corrosion developed because H<sub>2</sub>S gas and water vapor diffuses through the thin protective organic layer on the resistor, and subsequently reacts with the silver conductor layer. Corrosion was facilitated by poor overlapping of the solder and nickel layer and, in particular the glass binder over the glass overcoat, which allowed silver and sulphur to diffuse along the interface. In addition, this poor overlapping allowed contact between the nickel layer and the silver layer resulting in the development of an electrochemical corrosion cell. The main corrosion products that developed were silver sulfide (Ag<sub>2</sub>S) and nickel sulphur residue.
An electrical failure in non-permanent gold plated connectors, detected during routine testing in the assembly line of mobile phones, is investigated. The connectors are coated with Electroless Nickel/Immersion Gold (ENIG) plating. The failure was observed to be caused by galvanic corrosion of nickel underlying the gold plated surface. This was made possible due to imperfections in the gold layer, which provided access to the Nickel layer and ultimately the Copper substrate at later stages of the corrosion process. Direct evidence of this mechanism is shown both in top view and in cross-sectioned samples. The imperfections observed have rounded edges, indicating that they were formed during manufacturing of the parts, as reported in previous literature sources.
Reliability of low power electrical contacts such as those in hearing aid battery-spring systems is a very critical aspect for the overall performance of the device. These systems are exposed to certain harsh environments like high humidity and elevated temperatures, and often in combination with high levels of salt from human perspiration and environmental pollutants. In addition, the design aspects of such systems often call for multi-material combinations of substrate and coatings for catering to various requirements such as electrical conductivity and wear resistance, which in turn enhance the susceptibility of these systems to galvanic corrosion. In this study, traditional behind the ear (BTE) hearing aid systems, which failed during service were analysed. Failure analysis was performed on the dome type battery-spring contact systems. The morphology of the contact areas was observed using scanning electron microscopy, and the compositional analysis of the corrosion products and contaminants was performed using energy dispersive X-ray spectroscopy. Wear track morphology was observed on the contact points, and the top coating on the dome was worn out exposing the substrate spring material. The obtained results were correlated to the underlying corrosion mechanism and the failure mode is presented.
The corrosion failure of a printed circuit board (PCB) with electroless nickel/immersion gold (ENIG) surface finish in a hydrogen sulfide-containing humid environment was analyzed in this work. To establish a comprehensive mechanism for the damage, the exposed surfaces were characterized by visual inspection, scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It was realized that merely copper traces under the edge of soldermasks (on electrical junctions) suffer a galvanic-type corrosion reaction with hydrogen sulfide and moisture adsorbed, forming dominantly copper sulfides and a small amount of copper sulfate and oxide. The creep of the corrosion products on the surfaces of ENIG-plated layers, tin-based solders and adjacent soldermasked areas was also found to be responsible for creating short circuits on the outer layers of the miniaturized PCB.
Atmospheric corrosion has vast consequences on the reliability of electronic connectors. This study determined the corrosion resistance of Ni/Ni–P plating metallurgy as a function of plating current density and plating thickness. Discrepancy was observed in the neutral salt spray (NSS) and mixed flowing gas (MFG) tests. Thicker Ni–P deposits displayed superior corrosion resistance in MFG tests while thinner Ni–P deposits performed better in NSS tests. This disparity was attributed to the intrinsic corrosion susceptibility of Ni–P against chlorine or sulfur assisted corrosion. Corrosion products were analysed for better understanding of the corrosion mechanism. NSS test produced green corrosion residues consisting of CuCl (nantokite) and CuCl2(OH)3 (clinoatacamite) and brown residues consisting of Cu2O (cuprite). MFG test produced sulfides of copper (major) and nickel (minor).
Electroplated gold coupons with well-defined porosity were exposed in several classes of field environments for a few months to seven years. Parallel laboratory studies were conducted in dilute, flowing, mixed-gas environments. The results revealed that porous gold plating degrades at widely differing rates and by varying mechanisms, depending on the class of environment. Degradation from exposure to single gases as well as mixed gases containing only sulfur-bearing pollutants, was relatively benign compared with field rates, even at concentrations of a few hundred parts per billion. Mixed gases of H//2S/NO//2/Cl//2 produced corrosion at rates useful for accelerated tests and with realistic mechanisms.
The failure of the main telephone system in a marine products factory due to copper sulfide (Cu2S) creep was analyzed by measurement of hydrogen sulfide (H2S) in the atmosphere, elemental analysis with energy dispersive X-ray spectroscopy, and cross-sectional observation of vias in the printed circuit boards. Indoor H2S concentrations were higher than outdoor ones and these corresponded to the G2 and/or G3 levels defined in ISA S71.04–1985. The chemical composition of the copper sulfide creep indicates that it consisted of copper, oxygen, and sulfur. Cross-sectional observation and elemental mapping analysis showed that Cu2S creep initiated not at the edge of the organic coating (organic solder preservative, OSP) inside the vias but mainly at defects in the organic coating covering the copper.
Zinc-air batteries, despite their advantages of high energy density, operational safety, economic and technical viability, are limited by the problem of electrolyte leakage. This study presents a study on this problem and its effects on the performance of a zinc air battery. To elucidate the cause(s) of leakage, the following experiments were performed: determination of the surface properties of a film of PTFE (polytetrafluoroethylene) (main constituent of porous air electrode and porous diffusion layer), air-cooled discharge with two auxiliary tests porous air electrode voltage analysis and electroosmosis. The experimental results showed that: the hydrophobicity of a PTFE film is progressively reduced when it is soaked in a solution of KOH; liquid infiltration is most prominent when KOH solution is used as the conductive medium; in addition, temperature and voltage also affect the liquid infiltration phenomenon.
Corrosion study was performed on Au-Al wire bonds, thin layers of sputter deposited Au and Al, and Au-Al intermetallic nuggets. The test environment was iodine-vapour in air (1 mg/L) at 85 °C with varying relative humidity, and 500 mg/L of KI in water. GDOES, XRD, SEM EDS, wire bond shear, and electrochemical testing were used to characterize the samples. Failures of Au-Al wire bonds were found to be primarily attributed to the corrosion of Al via formation of Al iodides and consequent formation of Al oxides and/or hydroxides. Most susceptible to corrosion are Al metallization and Al rich intermetallic phases.
Microelectronic devices consist of a number of corrosion sensitive metallic combinations such as gold-aluminium and zinc coated steel. Polyamides (PAs) are well known packaging materials for microelectronic devices such as integrated circuits. Iodide based stabilisers are used in PA, and degassing of the iodine from the packaging materials can introduce significant corrosion problems on the microcircuit assembly. The investigations in this paper focus on the effect of iodine containing PA stabilisers on the corrosion of zinc coated steel parts and gel protected gold-aluminium wire bond connections, and elucidation of the corrosion mechanisms.
In many power electronics products, such as low voltage LV motor drives, the mechanical and electrical connection between printed circuit board assemblies (PCBAs) is obtained though board-to-board connectors. A common failure mechanism for these components is fretting corrosion. This failure mechanism results from mechanical micro-motion of two parts with respect to each other and causes a wear damage at the asperities of the contact surface resulting in an increase of the ohmic resistance which finally triggers various device failures. Failures resulting from interrupted communication path may create different effects at the product level depending on the power electronic circuit diagram. In this paper investigation on fretting corrosion on board-to-board connectors was performed. The chemical composition and microstructural analysis at the junction part of the connectors were performed for as new samples and after aging testing which includes stressors like humidity, temperature, temperature cycling and vibration. Scanning Electron Microscopy (SEM) and energy dispersive X-ray analysis (EDX) showed aging effect on the intermetallic compound (IMC) material correlated to intermetallic growth and oxidation.
Conventional surface-mount chip resistors have wraparound terminals on the ends of the substrate. When such surface-mount resistors are soldered to a printed circuit board, solder covers the entire surface of the terminals. This forms fillets, resulting in the occupation of an additional area for mounting. A flip chip resistor is a resistor that has no side electrodes and is soldered with its printed side towards the printed circuit board. With this configuration, solder fillets are not formed. thus decreasing the amount of circuit board space required and increasing the mounting density, particularly in the case of small chip sizes. On the other hand, face-down mounting used for flip thick film chip resistors adds some special requirements. For example, the terminals should be better protected from the corrosive influence of the flux residue, the insulation voltage between the resistor and a PC-board trace running between the terminations should be at least 200 V, etc. The objective of the present development is to improve the resistor's quality and offer fillet-less flip chip thick film resistors having high reliability that enables high-density mounting. These reliability concerns were avoided by using specially designed, patent-pending, polymer conductive and protective layers. Because the final design is not based on expensive noble materials, the resistors are acceptable for cost-sensitive applications.
Mobile phone dome–key pad system is the device that connects the phone keys to the printed circuit board (PCB). The material combination for a typical dome–key pad system is Ag/AISI 202 steel for the dome and Au/Ni/Cu for the key pad. Under humid conditions dome–key pad system is susceptible to multiple corrosion problems. In this paper, the corrosion susceptibility of dome (Ag/AISI 202 steel) and key pad system (Au/Ni/Cu) is investigated with an aim to understand the corrosion performance of such multi-material combinations in chloride containing environment. Investigation includes microstructural studies, polarization measurements using microelectrochemical technique, salt spray testing, and corrosion morphology analysis. The immersion Au layer on pads showed pores and rolled bonded silver layer on dome had cracks and kinks. The difference in electrochemical behaviour of the metallic layers together with imperfections in the top layer resulted in severe pitting due to galvanic coupling. However, corrosion performance of the pads was much worse than domes. The results are applicable to a broad spectrum of PCB parts where similar material combinations are employed, especially Au/Ni/Cu.
Thermal exposure of Au-Al ball bonds results in the transformation of Au-Al phases across and lateral to the ball bond that
affects their service life. The phase transformations across and lateral to the Au-Al ball bond were described by partial
reactions at each of the interphase boundaries. Based on a model for the mass distribution of Au from the Au phase or the
Au-rich phases towards the Al phase or the Al-rich phases, volume changes associated with the partial reactions were calculated.
Except for the Au4Al and AuAl2 phases, theoretical analysis showed that the growth of all the Au-Al phases across the ball bond results in volumetric shrinkage.
The growth of the Au-Al phases across the bond is restricted due to the limited bonded Al metallization available to take
part in the interdiffusion reactions. The supply limitation of the bonded metallization gives rise to reverse transformations
that result in the formation of the Au4Al phase across the entire reaction zone across the ball bond. Except for the AuAl2 phase, theoretical analysis showed that the reverse transformation of all the Au-Al phases across the ball bond is associated
with minimal volume change. A “Criterion for Inward Lateral Growth” that governs the growth of Au-Al phases laterally into
the ball bond was developed. Theoretical analysis showed that except for AuAl2, the lateral growth of all the Au-Al phases results in volumetric shrinkage. The lateral phase transformations are essentially
reverse transformations due to no-supply of Au. Theoretical analysis showed that all the lateral reverse transformations also
result in volumetric shrinkage.
The gold-aluminum ball bonds were thermally exposed at constant elevated temperatures and the resultant phase transformations were studied. The as-bonded microstructure of a Au-Al ball bond consisted of a reaction zone between the Au bump and the bonded Al metallization. After the complete consumption of the bonded Al metallization, the Au-Al phases reverse transformed resulting in the formation of the Au 4Al phase in the entire reaction zone across the ball bond. It was observed that the presence of a phase in a particular location of a ball was dependent on the time and temperature of thermal exposure.
Corrosion of components and sub-assemblies on an electronic Printed Circuit Board Assembly (PCBA) is a major reliability concern. Both process and user related contamination will influence the corrosion reliability of a PCBA and the electronic device as a whole. An important process related contamination is solder flux residues which can act as a corrosion promoter in humid atmosphere due to the presence of ionic substances and a resin component. The presence of ionic substances will increase the conductivity of a condensed water layer and influence corrosion processes, depending on the species present. The resin component can easily attract dust during operation, which will eventually make surfaces hydrophilic and are thus become a potential source for ions. This paper describes the failure analysis of tactile switches, used in PCBAs mounted in wind turbines. More detailed investigation of the electrochemical behavior metallic materials (alloys) used in the switch and risk of electrochemical migration (ECM) between the switch components in presence of flux residues was also carried out. Investigations included potentiodynamic polarization measurements on the switch electrodes using a micro-electrochemical technique, in situ ECM studies, and scanning electron microscopy (SEM). Failure of the switches was found to be either due to the flux residue acting as an insulating layer or as a corrosion accelerator causing ECM.
Animal welfare and environmental protection are increasingly important. Housing systems must be found that offer animal welfare while minimizing the overall emissions of ammonia and greenhouse gases. The straw flow system is an animal friendly housing system for fattening pigs, which can be operated economically on commercial farms. Emissions from conventional slurry based pig houses have been intensively studied, but more research is needed into straw based systems. In this study, we quantified emissions of ammonia and greenhouse gases from a straw flow system with or without daily removal of slurry to an outside store. The effect of applying a solid cover during outside storage was also examined.
A silicone coated power module, having silver conducting lines, showed severe corrosion, after prolonged use as part of an electronic device in a pig farm environment, where sulfur containing corrosive gasses are known to exist in high amounts. Permeation of sulfur gasses and humidity through the silicone coating to the interface has resulted in three corrosion types namely: uniform corrosion, conductive anodic filament type of Ag2S growth, and silver migration with subsequent formation of sulfur compounds. Detailed morphological investigation of new and corroded power modules was carried out, and possible theoretical explanation for various corrosion mechanisms has been attempted.
A simple chemical method has been used for the conversion of thin films of Ag into Ag2S films. Thin, uniform and large-area films of Ag were prepared by chemical deposition using the ‘adsorption-reduction’ method on glass substrates and dipped in Na2S solution to be converted into Ag2S films. Their structural, electrical and optical properties have been studied.
A defective printed circuit board assembly that exhibited excessive current leakage was examined to determine the responsible failure mechanisms. Observation of the failure site (determined electrically) by optical and electron microscopy revealed an area in the circuit board where debonded fiber bundles bridged a plated-through-hole (PTH) to a copper plane. This phenomenon is highly suggestive of conductive filament formation.
Tarnish films that form on copper surfaces at high humidity can creep over adjoining gold surfaces, causing increases in the
contact resistance of the gold. In many cases, however, when gold‐plated contacts having exposed areas of copper are removed
from equipment used for extended periods of time in environments known to contain sulfiding compounds, there has been little
or no evidence of creepage. This protection against tarnish is caused by a naturally formed oxide and has been duplicated
in the laboratory. When copper sulfide tarnish films do creep over gold surfaces, distinctive periodic bands are formed. The
humidity dependence of the rate and maximum distance of the creepage have been studied.
Purpose
– To show how the use of conductor spacings below 4 mil in printed wiring boards (PWBs) can introduce an unanticipated failure mechanism, leading to current leakage and short circuit failure.
Design/methodology/approach
– The tests in this study were conducted in accordance with IPC‐TM‐650 2.6.25, using boards designed with conductor spacings between plated through holes (PTHs) ranging from 6 to 3 mil and from 8 to 3 mil between PTHs and ground planes. The board types and conductor spacings were selected to include current and future printed circuit board fabrication technology.
Findings
– For PWBs that may be used in harsh environments where the relative humidity and temperature may approach those of the test environments, even for relatively short periods of time, spacings of 4 mil or less in the materials tested may not be appropriate. However, it is unlikely that the 85°C and 85 percent RH conditions are the minimum conditions to induce this failure mechanism. More tests at lower temperatures and relative humidity combinations should be conducted to evaluate conditions at which this type of failure begins.
Originality/value
– The value of the paper lies in that the tests show that the IPC industry standard for conductive filament formation (CFF) testing of PTH‐PTH conductor spacings of 4 mil or less, at 85°C/85 percent RH can introduce a CFF variant failure mechanism, and therefore, may need to be modified to ensure that the test conditions accelerate the CFF mechanism and not other low resistance paths.
A scanning electron microscope (SEM) and transmission electron microscope (TEM) both with energy dispersive x-ray spectrometers (EDS), have been used to Investigate wire bond failures due to corrosion and oxidation. We have found that the bond strength is reduced by the oxidation of the intermetallic compounds Au4Al and Au5Al2. This results in a cellular and porous microstructure consisting of Au rich cell walls and an amorphous Al rich cell Interior. The decomposition reaction is accelerated when the bonds are aged in the presence of epoxy molding compounds at temperatures of 175°C to 200°C. An analysis of the outdiffusing products from the epoxy links the bond degradation with the presence of halogen-containing flame retardants.
Dust in pig confinement buildings may create negative health effects on humans as well as on the animals. Measures to reduce the dust concentration in the air are therefore urgent. The mass balance of dust as well as the efficiency of different dust-reducing measures have been investigated and analysed. The investigations have shown that the generation of dust is affected by activity, number of pigs and also by the weight of the pigs. Increased ventilation rate, electrostatic air cleaning and removal of dust by vacuum cleaners have had limited effect on the dust concentration. It has been observed that the type of ventilation technique but also the type of housing system influence the generation of dust. Spraying of small water droplets as well as an oil mixture have resulted in a significant reduction of the dust concentration.
Creep corrosion is a mass-transport process during which solid corrosion products migrate over a surface. It has been identified as a failure mechanism responsible for the malfunction of electrical contacts and connectors. For components with noble metal pre-plated leadframes, creep corrosion is a potential reliability risk for long-term field applications. This paper explains the source, process and possible products of creep corrosion on integrated circuit (IC) packages. The operating environment for telecom equipment is introduced as an example demonstrating the corrosive environments for electronic components. Field failure due to creep corrosion on plastic encapsulated components with palladium pre-plated leadframes is presented and analyzed. Similar phenomenon has been reproduced in an accelerated manner using mixed flowing gas (MFG) testing in the laboratory.
Swine operations can affect air quality by emissions of odor, volatile organic compounds (VOCs) and other gases, and particulate matter (PM). Particulate matter has been proposed to be an important pathway for carrying odor. However, little is known about the odor-VOCs-PM interactions. In this research, continuous PM sampling was conducted simultaneously with three collocated TEOM 1400a analyzers inside a 1000-head swine finish barn located in central Iowa. Each TEOM was fitted with total suspended particulate (TSP), PM-10, PM-2.5 and PM-1 preseparators. Used filters were stored in 40 mL vials and transported to the laboratory. VOCs adsorbed/absorbed to dust were allowed to equilibrate with vial headspace. Solid-phase microextraction (SPME) Carboxen/polydimethylsiloxane (PDMS) 85 microm fibers were used to extract VOCs. Simultaneous chemical and olfactometry analyses of VOCs and odor associated with swine PM were completed using a gas chromatography-mass spectrometry-olfactometry (GC-MS-O) system. Fifty VOCs categorized into nine chemical function groups were identified and confirmed with standards. Five of them are classified as hazardous air pollutants. VOCs were characterized with a wide range of molecular weight, boiling points, vapor pressures, water solubilities, odor detection thresholds, and atmospheric reactivities. All characteristic swine VOCs and odorants were present in PM and their abundance was proportional to PM size. However, the majority of VOCs and characteristic swine odorants were preferentially bound to smaller-size PM. The findings indicate that a significant fraction of swine odor can be carried by PM. Research of the effects of PM control on swine odor mitigation is warranted.
It is a common practice in the midwestern United States to raise swine in buildings with under-floor slurry storage systems designed to store manure for up to one year. These so-called "deep-pit" systems are a concentrated source for the emissions of ammonia (NH3), hydrogen sulfide (H2S), and odors. As part of a larger six-state research effort (U.S. Department of Agriculture-Initiative for Future Agriculture and Food Systems Project, "Aerial Pollutant Emissions from Confined Animal Buildings"), realtime NH3 and H2S with incremental odor emission data were collected for two annual slurry removal events. For this study, two 1000-head deep-pit swine finishing facilities in central Iowa were monitored with one-year storage of slurry maintained in a 2.4 m-deep concrete pit (or holding tank) below the animal-occupied zone. Results show that the H2S emission, measured during four independent slurry removal events over two years, increased by an average of 61.9 times relative to the before-removal H2S emission levels. This increase persisted during the agitation process of the slurry that on average occurred over an 8-hr time period. At the conclusion of slurry agitation, the H2S emission decreased by an average of 10.4 times the before-removal emission level. NH3 emission during agitation increased by an average of 4.6 times the before-removal emission level and increased by an average of 1.5 times the before-removal emission level after slurry removal was completed. Odor emission increased by a factor of 3.4 times the before-removal odor emission level and decreased after the slurry-removal event by a factor of 5.6 times the before-removal emission level. The results indicate that maintaining an adequate barn ventilation rate regardless of animal comfort demand is essential to keeping gas levels inside the barn below hazardous levels.
Determining the electrical characteristics of lead-free solder finishes, assessing the reliability of lead-free solder coatings while comparing their behavior to that of current tin-lead solder are necessary before implementing this material change in electronic separable connectors. Tin-lead solder alloys are the most commonly used non-noble contact finish materials in the electronic industry due to their low cost and ease of manufacturing. Since surface oxides of tin-lead alloys can be easily displaced by the mechanical deformation and wiping action of contact surfaces, low contact resistance can be easily obtained. However, a limiting factor in the use of tin-lead solder alloys separable connections is their susceptibility to fretting corrosion. Similar to tin-lead alloys, lead-free alloys are also expected to show susceptibility to fretting corrosion due to their tin content. In this study, two lead-free alloys, tin-silver-copper and tin-copper, as contact coatings, were investigated and compared with eutectic tin-lead alloy for their fretting corrosive behavior. An automatic contact resistance probe developed at the CALCE center was used to measure the contact resistance and introduce fretting corrosion. The effects on fretting corrosion at different temperatures and fretting amplitudes were examined in this study.
The author examines data gathered from a multiyear in-depth
analysis of signal and power connectors used in aircraft as well as
connectors used on ground-based computers, flight simulators and test
equipment. The equipment was from the period 1954-1986 and included a
wide range of connector technologies and connector finishes including
gold, silver, rhodium, and tin. All types of connectors were evaluated
including circular, rectangular, card edge, ZIF, and RF connectors of
both military and commercial type. Analysis of field failures was
performed using SEM (scanning electron microscope) and EDX technology.
Gold over nickel plating showed the best performance of all of the
finishes. It shows the capability to resist corrosion even after many
years, and with a nonporous nickel underplate there is no diffusion of
base metals through the gold
Two approaches have been used with some success to counter the effects of the high and volatile costs of gold as used in electronic connectors. One emphasizes gold conservation, using selective plating techniques wherever applicable and reduced-thickness coatings where possible. That approach is reviewed, and the successes and practical limitations pointed out. The other approach, to develop alternative materials, particularly palladium, is also discussed. Functional problems, some confirmed and others anticipated, have limited the general applicability of this approach. A third approach has proved very successful. Palladium plating was developed, not as a surface contact material, but as an additional barrier undercoat for gold. This approach is shown to permit ultra-thin gold surface layers to be used, with performance properties equal to and in some respects superior to conventional gold platings. Production prototype data are provided for an optimized composite layered coating which we call AMP-Duragold.®
Our recent publication provided an assessment of the performance of thin porous gold in an office environment. We concluded that thin gold (0.380-0.75 µm) on printed wiring board (PWB) fingers provided acceptable performance primarily because of the benign nature of the office environment. Examination of samples with field life up to nine years also revealed the absence of the classical failure mechanism of pore and/or edge creep corrosion on about 20 000 plated surfaces examined. Work since that last paper leads us to believe that nickel oxide formation is the predominant degradation mechanism. For this reason, we chose the thermal aging test at 125°C to model field performance. Data at exposures of about 1500 h appear to approximate a field life of about ten years for copiers. Using thermal aging, we assessed the factors affecting the contact performance of thin gold. The interactive effect of connector characteristics, wear, and gold thicknesses was evaluated in unlubricated system. Gold thickness on PWB contact fingers ranged from 0-1.0/µm over nickel underplating. For applications requiring 25 insert/ withdraw (I/W) cycles the factors affecting thin gold (0.380-0.750 µm) performance are 1) thickness determines the extent of wear, severity of underlayer exposure, and ultimately the extent of contact degradation, 2) wear on contact springs is more severe than on PWB fingers, 3) connector characteristics such as normal force, contact geometry, and gold thickness affect contact performance. A minimum of 0.380 µm of gold on PWB fingers is recommended. For applications with a lesser number of I/W requirements (<25), flash gold (0.10-0.25 µm) appears promising with two of the three connector types tested even though the finger surfaces appear eroded to the base underlayer. Gold dot (which is very thick) performed acceptably even up to 200 I/W. The advantage of lubrication on thin and flash gold is a logical extension of this study.