Present Research Status of Lead-free Solder Reinforced by Nanoparticles

The development of electrical industry comes with the improvement of packaging materials. Advancements in science and technology has put much emphasis on the properties of solder alloy because the electronics is developing towards increasingly higher integrated level, finer pitch and severer service conditions. Compared with lead-free solder alloys, the traditional SnPb solder was widely used in the electrical industry due to its low cost and excellent properties. However the application of Pb is prohibited currently due to its toxicity and lead-free solder alloy has become the trend in electronical packaging material. But presently, lead-free solder alloys have some disadvantages, such as high cost, poor wettability and reliability, unsatisfactory melting property, which fail to meet the demand of electrical industry. Therefore, searching the method to improve the properties of lead-free solder seems to be worthy of attention and is a critical topic for the design of excellent lead-free solder to substitute SnPb solder alloy. So far, researches on modified lead-free solder are concentrated in microalloying and nanoparticles strengthening. Microalloying is to improve the properties of lead-free solder by doping alloy elements, such as Ag, In and rare earth elements. A great number of researches on lead-free solders modified with alloy elements have been carried out in the past decades but they are all proved to only improve a few properties of solders, which do not come up to the expected standard. Nanomaterials have attracted great attention due to their special size and property, and moreover as the ideal reinforcement, nanoparticles could influence the microstructure and performance of metal materials. The properties of lead-free solder alloy could be significantly enhanced by dispersed nanoparticles in solder matrix, the majority of which are metal nanoparticle, oxide nanoparticle, ceramic nanoparticle and carbon-based nanoparticle. In this paper, the present research status of lead-free solder alloy reinforced by nanoparticles is reviewed systematically. First of all, the cha-racteristics of three methods to prepare the composite lead-free solder alloy modified with nanoparticles are introduced. Then the effect of doping nanoparticles on the microstructure and properties of principal lead-free solder alloys is discussed respectively, such as SnAgCu, SnBi, SnZn, SnCu solder. In addition, the strengthening mechanism of nanoparticles is analyzed. Moreover, limitations of lead-free solder reinforced by nanoparticles are summarized and the development trends of researches on lead-free solder alloy reinforced by nanoparticles are forecasted to provide the reference for the future investigation of lead-free solders. © 2019, Materials Review Magazine. All right reserved.