INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

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1 INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) Internatonal Journal of Advanced Research n Engneerng and Technology (IJARET), ISSN (Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME ISSN (Prnt) ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME: Journal Impact Factor (0): 7.87 (Calculated by GISI) IJARET I A E M E APPLICATION OF BO-WILSON EPERIMENTAL DESIGN METHOD FOR ELECTROLESS COPPER PLATING Hameed Hussen Alwan Electrochemcal Engneerng Dept. / College of Engneerng / Babylon Unversty /Iraq ABSTRACT In ths study, electroless copper platng was done by used Box-wlson expermental desgn as expermental desgn method to fnd the effect of most controllable varables on electroless copper platng process. To study these effect four varables were consdered as most domnate varables. These varable are; Formaln concentraton n rang M, CuSO concentraton n rang M, temperature n rang 0-70 C and, ph soluton n rang -. These four varables are manpulated through expermental work by usng Box-wlson expermental desgn by proposed second order polynomal model to correlate the studed effect of these varables on deposted copper layer thckness. The predcated models are found after analyzng statstcally as follows: y = Where y s the deposted copper layer thckness, formaln concentraton, CuSO concentraton, temperature and, soluton ph. The study shows that formaln and CuSO concentratons have great sgnfcance effect on the deposted copper layer thckness whle the temperature and ph soluton have small dependence on layer thckness. Optmum condtons for gettng the maxmum deposted copper layer thckness are obtaned by usng optmzaton method on the above model. Keywords: Electroless Platng, Copper, Box-Wlson Expermental Desgn. 6

2 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME INTRODUCTION Electroless deposton of metals and alloys has a very sgnfcant practcal mportance n modern technology especally n the producton of new materals for applcatons n electroncs, wear and corroson resstant materals, medcal devces, battery technologes, etc. All solutons for electroless metal deposton have many smlartes, but dependng on the metal or alloy to be deposted, there are also some dfferences. Typcally, the consttuents of a soluton for electroless metal deposton are; source of metal ons, complexng agent, reducng agents, stablzed and nhbtor.e.electroless copper deposton, CuSo s used manly as the source of copper ons. [] Electroless platng s a wet chemcal platng technque utlzed by semconductor ndustry to depost thn flms of metal or metal alloy over a substrate durng fabrcaton or packagng of semconductor devces. Electroless platng can be accomplshed wth relatvely low cost toolng and materals as compared to electroplatng. Further, Electroless platng s selectve, provdes excellent step coverage and good fllng capabltes. [] Electroless copper platng nvolves the reducton of copper ons to copper metal from soluton contan copper ons.e. CuSO and the surface catalyzed oxdaton of a reducng agent. These processes are wdely used n the fabrcaton of prnted crcut boards due to ther conformal deposton, low cost, and smple equpmental setup. Commercal electroless copper platng solutons often use formaldehyde or ts dervatves as reducng agents because of ther hgh deposton rate and the excellent mechancal propertes of the copper deposts []. The complexng agent such as ethylene damnetetra acetc acd EDTA, a reducng agent such as formaln and ph adjustng agent such as alkal hydroxde as man components. [] The soluton ph s a very mportant factor n the electroless deposton, ndeed, t affects both anodc and cathodc reactons and varous phenomena assocated wth the structure and composton of the metal-soluton nterphase. The platng rate ncreases remarkably when the soluton ph ncreases[]. MchnarSone et.al show that deposton rate ncreased wth an ncrease n ph, fne copper partcles were generated, and the stablty of the bath decreased at a ph greater than 6.5. As the bath temperature ncreased, the deposton rate ncreased up to 50 C, but partcles were formed n the bath. [5] In ths study, the Box-Wlson expermental desgn method was used n order to nvestgate the effects of mportant controllable varables on copper electroless platng. The expermental desgn s a response surface methodology used to evoluton the dependent varable (thckness of copper deposted) as a functon of ndependent varables (CuSO concentraton, Formaln concentraton, ph soluton and Temperature). Optmum condtons for achevng the maxmum flm thckness deposted are obtan from optmzng the correlaton. EPERIMENTAL WORK Materal Carbon steel (00 mm long x 50 mm wde x mm thckness) as a substrate plate. Chemcals CuSO as a copper ons source, Formaln as reducng agent, EDTA as complexng agent and NaOH for ph adjustng. Procedure The substrate was mechancally polshed down 00 by emerypaper, dpped nto 5% NaOH soluton at 60 C for 5 mnutes, rnsed wth water and dpped n 5% HCl soluton at room 7

3 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME temperature for mnutes and, after that the substrate was dpped n the electroless platng soluton (CuSO, Formaln, EDTA and NaOH) the soluton composton was prepare accordng to the experment desgn. The substrate was weghted before and after mmerson n a soluton, the soluton temperature was adjusted to desred value and for requred tme. The thckness of copper deposted thckness calculated by below equaton: Y ( W = W ) 0 Sρ () Where Y= coatng thckness n mcron (µm). W = weght of a specmen before mpressed n soluton n gram W = weght of a specmen after mpressed n soluton n gram. S = surface area n dm. ρ = densty n g / cm Box-wlson experment desgn Box-wlson desgn s a response surface methodology RSM, and emprcal modelng technque, devoted to the evaluaton of relatonshp of a set of controlled expermental factors and observed results, the optmzaton process nvolves three step ;statstcal desgn experment, estmate coeffcent for mathematcal model, and predctng the response [6]. Response surface methodology or (RSM) s a collecton of mathematcal and statstcal technques useful for analyzng problems where several ndependent varables nfluence a dependent varable or response, and the goal s to optmze ths response,. And q denote the ndependent varable that are contnues and controllable by the expermenter wth neglgble error. [7-8] The operatng parameters: concentraton of reducton agent formaln ( ), copper on concentraton ( ), operatng temperature ( ), and soluton ph ( ). The response s the thckness of copper deposted layer (y).for four varables the quadratc polynomal equaton can be represented as follows: y b 9 q q q = bo + = b + = b + j y = b o 0 b 5 j 6 () 7 8 () Where y s the predcated copper layer thckness (µm) b 0 constant, b, b, b and, b lnear coeffcents, b 5, b 6, b 7 and b 8 quadratc coeffcents, b 9, b 0, b, b, b and, b cross-product coeffcents. q, number of varables and n ths case are q =. 8

4 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME A prelmnary step s to set up between coded level and the correspondng real varables whch are requred to determne the expermental range by the followng equaton: coded = real cen cen mn () q The number of expermental run requred to cover range for four varables n ths case. N N = = q + q = 8 (5) (6) The coded varables tae values between - and, and accordng to these values the range of real varables for the system can be represented n tables() and (). Table (): The expermental range of varables Reducton agent concentraton (M) Copper sulfate concentraton (M) Temperature ( C) ph Table (): Relatonshp between coded and real varables Varables Levels,,, =Reducton agent concentraton (M) =Copper sulfate concentraton (M) =Temperature( C) =ph.5.5 9

5 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME Table (): expermental desgn condton accordng to a Box-Wlson experment desgn wth four ndependent varables coded real x x x x Formaln CuSO Temp. Conc. M Conc. M C ph RESULTS AND DISCUSSION Table - shows the expermental data (observed practcally) and predcated (Calculated by software) values of the thckness of copper layer plated, the expermental results were modeled usng a STATISTIC software Ver.5.5A, regresson analyss to determne the coeffcents of response model (equaton ). The calculated coeffcents lsted n table 5. The determnaton coeffcent between the observed and predcated values was estmated of second order polynomal regresson by usng, the number of teratons was termnated when the proporton of varance accounted for was (99.87%) and the correlaton factor R was equal (0.9997). 50

6 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME Table (): Expermental data and predcated values of the thckness of copper layer plated coded x x x x Formaln concentrato n (M) real Copper sulfate concentrato n (M) Temp. Observed Expermenta l Thckness Y. Predcted thckness y Resdual E=Y-y C ph 5

7 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME Table 5: Coeffcents for the response functon Coeffcent. B 0 B B B B B 5 B 6 B 7 Value Coeffcent. B 8 B 9 B 0 B B B B Value Correlaton Coeffcent R Varance explaned % 99.87% Correlaton the four varables wth deposted copper layer thckness, the followng response was obtaned y = (7) For determnaton the sgnfcance of parameters n the above model, table () clearly shows Y (observed expermentally value) and y (predcated value by model) and ts possble to compute the resdual value as E = y - Y (8) E Value whch are tabulated n the last column n table (), ths can be used to calculate E. An estmate of the expermental error varance Sr whch calculated as followng: γ = 8 5 = 8 5 n number of model coeefcents S s number of = the expermats ΣE r = = γ The estmated varance of coeffcents under nomenclature followng formula: Sb was calculated by the S b = S r (9) Where represents the sum of square of the correspondng elements of varable 5

8 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME Table 6: F-test results for the mathematcal model coeffcents Coeffcent. B B Varance Sb =Sr / F value =B /Sb F 0.95 (,)=,6 B S * B S B S B S B S B S B S B S B E NS ** B E NS B E NS B -.E E E-07 NS B -.E E E-07 NS B -.E E E-07 NS *Sgnfcant ** non-sgnfcant The F-test applcaton lead to change the equaton () to below equaton (0) after we canceled the non-sgnfcant coeffcents y = (0) Accordng to equaton (0) and by usng Hook & Jeeves pattern [9], the optmum condtons were obtaned.the optmum condton of studed varables n coded and real form are lsted n table (7). Table 7: optmum condtons n coded and real values Varables coded Optmum Real = Formaln concentraton (M) M = Copper sulfate concentraton (M) M = Temperature ( C) C = ph.67. 5

9 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME.00 Copper layer Thkness( µm) Reducton on Conc. (M) Fgure (): shows the effect of reducton on concentraton (formaln) on the deposted copper layer thckness.50 Copper layer Thcness (µm) Copper on Conc. (M) Fgure (): shows the effect of CuSO concentraton on the deposted copper layer thckness Dumesc et al. [0] usng formaldehyde as a reducng agent he was reported that an ncrease n the formaldehyde concentraton from 0.0 to leads to a lnear ncrease n the ntal deposton, and ths s agree wth fgure (). The overall reacton for electroless copper deposton, wth formaldehyde (HCHO) as the reducng agent, s; Cu + + HCHO + OH - = Cu + HCOO - +H O+H () The effect of copper ons concentraton on copper deposted layer thckness s shown n fgure (); there are hgh rate n ncreasng of copper deposted layer thckness through ncreasng n CuSO concentraton, and ths come from the fact that CuSO represent the copper ons source, whch has ablty to depost under the expermental condtons. 5

10 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME.00 Copper Layer Thcness (µm) Temperture ( C ) Fgure (): shows the effect of soluton temperature on the deposted copper layer thckness Copper Layer Thcness (µm) ph soluton Fgure (): shows the effect of soluton ph on the deposted copper layer thckness Electroless copper deposton s affected by the ph n two dstnct ways. Frst, OH - ons are reactants n the overall reacton (equaton ) and the below partal anodc reacton. Hydrolyss of Formaln: H CO + H O H C (OH) () H C (OH) + OH - H C(OH)O - +H O () H C(OH)O - [HC(OH)O - ] ads +H ads () Where the subscrpt ads denote adsorpton of speces and [HC(OH) O - ] ads s electroactve speces. Charge transfer, the electrochemcal oxdaton (desorpton)of electroactve speces, proceeds accordng to the reacton. [HC(OH)O - ] ads + OH - HCOO - +H O + e (5) Thus nfluence these reactons n a drect way (prmary ph effects).second, ph affects varous phenomena assocated wth the structure and composton of the metal soluton nterphase. 55

11 680(Prnt), ISSN (Onlne) Volume 5, Issue, Aprl (0), pp IAEME All these phenomena modulate the rate of electroless copper deposton n an ndrect way (secondaryph effects). CONCLUSIONS The Box-Wlson statstcal expermental desgn procedure was seen to be applcable n modelng to evaluate the effect of mportant varables on copper electroless platng. The second order polynomal regresson analyss of response y (deposted copper layer thckness) n term of four varables (.e. concentraton of reducton agent formaln ( ), copper on concentraton ( ), operatng temperature ( ), and soluton ph ( ) gves equaton (0) whch adequately descrbes the behavor of the electroless copper platng through studed range. The optmum condtons as predcated s concentraton of reducton agent formaln (0.5 M), copper on concentraton (0.059 M), operatng temperature (66. C), and soluton ph (.). The deposted copper layer thckness ncreasng wth ncreased n all four varables, these ncreasng contnue untl they reached to the optmum pont and full down. ACKNOWLEDGMENTS The author would lke to thank the Electrochemcal Engneerng Department at Babylon Unversty for supportng and approvng ths research. REFERENCES [] Klen et al., Electroless Platng Bath Composton and Method of Use, US patent B, Mar. 0, 00. [] Jun L and Paul A. Kohl. The Acceleraton of Nonformaldehyde Electroless Copper Platng, Journal of the Electrochemcal Socety, 9 () C6-C66 (00). [] Morshata et al. Electroless copper soluton, US patent 09997, Jul., 987. [] T. Ank et al. Influence of ph Soluton on Electroless Copper Platng Usng Sodum Hypophosphte as Reducng Agent, Int. J. Electrochem. Sc., 7 (0) [5] MchnarSone et.al, Electroless copper platng usng FeII as a reducng agent, ElectrochmcaActa 9 (00) 8. [6] Zvorad R. Lazc, Desgn of Experments n Chemcal Engneerng, Wley-VCH VerlagGmbh& Co. KGaA, Germany, 00. [7] Anderson, Chem. Eng. Prog., vol. 55, No., (959) P. 6, Statstcs n the Strategy of Chemcal Experment. [8] Wllam &Gertruds, Expermental Desgn, John Wley & Sons, Inc., London, (956). [9] Jeffwn and Hamada, Experments; Plannng, Analyss, John-Wley and sons, New York, 000. [0] J. Dumesc, The Rate of Electroless Copper Deposton by Formaldehyde Reducton, J. Electrochem. Soc., (97) 05. [] Hameed Hussen Alwan, Adsorpton Mechansm for Corroson Inhbton of Carbon Steel on HCl Soluton by Ampclln Sodum Salt, Internatonal Journal of Advanced Research n Engneerng & Technology (IJARET), Volume, Issue 7, 0, pp. 6-6, ISSN Prnt: , ISSN Onlne: