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Corrosion failure analysis of printed circuit boards exposed to H 2 S-containing humid environments
Abstract
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.
... Printed circuit boards (PCBs) are the heart of the communication and electronics industry. Most of time, PCBs are often exposed to humidity leading to the corrosion of printed circuit boards and subsequent failure of the electronic devices [1][2][3][4][5]. Currently, electrically conductive adhesives [6], nanosized Ag paste [7], and carbon nanotubes [8] are the most commonly used packaging materials in the electronics industry. ...
It is of great interest and challenge to simultaneously improve the storage stability and bond strength of one-component addition-cure liquid silicone rubber (OLSR) coating for electronic circuit board. In this work, we proposed an efficient approach to address this issue by incorporating both cyano-modification platinum catalyst (CN–PT) and urethane-containing poly(hydromethylsiloxane) (N-PHMS) into OLSR coating using a mechanical mixer. The CN–PT and N-PHMS were synthesized through thermal polymerization reaction and hydrosilylation reaction, respectively. The OLSR coating containing 0.3 phr CN–PT and 3 phr N-PHMS showed the best properties, with a tensile bond strength of 1.63 MPa, a storage period > 180 d at 25 °C, and a curing rate < 2 h at 80 °C. The salt-spray resistance and continuous power-on performance of OLSR coating were also improved, compared with pure OLSR coating. The synergism of CN–Pt and N-PHMS on the enhancement of both the storage stability and bond strength of OLSR coating was also explored. Our findings exhibited great potentials for fabricating OLSR coating with excellent long-term stable service performance including high storage stability and protective ability.
... However, traditional packaging materials are not suitable for modern electronic packaging of printed circuit boards because of high conductivity and cost. In general, silicone rubbers coating is widely used in protection of PCBs because of its good dielectric properties, water repellency, ultraviolet durability, excellent chemicals and thermal degradation resistance [9,10,11]. Nowadays, solvent-based condensation-cure silicone rubber coating [12] for the protection of PCBs is one of the few commercialized coatings. During the curing process of solvent-based condensation-cure silicone coating, the solvents and small molecules will be released leading to the pollution of the environment and the PCB [13], even the reduction of the reliability and the service life of electronic products. ...
It is of great interest and challenge to simultaneously improve the storage stability and bond strength of one-component addition-cure liquid silicone rubber (OLSR) coating for electronic circuit board. In this work, we proposed an efficient approach to address this issue by incorporating both cyano-modification platinum catalyst (CN-PT) and urethane-containing poly(hydromethylsiloxane) (N-PHMS) into OLSR coating using a mechanical mixer. The CN-PT and N-PHMS were synthesized through thermal polymerization reaction and hydrosilylation reaction, respectively. The OLSR coating containing 0.3 phr CN-PT and 3 phr N-PHMS showed the best properties, with a tensile bond strength of 1.63 MPa, a storage period > 180 d at 25°C, and a curing rate < 2 h at 80°C. The salt-spray resistance and continuous power-on performance of OLSR coating were also improved, compared with pure OLSR coating. The synergism of CN-Pt and N-PHMS on the enhancement both the storage stability and bond strength of OLSR coating was also explored. Our findings exhibited great potentials for fabricating OLSR coating with excellent long-term stable service performance including high storage stability and protective ability.
... For example, airborne sulfur dioxide negatively impacts the safety and readiness of military equipment (e.g., an F-14 aircraft crash due to corrosion of its landing gear), requiring the U.S. to spend $20 billion annually to deal with corrosion issues. 1 Biotic corrosion, commonly termed as microbiologically influenced corrosion (MIC), turns harmless sulfates into aggressive sulfides to degrade copper components of pipelines, 1 transformers, 2 printed circuit boards, 3 and mechanical equipment, 4 all under ambient conditions. Sulfur corrosion is typically controlled by introducing a protective coating layer of polymers such as VOC alkyd, silicone alkyd, polyurethane, latex, epoxy, and polyamides. ...
Corrosion by sulfur compounds is a long-standing challenge in many engineering applications. Specifically, designing a coating that protects metals from both abiotic and biotic forms of sulfur corrosion remains an elusive goal. Here we report that atomically thin layers (∼4) of hexagonal boron nitride (hBN) act as a protective coating to inhibit corrosion of the underlying copper (Cu) surfaces (∼6-7-fold lower corrosion than bare Cu) in abiotic (sulfuric acid and sodium sulfide) and biotic (sulfate-reducing bacteria medium) environments. The corrosion resistance of hBN is attributed to its outstanding barrier properties to the corrosive species in diverse environments of sulfur compounds. Increasing the number of atomic layers did not necessarily improve the corrosion protection mechanisms. Instead, multilayers of hBN were found to upregulate the adhesion genes in Desulfovibrio alaskensis G20 cells, promote cell adhesion and biofilm growth, and lower the protection against biogenic sulfide attack when compared to the few layers of hBN. Our findings confirm hBN as the thinnest coating to resist diverse forms of sulfur corrosion.
... The increase in the number of PCB layers makes the circuit more complex, which leads to a variety of PCB failure problems, such as open circuit, short circuit, environmental corrosion, contamination, delamination, leakage current and so on [2]. Some published works [3][4][5][6] reported that the corrosion failure of the PCB samples with electroless nickel immersion gold layer occurs in a corrosive environment, such as H 2 S-containing humid or H 2 S containing some oxidizing gas. ...
The leakage current phenomenon of a commercial ten-multilayer printed circuit board (PCB) occurred. Preliminary examination shows that there was a short circuit between the PIN_2 and POUT_4 networks of the PCB measured by a high-resistance meter, after a high-temperature aging treatment. In this case, microstructure and morphology of several layers for PCB sample were observed by optical microscopy, scanning electron microscopy and three-dimensional imaging x-ray microscopy. The chemical composition of the layer was determined by energy-dispersive spectroscopy. After observation and analysis, the results show that the leakage current failure cause of the PCB was that the metal powder impurities were found between the layers of PIN_2 and POUT_4 network, which caused the drop in the electric resistance between the two networks, resulting in the occurrence of the leakage current. The chemical composition of the impurity was only composed of copper.
... The formation of nickel sulfate can be attributed to the possible presence of SO 2 traces in the environment. In this regard, an amount of sulfuric acid can be created in the adsorbed layer via the below reaction [14]: ...
A batch of fire detectors used in the aircraft has been corroded under containing sulfur atmosphere. The fire detector was made of guide rods, seat plate, bimetallic strips, ring gasket, moving contact part and spring part. The former three components were deposited with electroless nickel-phosphorus layer. The morphology and microstructure of surface and cross-section of the layer were characterized by optical microscopy and scanning electronic microscopy. The chemical composition and phases of corrosion products were determined by energy dispersive spectrometer and X-ray diffraction, respectively. The results show that the corrosion products were mainly composed of nickel sulfate and its hydrate, indicating the layers aggravated by sulfur substances or compounds. The surface of the layer exhibited lots of microdefects, including pitting, microcracking and micropores. The failure causes of fire detectors under corrosive environments were further addressed and discussed. The failure model of electroless nickel-phosphorus layer was also established.
... The XPS spectrum of O 1s, Cl 2p, Cu 2p and S 2p core levels of the corrosion product on the surface of the damaged copper wire are presented in Fig. 7. The orbital peak of O 1s is about 531.59 eV (Fig. 7a), which is corresponding to the divalent oxygen [21,22]. The orbital peaks of Cl 2p is 198.05 eV and 199.60 eV (Fig. 7b). ...
For the inverter in the new energy vehicle, the existence of the power module provides it have the function of converting direct current (DC) in the battery pack into three-phase alternating current (AC) driving the motor. Therefore, the reliability of the power module is significant to ensure the stable operation of vehicles. In this paper, a failure case about premature delamination between the copper bridge and epoxy molding compound (EMC) in the power module during power cycling tests was reported. To find out the causes of premature delamination, a series of characterization methods including thermogravimetric analysis (TGA), inductively coupled plasma-mass spectrometry (ICP-MS), ion chromatography (IC), three-dimensional stereo microscope (3D-SM), metallurgical microscope (MM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were adopted. The analysis objects contained the EMC, circulating water, copper strips in different stages, copper bridges and decapped power modules, which were all covered in the manufacturing process of power modules. By comprehensive analysis, over-corrosion on the copper strip surface and overlapping skins on the copper bridge surface were determined as the root causes of premature delamination. Based on the conclusions, corresponding countermeasures were also proposed. This paper gives a kind of pre-analysis method to the possible failure of the components, so it is meaningful for how to effectively prevent the failure of the components during assembly process.
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.
Electrochemical impedance (EIS) and thin electrical resistance (ER) sensors were invented for atmospheric corrosion measurement of copper (Cu) during cyclic wetting–drying/high–low temperature tests and field exposure tests. Three-month field exposure results showed that average corrosion rate of Cu measured by ER sensor was well in accordance with that by weight loss method. During cyclic wetting–drying test, EIS was proven to reflect sensitively time of wetting and drying on the surface of sensor. Although corrosion rate obtained from EIS had a similar tendency to that obtained from ER sensors, the former was more dependent on environmental humidity than the latter. When relative humidity was low than 60%, corrosion rate of Cu measured by EIS was much lower than that by weight loss method, mainly attributing to the fact that impedance sensor failed to detect corrosion current of interlaced Cu electrodes due to the breakdown of conductive passage composed of absorbed thin liquid film under low humidity condition. Promisingly, ER sensor was proven to be more suitable for atmospheric corrosion monitoring than electrochemical techniques because it could sensitively monitor thickness loss of Cu foil according to the Ohmic law, no matter how dry or wet the sensor surface is.
An access state detection (ASD) method for the serial port sensor module in micro control system is proposed according to the work mechanism with which the micro control system gets data by serial port and the working feature of serial port sensor module. The micro control system detected the access state of serial port sensor module by examining the serial port receive flag of microcontroller, or by examining the serial port receive interruption of microcontroller. And based on these, the system determined the access state of sensor module, and then took effective measures to make sure the system ran well. Besides, the related safeguard mechanisms were also established to ensure the ASD was effective and reliable. The ASD method was applied to two micro control systems based on different serial port sensors, and good results were achieved. The practice indicates that, with the serial port sensor module ASD, the micro control system can detect the access state of serial port sensor module in micro control system accurately and taking effective measures in time for it, avoid suffering the adverse effects caused by the abnormal access state of serial port sensor module, and improve the comprehensive performance of micro control system.
The initial atmospheric corrosion of copper was investigated by electrical resistance sensor under different environmental factors (relative humidity, temperature, and NaCl loading density). The corrosion rate of Cu increases evidently with NaCl loading density, temperature and RH, but decreases with prolonged test. 2-phenyl imidazoline (2-PI) presents increasing inhibition efficiency on Cu with elevated temperatures at low NaCl loading density (≤40 μg/cm²), mainly due to that elevated temperature enhances the vapour pressure of 2-PI, however, 2-PI shows inferior performance on pre-corroded Cu at high NaCl loading density, possibly due to that the defective corrosion product layer formed at high RH retards the adsorption of 2-PI. Finally, molecular dynamic simulations were conducted to evidence the competitive adsorption advantage of 2-PI against H2O on Cu2O surface through chelation of 1-N of imidazoline with Cu(I).
The corrosion behavior of immersion silver printed circuit board copper (PCB-Cu-ImAg) under a thin electrolyte layer (TEL) was studied by electrochemical tests and surface analysis. The results showed that galvanic effect accelerated the corrosion of PCB-Cu-ImAg and reduced the protective effect of silver-coating. The reduction of TEL thickness not only promoted the corrosion of PCB-Cu-ImAg, but also strengthened the galvanic effect. At the beginning of exposure to TEL, the potential difference decreased, but the galvanic current densities increased with decreasing TEL thickness because of the significant decrease of the total resistance. Because of the continuous formation and accumulation of corrosion products, the galvanic current densities decreased in the later stage of exposure to TEL.
Initial atmospheric corrosion of clean copper and NaCl-deposited copper was investigated by quartz crystal microbalance and electrochemical impedance spectroscopy. 2-phenyl imidazoline(2-PI)exhibits increasing inhibition efficiency with temperature on chloride-induced atmospheric corrosion of Cu. However, on the NaCl-deposited Cu, adsorption amount of 2-PI is much higher than that on clean Cu possibly due to that rough corrosion products entrap lots of 2-PI molecules. The adsorption of 2-PI on corroded Cu is suggested to obey a capillary condensation and entrapment mechanism, but in dry argon atmosphere, it obeys a simple pseudo first-order model for lack of corrosion products.
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.
Hydrogen sulphide (H2S) is considered one of the most corrosive atmospheric pollutants. It is a weak, diprotic, reducing acid, readily soluble in water and dispersed into the air by winds when emitted from natural, industrial, and anthropogenic sources. It is a pollutant with a high level of toxicity impairing human health and the environment quality. It attacks copper forming thin films of metallic sulphides or dendrite whiskers, which are cathodic to the metal substrate, enhancing corrosion. H2S is actively involved in microbially influenced corrosion (MIC) which develops in water, involving sulphur based bacteria, in oxidizing and reducing chemical reactions. H2S is found in concentrated geothermal brines, in the atmosphere of geothermal fields, and in municipal sewage systems. Other active atmospheric pollutants include SOX, NOX, and CO. This investigation reports on the effects of H2S on copper in microelectronic components of equipment and devices, with the formation of nonconductive films that lead to electrical failures.
A overview has been presented on the topic of alternative surface finishes for package I/Os and circuit board features. Aspects of processability and solder joint reliability were described for the following coatings: baseline hot-dipped, plated, and plated-and-fused 100Sn and Sn-Pb coatings; Ni/Au; Pd, Ni/Pd, and Ni/Pd/Au finishes; and the recently marketed immersion Ag coatings. The Ni/Au coatings appear to provide the all-around best option in terms of solderability protection and wire bondability. Nickel/Pal ftishes offer a slightly reduced level of performance in these areas that is most likely due to variable Pd surface conditions. It is necessmy to minimize dissolved Au or Pd contents in the solder material to prevent solder joint embrittlement. Ancillary aspects that included thickness measurement techniques; the importance of finish compatibility with conformal coatings and conductive adhesives; and the need for alternative finishes for the processing of non-Pb bearing solders were discussed.
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.
Updated to include recent results from intensive worldwide research efforts in materials science, surface science, and corrosion science, Corrosion Mechanisms in Theory and Practice, Third Edition explores the latest advances in corrosion and protection mechanisms. It presents a detailed account of the chemical and electrochemical surface reactions that govern corrosion as well as the link between microscopic forces and macroscopic behavior. Revised and expanded, this edition includes four new chapters on corrosion fundamentals, the passivity of metals, high temperature corrosion, and the corrosion of aluminum alloys. The first half of the book covers basic aspects of corrosion, such as entry of hydrogen into metals, anodic dissolution, localized corrosion, stress corrosion cracking, and corrosion fatigue. Connecting the theoretical aspects of corrosion mechanisms to practical applications in industry, the second half of the text discusses corrosion inhibition, atmospheric corrosion, microbially induced corrosion, corrosion in nuclear systems, corrosion of microelectronic and magnetic data-storage devices, and organic coatings. With contributions from leading academic and industrial researchers, this bestselling book continues to provide a thorough understanding of corrosion mechanisms-helping you solve existing corrosion challenges and prevent future problems.
This paper reports a study on the corrosion damage of a copper pad coated with electroless nickel-phosphorus/immersion gold in a sulfur-containing atmosphere. For this purpose, the surface and cross section of the pad showing localized corrosion products were analyzed by optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. According to the results, slightly nickel and predominantly copper suffered from corrosion attacks, accompanied by the formation of mainly sulfide with a small fraction of sulfate. Considering the characterized configurations of the pad and corrosion products, a sequential mechanism was established to interpret the galvanic-pitting corrosion attack of both species. In this regard, the nanoporous immersion gold surface acted as the cathode in the bimetallic degradation of nickel, whereas the environmental attack of copper was accelerated because of its electrical contact with cathodic nickel and gold via the formation of a trimetallic galvanic microcell.
Cu samples are exposed to 75% relative humidity in flowing air containing 0.25 ppm SO2 and NO2.
The atmospheric corrosion behaviour of PCB-HASL (electronic materials) in a polluted marine atmosphere environment was investigated by stereology microscope, SEM, EIS, XPS and SKP. It was found that deposition of chloride ions and SO2 gas played a pivotal role in atmospheric corrosion, which contributed to an obvious undulation of the corrosion rate. In the late exposure test, the expansion of the corrosion products gave rise to the abscission of the protective coating layer (Sn), which resulted in substrate Cu directly exposing to atmospheric environment of Xiaomai Island and causing the Cu gradually corrosion.
Electronic industry uses a number of metallic materials in various forms. Also new materials and technology are introduced all the time for increased performance. In recent years, corrosion of electronic systems has been a significant issue. Multiplicity of materials used is one reason limiting the corrosion reliability. However, the reduced spacing between components on a printed circuit board (PCB) due to miniaturization of device is another factor that has made easy for interaction of components in corrosive environments. Presently the knowledge on corrosion issues of electronics is very limited. This paper reviews briefly the materials used in electronic systems, factors influencing corrosion, types of corrosion observed in electronics, and testing methods.
Corrosion of complex electronic equipment is an increasingly serious problem, causing expensive damage. Corrosion occurs through out the entire life cycle during different stages of manufacturing, assembly, transport and stor- age of components and assemblies and during field operations of the equipment. Presence of moisture, chloride, sulphur dioxide, hydrogen sulphide and other airborne corrosives, meteorological parameters etc influence the occurrence of cor- rosion. The present review describes the current understanding mechanism of corrosion of electronic components and equipments in different environmental conditions. The various corrosion testing methods and methods of corrosion pre- vention in these electronic devices have also been elaborated.
Corrosion products formed on copper plates exposed in urban, rural/coastal, and hot spring areas in Japan were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and coulometric reduction. The exposure tests were carried out for a month in summer. XRD patterns showed that hydrated copper sulfate [Cu4SO4(OH)(6).H2O, posnjakite] and cuprite Cu2O were formed on copper surfaces exposed in urban and rural/coastal areas. The existence of sulfate salt agrees well with the XPS spectra. Sulfur dioxide and particulate sulfate such as ammonium sulfate and sea salt are both possible origins of this sulfate. In contrast, XRD revealed that the only corrosion product formed on the copper exposed in the hot spring area was cuprite Cu2O, although the amount of sulfur on the surface of this sample was the highest. Coulometric reduction analysis showed that there was copper sulfide Cu2S in corrosion products formed on copper exposed in the hot spring area. Posnjakite Cu4SO4(OH)(6).H2O is initially formed in addition to cuprite Cu2O when copper is exposed in urban and rural/coastal atmospheres. This crystalline phase is located at and near the copper surface. Initially formed posnjakite Cu4SO4(OH)(6).H2O may change to brochantite Cu4SO4(OH)(6), which is a typical patina component that appears after further exposure. (C) 2001 The Electrochemical Society.
The possible use of Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS) and Raman spectroscopy for surface studies of thin (<10 nm) corrosion products on Cu has been explored. Cu samples were exposed to 75% relative humidity and 25°C in flowing air, with additions of 0.25 ppm of SO2 and NO2. X-ray photoelectron spectroscopy (XPS) and cathodic reduction revealed that the corrosion products consisted mainly of an initially formed layer of Cu(I) oxide, a layer of Cu sulfite growing outside the oxide, and a layer of Cu(II) nitrate growing outside the sulfite. FT-IRAS lines from approximately 1-nm-thick films of sulfite or nitrate can be detected and interpreted, in close agreement with the results obtained by XPS. The only phase to be detected by Raman spectroscopy was Cu2O, which most likely is due to a resonance Raman enhancement.
The tin passivation in borate buffer was studied using potentiodynamic curves recorded at high scanning rate (9 V min−1, 3.6 V min−1). The most important feature of these curves is the presence of a current peak at around — 1180 mV (vs sce) which had not been previously observed. The nature of the passive film formed in the vicinity of this potential was characterized using in situ Mössbauer measurements.On the basis of these results it was concluded that in borate buffer solution: (a) the passive film formed at more negative range of potentials (− 1180 to − 780 mV) is duplex, consisting of highly amorphous Sn(OH)2 or hydrated stannous oxide and SnO2 or Sn(OH)4; (b) at more positive potentials, the passive layer consists only of Sn(IV) hydroxide or oxide which ensures a more efficient passivation.
XPS analysis of different forms of copper sulfate, including antlerite, brochantite, posnjakite, chalcanthite and anhydrous copper sulfate, as well as pure copper and its oxides cuprite and tenorite, was carried out. These products most often occur when dealing with atmospheric corrosion of copper and bronze in sulfur-bearing environments. These compounds were minerals, commercial products, or grown on pure copper by artificial weathering. Spectral features such as peak energy and line shape for Cu 2p, Cu LMM, O 1s and S 2p bands were examined. Comparison of the measurements obtained proves the efficiency of XPS in differentiating the various compounds. Copyright © 2004 John Wiley & Sons, Ltd.
EMC and the Printed Circuit Board: Design, Theory, and Layout Made Simple
- M I Montrose
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The Path to Robust Electronics-Preventing Corrosion of PCB Assemblies, 57 OnBoard Technology
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