Studies On Preparation And Properties Of Metallized PMMA

Polymethylmethacrylate (PMMA) is used widely in fields of auto, advertisement, medicine,telecommunication, etc. due to its excellent properties, such as ligh weight, good chemicalstability and easy processing. Also, due to the wide application of acrylate adhesive, developingplating technology on PMMA has a great significance to integrated EMC. If its surface isdeposited by copper and nickel through electroless and electro plating, the PMMA will beimparted with metal gloss, conductivity and electromagnetic shielding effectiveness and othergood properties, which can be further applied in other fields.Formaldehyde is utilized as reducing agent in traditional way to produce good copper layer,but it cannot meet environmental demand nowadays yet as unstable bath and formaldehydeemission during process is existed in this kind of system. In this case, it is necessary and urgent todevelop novel copper electroless plating bath system. Sodium hypophosphite plating system staysas a research hotpot with its high bath stability, little corrosion for substrate and wide range ofoperation parameters. However, the nickel content in the copper deposition from this method isrelatively high compared to formaldehyde system, which affects the conductivity and needsfurther study.Sodium hypophosphite and sodium citrate is chosen as reducing agent and stablizer in thispaper to deposite copper on PMMA surface. The orthogonal experiment result illustrates theimportance of factors affecting copper resistance and deposition rank from nickel sulfate,temperature, pH, copper sulfate, sodium citrate to sodium hypophosphite. The basic bathcomposition and operating parameters obtained from orthogonal experiment is CuSO4·5H2O8g/L,C6H5Na3O7·2H2O12g/L, H3BO330g/L, NiSO4·6H2O1.6g/L, NaH2PO2·H2O36g/L, pH8.5andtemperature70℃. The basic condition and parameters areoptimized through single-factorexperiment, considering the copper quality, adhesive strength and bath stability as criteria, wherethe NiSO4·6H2O, CuSO4·5H2O/C6H5Na3O7·2H2O, NaH2PO2·H2O, H3BO3, pH and temperatureare1.4g/L,11:19.25,36g/L,30g/L,9.0and70℃, respectively. Uner optimum conditions, the maintest result of copper layer on PMMA surface is followed as: resistance50~60mΩ/sq, adhesive grade2~3, deposition rate6.5~7μm/h.The deposition rate under different nickel sulfate, copper sulfate, sodium citrate, sodiumhypophosphite concentration, pH and temperature are measured when other factors are taken asconstant. The kinetic equation of copper plating using sodium hypophosphite as reducing agentis obtained by regression analysis.After that, the effects of thiourea, potassium ferrocyanide and PEG6000on electrolesscopper plating are studied. The result shows that the deposition rate decreases firstly and thenascends with the thiourea concentration increasing, also the copper layer micro-morphology isameliorated when the number of spherical grain increases. The layer element is not obviouslyaffected by thiourea. The growth of (111) crystal face is promoted and inhibited when theconcentration is below and above0.5ppm, respectively.It is likely that potassium ferrocyanide can reduce copper deposition rate obviously anddesend the aggregation of copper particle on PMMA surface thereby improving the metal gloss.The growth of (111) crystal face can be promoted in improving the potassium ferrocyanideconcentration. It is believed that the whole reaction process is controlled by inhibiting cathodicpolarization.The compactness and conductivity of copper layer can grow when the PEG6000is between10and15ppm, while the concentration is above20ppm, copper layer will be discontinuous due tothe too low deposition rate. The micromorphology of copper layer obtained from available PEG6000concentration can be ameliorated although the nickel content would be increased. There is nobig influence on the crystal face growth under different PEG6000concentration.The quality of copper layer can be improved when thiourea, potassium ferrocyanide and PEG6000in bath are0.5ppm,4ppm and10ppm, respectively, at which the resistance can go down to40~45mΩ/sq, the adhesive strength is up to1~2grade and the color of layer will change fromdark brown to copper red.Nickel electroplating is carried out on PMMA surface after copper electroless plating. Theeffects of nickel sulfate, pH, temperature and current density on layer quality, current efficiancyand bath electrochemistry properties are studied through orthogonal and single factor experiment,leading to optimum condition for this system shown as below, NiSO4·6H2O180g/L, NiCl260g/L,H3BO360g/L, pH5~5.5, temperature60℃, current density3~4A/dm2.Adding thiourea and cumarin into bath can improve nickel layer quality, since thiourea canrefine the crystal grain, while too high thiourea concentration will cause excessive cathodicpolarization which reduces deposition rate and current efficiency and leads to flaws like bubble and pinhole on layer surface. Therefore, the thiourea concentration is chosen at2~3mg/L.Relatively low courmin concentration (10mg/L) is likely to reduce cathodic polarizationthereby increasing deposition rate and current efficiency. However, with this courminconcentration, the nickel layer will be cracked and cannot be used in industry. The cathodicpolarization increases and the refinement of crystal grain appears during the process of addingthe courmin continuously, while the current efficiency will go down to some extent. After acomprehensive consideration, the courmin concentration is selected at20~30mg/L to obtainbetter nickel layer.Since the single additive cannot achieve the optimization between layer quality and currentefficiency. Therefore, it is necessary to develop novel complex additives to ameloraite the layerquality and bath properties simultaneously.