Preparation And Characterization Of High Reliability Solder Joint With Nano-particles Addition

Solder joints are an essential component in the electronic devices，which canprovide electrical and mechanical connection. The use of traditional tin-lead solder hasbeen limited due to the toxicity of lead and the compounds of lead. It is recognized thattin-silver-copper (SAC)305is the best substitute for the Sn-Pb solder, low silver solderSAC105has advantages of low silver content, low cost. However, the strength, fatigueresistance of this solder is lower than SAC305. The purpose of this study is addingsome particles to low silver solder to replace Ag, reduce the cost, improve strength andfatigue resistance of low silver solder.First of all, ceramic particles are taken into consideration. In order to explore areasonable add-particle method, six experimental methods have been tested. Mechanicalmixing is the best choice to add the ceramic particles to the paste finally, at the sametime, the solder joints are made of industrial scraper and reflow soldering. This methodcan be used to calculate the content of the particles added, at the same time, it is foundthat this method can realize the addition of the ceramic particles, but the effect ofadding is poor when compared with the paste reflux separately. The reasons for this canbe described as: the solder ball and the solder paste are not melted at the same time,while the ceramic particles are non-wetting and non-reactive with the solder, they areattached to the surface of solder joints during the reflow process, so it is difficult toform an effective addition.Next, some of the factors that influence the hardness of solder will be researched inthis paper, it is found that the crystal orientation is a most important factor that affectthe hardness of the solder. The difference between hardness of solders with differentcrystal orientation can reach about40%. However, the grain boundaries and eutecticphase have no effect on the hardness of solders, simultaneously along with theemergence of indentation in the hardness test, the recrystallization phenomenon willgenerate around the indentation.At last, some nanoparticles those can react with the solder are added due to theresult of ceramic particles is not satisfactory, Ni and Cu nanoparticles are selected inthis article. After the addition of Ni and Cu, the total amount of the compound in thesolder organization increased, the cellular structure of β-Sn is of high integrity, and abetter organization of the grid is gotten overall the whole solder. With the increase ofthe particles added, the tissue changed significantly, chunks of compound appeared atthe same time. In addition to the content of particles added, the temperature has asignificant impact on the tissue, too. As temperature increases, the massive compoundbecomes bigger and the amount of chunks becomes lager. The tissue is destroyed whenthe temperature reaches280degrees. Otherwise, after the addition of nanoparticles, the hardness of the solder and the strength of the solder joints improve, and it can preventthe appearance of solder recrystallization.