Researches On Properties Of Nanoparticles Composite Lead-free Solders And Its Micro-joined Joint

Considering the melting point, welting ability, mechanical properties and cost, it has not been found the perfect substitute of Sn-Pb solder because of its toxicity. So it is very important to design and develop new lead-free soldersSn-3.5Ag lead-free composite solders were respectively composed with different amounts of Ni nanoparticles and Cu nanoparticles. Different kinds of composite solders were produced by using mechanical stirring method. In order to analyze the effect of the nanoparticles on the properties of the Sn-3.5Ag lead-free solder, the melting point, wetting ability and microhardness of the composite solders were researched respectively. Moreover, the reliability of the micro-joined joint and the IMC in the micro-joined joint were also studied. The aim of this study was explaining the changing of the reliability by the changing of the IMC in the micro-joined joint. The main conclusions are as follows:(1) The melting point of the composite solders which were added Cu nanoparticles is lower than Sn-3.5Ag solder. The wetting ability decreased after adding Cu nanoparticles. The microhardness of the composite solder is higher than Sn-3.5Ag solder.(2) The melting point of the composite solders which were added Ni nanoparticles is lower than Sn-3.5Ag solder. The wetting ability is also increased after adding Ni nanoparticles. The microhardness of the composite solder is lower than Sn-3.5Ag solder.(3) Adding Cu nanoparticles make much effect on IMC on the interface of the micro-joint and the inside of the solder. The variation of shear property with the reflow time and the amount of the Cu nanoparticles is quite complicated. This phenomenon may be induced by the voids in the solder, and the changing of the IMC on the interface and the inside of the micro-joined joint. The mechanical bend fatigue property is promoted by adding Cu nanoparticles, but the reliability of mechanical bend fatigue decreases with increasing the amount of the Cu nanoparticles. When the amount of the Cu nanoparticles is 0.5%, the mechanical bend fatigue strength is the best.(4) Adding Ni nanopartilces also make much influence on the composition, morphology of the IMC and the thickness of IMC. When reflow time is 60s and 120s, the shear property of the Ni nanoparticles composite solder decreases. With the reflow time prolong to 240s, the shear property of the Ni nanoparticles composite solder increases. The mechanical bend fatigue property is promoted by adding Ni nanoparticles. When the amount of the Ni nanoparticles is 0.5%, the mechanical bend fatigue strength is the best.(5) After adding nanoparticles, the fatigue cracks are not found on the IMC layers which connect the BGA and bonding pad. Yet, the fatigue cracks in the Sn-3.5Ag solder is almost found on the IMC layers which connect the BGA and bonding pad. This phenomenon indicates that the strength of the IMC layers which connect the BGA and bonding pad is increased by adding nanoparticles. This may be the main reason that the fatigue property of the nanoparticles composite solder is higher than Sn-3.5Ag solder.