![]() Ionic contaminants can arise from service environment, human handling or from the manufacturing processes 1, 15 such as the assembling process 12. These contaminants accelerate the corrosion process and are expected to promote the ECM. The presence of hygroscopic contaminants facilitates water condensation on the surface and increases the electrolyte conductivity. The risk of condensed ECM increases when the electronic device is exposed to temperature fluctuations due to the difference between the device interior conditions and external climates 14. Humid ECM occurs when a thin invisible moisture film is adsorbed on the surface while condensed ECM occurs in a visible layer of condensed water. Thus, the investigation into ECM of Sn is crucial for the electronics industry.ĮCM can be categorized into humid ECM and condensed ECM 1, 13. This problem has posed great challenges to the reliability of electronic devices. A large part of the directly exposed interconnects on the printed circuit boards (PCB) consists of Sn and its alloys, but worst of all Sn and Sn solder alloys are susceptible to ECM 5, 7, 12. Meanwhile, Sn-based Pb-free solder alloys are widely employed as solder interconnects in electronic devices 2, 10, 11. In response to the prohibition of lead (Pb) containing materials by the Restriction of Hazardous Substances (RoHS) Directive, pure tin (Sn) is widely adopted for the surface finishing of electronic devices 9. This eventually leads to short-circuiting, which is a catastrophic failure in electronic devices 7, 8. The dissolved metal ions are electrodeposited at the cathode as dendrites, which propagate through the electrolyte and connect the two electrodes. This is followed by the migration of the metal ions from the anode to the cathode. The corrosion or the dissolution of the conductive metal anode releases the metal ions into the electrolyte. Under the influence of a bias voltage, the conduction lines become two oppositely charged electrodes. The electrolyte results from the adsorption or condensation of moisture which connects the two conduction lines in the presence of contaminants. ECM is an electrochemical reaction which occurs in the presence of electrolyte and applied potential difference. Consequently, the life span of devices is reduced, sometimes experiencing catastrophic failure.Įlectrochemical migration (ECM) 3, 4, 5, 6, 7 is one of the corrosion related problems encountered in electronic devices. The reduced distance between the conduction lines due to a smaller pitch accelerates the corrosion process. During manufacturing and in service, these devices are exposed to high humidity which leads to the formation of a corrosion cell. The increasing number of leads and closer spacing between them have made electronic devices more vulnerable to corrosion related damages 1, 2. The increasing demand towards miniaturized electronic devices has led to the development of higher density electronic packages with smaller components. The mechanisms of the ECM process of Sn in the presence of Br − are also suggested. The main products of the ECM reactions are identified as Sn dendrites and tin hydroxide precipitates. However, the probability of ECM failure follows a normal distribution initially, but later increases with the Br − concentration. The results confirm that the rate of anodic dissolution of Sn monotonously increases with the Br − concentration. The products of ECM were characterized by scanning electron microscope coupled with an energy dispersive X-rays spectrometer (SEM/EDX) and X-ray photoelectron spectrometer (XPS). Polarization test was carried out to study the correlation between the corrosion properties of Sn and its ECM behaviour. Water drop test (WDT) was conducted in the two-probe semiconductor characterization system under an optical microscope as an in-situ observation. This work systematically investigates the ECM of tin (Sn) in the presence of bromide ions (Br −) in the range of 10 −6 M to 1.0 M. The presence of ionic contaminants affects the ECM process. The miniaturization of electronic devices and the consequent decrease in the distance between conductive lines have increased the risk of short circuit failure due to electrochemical migration (ECM).
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