Study On Chromium-free Etching Progress Of ABS Resin Surface Electroplating Pretreatment

Since the ABS resin has entered the sight of people,with its excellent overall performance and low price,it is favored by the manufacturing industries of the electrical,mechanical,and light industrial fields,automobiles,airplanes and ships.ABS resin is a thermoplastic resin consisting of three monomers of Acrylonitrile,Butadiene and Styrene.The relative content of different monomers can be changed freely with the difference of their performance bias.At the same time,the metallization of the ABS resin surface also has a wider range of application prospects.However,the inherent structural composition of the ABS resin results in a certain degree of hydrophobicity of the ABS surface.It needs to be etched to increase the substrate surface roughness and hydrophilicity.The traditional etching process adopts chromic anhydride/sulfuric acid system to treat the ABS surface.The surface roughness and hydrophilicity of the treated ABS is greatly improved,which provides the conditions for electroless plating.However,the chromic anhydride component in the traditional etching system will seriously pollute the environment.In this paper,two new environmental-friendly chromium-free etching systems,namely HNO₃/H₂SO₄/Ni²⁺system and S₂O₈^2-/Fe²⁺system,were proposed and studied respectively to replace the traditional chromic anhydride/sulfuric acid system for avoiding the effect of this defect.This paper first studied the effect of HNO₃/H₂SO₄/Ni²⁺etching system on ABS.the etching conditions are as follows:HNO₃ 250ml·L^-1?H₂SO₄ 250ml·L^-1?NiSO₄ 50g·L^-1,the etching reaction temperature is 60°C,etching reaction time is 20 min.The surface of the resin can be well etched,then ABS can be successfully electrolessly plated and plated after etching.The open circuit potential of the etching system under this concentration ratio was continuously studied,and the open circuit potential value was about 1.057V.After scanning electron microscopy?SEM?and atomic force microscopy?AFM?tests,it was found that a large number of uniformly distributed micropores were produced on the surface of the ABS resin after etching,and the roughness was significantly improved.The average roughness?Ra?was increased from2.51nm to 21.9nm,the root mean square roughness?Rq?was increased from 3.21nm to 27.5nm.The contact angle analyzer was used to test the ABS surface after etching.It was found that the contact angle value was decreased from 97.88°to about 62.16°.At the same time,the adhesion strength between the surface of the ABS resin and the plating layer after the electroless copper plating and electroplating of the copper and nickel plating was examined using a adhesive strength tester,and the adhesive strength between the electroless copper plating layer and the ABS resin was measured to be about 2.09MPa.The adhesive strength between the coating and the substrate is about 3.33MPa after electroplating.Fourier-infrared spectroscopy?FT-IR?and X-ray photoelectron spectroscopy?XPS?were used for detection and analysis.The results showed that a large number of hydrophilic groups such as hydroxyl and nitro were produced on the surface of the ABS resin treated by the HNO₃/H₂SO₄/Ni²⁺etching system.In this paper,another new type of chromium free etching system S₂O₈^2-/Fe²⁺system can also be used for the better etching of the surface of the ABS resin,the electroless plating and electroplating can be successfully carried out after the etching treatment.When the S₂O₈^2-/Fe²⁺system has sodium persulfate 2.43g·L^-1,ferrous sulfate 1.95g·L^-1,citric acid 2.64g·L^-1,the etching temperature is 50°C,and the etching time is 15min,it is the best condition for etching.The open circuit potential was 0.568V.The ABS resin after etching can produce a large number of uniform micropores,and the roughness is greatly improved.The adhesive strength between the electroless copper coating and the ABS resin was about 1.73MPa,and the adhesive strength of the coating and the matrix was about 2.80MPa after electroplating.The contact angle was57.60°.It was found that a large number of hydroxy groups and carboxyl groups were produced on the surface of the ABS resin treated by the S₂O₈^2-/Fe²⁺etching system.