Plating Formation Mechanism And Cold-Drawing Behavior Of Cu-Ag And Cu-Au Composite Bonding Wires

Gold bonding wires and copper bonding wires have been widely applied in the semiconductor packaging industry.The rising gold expense and the increasing demand of the semiconductor package have promoted endogenous advancement in copper bonding wires significantly.However,the application of copper bonding wires is limited by the poor oxidation.One of the current research focuses is the preparation of the anti-oxidation copper-based composite bonding wires.With excellent oxidation resistance and the same deformation-slip mechanism with copper,silver and gold could be coated on copper to process the copper-based bonding wires.As a result,combining cheap copper and anti-oxidized silver and gold,copper-silver(Cu-Ag)and copper-gold(Cu-Au)composite bonding wires could have broad application prospects in the field of semiconductor packaging.In this thesis,Cu-Ag and Cu-Au bonding composite wires were processed using a thick copper rod,followed by plating and cold-drawing.The microstructures of copper-based silver/gold plating process and cold-drawing process were characterized by Scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD),and the effects of these two processes on the formability of Cu-Ag and Cu-Au bonding composite wires were studied.The methodology of characterizing the preferred crystallite direction and degree was summarized and verified based on TEM and XRD in the silver and gold plating.The following conclusions were obtained.TEM was employed to analyze the copper-silver interface in the nicotinic acid electroplating.The formation of nano-scale silver crystallites in the intermediate layer was the result of the competing reaction between chemical plating and electroplating.The formation of silver columnar particles,which are perpendicular to the surface of copper substrate,is dominated by silver electroplating.March-Dollase function was introduced to give an insight of the silver plating on the copper plate.With the increase of the plating time and current density,both the preferred orientation degree of crystallites <111> and strain energy increased.The depth of the silver layer is proportional to the plating time and current density.The coordinating forming behavior mechanism was fully discussed in the superplastic cold-drawing deformation based on the strong <100> preferred orientation and columnar silver particles,including the <111> preferred silver crystallites.The larger grain size and smaller strain energy in the silver layer are beneficial to the preparation of Cu-Ag bonding wires in the superplastic deformation.There are no cracks on the outer surface of Cu-Ag composite bonding wires with outstanding mechanical properties for the packaging,which can meet the need of industrial requirements.Compared with pure copper bonding wires,CuAg composite bonding wires show significant antioxidant performance.TEM was employed to analyze the copper-gold interface in the nicotinic acid electroplating.The formation of nano-scale gold crystallites in the intermediate layer was the result of the competing reaction between chemical plating and electroplating.The formation of <111> preferred lamellae gold,which stacked in the outer of intermediate layer randomly,was dominated by gold electroplating.What is more,the formation mechanism of <111> preferred lamellae gold was analyzed in the view of coordination structure of gold ion and surface energy.The distributed nanoscale gold crystallites with low strain energy play a lubricated role in the superplastic cold-drawing deformation,based on the strong <100> preferred orientation and gold random texture.The nano-sized lamella gold with small hardness left linear dents parallel to the drawing direction during the superplastic cold-drawing deformation.The dents almost disappeared after continuous annealing.There are no cracks on the outer surface of Cu-Au composite bonding wires with outstanding mechanical properties for the packaging,which can meet the need of industrial requirements.Compared with pure copper bonding wires,Cu-Au composite bonding wires show significant antioxidant performance.There are small linear dents on the surface of Cu-Au bonding wires after colddrawing.The dents are weakened and there are no cracks on the surface of Cu-Au bonding wires.Cu-Au bonding wires show outstanding mechanical properties and significant oxidation resistance.In order to characterize the crystallite information,it is considerable to give a detailed insight in determining the preferred orientation,on the basis of TEM and XRD.It is defined as preferred orientation of crystallites with certain orientation relationship with the microscopic coordinate system.The sample have no preferred orientation of crystallites absolutely,provided that all the crystallites are spherical.TEM,combined with diffraction,is an effective and direct means to determine the preferred orientation of the crystallites,while XRD is a statistical means to determine the structure information of crystallites.In the framework of whole powder diffraction fitting(WPPF),the refinement and further derivative deduce are carried out to determine the preferred orientation degree of crystallites,which could compensate the drawbacks of reconstructing real threedimension with two-dimension TEM image.