Study Of The Preparation And Application Reliability Of Fe₃O₄Nano-composite Solder

The rapid development of semiconductor technology and electronic manufacturingtechnology propels the replacement and updating of traditional electronic packagingprocesses and materials. Electronic packaging lead-free solder alloys almost completelyreplaced the SnPb solder alloys, which have been widely applied in the novel electronicproducts, one of which is SnAgCu solder alloy. Even so, as the electronic products andmicroelectronic systems become more and more integrated, multifunctional and small, itmakes a more severe application condition of traditional SnAgCu solder alloy, such as hightemperature and high density of the current through the solder bump, and urges higherrequirements for its application reliability. Therefore, it becomes a crucial issue to createnovel lead-free solder alloys for application.In this study, Fe3O4nanoparticles were synthesized by chemical co-precipitation process,and were successfully mixed with Sn3.0Ag0.5Cu solder alloy to prepare novelnano-composite solder alloys. The wettability, melting point, pasty range were first studied.It shows that after adding appropriate concentration of Fe3O4nanoparticles into theSAC305solder the wettability of the composit solder were obviously increased. Eventhough the melting point and pasty range of nano-composite solders were slightly increasedafter the addition of Fe3O4nanoparticles, the novel solder alloys can still be adapted inthose instrumentation and parameters in the production process in electronic manufacturingindustry. It is noteworthy that the concentration of Fe3O4nanoparticles added in the solderhas a relationship with the improvement extent of solder wettability. Adding appropriateconcentration (0.5wt.%) of Fe3O4nanoparticles can obviously increase the wetting force ofcomposite solder, while excessive concentration (1.0wt.%) of nano-Fe3O4added in thesolder will impair the improvement extent of wettability of solder.The composite solder with nano-Fe3O4have a better application reliability duringisothermal aging at150oC than the solder without adding nanoparticles. The growth rate ofIMC at Cu/solder interface decreased after Fe3O4nanoparticles were mixed into theSAC305solder. It is notable that the concentration of nano-Fe3O4added into the solder hasa V-type relationship with the formation and growth rate of interfacial IMC duringsoldering and aging respectively. Slight addition amount of Fe3O4nanoparticles in thesolder will obviously increase the inhibition effect of the growth of interfacial IMC, while excessive addition amount of nano-Fe3O4will impair the inhibition effect. A similarregulation was obtained in the electromigration experiments. Whether the environmenttemperature or current density is high or not, a same effect of Fe3O4nanoparticles on thegrowth rate of solder bump interfacial IMCs at anode side was observed. When the additionconcentration of nano-Fe3O4is smaller than0.5wt.%, the growth rate of interfacial IMC atanode side of solder bump. While a higher addition concentration of nanoparticles in thesolder will make a better inhibition effect of growth rate of interfacial IMC at anode. On theother hand, when the addition concentration is larger than0.5wt.%, with the additionconcentration increasing the growth rate of interfacial IMCs at solder bump anode side willincrease.The reason for Fe3O4nanoparticle concentration affecting interfacial IMC formation andgrowth might be attributed to nanoparticles’ adsorption on solid surface, including thesurface of interfacial IMCs and Cu coupon. The real adsorption amount of Fe3O4nanoparticles on the solid surfaces influences the effect of nanoparticles on interfacial IMCgrowth. Nanoparticles adsorbed on the surface of the Cu substrate act as diffusion barrierand impede the reaction and the inter-diffusion of Sn and Cu atoms through solder/Cuinterface, which decrease the interfacial IMC thickness during soldering and slow down theIMC growth during isothermal aging. However, with excessive addition of Fe3O4nanoparticle in the SAC305solder, the nanoparticles will be more easily to agglomerateand transform into large particles. The agglomerated and large Fe3O4particles will not trendto adsorb on the surface of Cu coupons due to their lower surface energy. Therefore, thereal adsorption amount of Fe3O4nanoparticles declines, which decreases the improvementextent of the obstruction of the reaction and diffusion of Sn and Cu. Finally, the more thereal adsorption of nanoparticles on the solid surface, the better the improvement effect willbe.