The Preparation And Drawing Of Cyanide-free Silver Plating Copper Bar

Copper bonding wires have been widely applied in the field of electronic packaging on integrated circuits due to their good electrical properties,mechanical properties,thermal properties and relative low price.However,the poor oxidation resistance and corrosion resistance of copper bonding wires severely limits its wide application.Therefore,processing copper-based composite bonding wires with low cost,better oxidation resistance and corrosion resistance is an new challenge in the electronic packaging industry currently.Silver is an ideal coating material owing to its excellent conductivity,good corrosion resistance and oxidation resistance.The preparation of the Cu-Ag composite bonding wires is a good choice with the combination of low-price copper and better antioxidant and corrosion resistance silver.Generally,three main procedures,electroplating,cold-drawing and annealing,are the necessary procedures to process Cu-Ag composite bonding wires.This paper mainly investigated the basic behaviors of electroplating process and researches on the cold-drawing process.At present,the noble metals are electroplated by the means of continuous electroplating or chemical plating on thinner copper wires,to process the copper/noble metals composite bonding wires in the industry.In this paper,a certain thickness of the silver layer was plated on a copper rod with a large diameter and drawing subsequently,thus rendering simplified process and low cost.In order to protect the environment,plating silver on copper rods with a cyanide-free system was explored in this paper.The effects of temperature,current density and time on the structure of silver layer,surface morphology,thickness and preferred orientation were investigated in the process of plating silver with a cyanide-free niacin system.The results indicated that the fitted function of the thickness in the coated silver layer verse the current density with plating 30 min is T=-73.4ρ~2+106.9ρ+1.5,(0.1≤ρ≤0.8),where T andρstand for the thickness of the silver layer and the current density,respectively.The fitted function of the thickness in the plated silver layer verse time(t)is T=0.52t+3.32(5≤t≤60),provided that the current density of 0.2 A/dm~2 is kept throughout the electroplating.Scanning electron microscopy(SEM)and atomic force microscopy(AFM)were used to characterize the surface morphology and the flatness of the plated silver layer.With the plating time,current density,and temperature kept at 30min,0.2 A/dm~2,30℃,microscopically the smooth and bright surface is obtained,which is due to the fine and compact silver particles on the microcosmic point.X-ray diffractometer(XRD)was employed to detect the texture coefficients and crystallographic orientation of the plated silver layer.The planes of{220}are always preferred with the plated temperature,current density of plated time kept30℃,0.1 A/dm~2,0.2 A/dm~2,0.4 A/dm~2 and 30 min,60 min.The electroplated Cu-Ag rod at the temperature of 30℃,current density of 0.2 A/dm~2,and plated time of 30 min was characterized by transmission electron microscopy(TEM).<110>,the close-packed direction of face-centered cubic structure are the growth direction of the columnar silver particles.The main growth direction of the silver layer thickness is consistent with the conclusion obtained in XRD.The corrosion resistance of the coated silver layer were tested by an electrochemical workstation.The best corrosion resistance was obtained at the plated temperature,current density and the plated time 30℃,0.2 A/dm~2 and 30 min.Cu-Ag rods with a diameter of 8 mm were drawn-out using a universal testing machine.And the surface morphology was observed and analyzed with SEM.During the drawing process,the plated silver layer became brighter and more uniform.What is more,the coated silver film and copper substrate deformed consistently without breaking off.It was confirmed by spectral line scanning that there was no element diffusion and intermetallic compound formatted in the silver layer and the copper substrate.After Cu-Ag rods at the plated parameter of30℃,0.2 A/dm~2 and 30 min were drawn twice to 7.32 mm,the preferred orientation of plated external silver changed from{220}to{311}.