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With the promulgation and implementation of the ban on lead-free, the new lead-free solder has been vigorously the development and application. In order to overcome the high cost of existing lead-free solder defects and poor impact resistance, low silver lead-free solder has a very important significance. The SAC solder matrix to study when the silver content less than 1% (mass percentage), Cu and add elements Ni, Bi solder melting point, wettability, microstructure of IMC. Meanwhile, the growth mechanism of the weld interface intermetallic compound. The results showed that: With increasing the content of Ag, Sn-xAg-0.5Cu solder melting point and melting the end of the temperature drop, the melting process is shortened, decreased wettability; increasing the content of the Sn-0.7Ag-xCu the melting point of the brazing material with Cu decreases and then increases to a minimum value of melting point in the content of 0.5wt%, to 216.20 ° C. With increasing Cu content, solder spreading area reduced increase after adding small amounts of Ni, SAC0705 solder alloy melting point is slightly higher, the melting path length, a slight improvement of the wetting properties; Bi elements may be reduced The SAC solder melting point of the alloy, but with the Bi content increased, the brazing alloy melting range is gradually increasing. The addition of Bi is increased SAC-based brazing material spreading area, so that the wettability has been significantly improved. Sn-0.7Ag-0.5Cu/Cu interface IMC as a cobblestone-shaped Cu6Sn5 grain diameter is 2-3μm, IMC interface after adding 0.05wt% of Ni element becomes the vermicular (Cu1-xNix) 6Sn5, grain size significant thinning, diameter about approximately 1; adding Ni element, the IMC layer thickness; after adding Bi solder formed by interfacial IMC composition has not changed, or Cu6Sn5 has changed significantly, but the IMC morphology, cobblestone shape becomes angular edge cube shape, the grain size increased approximately 3-4μm; adding Bi element of IMC layer thickness. Compared to the high silver solder, Sn-3.0Ag-0.5Cu, the solder Sn-0.7Ag-0.5Cu anti-aging aging properties decreased IMC growth rate significantly increased; after adding Ni element, the brazing material SAC0705 the aging properties of anti-aging has improved, especially after aging to form a compound layer is very thin (CuxNi1-x) 3Sn metal, Ni added to the IMC layer growth inhibition; Bi added to the weld interface IMC growth rate dropped significantly, low in Sn-3.0Ag-0.5Cu/Cu of IMC growth rate. Bi improved solder anti-aging properties. Based on the microscopic phenomena in the weld interface before and after aging, the the IMC formation mechanism, the establishment of a growth model IMC formation and growth process in the high-temperature melting and the aging process. : IMC growth is generally divided into two stages: the early growth stage, and grew up in the late stage. Growth stages are the following modes: 1. Wrapping the growth of columnar growth, dendritic growth. Grew up the stage, including the merger and annexation of two modes.
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