초임계 CO2를 이용한 copper의 nickel 전해도금

박지영, 이윤우, 김재덕, 이창하*, 임종성

한국과학기술연구원 국가지정 초임계유체 연구실, 연세대학교 화학공학과*

Electroplating of nickel on copper substrates in supercritical CO2

Ji-Young Park, Youn Woo Lee, Jae-Duck Kim, Chang-Ha Lee,* Jong Sung Lim

National Research Lab. for Supercritical Fluid, KIST

Dept. of Chem. Eng., Yonsei University*

Introduction

Electroplating is employed in industry to improve the appearance of surfaces, to give the good corrosion protection on the substrate, to improve the wear resistance by hard facing of the relatively soft substrate, and sometimes to provide the good electrical and thermal contact. In plating process, acid and alkali aqueous solutions, a cyanide, chromium, heavy metal, corrosive materials, and toxic substances were used, the pollution of working environment raised because of waste water. Since the latter half of 1990's, the research about the effective method to treat the waste water were began centering around industries and research organizations. By this tendency, cleaning techniques were required in plating technology in domestic plating industries and for that reason, the current equipment are in need of changing into the environmental friendly-technical installations.

In this paper, we offer the new idea, the technology to reduce the plating solution by using sc CO2. This is the method that the plating solution in sc CO2 emulsion using fluorinated analogues of AOT with the 'CO2 philic' tail and the 'hydrophilic' group[1] was formed and Ni in this emulsion have deposit in Cu substrate. This process has advantages of the high speed-plating, the plating in detail and the reduction of plating solution. Prior to achieving this study, Ni electroplating on Cu plate in solution composed of CO2 and plating solution was practiced. This electroplating by the new technology was result in reducing the plating solution (1/4~1/7times). Quality value of plated ware evaluated by using the plating thickness, corrosion resistance, uniform on surface of plated ware, and efficiency of plating. We are trying to develop the quality of plated ware and more detailed study is now in progress.

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

Experimental

Chemicals Nickel chloride (NiCl2□6H2O), nickel sulfate (NiSO4□6H2O), boric acid (H3BO3), carrier, brighter, antipitting agent, and water were prepared for the nickel plating solution and supplied from Incheon chemical Co.

Composition of nickel plating solution NiCl2□6H2O of 50g, NiSO4□6H2O of 200g, H3BO3 of 50g, carrier of 10ml, brighter of 2ml, antipitting agent of 1ml per H2O of 1000ml. Nickel sulfate (NiSO4□6H2O) is the principal source of nickel ions, nickel chloride (NiCl2□6H2O) improves anode dissolution and increases solution conductivity, and boric acid (H3BO3) helps to produce smoother and more ductile deposits [1].

		□		Pretreatment
		□	- Solvent cleaning - Pickling - Neutralization. - Washing
		Electroplating baths
		□
		Plating bath in supercritical CO2
		□		After treatment
		Electroplating of nickel Ni+2 +e+2□Ni [2]	□	- Washing & Drying
		- 2A, 5min		□
				Plated ware
Figure 1. Electroplating process of Nickel in supercritical CO2

Experimental procedure The experimental procedure of the nickel electroplating on copper was represented as follows. The copper plate was prepared after getting rid of impurities by using pretreatment agent (PC-732 10% aqueous solution). A newly designed high-pressure view-reactor equipped with a nickel anode and a copper cathode was manufactured. CO2 was introduced into the cell. The temperature of the entire system was maintained constantly by controlling the temperature of the air bath. When the desired temperature was attained, plating solution was introduced by using the high pressure pump. Plating solution in CO2 was mixed by magnetic stirrer. Electroplating temperature was 50oC and the pressure was 15.10 MPa and constant current of 200 mA was supplied for 5 min.  After electroplating, the copper plate plated with nickel was taken out the cell and washed, and dried completely. (electroplating in atmospheric condition was the same as supercritical condition and the experimental procedure was omitted)

Figure  2. The schematic apparatus for electroplating in sc CO2

Quality valuation of plated ware  The quality of plated wares in supercritical CO2 and atmospheric condition was evaluated by using three items such as 1) thickness measurement (SEICO instrument, SFT 720, X-Ray Fluorescence spectrometer, XRF), 2) uniform evaluation on nickel surface by SEM photographing, 3) corrosion resistance by CASS method. These results were shown in Table 1, and Fig. 3 (a~d).

Results and discussion

Nickel weight plaed Under ideal conditions, 0.2 A flowing for 5min will deposit 0.01824g (=(0.2A□300sec/96,500)?(58.7/2)), 1.0944g/A□hr [3]. The quality valuation of plated ware was estimated as follows.

The surface uniformity The surface of nickel on copper was observed by the analysis of SEM in detail (10,000 magnificace). The minute particles were distributed uniformly on surface plated in sc CO2, and the thick particles were distributed on surface plated in atmospheric condition without CO2 relatively, In case of surface plated uniformly, it is known that the properties such as ductility, hardness, and corrosion resistance is good,

The surface thickness The thickness of surface plated was measured by using X-Ray Fluorescence spectrometer (XRF) which didn't break the sample in accordance with the Korean Standard (KS D 0246). the surface plated in atmospheric condition was 1.097 times as thick as that in sc CO2 condition. This result was shown in Table 2.

The corrosion resistance The corrosion resistance was measured by using CASS method in accordance with the Korean Standard (KS D 8334). Both two nickel plated began to corrode after 24hrs. Although the thickness plated in sc condition was thinner than that in atmospheric condition, it was less corrosive than that. When we consider various things such as uniformity, hardness, ductility, and corrosion resistance, synthetically, the plating in sc CO2 is better than the plating in 1atm without CO2.

Conclusion

In this paper, the nickel electroplating on copper plate by using the new idea, the technology to reduce the plating solution was offered. The plating solution was reduced to one-fourth by this method. The plated ware plated in this condition has good quality in uniformity, hardness, ductility, and corrosion resistance. This research is will be up to the expectation of a great help for reducing the waste water in plating process. Now, we are trying to develop the quality of plated ware and more detailed study is now in progress.

Table. 1 Results of Nickel plating

plating solution (□)	T(oC)	P(MPa)	time (min)	current (□)	thickness (□)
atmospheric condition, P=0.1 MPa
80ml	50	0.1013	5	200	18.88
supercritical condition, T(oC)= , P=0.1 MPa
20ml	50	1.521	5	200	17.21

Acknowledgement

This work has been supported by the National Research Laboratory Program for Supercritical Fluid and the authors would like to thank to the Ministry of Science and Technology, Korea.

Literature Cited

1. K. Harison, J. Goveas, K. P. Johnston, et al, Langmuir, 10, 3536, 1994.

2. Y. C. Roh, J. of Korea Ind & Eng. Chemistry, 10 (1), 67, 1999

3. L. S. Oh, Y. H. Bai, a collection of learned papers (Pukyung Univ.), 2 (2), 379.