At present, the ways to improve the performance of lead-free solders mainly has two kinds: alloying lead-free solderand composite solder method. Alloying is mainly the lead-free solder alloy preparation by multiple line system to improve the properties of lead-free solders, and composite solder method is to improve the performance of lead-free solders by adding nano oxide, intermetallic compound or other high stability existing in the system of particles to thefiller. This article through to the SAC lead-free solder of adding nano TiO2 particles or multi walled carbon nanotubes (MWCNTs) to prepare SnAgCu-XTiO2 composite brazing alloy and SnAgCu-XMWCNTs composite solder, and the composite melting point of the solder,wettability, microstructure, mechanical properties andthermal fatigue properties were studied. The main research contents and results are as follows:
Preparation of composite solder with different proportion ofstrengthening particles 1, by ball milling and powder metallurgy method, and the composite solder composition,melting point and wettability are analyzed. Strengthening particles added no reaction with substrate solder, phase composition does not change the matrix solder; composite solder melting point slightly lower than SAC solder, which is beneficial to improve the solder welding process, and not on the current brazing technology and equipment impact;composite solder wetting angle is less than the SAC filler metal, composite solder spreading area more than SACsolder.
2, the morphology of microstructure of brazed joints were analyzed with scanning electron microscope. The analysisfound that organizational scallop interface brazing joints for the intermetallic compound Cu6Sn5; composite soldertissues than SAC solder is tiny, composite solderintermetallic compound layer thickness than the SAC solderthin, strengthening particles mainly by surface adsorptioneffect of thinning solder organization.
3, study on the mechanical properties and the servicereliability of SAC solder joint and the composite solders.Microhardness of the composite solders was significantly higher than that of SAC solder alloy, the composite solder joints in ultimate tensile strength and shear strength is stronger than that of SAC solder; QFP solder joint and thechip resistor composite solder is higher than the service reliability of SAC solder.
4, the SAC filler metal and composite solder thermal fatiguecapability were studied. After multiple reflow or isothermal aging, the comprehensive properties of SAC solder alloyand composite solders were decreased, the intermetallic compound layer thickness and morphology of intermetallic compounds by ellipsoidal deformation into a rod, strength decrease of brazed joint tensile strength and shear, but the performance of composite solder is significantly better than the SAC solder. Exhibit a specific thermal fatigue capability of SAC solder is better.
5, the nano TiO2 particles and nano carbon tube surface modification of. Through the principle of chemical deposition method and using the disproportionation reaction of success is coated with a layer of copper on the surface of nano TiO2 particles, are combined to realize theactivation point and surface copper atoms of carbon nanotubes.