Investigation On Brazing Process Of New High Silicon Aluminum Alloy

The new lightweight20~70wt%Si-Al alloys have been shown to have acomprehensive performance, which meets the basic requirements of advancedelectronic packaging material system. Most importantly, the materials of the serieshas low controlled coefficient of thermal expansion, lightweight, easy-processingand other features by composition optimization design, and it can be achieved tomatch the CTE of chips and other semiconductor materials (such as:silicon andgallium arsenide).Secondly, the materials of the series also have re-processingcapability and other features. However, domestic research of the solderingproperties and packaging joint thermal fatigue performance, which have a closerelation with the promotion application of the materials is still relativelysmall.Because high Si-Al alloy contains a lot of hard silicon phase, the wettingproperty of solders is too poor to realize effective connection with ordinarysoldering method. Therefore, it is adopted to electroplate nickel, gold and copperlayer method after electroless nickel plating in65Si35Al alloy to effectivelyimprove the new lightweight65Si35A1composite material soldering performancein the test. The soldering tests of different electroplating65Si35Al alloy samplesby Sn-Pb, Sn-Ag-Cu, Sn-In, Sn-Bi soft solders are analyzed, including thewelding joint microstructure and morphology, phase classification withmetallographic microscope, the scanning electron microscope(SEM) and energyspectrum analysis (EDS),to discuss the influence of the soldering technologicalparameters on joint quality, analyse the reasons of joint producing macro defectsand micro defects and the difference of solder wetting properties. In addition, apart of joint specimen are tested by the thermal fatigue.The main conclusions areas follows:⑴Both electroplating Ni, electroplating Au and Cu can achieve a high Si-Alalloy surface coating.The binding of coating and the substrate base material,coating and the other coating interface is in good condition.⑵Microscopic analysis of65Si35Al alloy coating sample section shows thatNi coating and base metal, the coating interface produce a certain degree ofelement diffusion, and the interfacial bonding is in good condition.⑶Microstructure analysis of soldering joint after plating of65Si35Al alloyshows that regardless of Ni or Au coating, the interface zone of coating and the other coating, and coating and the substrate65Si35Al alloy, brazing layer and thecoating produces a certain degree of element diffusion. The bonding status of theinterface zone is good.⑷Comparing different coatings of the same solder, the wetting property ofAu coating is the best, and the Au elements after soldering completely spreadthroughout the weld center, but Ni coating and filler only produce a littlediffusion.⑸It is easy for the soldering seam of65Si35Al alloy with Si-Bi series solderby furnace brazing to appear more voids,so the heating temperature should betaken higher (usually50℃higher than the eutectic temperature of the Si-Bisolder),and the defects of brazing seam apparently decrease.In addition, thewelding surface clean degree has a large influence on the quality of the joint.⑹The thermal fatigue tests of a part of the soldering joint show that Thecoatings after20times thermal cycling from liquid nitrogen-ethanol ice bath(-50℃)to120℃have no bubbles and spalling phenomena,therefore,the bonding of thecoating and the substrate is good,and the thermal fatigue performance of thesoldering joint has a good stability.