Study On The Properties And Growth Mechanism Of Electroless Gold/Silver Plating Coating For 3D Plus

In the process of 3D Plus packaging,electroless nickel plating/replacement gold plating(ENIG)process is the key surface treatment step.It realizes the surface metal graphics of potting devices,which not only improves the packaging density but also ensures the reliability of devices in service.With the development of electronic industry and aerospace industry,put forward the new requirements of ENIG gold layer thickness,ENIG process,this paper get the gold layer is thinner(100-200 nm),using sodium sulfite-sodium thiosulfate chemical plating system got high quality microns thickness of gold layer,and discussed the growth mechanism of the chemical plating layer,The processing of micron electroless silver plating layer was carried out.The main research results are as follows:The effect of pretreatment on electroless nickel plating was investigated,and the optimal pretreatment process was obtained as follows: preimmersion for 10 min,activation for 15 min,gelatinization for 5 min,and washing for 5 min.Scanning electron microscopy(SEM),X-ray diffraction(XRD)and electrochemical testing methods were used to compare the corrosion resistance of Ni-P layers with different P contents.It was found that the increase of P content in Ni-P layers promoted the amorphous transformation of the coatings,thus improving the corrosion resistance.In the study of chemical gold-plating process of Ni-P layer surface,the single factor and orthogonal experiment were used to explore the role of each component in the plating solution,and the optimal chemical gold-plating process parameters were obtained: Under the conditions of sodium gold sulfite 0.6 g/L,sodium sulfite 0.3 mol/L,sodium thiosulfate0.2 mol/L,polyethylenimine 10 g/L,temperature 80 ?.the gold layer is dense,high purity,strong corrosion resistance,good thermal shock resistance.Combined with the change of electrode potential in the process of chemical gold-plating,the influence of each component in the bath on the deposition of gold layer was explored,and it was found that the addition of sodium thiosulfate promoted the growth of gold layer.Then the influence of sodium thiosulfate concentration on the thickness of gold layer was analyzed by means of ICP,SEM and XRD,and it was found that when the concentration of sodium thiosulfate was 0.2 mol/L,The thickness of gold layer is the largest,and the growth mechanism of electroless thick gold layer is proposed based on ICP test results.Combined with the mechanism of electroless gold plating,the electroless silver plating system was designed.The optimal process parameters were obtained by orthogonal experiment: silver nitrate 0.2 g/L,ammonia water 55 g/L,ethylenediamine 18g/L,polyethyleneimine 10 g/L,temperature 50 ?.The electrochemical test shows that the addition of ethylenediamine can increase the thickness of silver layer.The effect of ethylenediamine concentration on the thickness of silver layer is analyzed by SEM and XRD.The results show that the thickness of silver layer is 1.18 ?m when ethylenediamine is 18 g/L.