A review on nanodispersed lead-free solders in electronics: synthesis, microstructure and intermetallic growth characteristics

Abstract

Lead-free solder research has witnessed a great jump in the past decades due to the increased restrictions over the use of toxic lead-bearing solder alloys. Among the representative lead-free solders (Sn–Cu, Sn–Bi, SnZn, Sn–In, Sn–Ag, Sn–Ag–Cu (SAC)), the most popular SAC alloys have emerged as promising candidates for the replacement of traditional Sn–Pb alloys. However, owing to the various concerns over the presence of brittle intermetallic compounds (IMCs) like Ag₃Sn and Cu₆Sn₅ in these alloys, their applications in modern microelectronic packaging devices have been limited. Numerous nanoparticle-reinforced solder candidates have been recommended over the years as an alternative to the existing lead-free solder alloy candidates to restrain the IMCs growth and improve solder joint reliability. In this review, we present a thorough survey of different types of lead-free solders, their important fabrication routes, interfacial reactions with common metal substrates, and the mechanical properties of these multicomponent alloys. We have made a comparative overview of lead-free soldering alloys and nanoparticle-reinforced solders produced by different synthesis routes including aqueous solution-based pulse electrodeposition, solid-state powder metallurgy, and melting and casting route. The effect of these synthesis methods, their respective process parameters, as well as the addition of different alloying elements and ceramic reinforcements on the microstructure and interfacial modification of lead-free solders has been highlighted in detail. Important properties required for soldering alloys to maintain the reliability of solder joints in the recent microelectronic applications and future guidelines are also presented.