**5.4. Solderability**

tant for co-electrodeposition of nanocomposites. For example, in Ni–SiC deposition, the applicationofPCresultsintheproductionofcompositecoatingswithhigherfractionofparticles, andbetterpropertiesthanobtainedwithDCplating.[89]Inanothertechniqueofpulsereversing, the pulsed-reverse current (PRC) technique, a stripping time is also applied to the pulse waveform, during which the surface projections are dissolved and produce more smooth deposit.[90] The Zn matrix nanocomposite reinforced with the TiO2 nanoparticles using the PRCtechniquehasbeenshowntoimprovetheembeddedTiO2particledensityinthematrix.[91]

The original driving force for the preparation of nanocomposite solders was to improve the mechanical, thermal, and corrosion resistance of the solder alloys to utilize them in high temperature, harsh service conditions. The properties that are improved compared to the

The density of a microelectronic device is very important for developing portable electronic goods. There are various reports which show a reduction in density values in nanoparticle reinforced composites. [18, 21, 41] Zhong *et al.* reported that the Al2O3 reinforced Sn matrix composite is lighter compared to monolithic matrix, while Babaghorbani *et al.* found that SnO2 reinforced Sn–3.5Ag matrix did not show any change in density. This may be due to the

The electrical conductivity of a metal matrix is a function of various factors like fraction of secondary reinforcement phase, fraction of pores, size and shape, and the metal matrix. [92, 93] Nai *et al.* observed that the dispersion of CNT in the Sn based matrix does not decrease the conductivity of the matrix.[94] They correlated this fact with the low volume fraction of pores as well as reinforcement in the solder matrix. This type of behavior has been also observed by Sharma *et al*. for Sn–CeO2 and Sn–Ag/CeO2 nanocomposites.[41, 95] Babaghorbani *et al.* studied the electrical properties of nanocomposite solders in detail and reported that nano-sized reinforcements is advantageous in not degrading the electrical conductivity of the device, while micron sized particles can degrade the conductivity values .[96] This further confirms the unique properties of nanocomposite solders for electromigration property microelectronic packaging devices. Recently, it has been demonstrated the nanoparticles reinforced solders can be promising candidates for preventing electromigration failure in electronic packaging

There is wide distribution of results on the thermal behavior of solders.[18, 22, 23, 41, 95, 98, 99] The melting points of the nanocomposite solders generally decreases with an increase in

fact that the matrix and reinforcement have the similar values of density.[21, 25]

**5. Properties of electro-composites**

262 Electrodeposition of Composite Materials

**5.1. Density**

devices.[97]

**5.3. Melting point**

**5.2. Electrical conductivity**

conventional Pb–Sn solder are summarized as follows:

During soldering, in order to form a proper metallurgical bond between two materials, wetting must take place. There is an increase in solder wetting onto the metallic substrates after addition of the nanoparticles in the solder matrix. The high surface energy nanoparti‐ cles decrease the surface tension and wetting angle and results in the improved solderabili‐ ty. However, too much addition of nanoparticles in the solder may degrade the wetting properties due to the increase in agglomeration of nanoparticles in the molten alloy.[35] Additions of metallic additives also have been shown the similar behavior where the wetting decreases due to the increase in surface tension and oxidation of the reinforcing phase.[100] Recently, Sharma *et al*. investigated the solderability of Sn–Ag–Cu alloy reinforced with La2O3 nanoparticles in terms of spreading ratio and wetting balance measurements. They also found that the wetting is improved up to an optimum amount of La2O3 nanoparticles and decreas‐ es beyond that due to the increase in surface tension and melt viscosity.[19]
