Binuclear Copper Complex Ink as a Seed for Electroless Copper Plating Yielding >70% Bulk Conductivity on 3D Printed Polymers

Abstract

COMMUNICATION (1 of 7)in general, Internet of things (IoT) applications. [5] One approach to obtaining electronics on 3D surfaces is based on printing electrical circuits on flat surface, followed by reshaping them into 3D structures. [3b] A well-known example of such process is the thermoforming of thermoplastics with embedded circuits. [6] The drawback of this method is that it is limited in its possible patterns due to the dimensional changes that take place during the thermoforming stretching process, and the limitation to thin plastic films. Another method is by direct printing of conductive inks onto the 3D surfaces, with conductive inks composed of metal NPs. [1b,5,7] However, after printing, the NPs require a sintering process to decompose the organic stabilizers and to render it electrically conductive. Typical sintering processes are based on thermal treatment at elevated temperatures, which can damage some of the polymers that are currently used in typical 3D printers (T g < 80 °C). [8] The prerequisite for low sintering temperature results in low conductivity and poor surface smoothness. For low-frequency antenna applications, the result might be satisfying. However, for highfrequency applications, high conductivity and smooth surfaces are required. Accordingly, there is still an unmet need for a new scientific approach that would result in high conductivity, high surface smoothness, as well as perform at low temperature and low cost. A suitable approach to address these obstacles is the electroless copper plating (EP), which is commonly used to form highly conductive metallic structures. A typical EP process is composed of two main steps: first, a catalyst seed is deposited onto the designated substrate, followed by immersing into a metal salt solution with a reducing agent, resulting in metal coating of the pattern composed of the catalyst. Commonly reported seeds for 2D substrate are based on palladium (Pd), silver, and poly(dopamine). However, each of these materials has its limitations. For example, Pd [9] and silver, [3a,10] which are extensively reported, are very costly materials. With seeds based on poly(dopamine), [11] the obtained bulk resistivity is six times higher than that of bulk copper, which is not sufficient for EP processes. Copper-based seeds were also reported for 2D substrate by either sequential printing of copper salt and strong reducing agents [12] or by laser-induced forward transfer (LIFT) technique. The latter resulted in poor resolution and low 3D printed electronics is an emerging field of high importance in both academic research and industrial manufacturing. It enables fabrication of 3D devices with embedded or conformal electronic circuits, which are relevant to a variety of applications, such as Internet of things, soft robotics, and medical devices. Patterning of electrical conductors with conductivity higher than 50% bulk copper is challenging and usually involves electroless or electrolytic deposition processes that require the use of very costly catalyst, ma...

Fabrication of Copper Patterns on Polydimethylsiloxane through Laser-Induced Selective Metallization

“…It can meet the development of electronic components for simplification, refinement, and environmental friendliness. Compared with photolithography, − ink printing, − screen printing, and microcontact printing, LDS has flexible design characteristics and is suitable for large-scale production. Currently, almost all mobile phone antennas used for five-generation (5G) communication are manufactured through LDS technology.…”

Polymer‐Assisted Metal Deposition (PAMD) for Flexible and Wearable Electronics: Principle, Materials, Printing, and Devices

“…To ensure the stable and high performance of these flexible and wearable electronic systems, it is necessary to find suitable soft electrical conductor, which serves as the transporting channel for the electrical signals to trigger appropriate actions of such devices. Despite an intensive research effort on developing new types of conductive materials such as conducting polymers and carbon nanotubes, metal—the most conventional conductor—still outperforms significantly in terms of the electrical conductivity, device compatibility, materials stability, and cost‐effectiveness . In particular, with the recent understanding of the nanomechanics of the metal and the soft structural design, metal conductors are indispensable for most of the flexible and wearable applications.…”

Laser induced selective electroless copper plating on polyurethane using EDTA-Cu as active material

“…Therefore, choosing of suitable active materials, reducing their particle size, increasing the uniformity of particles and minimizing the laser heat affected zone, are the main ways to improve the fineness of FCEM. In recent years, a variety of materials has been used as active materials to prepare FCEMs, such as palladium oxide [4][5][6][7], copper aluminate [8] and carbon nanotubes [9][10][11][12]. These materials, however, showed different processing problems that limited development of FCEMs.…”