Electronics corrosion mechanisms

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

Stream of electrons flowing (by convention) from anodic (+) to cathodic (-) areas of a metal. Part of the overall corrosion mechanism. 

It is considered that the slope AEcotr/ApH has mechanistic significance. Various corrosion mechanisms for iron in acid media have been proposed in the literature. One of them (the catalytic mechanism) is based on the value AEcon./ApH = -47 mV another (stepwise electron transfer mechanism) is based on the value -59 mV. (a) Using the values in Table P.3 calculate the estimate of standard deviation of the slope, Ssi, and establish if it is low enough to discriminate between the two mechanisms above. 

The approach presented in this paper is of a universal character as it applies equally to all irregular interfaces, irrespective of their composition, solid growth or solid attack procedure. Hence, its application to electrocatalysis and corrosion processes appears to be of great practical relevance as it comprises the effect of the dynamics of solids on their shape, their crystalline quality and consequently, on their electronic and mechanical properties. 

Equation 10.1 illustrates the most common corrosion mechanism involving an electrochemical process essentially metal oxidation, and necessitates the removal of electrons from a metal. Equations 10.2 and 10.3 illustrate the release of electrons from iron metal to produce first ferrous ions followed by conversion to ferric ions by further oxidation. 

The further correlation of electronic properties of metals and the corrosion or oxidation rate is being pursued with the faith that this approach greatly aids our understanding of corrosion mechanisms and that better... 

Sweet Corrosion. It is caused by the presence of dissolved COj in the prodnced llnids. CO2 reacts with water to form carbonic acid (H2CO3), which dissociates to form hydrogen ions and the carbonate ion. At the anodic sites, the metal atoms give np electrons and dissolve to form metal ions. These electrons are taken up by hydrogen ions at cathodic sites to form atomic hydrogen. Bicarbonate ions, however, react to form a protective iron carbonate film, and the rate of corrosion depends on the stability of this film [2]. The corrosion mechanism can be represented by the sketch shown in Figure 11.7. 

Column 4 describes the failure modes of the component. One row is typically used for each component failure mode. Examples of component failure modes include fail short, fail open, drift, stuck at one, stuck at zero, etc., for electronic components. Mechanical switch failure modes might include stuck open, stuck closed, contact weld, ground short, etc. Column 5 describes the cause of the failure mode of column four. Generally this is used to list the primary "stress" causing the failure. For example, heat, chemical corrosion, dust, electrical overload, RFI, human operational error, etc. 

Although structural, electronic, and conductivity properties of polyaniline are well known, oxidative corrosion mechanisms are not completely understood. It is accepted that for corrosion to occur both oxygen and water must come into contact with the surface. Therefore any barrier material will limit corrosion to some degree. To date, aniline-based coatings have been shown to provide a level of protection beyond the simple barrier limit. In these studies, epoxy-based coatings are com-... 

Corrosion mechanisms in electronic components have been the subject of intense study. Since electronics are largely found indoors and/or within packages or cabinets, the mechanisms leading to corrosion problems are not easily defined. Problems are compounded by the fact that these systems are fabricated by a number of complex processes and consist of a variety of dissimilar materials. Miniaturization and the requirement for high component density has resulted in smaller components, closer spacing, and thinner metallic paths. Thus, the effect of bias potentials and small defects is magnified. 

Bias potentials provide corrosion mechanisms due to both anodic reaction and cathodic reaction. These reactions include the formation of acidic or alkaline electrolytes, and ion migration. Pore corrosion and corrosion product creep, galvanic corrosion, and firetting corrosion in connectors are other important mechanisms with electronics. Many of these mechanisms occur due to processing related corrosive residues. 

One of the most widely investigated effects is the atmospheric sulfidation of silver used in electronics. The mechanisms of silver corrosion in polluted dry and humid atmospheres have been studied [28]. For example, the reaction of silver and H2S in air can occur directly... 

Connectors are a critical part of an electronic S5rstem. Corrosion mechanisms at connector interfaces include pore corrosion, corrosion product creep, fretting, and SCC and general attack. Pore corrosion in connectors is associated with surfaces plated with gold or other precious metals. Corrosion product creep in connectors usually involves copper corrosion products originating from exposed base... 

The importance of surface and chemical analysis techniques in electronics corrosion testing cannot be overstated. These powerful tools contribute to solving problems and elucidating corrosion mechanisms in simple and complex systems. Chemical analysis techniques include infrared (IR), ultraviolet (UV), and RAMAN spectroscopy X-ray diffraction atomic adsorption emission and mass spectroscopy gas and liquid chromatography and optical and transmission electron microscopy. Surface analytical techniques include electron spectroscopy for chemical analysis (ESCA), Auger, secondary ion mass spectroscopy (SIMS), and ion scattering spectroscopy (ISS). These important techniques used in conjunction with corrosion tests are described in another section of this manual. 

Electronics corrosion is a unique subject because it occurs largely indoors or inside packages or cabinets. Therefore, classical corrosion tests do not generally apply. In addition, many failure mechanisms are unique to these systems and therefore are not treatable by classic corrosion kinetic fundamentals. This chapter therefore describes the various corrosion mechanisms important in electronics and lists the various test methods that are used in the industry. 

Both electrochemical oxidation and thermal degradation of carbon in humid air at temperatures <125°C have been reported, and it seems established that these corrosion mechanisms are accelerated by the presence of Pt. Carbon corrosion will first modify the surface of the support, which will become less hydrophobic. It has also been reported that carbon corrosion may enhance the mobility of Pt on the surface, accelerating the Pt sintering discussed above. Further carbon corrosion will degrade the electron-conducting network, rendering ft particles inactive. 

Because of their fine golden color, high hardness, and extreme corrosion resistance, TiN films deposited by CVD techniques are becoming common in both electronic and mechanical applications. 

Nevertheless, there are many instances where electrochemical corrosion mechanisms may play a primary role in affecting the service performance of bonded joints. It should be noted that such mechanisms of attack involve both the presence of (a) anodic sites, where reaction with the metallic substrate occurs and electrons are generated, and (b) cathodic sites, where the electrons are consumed. The major reaction leads to the generation of hydroxyl ions, and the liquid present at these sites will become strongly basic and so possess a relatively high pH. Thus, typically an aqueous (electrolyte) layer needs to be present, since, without such an aqueous film, no electrical current can flow from the anodic to the cathodic sites. These aspects are illustrated, for example, by the schematic electrochemical corrosion mechanism for an organic coating on a steel substrate shown in Fig. 4, which is discussed in detail in Section 2.S.2.2. 

Corrosion in subcritical water and high-density SCW is an electrochemical process involving distinct oxidation and reduction half-reactions that can be separated as long as there is both electronic and electrolytic contact between anodic and cathodic sites. The low ionic conductivity of low-density SCW does not favor such separation and the corrosion mechanism becomes analogous to gas-phase oxidation. 

Grain boundary and electron movement the corrosion mechanism of nanocrystalline metals... 

---