Study On The Preparation And The Solderability Of Sn-58Bi Composite Solder

Sn-37 Pb solder has been widely used in the electronic packaging industry due to its excellent properties for many decades. However, it causesed many environmental and healthy issues due to the toxicity of Pb, Thus, developing alternative lead-free solders is on hand globally in recent years.Sn-Bi eutectic solder has received much attention in soldering electronic devices with poor heat resistance because of its low melting point, which is 139℃,but there ware many problems that we couldn’t ignore. The intermetallic compound in the system of Cu-Sn would become much coarsening during the multi-remelting and aging process, which can reduce the reliability of the joins. Besides, the frangibility and poor ductility are the major problems that need we solve.This article studied and discussed the possibility in solving the above problems through modifing Sn-58 Bi solder with graphene nanoplatelets and yttrium oxide.The results indicated that, after adding GNPs/Y₂O₃, the melting point and density of Sn-58 Bi composite solder did not change significantly. As for its microhardness, we found that the microhardness presented significantly improved trend due to the role of fine grain strengthening with 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ in Sn-58 Bi composite solder.In the soldering performance, after adding GNPs/Y₂O₃, the wettability of Sn-58 Bi composite solder had a certain influence. With the enhancement added, the contact angle between the Sn-58 Bi composite solder and Cu substrate exhibited substantially decreased and then increased. When the amount of GNPs added is 0.05 wt.% and Y₂O₃ additive amount is 0.1wt.%, the contact angle between the Sn-58 Bi composite solder and Cu substrate was minimum.The study on IMC growth kinetics in the system of Cu-Sn indicated 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ in Sn-58 Bi composite solder can suppress the IMC thichening. Besides, with the number of the remelting increasing, the shape of Cu6Sn5 directed the trend from needle strip to short /long rod. The statistics of the IMC thickness at different aging time was analyzed during the 90 ℃ isothermal aging process.The diffusion coefficient D in the system of Cu-Sn can be obtained by empirical diffusion formula. With the 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ added, the diffusion coefficient D was decreased, so that the IMC thickening was inhibited during the aging process. The study on the shape of IMC indicated, with 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ added, the roughness of the Cu6Sn5 surface was reduced.The test of the tensile properties of Sn-58 Bi composite solder alloy told us, with the 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ added, the tensile strength of the composite solder alloy was not particularly changed, which is about 70 MPa. Howere, with 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ added, the elongation of Sn-58 Bi composite solder alloy was increased particularly. The elongation of 0.05 wt.% GNPs/Sn-58 Bi composite solder alloy and 0.1wt.% Y₂O₃/Sn-58 Bi composite solder alloy was increased 20.8% and 47.4%. The shear test of the joint between Sn-58 Bi composite solder and Cu substrate indicated that the shear strength was increased 45.9% and 27.7% with the 0.05 wt.% GNPs and 0.1wt.% Y₂O₃ added.