Study On The Improvement Of Nano-SnO₂ Particles On Low-Ag SnAgCu Solder

Owing to the increasing attention to the environmental and health problems,the lead free solders play a crucial role in the packaging and interconnection of electronic products.Among all lead-free solders,SnAgCu solders have been considered as the most promising substitute for SnPb solder because of its excellent mechanical properties and wettability.However,the high content of Ag in SnAgCu solders bring many problems,such as large brittle intermetallic compounds,poor thermal reliability and high cost.In this study,the nano-SnO₂ particles were added into the low-Ag Sn1.0Ag0.7Cu to improve the comprehensive performance of lead-free solder.The effect of nano-SnO₂ particles addition on microstructure,thermal analysis,wettability,mechanical properties of SnAgCu solder as well as its wettability and interfacial intermetallic growth on Cu substrate were investigated.Nano-SnO₂ particles refined the ?-Sn phase and reduced the size of eutectic Cu6Sn5 and Ag3 Sn.The eutectic microstructure of composite solder was more uniform than original solder in solder matrix.When the SnO₂ concentration was 1 wt.%,the microstructure of the solder achieved the best grain refinement effect.The thermal analysis showed that the nano-sized SnO₂ particles had little effect on the melting point,but they decreased the pasty range.The addition of nano-SnO₂ particles reduced the contact angle and increased the wetting area of the solder on Cu substrate.However,excessive addition of nano-SnO₂ particles increased the contact angle and reduced the wetting area of the solder.The 1.0 wt.% SnO₂ nanoparticles improved the vickers hardness,yield strength and tensile strength by 22.5%,24% and 23%,respectively.The morphology of intermetallic compound at the interface was related to the soldering temperature.The prism-type Cu6Sn5 formed at SAC107/Cu and SAC107-1.0SnO₂/Cu interface when the soldering temperature was 260 °C or 280 °C.However,those Cu6Sn5 grains transformed from prism-type to scallop-type at the temperature of 320 °C.The morphologies of Cu6Sn5 grains affected absorption of Ag3 Sn particles.The scallop-type Cu6Sn5 with a high growth rate need to adsorb more nano Ag3 Sn particles to reduce its surface energy.With the addition of nano-SnO₂ particles,the Ag3 Sn particles at the interface were refined,and the nano Ag3 Sn particles with small size were more easily adsorbed on the surface of Cu6Sn5 grains.The shear strength of SAC107/Cu and SAC107-1.0SnO₂/Cu solder joints reached the maximum value at 300 °C,which was about 44 MPa and 46 MPa respectively.The morphology of the interfacial intermetallic compounds?IMCs?was changed from the hill-type to the continuous layer and the interface thickness of it increased gradually at 150 °C isthermal aging.The growth of the IMCs layer was a diffusioncontrolled process.With the nano-SnO₂ particles increased from 0 to 1.3 wt.%,the rate of the interfacial IMCs first decreased from 0.0475 m2/h to 0.0247 m2/h and then increased to 0.313 m2/h.When the content of nano-SnO₂ particles was 1 wt.%,the interfacial IMCs achieved the best inhibition effect during aging.At different temperatures aging,the activation energins for the growth of overall IMCs layer were 24.0 kJ/mol for SAC107-1.0SnO₂ composite solder and 14.3 kJ/mol for SAC107 solder.During the growth of Cu6Sn5 grains,the Ag3 Sn particles adsorbed on the surface of the Cu6Sn5 grains were pinned at the grain boundaries,which hindered the migration of the grain boundaries to the solder.The addition of nano-SnO₂ particles decreased the size of the pinning particles and increased the resistance of the interface migration.The shear strength of SAC107-1.0SnO₂/Cu was greater than SAC107/Cu under the same condition,due to the suppression of nano-SnO₂ particles on interfacial IMCs.