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14 SMT Magazine • April 2014 duce intermittent malfunctions and permanent failures, which cause severe economic loss. Miniaturization and high-density packing are other reasons for increased corrosion reli- ability problems for the electronic devices. In order to provide additional functionalities and increase the number of components per unit area on a PCBA, PCBs today are made with mul- tilayers, commonly 8–12 layers. The line width, distances, and sizes of the components on the PCBAs are then reduced considerably. Over the last 10 years, the size of electronics has been reduced by over 70%. For flip-chip ICs, minia- turization amounts to –90%. Even material loss on the order of nanograms can cause reliability problems. The average size of dew droplet formation on a surface at different temperatures varies from 20–50 mm at about 50% RH [1] . Hence, the smaller size of a PCB makes it easy for a local electrochemical cell to form, due to the forma- tion of a water layer connecting two electrical points, the thickness of which is determined by the humidity levels, conditions on the PCBA surface including cleanliness, roughness, and the relative temperature to the atmosphere. This article provides an overview of cli- matic reliability issues of electronic devices and components. Various aspects such as the PCBA materials and components, cleanliness issues, design aspects, and the environmental factors such as the humidity and temperature effects are discussed in relation to the corrosion and reliability problems. As a summary some sug- gestions for the corrosion mitigation are also discussed. Overview and Key Factors of Electronic Corrosion Corrosion issues on a PCBA surface under humid conditions can be summarized as shown in Figure 1. Three factors inherent on a PCBA surface, which are essential ingredients to cause corrosion, are: (i) the presence of metals/alloys, (ii) the potential bias/electric field, and (iii) the humidity levels determining the thickness of the water layer. These three factors together can cause formation of conventional electrochemi- CliMaTiC rEliaBiliTY OF ElECTrONiC DEviCES aND COMpONENTS continues fEATurE Figure 1: Schematic showing various factors on a PcBA surface causing leak current followed by corrosion such as ECM.