In this work, a method for the rapid synthesis of metallic microtracks on polyetherimide is presented. The method relies on the photosynthesis of silver nanoparticles on the surface of the polymer substrates from photosensitive silver chloride (AgCl), which is synthesized directly on the polyetherimide surface. The study reveals that the use of AgCl as a photosensitive intermediate accelerates the reactions leading to the formation of silver nanoparticles by up to two orders of magnitude faster than other photodecomposition schemes. The patterning can be conducted under blue light, with notable advantages over UV exposure. Polymers of significant interest to the microelectronics and 3D printing industries can be directly patterned by light using this photography-inspired technique at throughputs high enough to be commercially advantageous. Light exposures as short as a few seconds are sufficient to allow the direct metallization of the illuminated polyetherimide surface. The results show that the silver required for the seed layer is minimal, and the later copper electroless plating results in the selective growth of conductive tracks for circuitry on the light-patterned areas, both on flexible films and 3D printed surfaces. direct metallization [4] of modified photoresists, [5] which has the advantage that it can be directly patterned by UV photolithography [6] without vacuum process steps for the metal deposition. DOIThe metallization of polyimides has received particular attention, due to their mechanical strength, biocompatibility, chemical resistance, and ability to withstand high temperatures. Different approaches have been followed to achieve this metallization, such as embedding silver nanowires, [7] decomposing metalorganic compounds [8] or the activation of a palladium seed layer for future plating. [9] One proposed methodology for the fabrication of metallic tracks on polyimides is surface modification by ion exchange and subsequent plating. [10] This method has the advantage of avoiding any vacuum processing steps. Moreover, the organometallic bonds can be selectively broken by irradiation, enabling direct light patterning. Finally, the use of a photoresist acting as a mold for electroplating can be removed from the manufacturing process. The nanoparticles (NPs) resulting from the photoreduction of the free metallic ions can then be used as seeds for subsequent plating. This also permits patterning by direct laser writing, [11] which could accommodate the selective plating of contoured, 3D surfaces.This manufacturing process has a plethora of advantages, but its industrial implementation has been held back as the photopatterning stage has been too slow to be implemented for mass production. Moreover, the exposure energy must be limited in order to avoid damage to the polymeric substrate. [12] These limitations have triggered a search for new processes in order to obtain faster nanoparticle formation.One approach has been to use assisted photoreduction of the metallic ions with a mild reducing agent [...

This article reports the performance of different metallic ions and nanoparticles (Ag, Cu, Ni, Pd, Cr, Co, Au and Fe) used as seed layers, formed by chemical or optical reduction, for the electroless Cu plating of metal tracks onto polyetherimide (PEI). Plated Cu performance was tested by adhesion, electrical conductivity, plating rate, XPS, SEM, XRD and EDX analysis. The application of Cu and Ag seeds resulted in high quality electroless Cu deposits presenting strong adhesion properties and high conductivity ((2.0 ± 0.5) ×10 7 S/m and (3.6 ± 0.2) ×10 7 S/m, respectively) compared with bulk copper (5.96 ×10 7 S/m). Performance is attributed to the high surface density and uniformity of seed layers. Of the metals, only Ag ions were photoreduced under the conditions applied and were subsequently used to electroless Cu plate high quality track features of 150 µm width. The application of sulphuric acid pre-treatment to PEI prior to Ag ion exchange, improved the photoinitiated track formation process, as demonstrated by a threefold increase to both photoinduced Ag nanoparticle density on the surface and electroless Cu plating rate, as well as improved electroless Cu adhesion to PEI.

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