Preparation Of UV Curing Activated Slurry And Its Application In Electroless Copper Plating

PCB is the key electronic interconnection of electronic products, known as the "mother of electronic systems products". The manufacturing processes of PCB include additive and substractive methods. Substractive method is matured, secure and reliable, but it has some disadvantages such as long processes, high consumption of materials, serious environmental pollution. In recent years, additive method is becoming a hot spot in research for its advantage of highly technology, less resource consumption and environment friendly. In this paper, a material that can be used in additive method-UV curing activated slurry was successfully synthesized and its application in electroless copper plating was investigated.The electroless copper plating based on EDTA·2Na and K-Na tartrate (Tart) had been applied widely in the field of PCB for its mature technology and low costs, but the plating rate is too low to meet the development requirements of PCB. In order to improve the plating rate, we developed an electroless copper plating solution based on THPED-EDTA·2Na system. The effect of CuSO4,THPED,EDTA-2Na,additives and operating conditions on plating rate, bath stability and coating quality were characterized by electron microscopy (SEM),energy dispersive X-ray(EDS),X-ray diffraction(XRD) and electro-chemical workstation, respectively.Through the study of rapid electroless copper plating from THPED-EDTA-2Na system, we selected the suitable additives and confirmed the optimal compound additives by orthogonal experiments. Finally, it can be concluded that the optimal conditions are: CuSO4·5H2O 12 g/L, EDTA-2Na 5.8 g/L, THPED 10 g/L, HCHO 14ml/L,2,2’-dipyridyl 10mg/L,2-MBT 7mg/L, Organic compounds M 20mg/L, K4Fe(CN)6·3H2O ，0mg/L, Tween-80 15mg/L, pH 12.5～13.0 and temperature 50～60℃.Under the optimal operating conditions(T:50℃, pH value:12.5), the plating rate is 17.6μm/h and the bath is stable. The backlight level achieved 9th grade, the coating is smooth and bright, the crystallite size is small and intensified (111) plane orientation.The study of electrochemical characteristic shows that at potential around -0.48V is the irreversible oxidation reaction of HCHO which involves prior chemical reaction. At potential around -1.18V is the reducing reaction of Cu(Ⅱ),which also is an irreversible electrochemical reaction involves prior chemical reaction. The peak current density of oxidation reaction of HCHO increased with the addition of HCHO; decreased with the addition of THPED, EDTA·2Na,2,2’-dipyridyl, organic compounds M, K4Fe(CN)6 and Tween-80. The peak current density of Cu(II) cathodic reduction increased with the addition of CuSO4; first decreased then increased with the addition of THPED; first increased then decreased with the addition of EDTA-2Na and organic compounds M; decreased with the addition of 2,2’-dipyridyl; the K4Fe(CN)6 and Tween-80 has little effect on peak current density.2,2’-dipyridyl and K4Fe(CN)6 caused a more negative potentials, while organic compounds M caused the potential moved to the positive direction.A UV curing activated slurry was also successfully synthesized in this paper. The surface morphology, structure, element distribution, catalytic activity and process of electroless copper plating were characterized by Fourier transform infrared spectroscopy (FT-IR), SEM, EDS, XRD and electrochemical open circuit potential-time (OCP-t) techn-ique, respectively. Raw materials for activated slurry were screened and optimized after a number of compounds and comparative experiments, the influence of prepolymers, photoinitiators, monomers, concentration of AgNO3 and conductive carbon black on adhesion, catalytic activity and conductivity of copper deposits were studied. The optimum formulation of the UV curing activated slurry was as follows:PEA(tetrafunctional polyester acrylate) and PUA(bifunctional urethane acrylate) were prepolymers (PEA:PUA=4:6), TPGDA and TMPTA were reactive monomers(TPGDA:TMPTA=1:1), ITX+EDB and 907 were compounded as photoinitiator (ITX+EDB:907=1:1), AgNO3 is 7% and conductive carbon is 7%～12%.We coated the activated slurry on the PI, immersed it in the electroless copper plating bath. The copper deposited is small, the surface is smooth, dense and uniform, the adhesion force reached 100%, the square resistance is 0.046Ω/□.The backlight level achieved 9th grade.