**5.7. Electrochemical corrosion**

Electrochemical behavior of Sn based coatings is important in microelectronic packaging devices. The corrosion of Sn base coatings may deteriorate the microstructural properties of the solder joints and ultimately lead to entire failure of the device. For example, in marine applications, the chlorides ions from the sea can dissolve the solder joints by forming soluble compounds.[106] There are various forms of corrosion such as pitting, crevice, and/or galvanic corrosion of solder and substrate material. Therefore the corrosion of electronic devices may impose a serious threat among microelectronics community to produce corrosion resistant solder materials. However, there is a scarcity of information of electrochemical corrosion of the solder joints.[107, 108] It has been shown that presence of Bi in Sn–Bi solder can increase the dissolution of Sn slightly in sulfuric acid solution and vigorously in nitric acid solution compared to that of pure tin.[108, 109]. It has been noticed that lead-free solders are highly corrosion resistant towards chloride ion attack compared to conventional Sn-Pb solder. [110] Recently, Sharma *et al.* proposed that use of nanoparticles is better idea to avoid the localized dissolution of Sn coatings. If the nanoparticles are added in an optimum concentration in the solder matrix, the corrosion resistance of the solder matrix can improve significantly by setting up of homogeneous corrosion instead of preferential and sudden damage. The high surface energy nanoparticles in the solder matrix reduce the corrosion potential, corrosion current, and diffusion capacitance, thus increasing passivity of the solder coating.[111]

#### **5.8. Whisker growth mitigation**

Tin whisker growth in the Sn based coatings is a serious issue in microelectronic packaging devices. The driving force of these whisker growth is the generation of compressive stresses in the coatings on storage for a long time. When plated on a metallic substrate like copper, the Cu-Sn interdiffusion across the interface may give rise to the formation of Cu6Sn5, Cu3Sn etc., IMCs and grow with time causing a volume expansion of the interface. The expansion of the interface causes the setup of compressive stress in the coatings. Recently, it has been identified by various researchers that addition of nanoparticles may suppress the growth of IMCs and restrict the formation of whiskers in the matrix. Generally, the ceramic nanoparticles are very smaller compared to size of IMCs. Therefore they can easily attach with the growing IMC in the molten metal and restrict the growth of IMCs during solidification as predicted by the surface adsorption theory.[18, 19, 22, 41]
