J.H.-G. Ng

A direct-writing approach to the micro-patterning of copper onto polyimide

Purpose – The purpose of this paper is to present a novel manufacturing process that aims to pattern metal tracks onto polyimide at atmospheric pressure and ambient environment. The process can be scaled up for industrial applications.Design/methodology/approach – From a thorough literature survey, different approaches were carried out for processing polyimide. Following a design of experiments for the processing and various characterisation techniques, a micro‐coil was manufactured as a test demonstrator.Findings – The characteristics of some main formaldehyde‐based electroless copper baths were compared. The quality of the sidewalls was characterised and the performance of the process was assessed.Originality/value – This paper demonstrates a high‐value manufacturing technique that is mass manufacturable, low cost and suitable for use on 3D surfaces. Criteria required for the development of a direct‐writing process have been described. The issues surrounding electroless plating on polyimide have been ex...

Progress towards the development of novel fabrication and assembly methods for the next generation of ultrasonic transducers

The development trends of ultrasonic devices dictate that frequencies increase, electrode element counts increase, and element pitch dimensions shrink. The high density of the small pitch electrode elements combined with the challenging geometry of the device design, and considerations of acoustic impedance and signal interference, mean that new assembly and packaging techniques are required to be developed to form the interconnection between the high frequency ultrasound (HFUS) arrays and external circuitry. Novel assembly methods using photolithography of new epoxy composite alumina/SU-8 and high density flexible circuits, precision dicing of lead zirconate titanate (PZT) material, flexible circuits and SU-8 resin, powder blasting for vias structuring, and conductive and adhesive films bonding are considered as a mass-scale production approach.

An additive method for photopatterning of metals on flexible substrates

Here we present an additive and cost effective process for plastic electronic manufacturing. Metal tracks are fabricated on polyimide substrates via simple chemical processes combined with direct laser writing or photomask exposure. Laser write speed up to 0.5 m•s-1 and metal track linewidth as low as 5 μm were achieved. Further, this process was easily extended to 3D manufacturing; a helical silver track was written onto a cylindrical substrate. Selective electroless plating was also demonstrated on the photopatterned microstructures which showed promising conductivity close to that of bulk silver metal.

On the Use of Silver Nanoparticles for Direct Micropatterning on Polyimide Substrates

This paper proposes a direct micropatterning process based on the growth of photoreduced silver nanoparticles onto polyimide substrates. The silver nanoparticles are found to have sufficient catalytic efficiency for subsequent electroless plating. Characterization of the process indicates that UV energy dose and heat treatment have to be traded off against photo and thermal degradation of the polymer substrate. Factors affecting the adhesion of the final electroless metal deposit are also discussed.

Design and fabrication of PMN-PT based high frequency ultrasound imaging devices integrated into medical interventional tools

This paper presents the rational for in vivo biopsy and the main technical challenges that must be overcome to realize this application. These include the need to achieve a small array package, the need for high frequency operation for high resolution, and the need for economical manufacturing. An array design is described, with 64 elements at 100 μm pitch, made with PMN-PT piezocrystal and operating at 15 MHz, to demonstrate resolution of 100 μm and the advantages of imaging close up. Techniques adopted to reduce the challenges are described, including, for example, spiral winding of a flexible circuit to achieve external connections. Results from prototypes to date include measurement of pulse-echo signals from a 20 MHz single element piezocrystal piezocomposite and first production of a 5 MHz demonstrator device. Further work will focus particularly on the method of interconnection of the flexible circuit to the array, and incorporation of the array within a biopsy needle.

In-Situ Silver Nanoparticle Formation on Surface-Modified Polyetherimide Films

This paper extends the scope of a novel process previously reported by the group for the hydrolysis and subsequent metallization of polyimide substrates to encompass polyetherimide. Silver nanoparticles are grown in-situ by chemical reduction of silver ions implanted in the substrate. Factors affecting the level of hydrolysis are investigated, with temperature of the hydrolyzing solution found to be the key factor. The presence of silver nanoparticles is also confirmed by X-ray diffraction.

Design, manufacturing and packaging of high frequency micro ultrasonic transducers for medical applications

The challenges for the realization of a miniaturized high frequency ultrasonic transducer linear array lie in the interconnections on the fine pitch piezoceramic elements. Within the footprint the size of a needle, only peripheral interconnections can be allowed on the transducer array such that the acoustic operations on both faces of the vibrating piezoelectric elements are not obstructed. The very low maximum processing temperature allowed also poses difficulty for conventional bonding techniques. This article presents 3-dimensional packaging using spirally rolled flexible circuits, room-temperature anisotropic conductive bonding and stencil printing for the setup of a wafer-level production process flow.

Silver nanocluster formation using UV radiation for direct metal patterning on polyimide

This article presents progress towards the direct metallisation of polyimide via silver ion exchange and nanocluster formation. The aim of this research is to develop a more cost-effective process for the large-scale manufacturing of polymer based electronics. The benefits of this additive approach are the reduced number of fabrication steps and volume of waste materials compared to existing manufacturing processes. The metallization can be achieved by exposure to UV light from either a standard arc lamp or a laser of appropriate wavelength and power intensity. Presented here are results from exposure to a UV arc lamp.

UV direct-writing of metals on polyimide

Conductive micro-patterned copper tracks were fabricated by UV direct-writing of a nanoparticle silver seed layer followed by selective electroless copper deposition. Silver ions were first incorporated into a hydrolyzed polyimide surface layer by wet chemical treatment. A photoreactive polymer coating, methoxy poly(ethylene glycol) (MPEG) was coated on top of the substrate prior to UV irradiation. Electrons released through the interaction between the MPEG molecules and UV photons allowed the reduction of the silver ions across the MPEG/doped polyimide interface. The resultant silver seed layer has a cluster morphology which is suitable for the initiation of electroless plating. Initial results showed that the deposited copper tracks were in good agreement with the track width on the photomask and laser direct-writing can also fabricate smaller line width metal tracks with good accuracy. The facile fabrication presented here can be carried out in air, at atmospheric pressure, and on contoured surfaces.

UV direct-writing of metals on polyimide substrates

Copper micro-patterns have been fabricated on polyimide substrates without the use of evaporation techniques or photoresist materials. A novel easy light-directed metal patterning method has been achieved by using a photoreactive polymer reducing agent, methoxy poly(ethylene glycol) (MPEG) as a thin film coating. The interaction of UV light and MPEG in ethanol film enables the photoreduction of mobile silver ions previously incorporated within the surface-modified polyimide substrates. The silver nanoparticle patterns thus formed serve as a active catalytic seed layer for subsequent electroless copper plating. Narrow copper tracks with low resistivity close to that of bulk copper have been achieved.