Research On The Copper Surface Modification And Binding Force Of Interface For Coreless Packaging Substrate

The manufacturing process of coreless packaging substrate for supporting and conducting chips has been raised higher requirements to meet the development of multi-function,high frequency,high speed and high reliability of electronic products.Sputtering Cu/Ti technology was the core of coreless packaging substrate and the phenomenon of curcuit peeling often appeared for weak adhesion between the seed layer and resin substrate.At present,electroless nickel plating in the Electroless Nickel Electroless Palladium Immersion Gold?ENEPIG?was acid solution and high temperature conditions which can easily lead to solder mask falling from substrate.After ENEPIG surface finishing,conductive silver adhesives diffused seriously on the surface of pads,leading to wire bonding anomaly in the subsequent encapsulation.In this paper,the basic formula of low temperature electroless nickel plating was determined by studying the effect of bath composition,temperature and pH on the plating rate with single factor experiment.The optimum electroless nickel plating system was obtained by orthogonal optimization experiment:NiSO₄ 32 g/L,NaH₂PO₂32 g/L,C₆H₃NaO₇ 23 g/L,HN?CH₂CH₂OH?₂ 5 mL/L,NH₄Cl 25 g/L,accelerator D 0.3mL/L,stabilizer C 0.2 mL/L,pH=10¹1,T=45⁶0?.The nickel coating performance was characterized and results showed that the Ni-P alloy coating obtained under the low temperature electroless nickel plating system had the advantages of uniform and compact structure,strong binding force and good corrosion resistance.Compared with ordinary acid and high temperature method,the nickel obtained in the experiment had better corrosion resistance.The direct factor that determined the diffusion of conductive silver adhesives on the surface of pads was package substrate itself by discussing the diffusion degree of different kinds of conductive silver adhesives on the surface of pads.The diffusion degree was mainly affected by the roughness of copper surface before ENEPIG by analysing the mechanism of the diffusion.The effects of copper surface micro-etching amount and micro-etching system on the diffusion degree were discussed respectively and a method controlling the diffusion range of the conductive silver adhesives on the surface of pads in the range of 50?m was obtained.The copper was etched by adding corrosion inhibitor,H₂SO₄,and H₂O₂.Then,the packaging substrate was baked in the nitrogen atmosphere at 120? for 1 h after ENEPIG surface finishing accomplished.So,the gold layer atoms could be flat covered on the surface of pads.The influence of KMnO₄ desmear,plasma,HF treatment,conditions of seed layer and residence time on binding force were studied and the best parameters were determined by orthogonal optimization experiment.The rate of KMnO₄ desmear was2.0 m/min,plasma treated for 6 min and the speed of HF treatment was 2.0 m/min.Then,the fine circuit have completed under the condition of sputtering Ti 0.1?m,sputtering Cu 0.8?m,Nitrogen heating at 200?,and ensuring residence time more than 5 h.Peel test showed that the adhesion of?seed layer Cu/Ti?/prepreg systems was not less than 6 N/cm,and separation was not found in the interface between prepreg substrate and sputter-deposited Cu/Ti.