Research On Additives For EDTA-based Chemical Copper Plating Syste

With the rapid development of economic society and digital industry,the industrial system based on printed circuit board has put forward higher requirements for half addition process.As a key step in the semi-addition process,electroless copper plating process not only requires the printed circuit board produced by it to have the characteristics of miniaturization,high transmission rate and high performance,but also requires the production process to be simple and easy to operate,which can meet the industrial production.Based on the above requirements,the effects of additives on deposition rate,surface morphology and stress in electroless copper plating process were studied in this paper,and a electroless copper plating solution with higher deposition rate and higher quality was obtained.In this paper,a electroless copper plating system using disodium ethylenediamine tetraacetic acid as complexing agent was determined through research.The composition of the basic plating solution was as follows:Disodium ethylenediamine tetraacetic acid（EDTA·2Na）30 g/L,copper sulfate pentahydrate（Cu SO₄·5H₂O）10 g/L,formaldehyde（CH₂O）5m L/L,the solution p H was 12.5,through experiments to determine the electroless copper plating temperature of 70℃.Subsequently,the effects of various additives on the deposition rate of electroless copper plating and the quality of copper film were studied.The deposition rate and surface morphology of accelerators and stabilizers were investigated.It was found that the deposition rate of 2,6-diaminopyridine was the highest when 0.5 mg/L 2,6-diaminopyridine was added into the electroless copper plating solution of disodium ethylenediamine tetraacetate system,which reached 15.427μm/h.It was found that there was a good synergistic effect between the two.Although the deposition rate decreased somewhat compared with the single addition of 2,6-diaminopyridine,it was still higher than the deposition rate of the basic copper plating solution.The compound addition of the two increased the deposition rate of electroless copper plating and reduced the size of the crystal on the surface of the copper film.In order to alleviate the hydrogen embrittlement of electroless copper plating film,the surfactant sodium hydroxyethyl sulfonate was added to the copper plating solution.It was found that sodium hydroxyethyl sulfonate could form a good promoting effect with 2,6-diaminopyridine and 2,2-bidipyridine,so that the hydrogen generated by the reaction fell off from the surface of the copper film,reducing the surface tension,alleviating the hydrogen embrittlement phenomenon,which is conducive to the improvement of the quality of electroless copper plating.On this basis,the stress reducer nickel sulfate hexahydrate was added,and it was found that nickel sulfate hexahydrate could improve the quality of copper plating film and promote the smooth surface of copper plating film,so as to finally determine the composition of various additives in the electroless copper plating system of ethylenediamine tetraacetate disodium.Linear voltammetry was used to analyze electroless copper plating solution,and the acceleration mechanism of various additives on electroless copper plating solution was explained from the perspective of mixing potential theory.It was found that additives affected the deposition rate in electroless copper plating process by changing the peak current of anode oxidation and cathode reduction.X-ray diffraction（XRD）was used to test the stress of Cu（220）and Cu（311）crystal surfaces.When the concentration of nickel sulfate hexahydrate increased from 0mg/L to 0.4 mg/L,the minimum stress values of the two crystal surfaces were-27.31 MPa and-27.16 MPa,respectively.Atomic force microscope was used to test the surface roughness of the chemical copper film.It was found that the addition of nickel sulfate hexahydrate can effectively reduce the average roughness（Ra）of the copper film surface and make the copper coating smooth.The final composition of electroless copper plating solution obtained in this paper is:Disodium ethylenediamine tetraacetate 30 g/L,copper sulfate pentahydrate10 g/L,formaldehyde 5 m L/L,0.5 mg/L 2,6-diaminopyridine,0.5 mg/L 2,2-bidipyridine,0.4mg/L sodium hydroxyethyl sulfonate and 4mg/L nickel sulfate hexahydrate,plating temperature was 70℃,plating solution p H was 12.5.The deposition rate of electroless copper plating solution can be as high as 12.87μm/h,and the resulting coating is bright,powdery,smooth and compact,with low stress and roughness.