Cobley, Andrew

Danilova, Sofya

Graves, John

The formation of printed circuit patterns on non-conductive substrates has many applications in high 7 value sectors such as the electronics sector. Current semi-additive and subtractive circuit 8 manufacturing processes use photolithography to pattern substrates coated with a thin or relatively 9 thick metal film. This process is often wasteful and expensive. Using an innovative approach; 10 composite Fe3O4-Ag nanoparticles were synthesized and attracted to a magnetic field. The 11 nanoparticles catalysed electroless copper deposition. Such a catalyst is new to electroless plating and 12 was deposited selectively on a dielectric substrate using a gradient magnetic field. In this way, 13 subsequent electroless copper plating occurred exclusively where the magnetic field was applied, 14 whilst the remaining surface was free of deposited metal. The advantage of this additive method of 15 manufacture is that less material is needed and less waste is produced

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  Selective electroless metallization of non-conductive substrates enabled by a Fe3O4/Ag catalyst and a gradient magnetic field  Danilova, S, Graves, J & Cobley, A  Author post-print (accepted) deposited by Coventry University’s Repository  Original citation & hyperlink:  Danilova, S, Graves, J & Cobley, A 2018, 'Selective electroless metallization of non-conductive substrates enabled by a Fe3O4/Ag catalyst and 1 a gradient magnetic field' Materials Letters, vol 219, pp. 170-173 https://dx.doi.org/10.1016/j.matlet.2018.02.062   DOI 10.1016/j.matlet.2018.02.062 ISSN 0167-577X ESSN 1873-4979  Publisher: Elsevier  NOTICE: this is the author’s version of a work that was accepted for publication in Materials Letters. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Materials Letters, 219, (2017)] DOI: 10.1016/j.matlet.2018.02.062  © 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/  Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.   This document is the author’s post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it.  Selective electroless metallization of non-conductive substrates enabled by a Fe3O4/Ag catalyst and 1 a gradient magnetic field. 2 S. Danilova, J. E. Graves, A. J. Cobley 3 Functional Materials Group, Coventry University, UK 4 e-mail: danilovasophia@hotmail.com 5 Abstract: 6 The formation of printed circuit patterns on non-conductive substrates has many applications in high 7 value sectors such as the electronics sector.  Current semi-additive and subtractive circuit 8 manufacturing processes use  photolithography to pattern substrates coated with a thin or relatively 9 thick metal film. This process is often wasteful and expensive. Using an innovative approach; 10 composite Fe3O4-Ag nanoparticles were synthesized and attracted to a magnetic field. The 11 nanoparticles catalysed electroless copper deposition. Such a catalyst is new to electroless plating and 12 was deposited selectively on a dielectric substrate using a gradient magnetic field. In this way, 13 subsequent electroless copper plating occurred exclusively where the magnetic field was applied, 14 whilst the remaining surface was free of deposited metal.  The advantage of this additive method of 15 manufacture is that less material is needed and less waste is produced. 16 Keywords: Deposition, Electroless, Magnetic, Nanoparticles,  Selective.  17 1. Introduction 18 The utilization of a gradient magnetic field to enable selective metallisation via electrodeposition has 19 been widely researched [1-3]. The gradient magnetic field was created by permanent magnets which 20 were applied behind the substrate during electrodeposition. The electrodeposited layer had a higher 21 thickness in the area of maximum magnetic field and formed a pattern which replicated that of the 22 magnet array.  23 Selective metallization of non-conductive materials such as polymers is used extensively in a wide 24 range of high value manufacturing processes such as the formation of radio frequency identification 25 tags and the use of circuits for connecting wearable technology. Electroless deposition is often used 26 to metallise non-conductive materials. Typically, a Pd/Sn colloidal catalyst is employed although 27 alternatives have been investigated such as Ag and Cu [4-6]. Although several groups have attempted 28 to study the effect of a magnetic field on electroless plating, none had the specific aim of selective 29 deposition [7-9].  30 The synthesis of Fe3O4-Ag nanoparticles has been an area of research interest because of their unique 31 properties [10]. The objective of the present research was to synthesize composite Fe3O4-Ag 32 nanoparticles for electroless copper deposition.  The paramagnetic Fe3O4 particles would be attracted 33 by the magnetic field and form the required pattern, whilst the silver would catalyse the oxidation and 34 reduction reactions to initiate electroless plating. The aim of this study was to demonstrate that this 35 innovative approach to selective metallization of non-conductive materials has the potential to be 36 used for forming conductive circuitry on non-conductive substrates. 37 2. Methodology 38 The Fe3O4-Ag composite nanoparticles were synthesized according to a previously published 39 procedure [11]. The synthesized particles were dried in an oven overnight at 50 oC. In order to prepare 40 the catalyst solution, 0.01 g of Fe3O4-Ag composite nanoparticles were dispersed in 100 ml of reverse 41 osmosis (RO) water by magnetic stirring for 6 hours at 300 rpm. The pH of the solution was controlled 42 at pH=2 and adjusted by addition of concentrated (37%) HCl.  43 A non-conductive epoxy polymeric substrate of dimensions 30x30x3 mm was used for the electroless 44 plating. A Ni-Cu-Ni plated NdFeB magnet with dimensions of 10x5x2 mm was attached to one side of 45 the plastic substrate (Figure 1 (b)). The substrate was then placed in 500 ml of a commercial 46 ‘conditioner’ solution which cleaned and functionalised the surface of the substrate. This was 47 composed of 450 ml RO water and 50 ml Circuposit Conditioner 3320A (supplied by AGAS Electronic 48 Materials Ltd) and was operated at 46 oC with an immersion time of 5 min. The substrate was then 49 rinsed in water for 5 min and placed in the Fe3O4-Ag composite catalyst solution for 30 sec. The 50 substrate was placed face-down horizontally in this solution in order to diminish the influence of 51 catalyst particle sedimentation on pattern formation. The substrate was then rinsed in RO water and 52 placed in a commercial electroless copper plating solution composed of 420 ml  RO water, 75 ml 53 Circuposit 3350 M-1, 5 ml Circuposit 3350 A-1, 5.25 ml Cuposit Z-1 and 5.7 ml Cuposit Y-1 (supplied by 54 AGAS Electronic Materials Ltd) operated at 46 oC with an immersion time of 25 min. After electroless 55 plating, the substrate with the obtained selective deposit was rinsed in tap water and dried in air.  56 An overall schematic representation of the process is presented in Figure 1 (a). 57 A Sigma 500 VP scanning electron microscope was utilized in order to characterise the size of the 58 synthesised particles and the deposited film surface.  An X-MaxN 80, Oxford Instruments silicon drift 59 detector fitted in the SEM and was used to analyse the composition of the Fe3O4-Ag composite 60 nanoparticles. ImageJ software was employed for analysis of particle size and distribution.  Images of 61 the deposited copper and catalyst film were obtained using an optical microscope. 62 3. Results and discussion 63 An SEM image of the synthesized Fe3O4-Ag nanoparticles is presented in Figure 2 (a). The EDX mapping 64 of obtained image for Fe (Figure 2(b)) shows an even distribution of this element across the measured 65 area. For Ag (Figure 2(c)) the highest density occurs at points corresponding to  bright particles with 66 diameter of approximately 100 nm. This suggests that a composite material is formed which consists 67 of 36±9 nm Fe3O4 nanoparticles and 83±19 nm nanoparticles of Ag. In addition, the analysis of the 68 Fe3O4-Ag nanoparticles size distribution shows that there is an increase in the formation of larger 69 particles from 60 to 90 nm compared to the Fe3O4, where no particles larger than 70 nm are apparent 70 (Figure 2 (d)). 71 The composite Fe3O4 – Ag nanoparticles were dispersed in an aqueous acidic solution (pH = 2). The 72 addition of HCl was expected to enhance the electrostatic attraction of Ag and Fe3O4 nanoparticles 73 since the zeta potential of Ag nanoparticles is negative at all pH values[12] while Fe3O4 nanoparticles 74 are positive in an acidic environment [13], the maximum electrostatic attraction between Ag and Fe3O4 75 nanoparticles should be achieved at an acidic pH.  At neutral pH, Fe3O4 nanoparticles reach the 76 isovalent point and the nanoparticle surface will have no charge [13]. Under these conditions, 77 electroless plating experiments gave inconsistent results. 78 Electroless copper plating experiments were conducted to determine the suitability of the 79 nanoparticles to be patterned by a magnetic field and to act as a catalyst to initiate electroless copper 80 plating. As described in the methodology (Figure 1(a)) a magnet was attached to the back of the 81 substrate and it was observed that pure Fe3O4 nanoparticles were patterned by the magnetic field but 82 did not initiate electroless copper plating. The composite Fe3O4 – Ag nanoparticles were also deposited 83 selectively in the area of maximum magnetic field influence as shown in the optical microscope image 84 Figure 3(a). These nanoparticles initiated subsequent electroless copper plating which occurred 85 exclusively in the area where the magnetic field was applied as illustrated in Figure 3(b).  86 The SEM image of the substrate surface was obtained after electroless copper deposition (Figure 3(c)). 87 The image reveals that the deposited layer has a similar morphology to that obtained using a Pd 88 catalyst, although the coverage is not entirely continuous. 89 Conclusion 90 In this study, an innovative methodology for the selective metallisation of non-conductive materials 91 has been demonstrated. From this study, it has been proven that:  92  composite Fe3O4-Ag nanoparticles will act as a catalyst and initiate electroless copper plating, 93  the magnetic properties of this catalyst enable it to be patterned on a substrate by a magnetic 94 field, and 95  the combined catalytic and magnetic properties of the composite Fe3O4-Ag nanoparticles 96 enable selective metallisation of a non-conductive material. 97 Acknowledgements 98 This work was supported by Coventry University. 99 References 100 [1] P. Dunne, J.M.D. Coey, Patterning metallic electrodeposits with magnet arrays, Phys. Rev. B - 101 Condens. Matter Mater. Phys., 85 (2012) 1–21. doi:10.1103/PhysRevB.85.224411:32  102 [2] K. Tschulik, R. Sueptitz, J. Koza, M. Uhlemann, G. Mutschke, T. Weier, A. Gebert, L. Schultz, Studies 103 on the patterning effect of copper deposits in magnetic gradient fields, Electrochim. Acta, 56(1) (2010) 104 297-304. 105 [3] F. Karnbach, M. Uhlemann, A. Gebert, J. Eckert, K. Tschulik, Magnetic field templated patterning of 106 the soft magnetic alloy CoFe, Electrochim. Acta, 123 (2014) 477-484. 107  [4] J. E. Graves, M. Sugden, R. E. Litchfield, D. A. Hutt, T. J. Mason, A. J. Cobley, Ultrasound assisted 108 dispersal of a copper nanopowder for electroless copper activation, Ultrason. Sonochem., 29 (2016) 109 428-438. 110 [5] J. E. Graves, M. T. Goosey, D. Hirst, M.A. Poole An electrochemical pre-treatment and 111 catalysation process for ABS utilising silver(II) chemistry, Trans. Inst. Metal Finish., 79 (3) (2001) 90-112 94 113  114 [6] Z. C. Liu, Q. G. He, P. Hou, P. F. Xiao, N. Y. He, and Z. H. Lu, Electroless plating of copper through 115 successive pretreatment with silane and colloidal silver, Colloid Surface A, 257 (2005) 283-286. 116  117 [7] L. Chia-Chien, T.C. Chou, Effects of magnetic field on the reaction kinetics of electroless nickel 118 deposition, Electrochim. acta, 40(8) (1995) 965-970. 119 [8] T.P. Xuan, L. Zhang, Q.H. Huang, Crystallization behavior of electroless Co-Ni-B alloy plated in 120 magnetic field in presence of cerium, T. Nonferr. Metal Soc., 16(2) (2006) 363-367. 121 [9] Y. Yu, G. Wei, X. Hu, H. Ge, Z. Yu, The effect of magnetic fields on the electroless deposition of Co–122 W–P film, Surf Coat Technol, 204(16) (2010) 2669-2676. 123 [10] R. Ghosh Chaudhuri, S. Paria, Core/shell nanoparticles: classes, properties, synthesis mechanisms, 124 characterization, and applications, Chemical reviews, 112 (4) (2012) 2373-2433. 125 [11] J. R. Chiou, B. H. Lai, K. C. Hsu, D. H. Chen,  One-pot green synthesis of silver/iron oxide composite 126 nanoparticles for 4-nitrophenol reduction, J. Hazard. Mater., 248 (2013) 394-400. 127 [12] M. Sathishkumar, K. Sneha, S. W. Won, C.W. Cho, S. Kim, Y.S.Yun, Y.S., Cinnamon zeylanicum bark 128 extract and powder mediated green synthesis of nano-crystalline silver particles and its bactericidal 129 activity, Colloid Surface B, 73(2) (2009) 332-338: 130 [13] Z. Sun, F. Su, W. Forsling, P. Samskog, Surface Characteristics of Magnetite in Aqueous Suspension, 131 J. Colloid Interface Sci., 197(1) (1998) 151-159 doi:10.1006/jcis.1997.5239. 132 133 Figure 1. The schematic presentation of (a) standard and selective electroless plating under applied 134 gradient magnetic field and (b) magnet attachment set-up.  135 Figure 2. (a) SEM image of synthesised Fe3O4 – Ag composite particles, (b) EDX mapping of Fe, (c) EDX 136 mapping of Ag, (d) size distribution histogram of synthesised particles.  137 Figure 3. (a) The optical image of the selectively deposited composite Fe3O4 – Ag catalyst, (b) the 138 optical image of the selectively deposited copper layer, (c) SEM image of the deposited copper layer 139 obtained by gradient magnetic field application.  140  141 

Selective electroless metallization of non-conductive substrates enabled by a Fe3O4/Ag catalyst and a gradient magnetic field

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