| Traditional Sn-Pb solder is toxic, threating the environment and human health. Therefore, the development of a new high-performance lead-free solder is becoming increasingly important. Sn-Ag-Cu-based solders have become the most likely alternative to Sn-Pb solder because of its comprehensive propertises. However, its melting point is still relatively high. So, it is of great significance to improve its performance by rapid solidification technology, then do further research and analysis on its propertises.In this paper, rapidly solidified Sn-3.5Ag-0.7Cu solder produced by melt-spinning technique was chosen for the study. The microstructure, melting characteristics of the rapidly solidified Sn-3.5Ag-0.7Cu solder and the growth behavior of IMC at different soldering time were systemly researched. At the same time, laser was adopted to solder rapidly solidified Sn-3.5Ag-0.7Cu/Cu joint, to search suitable laser soldering process parameters. Finally, the shear strength and fracture morphology of both rapidly solidified and as-cast Sn-3.5Ag-0.7Cu/Cu solder joints were investigated. A series of in-depth study was conducted, expecting to provide valuable reference for the new development and usage of rapidly solidified lead-free solders in electronic packaging industry.The main conclusions were as follows:(1) Compared with as-cast Sn-3.5Ag-0.7Cu solder, the rapidly solidified Sn-3.5Ag-0.7Cu solder has more uniform microstructure, lower melting point and faster melting speed.(2) Under 250℃, when the soldering time was 3 s,5 s,10 s and 15 s, the size of Cu6Sn5 grain formed at rapidly solidified Sn-3.5Ag-0.7Cu/Cu interface was larger than that formed at the as-cast Sn-3.5Ag-0.7Cu/Cu interface, with the extension of soldering time, the morphology of Cu6Sn5 grain changed from small planar to scallop-shaped while the morphology of Cu6Sn5 grain formed at as-cast Sn-3.5Ag-0.7Cu/Cu interface began to appear planar after a long soldering time(15 s); when the soldering time is 30 s,50 s and 240 s, the IMC at rapidly solidified Sn-3.5Ag-0.7Cu/Cu interface was thicker than that at as-cast Sn-3.5Ag-0.7Cu/Cu interface; rapidly solidified Sn-3.5Ag-0.7Cu solder was suitable for low-temperature, short time soldering.(3) When the laser power was constant, with the scanning speed reduced, the morphology of Cu6Sn5 grain formed at rapidly solidified Sn-3.5Ag-0.7Cu/Cu interface changed from uniform and tiny scallops into prismatic, and the grain size ofprismatic Cu6Sn5 increased with the decrease of scanning speed; when the scanning speed reduced again, grains at the bottom were observed closely arranged; when the scanning speed was reduced again, large plate-like Cu6Sn5 grains were generated; in addition, the thickness of IMC decreased with scanning speed incresed. Fine and uniform scalloped IMC could be formed when soldered in a wide range of laser process parameters; when the energy was high, apparent stratified IMC identified to be intermetallic compounds Cu3Sn and Cu6Sn5 formed from Cu substrate to solder.(4) With the laser power was 50 w and the scanning speed was140 mm/min, IMC at rapidly solidified and as-cast Sn-3.5Ag-0.7Cu/Cu interface were tiny scalloped, but the grain size of the former was slightly larger; in the subsequent aging process, IMC became thicker with extended aging time, but the grain size of IMC at as-cast Sn-3.5Ag-0.7Cu/Cu interface was bigger than that at rapidly solidified Sn-3.5Ag-0.7Cu/Cu interface.(5) Under 250 ℃, soldering for 20 s,30 s and 50 s, the shear strength of rapidly solidified Sn-3.5Ag-0.7Cu/Cu joint was bigger than that of as-cast Sn-3.5Ag-0.7Cu/Cu joint; soldering for 80 s, then the opposite; the shear strength of as-cast Sn-3.5Ag-0.7Cu/Cu joint increased with soldering time, while the shear strength of rapidly solidified Sn-3.5Ag-0.7Cu/Cu joint decreased after the first increase with the soldering time increased. |
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