| Atmospheric corrosion is an electrochemical corrosion process of metals under thin electrolyte layer (TEL). Corrosion of electronic components is similar to atmospheric corrosion of metals, however, it is more complicated and more sensitive than usually atmospheric corrosion. With the development of modern science and technology, the miniaturization of electronic systems continuously increases, the volume and distance of electronic components further reduce, electronic materials become thinner, electric field gradient gets greater, which makes the corrosion of the modern electronic components more sensitive. Copper is an important electronic material and widely used in electronic components, and tends to occur various forms of localized corrosion in the atmosphere. Therefore, the study of the corrosion behavior and mechanism of copper in electronic components becomes more and more important.In this paper, we use a home-made experimental device and in situ investigate atmospheric corrosion behavior of copper printed circuit board (PCB-Cu) by traditional electrochemical methods, and study the effect of environmental factors, cyclic wet-dry condition, and electric field on the corrosion behavior and mechanism of PCB-Cu combining with surface analysis, and then provide the possible corrosion mechanism of PCB-Cu in a variety of environments. The main research work and results are as follows:1. Design of experimental device. Atmospheric corrosion generally occurs in the thin film (visible film), or absorbed thin film (invisible film). Now, there is not any study report of metal corrosion under absorbed thin electrolyte layer (ATEL) using electrochemical methods. So a set of the simulated device was designed in order to study the corrosion behavior of PCB-Cu under ATEL. The device effectively reduces the ohmic drop of between reference electrode and working electrode, and ensures uniformity of current distribution on the surface of working electrode.2. The effect of relative humidity (RH), chloride ion concentration and temperature on atmospheric corrosion behavior of PCB-Cu. The experimental results indicate that:The cathodic process of PCB-Cu under ATEL is dominated by the reduction of oxygen and corrosion products, and the cathodic polarization current densities increase with the increase of RH, Cl- ion concentrations and temperature at large cathodic overpotential, respectively. At the initial stage, the corrosion rate of PCB-Cu increases with increasing of RH, Cl- ion concentrations and temperature, respectively. However, at the later stage, the corrosion products formed and accumulated on the electrode surface affect the corrosion process, resulting that the corrosion rate presents the different trends. In addition, the corrosion rates of PCB-Cu under different RH are higher than those in bulk solution.3. The effect of periodic wet and dry cycle on atmospheric corrosion behavior of PCB-Cu. The experimental results indicate that:The corrosion process of PCB-Cu in a single wet-dry cycle can be divided into three distinct regions. Regionâ… is from the onset of the wet period to its end. Regionâ…¡is from the onset of the dry period until the stable potential reaches. Regionâ…¢is the last stage of dry period. The process of electrochemical reaction transforms from the cathode process to the anode process. The corrosion rate of PCB-Cu decreases at the initial stage then increases slowly and eventually attains the steady value at the last exposure stage in the whole wet-dry cycle process of 122 h. Furthermore, the higher corrosion rate, the shorter the time of obtaining the steady state. The corrosion rate of PCB-Cu increases with increasing temperature and prolonging of the dry period, and the minimum corrosion rates are observed after exposure for 50 h. But in the presence of (NH4)2SO4, the corrosion rate of PCB-Cu shows increasing trend at the initial stage, and the minimum corrosion rates are observed after exposure for 74 h.4. The effect of the steady state electric field on atmospheric corrosion behavior of PCB-Cu. The experimental results indicate that:The cathodic polarization current and the corrosion rate of PCB-Cu decreases with increasing intensity of the steady state electric field. The corrosion rate of PCB-Cu in presence of the external electric field is always lower than that in absence of the external electric field in the whole expose period. No matter whether the external electric field exists or not, the minimum corrosion rates are observed after exposure for 24 h. Under direct electric field, the probability of occurring pitting of PCB-Cu decreases, Dendrites were locally produced on the surface of the negative pole of direct electric field. The scale of dendrites changes faster and greater with increasing imposing voltage and expose time. The corrosion rate decreases under the steady state electric field, which may be attributed to the migration out of Cl- ions, which results in the reduction of Cl- ions content in ATEL on the studied location of PCB-Cu. When the chloride ions can not freely move out of PCB-Cu electrode surface, the chloride ions will locally enrich on the surface of the working electrode (external electric field) or the positive pole of direct electric field under the electric field, which causes the working electrode (external electric field) or the positive pole of direct electric field occurs serious localized corrosion.5. The effect of alternating electric field on atmospheric corrosion behavior of PCB-Cu. The experimental results indicate that:under alternating electric field, the corrosion potential of PCB-Cu negatively shifts, which indicates an increase of electrochemical activity of PCB-Cu. The corrosion rate of PCB-Cu increases with increasing the intensity and frequency of the alternating electric field. Alternating electric field obviously accelerates the anode process of PCB-Cu. The corrosion extent of PCB-Cu under alternating electric field increases, which may be attributed to the stray current generated by alternating electric field and the destruction of the disintegrate oxide film on the copper surface caused by alternating electric field. Furthermore, the corrosion extent of PCB-Cu under square wave electric field is more severe than that under sinusoidal AC electric field.
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