Surface & Coatings Technology 206 (2011) 1382–1388

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Surface & Coatings Technology

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A novel surface activation method for Ni/Au electroless plating ofacrylonitrile–butadiene–styrene

Xuejiao Tang a,⁎, Jingang Wang b, Chengjun Wang c, Boxiong Shen a

a College of Environmental Science & Engineering, Nankai University, Tianjin, 300071, PR Chinab Engineering Research Center of Seawater Utilization Technology, Ministry of Education, Hebei University of Technology, Tianjin, 300130, PR Chinac College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang, 325035, PR China

⁎ Corresponding author. Tel.: +86 2223503219; fax:E-mail address: tangxuejiao@163.com (X. Tang).

0257-8972/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.surfcoat.2011.08.064

a b s t r a c t

a r t i c l e i n f o

Article history:Received 18 November 2010Accepted in revised form 31 August 2011Available online 7 September 2011

Keywords:Surface activationAutocatalysisNon-cyanide electroless platingInterfacial reaction

Direct electroless metallization on acrylonitrile–butadiene–styrene (ABS) plastic with Pd-free activationmethod could reduce the cost of production. A novel surface activation method with the immobilization ofNi(0) nanoparticles by chitosan (CTS) film on ABS and then the deposition of Ni and Au on ABS were inves-tigated in this paper. X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FTIR) spectra andscanning electron microscopy (SEM) data revealed the related interfacial reaction mechanism in activationprocess. The Ni(0) nanoparticles immobilized by the CTS films were effective auto-catalysts in the nickel elec-troless plating process. The formations of Ni plating layers at different deposition time were observed by SEM.The x-ray diffraction (XRD) patterns revealed the Ni layer at 30 min was in an amorphous phase. Au was suc-cessfully plated on the Ni layers in a new, stable non-cyanide Au electroless plating bath with different reduc-ing agents. The chemical compositions of Ni/Au layers were analyzed by inductive couple plasmas (ICP) andion chromatography (IC) measurements. Inorganic element (P or S) from reducing agents made the surfacemorphology of Au layers different in SEM images. However, they did not change the Au crystallization phaseat all based on XRD patterns.

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1. Introduction

The engineering plastics have vast applications in electronic products.Demands for direct metallization on non-conducting plastics have beenvigorously increasing. In electroless plating, metallization can be carriedout evenly on non-conducting substrates. Electroless plating is consid-ered the most effective and promising metallization method.

The immobilization of catalysts for the activation procedure plays animportant role in metal electroless plating. The catalysts promote theoxidation of the reducing agent in the plating bath to initiate metal de-position onto the substrate. This step is the key point and can directlyaffect the quality of the plating layers. Many methods for activatingnon-conducting substrates have been developed [1–6]. A classic oneis the sensitization–activation method, wherein substrates aredipped in stannous chloride and palladium chloride solution. Metal-lic palladium [Pd(0)] clusters form on the surface and catalyze thesubsequent electroless plating [7,8]. However, Pd(0) catalysts aremainly immobilized on the substrate surface by physical adsorption.Complex processes and excessive noble metal waste add to thisproblem. Over the last few years, many studies have been devotedto methods of Pd(0) particle deposition such as spinning-on,

spraying, or dip-coating of organopalladium and inducing decompo-sition of them by ultraviolet–visible light, infrared, or laser [9–11].Direct electroless metallization of an insulating substrate (polymers,glasses, or ceramics) without first seeding the surface with Pd(0)catalytic clusters is an interesting challenge. Such a technique willreduce the cost of the metallization process.

Nickel (Ni), which is relatively less expensive than noble metals, wasused as auto-catalysts for Ni electroless plating in our previous studies.The successful results simultaneously resolved problems of conventionalactivation methods (such as complex processes and excessive noblemetal wastage). It was also found that CTS films had a good prospectfor immobilizing Ni catalysts onto the ABS substrate in the activationprocess for nickel electroless plating. These findings were very interest-ing and published in short and quick communications [12,13]. However,systematical work is required for reproducibility and the interfacial reac-tion mechanism needs to be verified by other analytical tools. Further-more, it is an interesting topic to observe the morphology of Ni layersat different deposition time and investigate the formation of Ni layers.

The deposition of Au on Ni layers was widely used in electronicproducts industry. Cyanide gold electroless plating on a Ni-platinglayer has long been utilized for the surface interconnection of electronicproducts. Considering safety and environmental concerns, cyanide-freeplating is a better choice and is strongly in demand now. Thiosulfate isone of the best ligand candidates, with its high stability constant andstrong chemical bonding force. It may be able to replace cyanide with

Table 1Composition and plating condition of nickel electroless plating solution.

Component Concentration(g/L)

Ni2+ 6Sodium hypophosphite 23Sodium citrate 20Triethanolamine 22Ammonium chloride 15Coumarin 0.03T 40±2 °CpH 8.5–9.5

1383X. Tang et al. / Surface & Coatings Technology 206 (2011) 1382–1388

the assistance of other stabilizers. However, the stability constant of Au(I) thiosulfate complexes is in the order 1026, which is still 1010 timesless than that of Au(I) cyanide complexes (1036) [14]. Inoue et al. [15]developed stable non-cyanide electroless gold (Au) plating bathsusing thiosulfate as the primary ligand, sulfite as the secondary ligand,thiourea as the reducing agent, and hydroquinone as the reducingagent regenerator. Although a soft, good quality Au layer was obtained,one of the stabilizers used (hydroquinone) is also a toxic compound.

To avoid such toxic compounds, a new and safe non-cyanide elec-troless Au plating bath was proposed in the present study. This plat-ing bath was also used to study the effects of reducing agents onthe Au plating layer. Monovalent Au ion (gold source) was stabilizedby thiosulfate and sulfite ligands, instead of the conventional toxic cy-anide. Sodium hypophosphite (NaH2PO2) was used as the reducingagent and sodium citrate as the stabilizer. The Au deposition immedi-ately started when the Ni-plating ABS foil was dipped into the new Auplating bath. The immobilization of Ni as catalyst sites by CTS filmformed on the ABS for Ni electroless deposition was studied. The for-mation of Ni/Au electroless plating layers was observed by scanningelectron microscopy (SEM). The components on the substrate surfaceafter etching and activation were investigated by x-ray photoelectronspectroscopy (XPS), and the related interfacial reaction mechanismwas discussed. The phase structures of the obtained Ni and Au layerswere characterized by x-ray diffraction (XRD).

2. Materials and methods

2.1. Materials

Chitosan (CTS; deacetyl degree ~92%) was purchased as industrialgrade powder from Xiamen Sanland Chemical Agents, Ltd. All otherchemicals used were of analytical grade.

2.2. Methods

2.2.1. Pretreatment procedures: etching and activatingAn etching procedure was employed to make the ABS foil surfaces

rough and hydrophilic. Traditionally, heavily polluting coarsing solu-tions, such as chromium-based ones, are used. In the present study,the etching was performed by dipping the foils in a mixed solutionof 1:4 hydrogen peroxide (H2O2; 30%) and sulfuric acid (H2SO4;98%) at room temperature [16]. The effects of etching time on ABSmorphology were studied, and 5 min was chosen as the most optimalfor the procedure.

After rinsing, the etched foils were dipped into 1% acetic acid so-lution containing 15 g/L CTS for 5 min at room temperature, andwere then dried at 60 °C for 15 min. These foils were denoted asABS–CTS. The ABS–CTS foils were immersed in nickel sulfate solution(NiSO4∙6H2O; 2.0 g/L) at 40 °C for 10 min. After rinsing, the foilswere dipped in a solution of potassium borohydride (KBH4; 3.0 g/L)at 40 °C for 5 min of reduction. ABS–CTS–Ni was then obtained.

A comparative study without the CTS film formation procedure wasalso carried out. The etched foils were directly dipped into the nickelsulfate solution, andwere then reduced by KBH4 under the same condi-tions as above. The obtained sample was denoted as ABS–Ni.

2.2.2. Electroless platingThe electrolessNi platingwas achieved by dipping the pre-nucleated

foils (ABS–CTS–Ni and ABS–Ni) into a solution containing sodium cit-rate (as chelating agent), sodium hypophosphite (as reducing agent),triethanolamine (as masking agent), ammonium chloride (as buffer),and coumarin (as stabilizer). The composition and deposition condi-tions of the NiP plating solution are given in Table 1.

The electroless Au deposition was achieved by dipping the rinsedNi-plating ABS foils into a solution containing thiosulfate and sulfiteligands (as chelating agents), sodium hypophosphite (as reducing

agent), and sodium citrate (as stabilizer). The stable non-cyanidegold plating solution is shown in Table 2, and the obtained Au platinglayer was denoted as Au–P. Another set of Ni-plated ABS foils weredipped into another Au electroless plating solution in which sodiumhypophosphite was replaced with thiourea as the reducing reagent.The corresponding layer was denoted as Au–S. Both of the depositiontimes were 15 min.

2.2.3. Surface characterizationThe chemical compositions of the foil surfaces and the chemical

reactions during the pretreatment procedure (etching and activating)were investigated by XPS and specular reflection Fourier transforma-tion infrared (FTIR) spectroscopy.

XPS spectra were recorded using a Kratos Axis Ultra DLD spec-trometer (UK) and employed with a monochromated Al-Kα x-raysource (hv=1486.6 eV), hybrid (magnetic/electrostatic) optics, aswell as a multi-channel plate and delay line detector.

Specular reflection FTIR spectra were recorded with a NicoletMAGNA-560 FT-IR spectrometer (USA) with a reflection angle of 30°.

The surface topographies of the etched ABS and the different layerswere characterized with a scanning electron microscope (SEM:SS-550,Shimadzu Corporation, Kyoto, Japan) at an accelerating voltage of 10 kV,using the secondary electron signal. The working distances are respec-tively shown in SEM surface micrographs (Figs.3–6).

XRDmeasurements of the deposited layersweremadewith a RigakuD/max-2500 18 KW powder diffractometer (Japan) using Cu-Kα radia-tion generated at 40 kV and 100 mA, and a scanning rate of 0.13 deg/s.

Chemical composition analysis of the deposited layers was performedon an ICP-9000 instrument (U.S.A. Thermo Jarrell-Ash Corporation) andDX-500 ion chromatograph (U.S.A. Dionex Corporation) equipped witha suppressed anion conductivity detector and IonPac AS20 column.

3. Results and discussion

3.1. XPS

The XPS spectra of CTS, etched ABS, and ABS–CTS–Ni are shown inFig. 1a–d.

As shown in Fig. 1a, the S2p3/2 photoelectron spectrum peak wasobserved at a binding energy of 168.7 eV for etched ABS. This peakcorresponds to the peak position of H–O–S(O2)–C6H4 [17] and wasdifferent from those of NiSO4 (169.2 eV) [18] and H2SO4 (169.6 eV)[19]. The sulfonic acid group [H\O\S(O2)\C6H4\] was introducedby the electrophilic aromatic substitution reaction of the phenylring from the ABS substrate during the etching treatment in H2SO4 so-lution. The etching time was very short to avoid over-roughness. Thechemical reaction occurred only with the functional group on the topsurface of ABS. The signal intensity of the H\O\S(O2)\C6H4\ bondwas not strong enough, and the other small peaks in Fig. 1a corre-spond to background noise.

Drying the CTS film on the ABS surface at 60 °C promoted the reac-tion between the sulfonic acid group and the amino groups (\NH2) ofCTS. New and stable \NH\S(O2)\C6H4\ (S2p3/2 absorption peak at abinding energy of 167.6 eV for ABS–CTS–Ni; Fig. 1b) functional groups

Table 2Composition and plating condition of gold electroless plating solution.

Component Concentration(g/L)

Gold chloride 4.5Sodium thiosulfate 11.2Sodium sulfite 100.0Sodium hypophosphite 10.0Sodium citrate 50.0T 80±2 °CpH 7.8–8.0

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formed. This formation indicated that the etching process could modifythe ABS surface from hydrophobic to hydrophilic. This formation alsoenhanced the adhesive strength between the CTS film and the ABS sub-strate through chemical reactions of their functional groups.

The N1s spectrum absorption peak in ABS–CTS–Ni (407.5 eV;Fig. 1c) was 8.3 eV higher than that of \NH2 in CTS (399.2 eV [20]).Chemical shifts of binding energies in XPS are a displacement effectin the spectrum absorption peaks, which results from changes inthe electron binding energy of atoms in different chemical states[21]. This result indicates that Ni bonded with the isolated electronsof the nitrogen atom. This binding caused the decreased thicknessof the electron clouds around nitrogen atoms and consequentlyshifted the binding energy higher. Therefore, Ni could be successfullyimmobilized on CTS films with higher adhesive strength by chemicalrather than physical adsorption.

In Fig. 1d, two Ni species peaks of Ni2p3/2 appeared in the XPS ofABS–CTS–Ni. The lower peak (at a binding energy of 852.8 eV) corre-sponded to the Ni2p3/2 peak of Ni [22]. The higher peak (at a bindingenergy of 857.8 eV) corresponded to the Ni2p3/2 peak of NiSO4 [23].These results indicate that metallic nickel [Ni(0)] successfully formedon the ABS–CTS–Ni after being reduced by KBH4.

3.2. Specular reflection FTIR

The ABS foils were too hard and thick to be made as thin as a KBrtablet, so traditional transmission infrared spectroscopywas unsuitable

155 160 165 170 175 180

Inte

nsity

168.7(a)

390 395 400 405 410 415

(c)

Inte

nsity

399.1 407.5

Binding Energy (eV)8

Fig. 1. XPS spectra of S2p3/2 photoelectron on the etched ABS surface (a) and S2p3/2 photoeleNi2p3/2 photoelectron on ABS–CTS–Ni surface (d).

for the structural analysis of the ABS surface. Specular reflection FTIRcan overcome the limitations of traditional transmission infrared. Spec-ular reflection FTIR spectra mainly reveal information from the surfaceof the samples.

The FTIR spectra of the unetched ABS, etched ABS, ABS–CTS,ABS–CTS–Ni, ABS–Ni, and CTS are shown in Fig. 2. The reactionsthat occurred during the pretreatment procedure were investigated.

ABS is a copolymer of acrylonitrile, butadiene, and styrene. Hence,the spectra of unetched ABS correspond to these three components.As shown in Fig. 2a, four peaks observed at 1600–1450 cm−1, thepeaks at 712 and 3035 cm−1 are all characteristic adsorption spectraof the phenyl ring [24,25] in styrene. The peaks at 2946 and2862 cm−1 are characteristic of the methylene groups of acrylonitrileand butadiene. The strong peak at 962 cm−1 is characteristic of poly-butadiene [26].

In Fig. 2b, the wider and stronger peak at 3400–2000 cm−1 is theoverlapping peaks of O–H and S–O. The peak appearing at 1381 cm−1

is characteristic of sulfonic acid groups. The weakening of the phenylring peak at 1600–1450 and at 712 cm−1 is also observed in Fig. 2b.These are all in agreement with the results of the XPS analysis thatH–O–S(O2)–C6H4– and –OH were formed on the ABS surfaces by theetching procedure. An electrophilic aromatic substitution reaction ofthe phenyl ring on the ABS surface occurred in the H2SO4 solution.In Fig. 2b, the signals at high wavenumbers were noisier becausethe surfaces were rougher in the etched than in the unetched ABS.Hence, the coarsing process is proven effective.

As mentioned above, specular reflection FTIR spectra mainly re-veal information on the surface of the samples. The characteristic ad-sorption spectrum of the CTS film in Fig. 2c is stronger and itencompasses the spectrum of the ABS substrate. Thus, the spectrumof ABS–CTS (Fig. 2c) was obviously different from that of etchedABS (Fig. 2b). Fig. 2c shows the wide absorption peak at 3400–3200 cm−1, which is the overlapping peak of O–H and N–H in theCTS film. The peaks at 3530 and 1599 cm−1 are the adsorption spec-tra of N–H in CTS. The peak at 1435 cm−1 is that of C–N in CTS. Theprimary hydroxyl group peak of CTS is at 1037 cm−1. All thesepeaks in Fig. 2c are in agreement with the ones in CTS (Fig. 2f), excepthere, the peaks at 1180–1100 cm−1 are stronger than those in CTS,

160 165 170 175

(b) 167.6

30 840 850 860 870 880

(d)

Binding Energy (eV)

852.8 857.8

ctron on ABS–CTS–Ni surface (b) and N1s photoelectron on ABS–CTS–Ni surface(c) and

4000 3500 3000 2500 2000 1500 1000 500

Wave Number / cm-1

a

b

c

d

Tra

nsm

ittan

ce /%

e

f

Fig. 2. FTIR spectra of the surfaces of unetched ABS (a) and etched ABS (b) and ABS–CTS(c) and ABS–CTS–Ni (d) and ABS–Ni (e) and CTS (f).

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due to the S–N and sulfonic esters. Again,\NH\S(O2)\C6H4\ groupformation in ABS–CTS was confirmed.

Compared with the ABS–CTS spectra (Fig. 2c), the peaks of N–H(1599 cm−1) and C–N (1434 cm−1) in the ABS–CTS–Ni (Fig. 2d)spectra both became weaker. The N–H peaks shifted from 3530 to3480 cm−1. Ni was already chemically chelated by the \NH2 groupin the CTS film, which corresponded to the XPS results. The adsorp-tion of the primary hydroxyl group at 1037 cm−1 intensified inABS–CTS–Ni. Involvement of primary hydroxyl groups in the com-plexation of Ni, as suggested above, corresponds to that of previousstudies [27,28]. Moreover, the formation of hydrogen bonds couldalso cause the blue shifting of the N–H and O–H peaks.

To confirm the importance of the CTS film in the pretreatmentprocedure, a comparative study without CTS film formation was per-formed. Specular reflection FTIR spectra of the ABS–Ni (Fig. 2e) showthat the shape of the ABS–Ni spectrumwas almost the same as that ofetched ABS (Fig. 2b). It was indicated that Ni was not adsorbed onto

Fig. 3. SEM photographs of ABS with different etching times. (a) 0 m

the etched ABS surface and the chemical reaction did not occur be-tween Ni and the etched ABS. Therefore, CTS is very important forimmobilizing the Ni catalysts onto the ABS surface.

3.3. SEM

For further investigation, SEM characterization was used to inves-tigate the effect of etching time on ABS morphology. The SEM micro-graphs of unetched ABS, as well as ABS etched for 5, 7, 9, and 11 minare shown in Fig. 3a–e.

As shown in Fig. 3, etching time significantly affects ABS surfacemorphology. The coarseness of the ABS surface is greatly increasedwith increasing etching time. Appropriate roughness strengthensthe adhesion between the CTS film and ABS (Fig. 3b), whereas over-roughing (caused by longer etching times) is not good and mayeven destroy the ABS substrate (Fig. 3e). The etching time of 5 minwas chosen as most appropriate.

To observe the formation process of the Ni/Au layers, the appear-ances of ABS–CTS and ABS–CTS–Ni with different plating times, aswell as the topographies of Au layers were characterized by SEM(Fig. 4a–e).

Fig. 4a shows an even and continuous CTS film formed on the ABSsurface after treatment with the CTS solution. Fig. 4b shows uniformnanosized particles evenly adsorbed onto the CTS film. Based on theXPS data of ABS–CTS–Ni, these particles are a mixture of Ni(0) nano-particles and NiSO4 crystals. Remnants of unreduced NiSO4 had no ef-fect on the subsequent electroless plating. The auto-catalysts Ni(0),obtained by KBH4 reduction, were capable of initiating the Ni electro-less plating. Ni deposition was achieved by dipping ABS–CTS–Ni foilsinto the Ni plating solution. The appearances of the substrate surfaceon which electroless Ni plating lasted for 2, 5, and 30 min are alsoshown in Fig. 4c–e.

Fig. 4c shows spherical Ni(0) cores on the CTS film (at 2 min ofplating) bigger than those in Fig. 4b. The cores were formed by thecatalytic reduction of Ni ion from the electroless plating solutionwith Ni(0) particles as effective catalyst sites [27]. The SEM micro-graph of Ni deposition at 5 min (Fig. 4d) shows that the Ni atoms

in (unetched), (b) 5 min, (c) 7 min, (d) 9 min, and (e) 11 min.

Fig. 4. SEM photographs of surfaces of ABS–CTS (a) and ABS–CTS–Ni (b) and Ni deposition at 2 min (c) and Ni deposition at 5 min (d) and Ni deposition at 30 min (e).

1386 X. Tang et al. / Surface & Coatings Technology 206 (2011) 1382–1388

nucleated and gradually clustered on the ridges of the Ni cores. Withlonger deposition times, the Ni atoms covered the Ni spheres ratherthan generated new nucleation sites on the CTS film. Thus, the Nispheres grew in size and coalesced to form larger clusters [29]. Therate of substance transfer during this period was controlled by thesurface reaction of the Ni catalytic reduction. When Ni depositionlasted for 30 min, a Ni plating player was obtained (Fig. 4e). The aver-age thickness of Ni layer at depositon time of 30 min was 7.2 μm fromweight increase.

The SEMmicrograph of ABS–Ni (Fig. 5) shows no Ni particle on theABS–Ni surface. As discussed in Section 3.2., Ni(0) was not adsorbedonto the etched ABS surface because Ni2+was only physically adsorbedand easily rinsed off. This weak adsorption could be slightly improved ifthe rinsing process is omitted after dipping the etchedABS foils in theNisolution. However, the KBH4 solution would be very easily exhaustedbecause of the excess Ni2+ on the surface. This would be a big wasteof resources and would increase the production cost, and the adhesionof Ni(0) onto the ABS surface would still be insufficient. In summary,CTS film formation plays an important role in the pretreatment proce-dure. The CTS film highly enhanced the adherence of metal catalysts

Fig. 5. SEM photographs of ABS–Ni surface.

onto the substrate by chemical adsorption for the subsequent electro-less plating.

The Au–P layer of average 0.05 μm thickness and Au-S layer of0.07 μm were obtained. Different inorganic element(P or S) was pre-sent in Au layers due to different reducing agent in Au plating bath.The metals on top surface (thicknessb5.0 μm) of layers on ABS weresampled and nitrified. The water-soluble ions were analyzed by ICPand IC measurement to evaluate the chemical compositions. Elementcontents in the layers were shown in Table 3. The data for Au–S/Ni–Pin Table 3 indicated that S was present in Au–S layer. The relative Pcontent to Ni (P:Ni) for Au–P/Ni–P was 0.068, higher than P:Ni inNi–P indicating P was present in Au–P.

Different inorganic element present in Au layers might affect theproperties of Au layers. The SEM photographs of the Au–P and Au–Slayers (Fig. 6) show uniformly sized and shaped Au particles in bothlayers. However, the shape of Au grains in Au–P is apparently differ-ent from that in Au–S. The former are bar-shaped and the latter areround (Fig. 6). The distinct surface topographies of Au–P and Au–Slayers suggested that element P (or S) affect the surface morphologyof Au layers and changed the growth of Au grains considerably.

3.4. XRD

The XRD pattern of the Ni plating layer deposited for 30 min ispresented in Fig. 7. A broad diffraction peak is observed at around45°, which originates from the Ni electroless plating layer. The XRDresults clearly reveal that the Ni layer was in an amorphous state[30,31].

Fig. 8 shows that the XRD pattern of Au–S is in accord with that ofAu–P. No peak shifts or broadening was observed. The crystallization

Table 3Chemical compositions of layers of Ni–P, Au–P/Ni–P and Au–S/Ni–P.

Element content (wt%) Ni Au P S P:Ni

Ni–P 93.5 – 6.1 – 0.065Au–P/Ni–P 85.4 8.3 5.8 – 0.068Au–S/Ni–P 88.0 6.0 5.6 0.24 0.064

Fig. 6. SEM photographs of surfaces of the Au–P (a) and Au–S (b) layers for deposition at 15 min.

1387X. Tang et al. / Surface & Coatings Technology 206 (2011) 1382–1388

state of the Au layer did not change despite the presence of elementalP (or S).

4. Conclusions

Ni/Au electroless plating on ABS was successfully carried out using apalladium-free surface activation method. XPS data revealed sulfonicacid group [H\O\S(O2)\C6H4\] and\OH formation on the ABS sur-face in the etching procedure. The etching time significantly affectedABS surface morphology. 5 min was chosen for etching procedure. The

30 35 40 45 50 55 60 65 70

Inte

nsity (111)

Fig. 7. XRD pattern of Ni layer for electroless deposition at 30 min.

30 40 50 60 70 80

(311)(220)(200)

(111)

(b)

(a)

Inte

nsity

Fig. 8. XRD patterns of the Au–P (a) and Au–S (b) layers for electroless deposition at15 min.

immobilization of auto-catalyst Ni(0) nanoparticles onto etched ABSin activation process was carried out through chemical adsorption byCTS film. FTIR spectra verified that the newactivationmethod enhancedthe adhesion between the CTS film and ABS foil by [\NH\S(O2)\C6H4\] formation on the interfacial surfaces. XPS and FTIR indicatedthat Ni(0) nanoparticles were immobilized through \NH2 chelationand complexation of the primary CTS hydroxyl groups. FTIR and SEM in-dicated no chemical adsorption between Ni and the etched ABS in theABS–Ni. Ni was easily rinsed off confirming the importance of CTS pre-treatment. A Ni–P plating layer was successfully obtained from an elec-troless Ni plating bath using the novel activation method. Au layerswere obtained on top of Ni layers with a new, stable non-cyanide elec-troless Au plating. Different inorganic elements present in the Au layerschanged the surfacemorphology but not the crystallization phase of Aulayers. How the inorganic element (P or S) exists in Au layers will be aninteresting future topic. This environmentally friendly Ni/Au electrolessplating on ABS process with cost-effective activationmethod is promis-ing for large-scale manufacturing.

Acknowledgments

The authors gratefully acknowledge financial support by the spe-cial fund for basic research of central colleges and universities inChina (65010451), the National Natural Science Foundation of China(NSFC 50976050) and the Key Special Technologies R&D Program ofTianjin (09ZCKFSH01900).

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