Soldering and interfacial characteristics of Sn-3.5Ag solder containing zinc nanoparticles

Driven by the necessity to improve the reliability of lead free electronic products and by the trend towards miniaturization, researchers are putting intense efforts to improve the properties of Sn based solders. One of the current approaches to improve the properties of Sn based solder is to add nanoparticles. A number of studies have been done on the effects of the addition of nanoparticles on the interfacial intermetallic compound (IMC) characteristics [1-3]. It has been found that the additions of Ni [1], Co [1,2] and Mo [3] nanoparticles substantially influence the characteristics of interfacial intermetallic compounds.The present work investigates the effects of Zn nanoparticles (up to 0.34%) on the melting point, wetting characteristics and interfacial structure between Sn-3.5Ag (SA) solder and copper substrate during reflow. The melting characteristics of nanocomposite solders were investigated by differential scanning calorimetry (DSC). The actual Zn content of the solder after reflow was determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The wetting angle and spreading rate were measured to investigate the solderability of nancomposite solder. High resolution field emission scanning electron microscopy (FESEM) was used to investigate the morphology of IMC formation at the solder/substrate interface during reflow. Results showed that addition of Zn nanoparticles suppressed the melting point of the solder. The wetting angle of the solder increased, while the spreading rate decreased with the addition of Zn nanoparticles. Cross sectional microscopy revealed that the typical scallop type Cu
₆
Sn
₅
and a very thin, flat Cu
₃
Sn formed in SA after 1x and 6x reflows. The addition of Zn nanoparticles substantially suppressed the growth of the interfacial IMCs. Addition of Zn has also suppresed the formation of Cu
₃
Sn significantly during aging. The mechanism of the influence of Zn nanoparticles is discussed.