- Email: [email protected]
Laser assisted fabrication of copper traces on dielectrics by electroless plating
Available online at www.sciencedirect.com
ScienceDirect
Available online atonline www.sciencedirect.com Available at www.sciencedirect.com
ScienceDirect ScienceDirect
Procedia CIRP 00 (2018) 000–000
www.elsevier.com/locate/procedia
Procedia CIRP 00 (2017) 000–000 Procedia CIRP 74 (2018) 367–370 www.elsevier.com/locate/procedia
10th CIRP 10th CIRPConference Conference on on Photonic Photonic Technologies Technologies [LANE [LANE 2018] 2018]
Laser assisted fabrication ofConference, copper traces on Nantes, dielectrics 28th CIRP Design May 2018, France by electroless plating A new methodology to analyze the functional and physical architecture of a, a a Ratautas *, Aldona Jagminienė , Ina Stankevičienė , Eugenijus Norkusa, existing Karolis products for an assembly oriented product family identification a a
Gediminas Račiukaitis PaulforStief *,Sciences Jean-Yves Dantan, Alain Etienne, Ali Siadat Center Physical and Technology, Savanoriu Ave. 231, Vilnius, LT-02300, Lithuania
* Corresponding Tel.:Supérieure +370-618- d’Arts 420-61. address: [email protected] Écoleauthor. Nationale et E-mail Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]
Abstract A new technology for circuit traces production: Selective Surface Activation Induced by Laser (SSAIL) enables to fabricate fine Abstract
metallic structure on dielectric materials – polymers and glass. SSAIL contains three main steps: The first step is surface modification by laser, second – chemical activation of modified areas and the last step is metal deposition by electroless plating. In today’s business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of A Picosecond laser was used for writing. The method has been investigated in detail for wide window of laser processing agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production parameters. Sheet resistance measurement of finally plated sample and laser processed surface roughness measurement were systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to carried out. This new technique can reduce production cost of circuit traces for molded interconnect devices.
analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2018 Authors. Published Elsevier This iscomparison an open access the CC BY-NC-ND license nature ofThe components. This fact by impedes anLtd. efficient and article choiceunder of appropriate product family combinations for the production (http://creativecommons.org/licenses/by-nc-nd/3.0/) (https://creativecommons.org/licenses/by-nc-nd/4.0/) system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster Peer-review under responsibility of the Bayerisches Laserzentrum GmbH. these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and Keywords: selective; MID; electroless plating; circuit; plastic, laser a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach. 1. Introduction devices. Moreover, it is a material-saving process as the © 2017 The Authors. Published by Elsevier B.V. metallization works selectively. Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
The technology for selective metal plating of polymers has There are several techniques of laser writing for selective a high prospect for nowadays and future electronics. plating of polymers: metal nano-ink printing [3], [4], [5], [6], Keywords: Assembly; Design method; Family identification Particularly in the fields where usage of electronics increases laser-induced selective activation (LISA) [7], [8] and laser rapidly, as the automotive industry, a huge amount of direct structuring (LDS) [8]. First one is a technique that uses electronic components should fit into the certain volume of a silver or gold nanoparticle paste as an ink [3]. The method 1.device. Introduction the product characteristics manufactured and/or In that case, printed circuit boards of 2D shape are of works in two range ways: and using inkjet and laser heating [4] and in this system. In this(LIFT) context, main which challenge inconvenient to use and therefore the technology of moulded assembled laser-induced forward transfer [5]the method usesina Due to the fastbecomes development in the [1]. domain of modelling and analysis now notand only to cope with single interconnect devices more important The laser donor substrate near the is specimen applies a laser from the communication and plating an ongoing trend of limited product range orforexisting product families, writing for selective of polymers candigitization also be usedand on products, back sidea of the donor substrate the lift-off process [6]. digitalization, are facing important to be able to analyze and tohas compare define 3D surfaces manufacturing since localised,enterprises and selective activation of a but Thealso nano-ink printing technology some products unsolvedtoproblem challenges today’s families. It can be observed classical existing polymer is inmade with market a laser environments: beam. Scanninga ofcontinuing the laser new whenproduct applied on 3D curved surfacesthat [3]. Laser-induced tendency reduction of simply productachieved development times and product are regrouped in process. function of clients features. beam on towards 3D surfaces can be technologically selectivefamilies activation is a 3-step The first or step is the shortened product is anfor increasing assembly oriented are hardly find. [2]. Another hugelifecycles. advantageInofaddition, the laserthere writing selective However, laser surface structuring in aproduct liquid families environment. Thistostep is demand customization, being at the sametechnology time in a global On to themake product familya level, products differ structure mainly inon twoa plating of against the printed circuit board is the used porous, sponge-like surface competition with of competitors all The overMID the world. This can trend, characteristics: (i) theisnumber components (ii) the production costs a prototype. technology be main polymer. The structure neededof to keep theand activation which inducing macro micro type of components (e.g. mechanical, electrical, easily isapplied eventhefordevelopment several newfrom layouts of to electronic particles inside cavities [8]. The second stepelectronical). is chemical markets, results in diminished lot sizes due to augmenting ClassicalThe methodologies single products activation. activation isconsidering performed mainly in a colloidal solution, product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 Theoptimization Authors. Published by Elsevier is an opencauses access article under theregarding CC BY-NC-ND license identify potentials in Ltd. the This existing difficulties an efficient definition and (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Peer-review under responsibility of the Bayerisches Laserzentrum GmbH.
2212-8271 © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 2212-8271 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of scientific the Bayerisches Laserzentrum GmbH. Peer-review under responsibility of the committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.144
368 2
Karolis Ratautas et al. / Procedia CIRP 74 (2018) 367–370 Author name / Procedia CIRP 00 (2018) 000–000
usually using the palladium-tin chloride. This step includes not only immersion a workpiece in the activation solution but also rinsing it after the activation. Rinsing is the critical and not easy task. All the colloidal particles must be washed away from the laser-untreated areas but should remain inside the porous surface structures. The last, third step is the electroless metal plating, usually with copper [5]. The process is very unstable regarding its spatial selectivity, and laser processing in a liquid complicates application for 3D surfaces. However, all of them, except LDS, have a limitation when it is being applied on a curved surface [4]. LDS is the method using precursors mixed in a polymer matrix. These precursor additives are activated during the laser writing process in order to become a catalyst for electroless deposition of the metal, and thus the laser-scanned area can be selectively plated [6]. LDS is a 2-step process. There are a few commercial materials for LDS available on the market, but most of them are based on expensive metal-organic fillers, usually including palladium [9], or spinel based complicated structures of copper oxide [10]. For our research our new method: selective surface activation induced by laser (SSAIL) was utilised. In the SSAIL method, pure plastics without any dopant (additives for LDS) can be used. SSAIL is a 3 step process. The first step is surface modification by laser, second - chemical activation of modified areas and the last step is electroless plating. In chemical activation step, unlike to the LISA case, the noncolloidal solution is used in the SSAIL technology. Palladium colloid activator which is employed in LISA technique [8] is very surface-active material and high spatial selectiveness using this solution is impossible to achieve. In the case of activation with palladium colloid, over-plated zones (where metal is on non-structured by laser areas) appears very often [7]. In SSAIL process picosecond laser is used, as it does not works with nanosecond laser. SSAIL method works for polymers which have higher temperature resistance, such as PC, ABS, PA, and PPA and also for soda lime glass. Considering the needs of MID market [9], we are looking for the way to reduce the price for manufacturing of circuit traces. Therefore new method is suggested. 2. Experimental setup 2.1. Materials For the SSAIL method, standard PC/ABS polymer T65 XF from Bayer was used. The plaques of 3 mm thickness was produced by injection moulding. The roughness (RMS) of the plaques was less than 0.2 µm 2.2. Laser A mode-locked Nd:YVO4 (PL10100, Ekspla) laser with a pulse duration of 10 ps were utilised. The fundamental harmonics at 1064 nm has been used. The M2 parameter of the laser beam was 1.1. The laser beam was controlled with a galvanometric scanner. Experimental scheme is shown in Fig.
1. The experiments were performed by changing the scanning speed (pulse overlapping), the average power of the laser, pulse repetition rate. Laser parameters used in the experiments are presented in Table 1. Table 1. Picosecond laser parameters Laser parameters:
PL10100 (Ekspla)
Wavelength
1064 nm
Pulse length
10 ps
Pulse repetition rate
10-100 kHz
Average power
0.1 - 6 (step 0.1) W
Scanning speed
0.3-3 m/s
Beam positioning
SCANgine (1064 nm)
Telecentric f-theta lens
+80 mm
2.3. Chemical activation for SSAIL method After the laser processing step, a specimen was immersed in a chemical activation liquid solution. 2.4. Electroless plating bath All the sample were electroless plated in a copper bath. The copper bath contained: copper sulphate 0.12 M, sodium potassium tartrate 0.35 M, sodium hydroxide 1.25 M, sodium carbonate 0.35 M, formaldehyde 1.2 M. PH was 12.45. Plating temperature 35º C. All specimens were plated for 60 min. The thickness of plated surface were 2-3 µm (measured by weighing of the sample). 2.5. Sheet resistance and surface roughness measurement Sheet resistance measurements test were applied for evaluation the plated surface quality. Sheet resistance has been measured using four probe method [10]. Surface roughness measured by stylus profilometer DEKTAK 100. 3. Results and discussion For the SSAIL method, picosecond laser irradiation was applied for polymer surface treatment. The biggest merit of this method is that standard polymer PC/ABS Bayblend T65 XF can be used which does not contain any LDS additives. The surface activation of this selective plating technique includes two steps. The first one is surface sensitization by the laser. This step is necessary to localise a chemical activator in the next step. The second part of the surface activation is chemical treatment in an activator solution. The last procedure is the same like in LDS – electroless plating. All steps are shown in Fig. 1. The method contains more steps, and it requires to control the parameters of activation step very precisely, but the spatial plating selectivity on undoped polymers is excellent (see Fig. 2)
Karolis Ratautas et al. / Procedia CIRP 74 (2018) 367–370 Author name / Procedia CIRP 00 (2018) 000–000
Fig. 1. Scheme of a SSAIL process
369 3
Fig. 3. Plated surface sheet resistance • and roughness dependence (laser processed, before plating) on the irradiation dose.
Fig. 4. Surface morphology of PC/ABS (Bayblen T65 XF) after processing with the picosecond laser. 2 W of Laser power, 60 kHz pulse repetition rate, 3 m/s scanning speed.
Fig. 2. Circuit produced using SSAIL approach on PC/ABS
For SSAIL process analysis, sheet resistance measurement of finally plated surface has been carried out. Electrical resistance dependence on laser irradiation dose is represented in Fig. 3. As shown in the figure resistance decrease with increasing laser irradiation dose for low values of pulse repetition rate: 10 – 20 kHz. However then 200 kHz is applied, the sheet resistance increase with increasing irradiation dose. Assuming that sheet resistance is reciprocally proportional for copper quantity on the plated surface, the resistance must decrease with increasing concentration of catalyst on the surface (from the second step). Scientifically the most interesting part becomes the selective activation process. One of the hypothesis could be that laser treatment increases the surface area very sharply. This could be seen in SEM image of laser processed surface of PC/ABS in Fig. 4. Therefore catalyst are adsorbed only on laser excited areas. Surface roughness measurement of laser treated thermoplastic surface has been performed in order to check this assumption. The results are represented in Fig. 3 plot.
The same laser processing parameters as used for plating and sheet resistance measurement were applied. Surface roughness – RMS (root mean square, represented as a dash lines) increase with increasing irradiation dose for all values of pulse repetition rate. While conductivity decrease with increasing irradiation dose for 200 kHz. Therefore change of surface roughness does not correlate with a change in sheet resistance of plated copper. Accordingly the amount of catalyst does not increase with increasing surface roughness for 200 kHz. We have conclude that the increase in the surface area after laser treatment is not the main factor leading to selective activation of the SSAIL technology. Other physical process which could influence activation is a coulomb interaction. Laser treated areas gains static charge [11]. Such surface in liquid environment has an electric potential, usually different form the untreated areas. In addition catalyst particles has zeta potential in a solution (12). Therefore if the catalyst’s zeta potential is opposite to a surface potential, catalyst could be forced by coulomb attraction to laser treated areas. Unfortunately the full mechanism of activation process is not fully understood yet. Conclusion PC/ABS Bayblend T65 XF polymer without any LDS additives can be selectively metal plated using the SSAIL method. The technique allows reaching the width of plated line and the separation distance between them in the range of tens of microns. Processing 3 m/s laser scanning speed is achieved for surface activation (limited by scanner
370 4
Karolis Ratautas et al. / Procedia CIRP 74 (2018) 367–370 Author name / Procedia CIRP 00 (2018) 000–000
properties). Selective activation of polymer surface processed by a laser is not only driven by increased surface area of modified surface. Moreover catalyst could be forced by coulomb attraction to laser treated areas. References [1] P. Amend, C. Pscherer, T. Rechtenwald, T. Frick, and M. Schmidt, A fast and flexible method for manufacturing 3D moulded interconnect devices by the use of a rapid prototyping technology, Phys. Procedia 5 (2010) 561-572. [2] 2.G. Tsoukantas, K. Salonitis, P. Stavropoulos, and G. Chryssolouris, Overview of 3D laser materials processing concepts, Proc. SPIE 5131 (2003) 224-228. [3] S. H. Ko, J. Chung, Y. Choi, C. P. Grigoropoulos, N. R. Bieri, T.-y. Choi, C. Dockendorf, and D. Poulikakos, "Laser-based hybrid inkjet printing of nanoink for flexible electronics," Proc. SPIE, vol. 5713, pp. 97-104, 2005. [4] R. Ramakrishnan, N. Saran, and R. J. Petcavich, "Selective Inkjet Printing of Conductors for Displays and Flexible Printed Electronics," J. Display Technol., vol. 7, pp. 344-347, 2011. [5] L. Rapp, J. Ailuno, A. P. Alloncle, and P. Delaporte, "Pulsed-laser printing of silver nanoparticles ink: control of morphological properties," Opt. Express, vol. 19, pp. 21563-21574, 2011.
[6] E. Biver, L. Rapp, A.-P. Alloncle, P. Serra, and P. Delaporte, "High-speed multi-jets printing using laser forward transfer: a time-resolved study of the ejection dynamics," Opt. Express, vol. 22, pp. 17122-17134, 2014. [7] Y. Zhang, H. Hansen, A. De Grave, P. Tang, and J. Nielsen, "Selective metallization of polymers using laser induced surface activation (LISA)— characterization and optimization of porous surface topography," Int. J. Adv. Manuf. Technol., vol. 55, pp. 573-580, 2011. [8] Y. Zhang, G. M. M. Kontogeorgis, and H. N. Hansen, "An Explanation of the Selective Plating of Laser Machined Surfaces Using Surface Tension Components," J. Adhes. Sci. Technol., vol. 25, pp. 2101-2111 2011. [9] J. K. M. Huske, J. Mller, G. Esser, "Laser Supported Activation and Additive Metallization of Thermoplastics for 3D-MIDs," Proc. LANE, 2001. [10] Q. J., S. Jiang, J. Meng, D. Xiangping, Z. T. Wu, EP2632734B1, Grant 2016 03 23, application 2013 09 04. [11] T. M. Hansen, K. Stokbro, O. Hansen, T. Hassenkam, I. Shiraki, S. Hasegawa, and P. Bøggild, "Resolution enhancement of scanning fourpoint-probe measurements on two-dimensional systems," Rev. Sci. Instrum., vol. 74, pp. 3701-3708, 2003. [12] D. Bäuerle, Laser Processing and Chemistry. Springer: Berlin; New York 2011. [13] R. Sprycha, Electrical double layer at alumina/electrolyte interface: I. Surface charge and zeta potential, J. of Colloid and Interface Sci., Vol. 127, Issue 1, 1-11, 1989.
ScienceDirect
Available online atonline www.sciencedirect.com Available at www.sciencedirect.com
ScienceDirect ScienceDirect
Procedia CIRP 00 (2018) 000–000
www.elsevier.com/locate/procedia
Procedia CIRP 00 (2017) 000–000 Procedia CIRP 74 (2018) 367–370 www.elsevier.com/locate/procedia
10th CIRP 10th CIRPConference Conference on on Photonic Photonic Technologies Technologies [LANE [LANE 2018] 2018]
Laser assisted fabrication ofConference, copper traces on Nantes, dielectrics 28th CIRP Design May 2018, France by electroless plating A new methodology to analyze the functional and physical architecture of a, a a Ratautas *, Aldona Jagminienė , Ina Stankevičienė , Eugenijus Norkusa, existing Karolis products for an assembly oriented product family identification a a
Gediminas Račiukaitis PaulforStief *,Sciences Jean-Yves Dantan, Alain Etienne, Ali Siadat Center Physical and Technology, Savanoriu Ave. 231, Vilnius, LT-02300, Lithuania
* Corresponding Tel.:Supérieure +370-618- d’Arts 420-61. address: [email protected] Écoleauthor. Nationale et E-mail Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]
Abstract A new technology for circuit traces production: Selective Surface Activation Induced by Laser (SSAIL) enables to fabricate fine Abstract
metallic structure on dielectric materials – polymers and glass. SSAIL contains three main steps: The first step is surface modification by laser, second – chemical activation of modified areas and the last step is metal deposition by electroless plating. In today’s business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of A Picosecond laser was used for writing. The method has been investigated in detail for wide window of laser processing agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production parameters. Sheet resistance measurement of finally plated sample and laser processed surface roughness measurement were systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to carried out. This new technique can reduce production cost of circuit traces for molded interconnect devices.
analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2018 Authors. Published Elsevier This iscomparison an open access the CC BY-NC-ND license nature ofThe components. This fact by impedes anLtd. efficient and article choiceunder of appropriate product family combinations for the production (http://creativecommons.org/licenses/by-nc-nd/3.0/) (https://creativecommons.org/licenses/by-nc-nd/4.0/) system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster Peer-review under responsibility of the Bayerisches Laserzentrum GmbH. these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and Keywords: selective; MID; electroless plating; circuit; plastic, laser a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach. 1. Introduction devices. Moreover, it is a material-saving process as the © 2017 The Authors. Published by Elsevier B.V. metallization works selectively. Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.
The technology for selective metal plating of polymers has There are several techniques of laser writing for selective a high prospect for nowadays and future electronics. plating of polymers: metal nano-ink printing [3], [4], [5], [6], Keywords: Assembly; Design method; Family identification Particularly in the fields where usage of electronics increases laser-induced selective activation (LISA) [7], [8] and laser rapidly, as the automotive industry, a huge amount of direct structuring (LDS) [8]. First one is a technique that uses electronic components should fit into the certain volume of a silver or gold nanoparticle paste as an ink [3]. The method 1.device. Introduction the product characteristics manufactured and/or In that case, printed circuit boards of 2D shape are of works in two range ways: and using inkjet and laser heating [4] and in this system. In this(LIFT) context, main which challenge inconvenient to use and therefore the technology of moulded assembled laser-induced forward transfer [5]the method usesina Due to the fastbecomes development in the [1]. domain of modelling and analysis now notand only to cope with single interconnect devices more important The laser donor substrate near the is specimen applies a laser from the communication and plating an ongoing trend of limited product range orforexisting product families, writing for selective of polymers candigitization also be usedand on products, back sidea of the donor substrate the lift-off process [6]. digitalization, are facing important to be able to analyze and tohas compare define 3D surfaces manufacturing since localised,enterprises and selective activation of a but Thealso nano-ink printing technology some products unsolvedtoproblem challenges today’s families. It can be observed classical existing polymer is inmade with market a laser environments: beam. Scanninga ofcontinuing the laser new whenproduct applied on 3D curved surfacesthat [3]. Laser-induced tendency reduction of simply productachieved development times and product are regrouped in process. function of clients features. beam on towards 3D surfaces can be technologically selectivefamilies activation is a 3-step The first or step is the shortened product is anfor increasing assembly oriented are hardly find. [2]. Another hugelifecycles. advantageInofaddition, the laserthere writing selective However, laser surface structuring in aproduct liquid families environment. Thistostep is demand customization, being at the sametechnology time in a global On to themake product familya level, products differ structure mainly inon twoa plating of against the printed circuit board is the used porous, sponge-like surface competition with of competitors all The overMID the world. This can trend, characteristics: (i) theisnumber components (ii) the production costs a prototype. technology be main polymer. The structure neededof to keep theand activation which inducing macro micro type of components (e.g. mechanical, electrical, easily isapplied eventhefordevelopment several newfrom layouts of to electronic particles inside cavities [8]. The second stepelectronical). is chemical markets, results in diminished lot sizes due to augmenting ClassicalThe methodologies single products activation. activation isconsidering performed mainly in a colloidal solution, product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 Theoptimization Authors. Published by Elsevier is an opencauses access article under theregarding CC BY-NC-ND license identify potentials in Ltd. the This existing difficulties an efficient definition and (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Peer-review under responsibility of the Bayerisches Laserzentrum GmbH.
2212-8271 © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 2212-8271 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of scientific the Bayerisches Laserzentrum GmbH. Peer-review under responsibility of the committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.144
368 2
Karolis Ratautas et al. / Procedia CIRP 74 (2018) 367–370 Author name / Procedia CIRP 00 (2018) 000–000
usually using the palladium-tin chloride. This step includes not only immersion a workpiece in the activation solution but also rinsing it after the activation. Rinsing is the critical and not easy task. All the colloidal particles must be washed away from the laser-untreated areas but should remain inside the porous surface structures. The last, third step is the electroless metal plating, usually with copper [5]. The process is very unstable regarding its spatial selectivity, and laser processing in a liquid complicates application for 3D surfaces. However, all of them, except LDS, have a limitation when it is being applied on a curved surface [4]. LDS is the method using precursors mixed in a polymer matrix. These precursor additives are activated during the laser writing process in order to become a catalyst for electroless deposition of the metal, and thus the laser-scanned area can be selectively plated [6]. LDS is a 2-step process. There are a few commercial materials for LDS available on the market, but most of them are based on expensive metal-organic fillers, usually including palladium [9], or spinel based complicated structures of copper oxide [10]. For our research our new method: selective surface activation induced by laser (SSAIL) was utilised. In the SSAIL method, pure plastics without any dopant (additives for LDS) can be used. SSAIL is a 3 step process. The first step is surface modification by laser, second - chemical activation of modified areas and the last step is electroless plating. In chemical activation step, unlike to the LISA case, the noncolloidal solution is used in the SSAIL technology. Palladium colloid activator which is employed in LISA technique [8] is very surface-active material and high spatial selectiveness using this solution is impossible to achieve. In the case of activation with palladium colloid, over-plated zones (where metal is on non-structured by laser areas) appears very often [7]. In SSAIL process picosecond laser is used, as it does not works with nanosecond laser. SSAIL method works for polymers which have higher temperature resistance, such as PC, ABS, PA, and PPA and also for soda lime glass. Considering the needs of MID market [9], we are looking for the way to reduce the price for manufacturing of circuit traces. Therefore new method is suggested. 2. Experimental setup 2.1. Materials For the SSAIL method, standard PC/ABS polymer T65 XF from Bayer was used. The plaques of 3 mm thickness was produced by injection moulding. The roughness (RMS) of the plaques was less than 0.2 µm 2.2. Laser A mode-locked Nd:YVO4 (PL10100, Ekspla) laser with a pulse duration of 10 ps were utilised. The fundamental harmonics at 1064 nm has been used. The M2 parameter of the laser beam was 1.1. The laser beam was controlled with a galvanometric scanner. Experimental scheme is shown in Fig.
1. The experiments were performed by changing the scanning speed (pulse overlapping), the average power of the laser, pulse repetition rate. Laser parameters used in the experiments are presented in Table 1. Table 1. Picosecond laser parameters Laser parameters:
PL10100 (Ekspla)
Wavelength
1064 nm
Pulse length
10 ps
Pulse repetition rate
10-100 kHz
Average power
0.1 - 6 (step 0.1) W
Scanning speed
0.3-3 m/s
Beam positioning
SCANgine (1064 nm)
Telecentric f-theta lens
+80 mm
2.3. Chemical activation for SSAIL method After the laser processing step, a specimen was immersed in a chemical activation liquid solution. 2.4. Electroless plating bath All the sample were electroless plated in a copper bath. The copper bath contained: copper sulphate 0.12 M, sodium potassium tartrate 0.35 M, sodium hydroxide 1.25 M, sodium carbonate 0.35 M, formaldehyde 1.2 M. PH was 12.45. Plating temperature 35º C. All specimens were plated for 60 min. The thickness of plated surface were 2-3 µm (measured by weighing of the sample). 2.5. Sheet resistance and surface roughness measurement Sheet resistance measurements test were applied for evaluation the plated surface quality. Sheet resistance has been measured using four probe method [10]. Surface roughness measured by stylus profilometer DEKTAK 100. 3. Results and discussion For the SSAIL method, picosecond laser irradiation was applied for polymer surface treatment. The biggest merit of this method is that standard polymer PC/ABS Bayblend T65 XF can be used which does not contain any LDS additives. The surface activation of this selective plating technique includes two steps. The first one is surface sensitization by the laser. This step is necessary to localise a chemical activator in the next step. The second part of the surface activation is chemical treatment in an activator solution. The last procedure is the same like in LDS – electroless plating. All steps are shown in Fig. 1. The method contains more steps, and it requires to control the parameters of activation step very precisely, but the spatial plating selectivity on undoped polymers is excellent (see Fig. 2)
Karolis Ratautas et al. / Procedia CIRP 74 (2018) 367–370 Author name / Procedia CIRP 00 (2018) 000–000
Fig. 1. Scheme of a SSAIL process
369 3
Fig. 3. Plated surface sheet resistance • and roughness dependence (laser processed, before plating) on the irradiation dose.
Fig. 4. Surface morphology of PC/ABS (Bayblen T65 XF) after processing with the picosecond laser. 2 W of Laser power, 60 kHz pulse repetition rate, 3 m/s scanning speed.
Fig. 2. Circuit produced using SSAIL approach on PC/ABS
For SSAIL process analysis, sheet resistance measurement of finally plated surface has been carried out. Electrical resistance dependence on laser irradiation dose is represented in Fig. 3. As shown in the figure resistance decrease with increasing laser irradiation dose for low values of pulse repetition rate: 10 – 20 kHz. However then 200 kHz is applied, the sheet resistance increase with increasing irradiation dose. Assuming that sheet resistance is reciprocally proportional for copper quantity on the plated surface, the resistance must decrease with increasing concentration of catalyst on the surface (from the second step). Scientifically the most interesting part becomes the selective activation process. One of the hypothesis could be that laser treatment increases the surface area very sharply. This could be seen in SEM image of laser processed surface of PC/ABS in Fig. 4. Therefore catalyst are adsorbed only on laser excited areas. Surface roughness measurement of laser treated thermoplastic surface has been performed in order to check this assumption. The results are represented in Fig. 3 plot.
The same laser processing parameters as used for plating and sheet resistance measurement were applied. Surface roughness – RMS (root mean square, represented as a dash lines) increase with increasing irradiation dose for all values of pulse repetition rate. While conductivity decrease with increasing irradiation dose for 200 kHz. Therefore change of surface roughness does not correlate with a change in sheet resistance of plated copper. Accordingly the amount of catalyst does not increase with increasing surface roughness for 200 kHz. We have conclude that the increase in the surface area after laser treatment is not the main factor leading to selective activation of the SSAIL technology. Other physical process which could influence activation is a coulomb interaction. Laser treated areas gains static charge [11]. Such surface in liquid environment has an electric potential, usually different form the untreated areas. In addition catalyst particles has zeta potential in a solution (12). Therefore if the catalyst’s zeta potential is opposite to a surface potential, catalyst could be forced by coulomb attraction to laser treated areas. Unfortunately the full mechanism of activation process is not fully understood yet. Conclusion PC/ABS Bayblend T65 XF polymer without any LDS additives can be selectively metal plated using the SSAIL method. The technique allows reaching the width of plated line and the separation distance between them in the range of tens of microns. Processing 3 m/s laser scanning speed is achieved for surface activation (limited by scanner
370 4
Karolis Ratautas et al. / Procedia CIRP 74 (2018) 367–370 Author name / Procedia CIRP 00 (2018) 000–000
properties). Selective activation of polymer surface processed by a laser is not only driven by increased surface area of modified surface. Moreover catalyst could be forced by coulomb attraction to laser treated areas. References [1] P. Amend, C. Pscherer, T. Rechtenwald, T. Frick, and M. Schmidt, A fast and flexible method for manufacturing 3D moulded interconnect devices by the use of a rapid prototyping technology, Phys. Procedia 5 (2010) 561-572. [2] 2.G. Tsoukantas, K. Salonitis, P. Stavropoulos, and G. Chryssolouris, Overview of 3D laser materials processing concepts, Proc. SPIE 5131 (2003) 224-228. [3] S. H. Ko, J. Chung, Y. Choi, C. P. Grigoropoulos, N. R. Bieri, T.-y. Choi, C. Dockendorf, and D. Poulikakos, "Laser-based hybrid inkjet printing of nanoink for flexible electronics," Proc. SPIE, vol. 5713, pp. 97-104, 2005. [4] R. Ramakrishnan, N. Saran, and R. J. Petcavich, "Selective Inkjet Printing of Conductors for Displays and Flexible Printed Electronics," J. Display Technol., vol. 7, pp. 344-347, 2011. [5] L. Rapp, J. Ailuno, A. P. Alloncle, and P. Delaporte, "Pulsed-laser printing of silver nanoparticles ink: control of morphological properties," Opt. Express, vol. 19, pp. 21563-21574, 2011.
[6] E. Biver, L. Rapp, A.-P. Alloncle, P. Serra, and P. Delaporte, "High-speed multi-jets printing using laser forward transfer: a time-resolved study of the ejection dynamics," Opt. Express, vol. 22, pp. 17122-17134, 2014. [7] Y. Zhang, H. Hansen, A. De Grave, P. Tang, and J. Nielsen, "Selective metallization of polymers using laser induced surface activation (LISA)— characterization and optimization of porous surface topography," Int. J. Adv. Manuf. Technol., vol. 55, pp. 573-580, 2011. [8] Y. Zhang, G. M. M. Kontogeorgis, and H. N. Hansen, "An Explanation of the Selective Plating of Laser Machined Surfaces Using Surface Tension Components," J. Adhes. Sci. Technol., vol. 25, pp. 2101-2111 2011. [9] J. K. M. Huske, J. Mller, G. Esser, "Laser Supported Activation and Additive Metallization of Thermoplastics for 3D-MIDs," Proc. LANE, 2001. [10] Q. J., S. Jiang, J. Meng, D. Xiangping, Z. T. Wu, EP2632734B1, Grant 2016 03 23, application 2013 09 04. [11] T. M. Hansen, K. Stokbro, O. Hansen, T. Hassenkam, I. Shiraki, S. Hasegawa, and P. Bøggild, "Resolution enhancement of scanning fourpoint-probe measurements on two-dimensional systems," Rev. Sci. Instrum., vol. 74, pp. 3701-3708, 2003. [12] D. Bäuerle, Laser Processing and Chemistry. Springer: Berlin; New York 2011. [13] R. Sprycha, Electrical double layer at alumina/electrolyte interface: I. Surface charge and zeta potential, J. of Colloid and Interface Sci., Vol. 127, Issue 1, 1-11, 1989.