Selective Electroless Metallization Research Articles

Self-activating metal-polymer composites for the straightforward selective metallization of 3D printed parts by stereolithography

The integration of multifunctional elements directly embedded in three-dimensional (3D) printed parts is the cutting-edge of additive manufacturing (AM) and it is crucial for enlarging as well as for strengthening AM role in industrial applications. Here, a straightforward and low-cost method that synergically combines stereolithography (SLA) and selective electroless metallization (EM) is presented for the fabrication of 3D parts characterized by complex shapes and end-use multifunctionalities (conductive, magnetic, mechanical properties). To this end, a novel photocurable composite based on acrylate resin loaded with nickel (Ni) particles is developed for high-resolution SLA-printing of features with self-catalytic properties for EM. Ni particles are loaded in the resin to trigger metal deposition avoiding time consuming and expensive laser-based surface activation. The effect of Ni content on SLA behavior as well as on the efficiency of EM process is studied. Metallized SLA cured samples show good electrical and magnetic properties as well as improved robustness with respect to their non-loaded counterparts. Then, selective metallization of 3D printed parts is successfully achieved by implementing a multi-material SLA-printing where loaded and non-loaded resins are properly interchanged with strong adhesion at the interface, thus offering a cost-effective approach for rapid prototyping of functional free-form features on 3D structures.

Self-Activating Metal-Polymer Composites for the Selective Electroless Metallization of 3D Printed Parts

Nowadays, polymer based additive manufacturing (AM) is widely recognized as a powerful technology for the fabrication of complex three-dimensional objects of virtually any shape in a time, material, and cost effective way. Thanks to their characteristic advantages over conventional manufacturing strategies, AM technologies are the subject of relevant research efforts. In particular, great attention is placed on developing novel 3D printable materials characterized by improved properties and, among all, by novel functionalities, such as magnetic [1] and conductive properties [2]. In order to do this, the most common strategy relies on doping polymeric matrices with nanoparticles, obtaining thus functional 3D printable polymeric composites.Metal containing composites, in particular, can be exploited for their magnetic properties or for their mechanical behavior but also for their potential capability to trigger electroless deposition. It is well-known that electroless plating requires the presence of a catalytic surface, which can be constituted by the metallic particles embedded in the 3D printed composite. In this way, the need to activate the surface of non-conductive polymeric 3D printed parts can be avoided [3]. In addition, metallization can be carried out selectively by fabricating parts in a multi-material printing process [4] with both metal loaded and non-loaded materials. Since only the layers that contain the particles can metallize, conductive regions can be alternated with insulating zones to create metallic functional patterns on the surface of printed parts. This approach can enable the 3D printing of selectively self-metallizing parts, with possible applicability in the production of flexible and highly tridimensional electronic circuits, radiofrequency devices, microelectromechanical systems or microfluidic setups.The present work focuses on the development of a stereolithography (SLA) printable composite based on an acrylate resin loaded with nickel microparticles and its application as self-catalytic material for electroless metallization. This approach, unprecedented for SLA resins, eliminates the need of noble metal activation of the surface. Moreover, the usage of Ni is of great interest also due to the other properties that it can potentially impart to the printed parts: improved mechanical properties, high thermal conductivity, magnetizability. The SLA printability of the metal-loaded resin is assessed and the morphological properties of the 3D printed composites are investigated. Subsequently, the functional properties of the composites are determined, placing a particular emphasis on their capability to trigger NiP and Cu electroless deposition. Finally, the possibility to selectively metallize only specific areas is successfully demonstrated by metallizing a Ni-loaded pattern printed on a Ni-free base.[1] Huber et al.; Appl. Phys. Lett. 109, 162401 (2016)[2] Postiglione et al.; Compos. Part A Appl. Sci. Manuf. 76, 110-114 (2015)[3] Bernasconi et al.; J. Electrochem. Soc. 164, B3059–B3066 (2017)[4] Choi et al.; J. Mater. Process. Technol. 211, 318–328 (2011)

Innovation Processing of Circuit Boards with FDM Printing and Selective Electrochemical Metallization

Additive processing like fused deposition modeling (FDM) can be used for customized products or prototypes. Due to the layer-by-layer structure it is possible to work flexibly and efficiently in geometry. In the electronics industry geometrically demanding circuit carriers can be built in relatively short times, but the processes are somewhat inflexible and take a series of processing steps. Circuit boards are made from layers of fiber-reinforced plastics and then joined by pressing. Vertical interconnects are made by copper plating. Finally, electronic components added via a soldering process.With FDM it is possible to work flexibly with regard to geometry, printing different materials, and a large selection of filaments is given. For a circuit board, one needs at least two filament materials (one insulator, one electronic conductor) to realize conducting lines.In this work we use FDM with different polymers for printing the substrate plate and conductor track structures in a single process. Some of the filaments are electrically conductive and can be used as conducting path structures. However, the electrical resistance of these filaments is significantly lower than conventional copper tracks. Especially for higher currents, chemical metallization of the polymer tracks with copper and tin is necessary. In the presentation we will discuss the preliminaries for achieving selective electroless metallization on selected FDM filament materials.

Photocurable Three-Dimensional Printing Resin to Enable Laser-Assisted Selective Electroless Metallization for Customized Electronics

Photocurable Three-Dimensional Printing Resin to Enable Laser-Assisted Selective Electroless Metallization for Customized Electronics

Fabricating patterned polyelectrolyte brushes by dynamic microprojection lithography for selective electroless metal deposition

AbstractThe emerging need for flexible and wearable electronics has been pushing the edge of the traditional electroless deposition (ELD) technique. With the rapid development of polymer‐assisted ELD (PAELD), its time‐consuming and possess‐complicated procedures have hindered the application of the technique. Here, for purpose of addressing the challenge, the work demonstrates a highly efficient and versatile method, based on the procedure consisting of the customized polyelectrolyte brushes patterns fabrication with the assistance of mask‐free dynamic microprojection lithography and sequential selective ELD (DML‐ELD), for the fabrication of arbitrary electrode on the silicon dioxide/silicon (SiO2/Si) substrate. The resistivity of the patterned copper electrode maintained around 0.062 Ω∙mm at room temperature, indicating the high reproducibility and stability of the method. Furthermore, an interdigital copper electrode fabricated with the DML‐ELD method was coated with a poly(vinyl alcohol) sensing layer, forming a sandwich structure for the ambient humidity detection. The sensitivity of the lab‐made humidity sensor achieves 0.82 pF/%RH (<80%RH) and 19.3 pF/%RH (>80%RH). The work has demonstrated the broad prospect of the proposed DML‐ELD method in the rapid and customized manufacturing of microcircuit fabrication for electronic devices.

Laser-induced surface activation and electroless metallization of polyurethane coating containing copper(II) L-tyrosine

In this work copper(II) L-tyrosine was firstly reported as effective precursors for laser-induced selective activation and electroless metallization of polyurethane coating. The compound in the form of powder was mixed at amount of 20 wt% with polyurethane resin to form the coating on the polycarbonate substrate. The coating was irradiated with excimer ArF laser which generated UV radiation of about 193 nm wavelength. Various laser fluences and number of laser pulses were applied to determine physicochemical changes of the coating surface layer. After irradiation coatings were electrolessly metallized. It was found that laser irradiation resulted in formation of cone-like surface geometrical structure. The high of the cones was dependent on the dose of irradiation, whereas their tops were covered with copper. The external surface layer of precipitated copper was oxidized. This, however, did not affect the possibility of the surface to be electrolessly metalized. The irradiated coatings was effectively metallized and thus deposited copper layer characterized with high adhesion strength.

Highly-facile template-based selective electroless metallization of micro- and nanopatterns for plastic electronics and plasmonics

A novel and universal patterned electroless metallization process for creating micro- and nanoscale metallic structures on plastic substrates is demonstrated.

Selective Electroless Metallization of Micro- and Nanopatterns via Poly(dopamine) Modification and Palladium Nanoparticle Catalysis for Flexible and Stretchable Electronic Applications.

The authors report a new patterned electroless metallization process for creating micro- and nanoscale metallic structures on polymeric substrates, which are essential for emerging flexible and stretchable optical and electronic applications. This novel process features a selective adsorption of catalytic Pd nanoparticles (PdNPs) on a lithographically masked poly(dopamine) (PDA) interlayer in situ polymerized on the substrates. The moisture-resistant PDA layer has excellent stability under a harsh electroless plating bath, which enables electroless metallization on versatile substrate materials regardless of their hydrophobicity, and significantly strengthens the attachment of electroless plated metallic structures on the polymeric substrates. Prototype devices fabricated using this PDA-assisted electroless metallization patterning exhibit superior mechanical stability under high bending and stretching stress. The lithographic patterning of the PDA spatially confines the adsorption of PdNPs and reduces defects due to random adsorption of catalytic particles on the undesired area. The high resolution of the lithographic patterning enables the demonstration of a copper micrograting pattern with a linewidth down to 2 μm and a silver plasmonic nanodisk array with a 500 nm pitch. A copper mesh is also fabricated using our new patterned electroless metallization process and functions as flexible transparent electrodes with >80% visible transmittance and <1 Ω sq-1 sheet resistance. Moreover, flexible and stretchable dynamic electroluminescent displays and functional flexible printed circuits are demonstrated to show the promising capability of our fabrication process in versatile flexible and stretchable electronic devices.

Mask-Free Selective Metallization on Glass By Controlling Surface Hydrophilicity

The trend in selective metallization for printed circuit board (PCB) is to replace lithography process because of its process complication and cost waste. Nowadays, there are many ways to selective metal deposition, like ink-jet technique or laser irradiation for electroless metal deposition. In this study, we develop an unique, novel method to realize selective electroless metal deposition by controlling surface hydrophilicity without the need of tedious photomask process. This technique is demonstrated by forming a superhydrophobic surface in the first step, and then laser patterning to allow bottom surface exposed. Those exposed surface was then metallized by a process involving “silane compound modification + nano-Palladium catalyst activation”. In particular, TiO2 nanoparticles is coated by spin-coating on the glass substrate. Then, the surface with TiO2 nanoparticles is modified by Perfluorooctyltriethoxysilane (PFOTES) in order to form a superhydrophobic surface. The water contact angle of the surface exceeds 150 degree at this stage. The superhydrophobic layer acts like a shelter that could prevent electroless plating reaction from the substrate surface. After that, laser beam is applied on the superhydrophobic surface to remove PFOTES/TiO2 so that the specific pattern is exposed. Finally, selective metallization is accomplished on the exposed surface using home-made Pd nanoparticles and commercial electroless metal solution. Figure 1

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

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

Electroless Metallization of Dielectric Surfaces

Electroless plating is a conformal and low cost deposition method that can improve the critical parameters of 3D Through-Si Vias (TSV) interconnects. It enables conformal barrier/seed layer deposition to improve the scalability and decrease the cost of TSV interconnects by replacing PVD barrier/seed method, which has the disadvantages of higher cost and poor step coverage. Another major application of selective electroless metallization technology includes transparent metal mesh for flexible displays and touch screens to replace expensive and brittle ITO. Activation of dielectric surfaces with catalytic nanolayers. Dielectric surfaces need to be activated prior to electroless plating. SiOX-NH2-Pd and TiOX-Pd activation methods were developed and characterized to achieve control growth of self-assembled catalytic nanolayers containing Pd nanoparticles. Characterization was performed using XRR, profilometry, FTIR, ellipsometry, SIMS and HR SEM. Thickness of the assembled nanolayers was measured to be < 30 nm on glass and silicon substrates. The characterization of the properties (morphology) and composition of self-assembled silane coupling agent with catalytic monolayers containing Pd nanoparticles was performed by using XRR, Profilometer and SIMS, respectively, to achieve low surface roughness (RMS <2 nm) and high uniformity (<10%, 1 Sigma) with low trace impurities (<100 ppm) of the substrate coating. The thickness of assembled catalytic nanolayers including SiOX-NH2-Pd and TiOX-Pd was measured by using XRR, ellipsometry, profilometry and HR SEM. The thickness ranges from 2 nm to 10 nm for SiOX-NHX nanolayers and from 15 nm to 30 nm for TiOX nanolayers. The surface roughness of catalytic nanolayers was measured by using XRR and profilimetry. The thickness uniformity measured at 9 points by profilometry was < 10%, 1 Sigma for SiOX-NHX and for TiOX while the surface roughness was < 2 nm for both types of nanolayers. Composition of nanolayers and trace impurities in nanolayers were characterized by FTIR and SIMS. FTIR data showed OH and CH absoption peaks in catalytic nanolayers. Composition of nanolayers (Ti, Si, Pd, CH, NH, O) were also qualitatively characterized by SIMS with no detectable trace impurities. Electroless metal deposition on catalytic nanolayers. Electroless NiWP (NiWBP) and CoWP (CoWBP) films (down to 30 nm thick) were deposited on catalytic nanolayers with surface roughness < 1 nm and thickness uniformity <10% @ 1 Sigma. The film properties were studied by using Profilometer, EPMA, XRD, DSC and HR SEM. Crystallization temperature was achieved of over 350 C for electroless Ni(Co) alloys. The concentrations of P and W in electroless plated films were over 12% and 2%, respectively. Electroless Co(Ni)WP(B)/Cu barrier/seed layers are effective barriers against copper diffusion with low surface roughness and high adhesion to the substrate. Conformal Ni alloy (Co alloy)/Cu layers were deposited on catalytic nanolayers to form barrier/seed layers for Cu interconnects. Selective and conformal (>95% step coverage) deposition of electroless Ni(Co)alloys/Cu was obtained inside TSV (< 5 µm size and > 10:1 aspect ratio) if photosensitive TiOX-Pd catalytic nanolayers were used. 5-20 μm wide Cu (up to 2 μm thick)/Ni (up to 0.1 μm thick) patterns were deposited to form copper patterns (redistribution layers, copper mesh et al). The adhesion of electroless plated metal to dielectric surface was measured to be over 65 MPa by using pull test. Plating bath metrology. Bath metrology was developed to control the quality and replenish the plating bath for both metals (Ni, Co, W, Pd) and reducing agents (hypophosphite, DMAB) in electroless plating baths (Ni, Co) with precision/tolerance (p/t) < 0.3. Standard solutions (LCL, Target, UCL) were prepared and linear calibration curves were obtained. UV-VIS analysis of Co was performed at 530 nm while UV-VIS analysis of Ni was performed at 390 nm with dilution in DI water. To analyze Pd, PdCl2 solution was diluted in IPA. To analyze tungstate, three solutions were used including solution #1: 12% SnCl2 in HCl, solution #2: 25% KSCN in DI water, and solution #3: 1.4 mL Solution #1 + 0.1 mL Solution #2. UV-VIS Absorbance data were taken at 398.5 nm. Hypophosphite and DMAB reducing agents were analyzed by using titration.

Metal deposition by electroless plating on polydopamine functionalized micro- and nanoparticles

A novel approach for the fabrication of metal coated micro- and nanoparticles by functionalization with a thin polydopamine layer followed by electroless plating is reported. The particles are initially coated with polydopamine via self-polymerization. The resulting polydopamine coated particles have a surface rich in catechols and amino groups, resulting in a high affinity toward metal ions. Thus, they provide an effective platform for selective electroless metal deposition without further activation and sensitization steps. The combination of a polydopamine-based functionalization with electroless plating ensures a simple, scalable, and cost-effective metal coating strategy. Silver-plated tungsten carbide microparticles, copper-plated tungsten carbide microparticles, and copper-plated alumina nanoparticles were successfully fabricated, showing also the high versatility of the method, since the polymerization of dopamine leads to the formation of an adherent polydopamine layer on the surface of particles of any material and size. The metal coated particles produced with this process are particularly well suited for the production of metal matrix composites, since the metal coating increases the wettability of the particles by the metal, promoting their integration within the matrix. Such composite materials are used in a variety of applications including electrical contacts, components for the automotive industries, magnets, and electromagnetic interference shielding.

Selective Electroless Metallization of Patterned Polymeric Films for Lithography Applications

The fabrication of electrical interconnects to provide power for and communication with computers as their component complementary metal oxide semiconductor (CMOS) devices continue to shrink in size presents significant materials and processing compatibility challenges. We describe here our efforts to address these challenges using top-surface imaging and hybrid photoresist/self-assembled monolayer patterning approaches, in conjunction with selective electroless metal deposition, to develop processes capable of fabricating appropriate submicron and nanoscale metal features useful as electrical interconnects, as well as plasma-etch-resistant masks and metal diffusion barriers. Our efforts focus on the development of cost-effective methods compatible with a manufacturing environment that satisfy materials and process constraints associated with CMOS device production. We demonstrate the fabrication of approximately 50-nm-width features in metal with high fidelity and sufficient control of edge acuity to satisfy current industry design rules using our processes and discuss the challenges and opportunities for fabrication of analogous sub-10-nm metal features.

Cover Picture: Fabrication of Elastomeric Wires by Selective Electroless Metallization of Poly(dimethylsiloxane) (Adv. Mater. 1/2008)

AbstractTricia Carmichael and co‐workers employ a simple, low‐cost method for the fabrication of patterned metal films on elastomeric poly(dimethylsiloxane) (PDMS) substrates, as described on p. 59. The metal/PDMS composites are electrically conductive and mechanically flexible, making them suitable for use in the fabrication of lightweight, flexible devices such as wearable electronics, biocompatible sensors, and artificial nerves, skins, and muscles. Copper wires on PDMS remain conductive when subjected to linear strains of up to 52 %. The utility of these wires is demonstrated by using them as laminated top contacts in an organic light‐emitting device.

Fabrication of Elastomeric Wires by Selective Electroless Metallization of Poly(dimethylsiloxane)

A simple, low-cost method for fabricating flexible copper wires on elastomeric substrates is demonstrated. The use of microcontact printing and electroless metal deposition rather than conventional photolithography and physical vapor deposition of metals makes the process inexpensive and operationally simple. Copper films on elastomers may be used to fabricate flexible electronic circuits and biocompatible electronic devices.

Metal pattern formation by selective electroless metallization on polypyrrole films patterned by photochemical degradation of iron(III) chloride as oxidizing agent

Fine metal patterns were formed by selective electroless plating on polypyrrole (PPy) patterns, which were prepared using the photochemical reaction of an oxidative polymerization agent such as FeCl 3. Selective metallization on the PPy patterns was performed by electroless plating that would occur due to the reducing power of PPy for PdCl 2 to palladium metal without other reductants such as SnCl 2, etc. This would be used as a novel preparation method of a metal electrical circuit.

Fabrication of Nanoscale Metallic Spirals Using Phospholipid Microtubule Organizational Templates

We describe the fabrication of metallic Cu spiral/helical nanostructures prepared via selective electroless metallization of a phospholipid microtubule template. The metallization template is created through selective, sequential adsorption of the oppositely charged polyelectrolytes, sodium poly(styrenesulfonate) (PSS) and poly(ethyleneimine) (PEI), onto nanoscale seams naturally occurring on the microtubule surface. A negatively charged Pd(II) nanoparticle catalyst is bound to the terminal cationic PEI layer of the multilayer film and initiates selective template metallization to form the helical Cu nanostructures. Details of the process are presented, and a mechanism and factors affecting the control of the feature critical dimensions are discussed.

Use of Low-Temperature Thermal Alkylation to Eliminate Ink Migration in Microcontact Printed Patterns

We demonstrate aqueous hydrogel-based microcontact printing of amine ligands into solvent-templated nanocavities of chloromethylphenyl-based siloxane or thin polymer films. Migration of pyridine ligands within films following printing, which can compromise pattern fidelity, is eliminated by heat treatment of the substrate. Gentle heating (e.g., 50 degrees C, 5 min) leads to the efficient alkylation of mobile pyridine adsorbate by the C-Cl bonds of the film, covalently tethering the adsorbate to the surface as a pyridinium salt. Subsequent binding of a Pd-based colloid to surface pyridinium (and remaining strongly bound and immobile pyridine ligand) sites permits selective electroless metal deposition and fabrication of patterned metal films.

Reduced electromigration of Cu wires by surface coating

Electromigration in on-chip Cu interconnections with a selective electroless metal coating, CoWP, CoSnP, or Pd, on the top surface of Cu damascene lines has been investigated. The 10–20 nm thick metal cap significantly improves electromigration lifetime by providing protection against interface diffusion of Cu which has been the leading contributor to metal line failure by electromigration.

Ion beam modification and patterning of organosilane self-assembled monolayers

The patterning and modification of organosilane self-assembled monolayers on Si native oxide surfaces by low- and high-energy ion beams were investigated. The nature and extent of low-energy (50–140 eV) Ar+ ion-induced modification of a 2-(trimethoxysilyl) ethyl-2-pyridine monolayer was studied by x-ray photoelectron spectroscopy and by the quality of the electroless Ni patterns obtained. C(1s) and N(1s) core level x-ray photoelectron spectroscopy indicated that the ion-induced modification of the monolayer involved loss of the ethylpyridyl chain by sputtering and/or decomposition. The type of modification was independent of the ion energy and fluence, but the extent of modification depended on both parameters. The modification of the pyridine monolayer was monitored by the percent loss in the N(1s) peak area; modification commenced at a fluence of 5×1014 ions/cm2 and was observed for all ion energies studied. However, selective electroless metallization occurred only for monolayers that suffered ≳50% loss in the N(1s) x-ray photoelectron spectroscopy signal. A damage saturation level of 80% N(1s) loss was indicated at an ion fluence of 9×1015 ions/cm2. A high-energy focused ion beam lithography system was also used to evaluate the high resolution patterning of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, (aminoethylaminomethyl) phenethyltrimethoxysilane, and pyridine monolayers by Ga+, Si++, Au+, and Au++ ions at energies ranging from 50 to 280 keV. The highest resolution metal features obtained were 0.3-μm-wide gaps on phenethyltrimethoxysilane and pyridine monolayers using Ga+ and Si++ ions. Aminopropyltrimethoxysilane monolayers were found to require ten times higher ion fluences to achieve comparable results with the phenethyltrimethoxysilane and pyridine monolayers for all ions investigated.