Research On Improving The Stability And Deposition Rate Of Electroless Copper Plating

This dissertation focuses on the problem of low deposition rate and stability inelectroless copper plating, and the effects of composition and operating paraments ofelectroless copper plating on the stability and deposition rate were studied in order toacquire a bath with high stability and deposition rate.Deposition rate was measured by gravimetric method and factors affecting thedeposition rate were studied, it showed that among factors of concentration offormaldehyde, types of complexing agent, concentration of complexing agent andtemperature, the main factors affecting the deposition rate were types of complexingagent and temperature. Electrochemical method was employed to characterize thedissociation rate of complexes of Cu2+with triethanolamine, Quadrol, and EDTA, theresults showed that the deposition rate was related to the dissociation rate of thecomplex and the deposition rate as a function of complexing agent increased in theorder: triethanolamine, Quadrol, EDTA. The stability of electroless copper bath wascharacterized using acceleration experiment of PdCl2, and the results showed that mainfactors affercing stability were concentration of formaldehyde and temperature.In order to improve the stability of electroless copper bath, the plating experimentat high temperature and loadage was used to select stabilizer from different additivesand four stabilizers:2-mercaptobenzothiazole （2-MBT）, thiourea, tween-60and asulfur-containing compounds were confirmed. The deposition rate and stability werecharacterizeed using gravimetric method and acceleration experiment of PdCl2,respectively. And the effects of concentration of each stabilizer on deposition rate andstability were studied and the appropriate concentration of these stabilizers were:thiourea5-7mg/L, tween-6040-50mg/L,2-MBT0.5-1mg/L, sulfur-containingcompounds5mg/L. The appearance and surface morphology of the coating werecharacterized using metalloscope and scanning electron microscope and the adhensionwas measured, the results showed that bath with sulfur-containing compounds or2-MBT could acquire bright and smooth coating while that with thiourea or tween-60were dark and rough, the size of coating particle increased in the order:sulfur-containing compounds<tween-60<2-MBT, and the adhension of coating acquiredfrom bath with any of the four stabilizers could meet the standards. The elements of thecoating were measured using energy dispersive spectrometer （EDS） and the resultsindicated that sulfur-containing compounds, thiourea and2-MBT were included in thecoating while dipyridyl couldn’t be included and tween-60could lead to the inclusion ofdipyridyl. Linea sweep voltammetry （LSV） and Electrochemical impedance spectroscopy （EIS） were employed to study the mechanism of additives, whichindicated that the effect of dipyridyl and tween-60were attributed to surface adsorption,sulfur-containing compounds was attributed to complexing with Cu （I） and thiourea wasattributed to surface adsorption and complexing with Cu （I）.The bath was optimized and a bath （KHT-1） with high deposition rate and stabilitywas finally acquired, the composition of KHT-1bath was:12g/L CuSO₄·5H₂O,10ml/Lformaldehyde,8.928g/L EDTA,12.6ml/L Quadrol,10mg/L dipyridyl,5mg/Lsulfur-containing compounds,20mg/L tween-60and0.5mg/L2-MBT. Improvementshad been obtained on deposition rate, stability and adhension compared with thecommercial bath IMT-8760, however, it should be recognized that the brightness, sizeof particle and the content of copper were all less inferior than that of IMT-8760.