Andrew J. Cobley

New evidence for the inverse dependence of mechanical and chemical effects on the frequency of ultrasound

Acoustic cavitation has been the subject of research and discussion for many years and it is the underlying driving force for sonochemistry. The collapse of acoustic cavitation bubbles in water near to a surface can bring about significant surface modification in terms of the mechanical damage caused by the asymmetric collapse of the bubbles which cause erosion and abrasion. A second effect of acoustic cavitation is the formation of short lived radicals caused by the breakdown of water inside the bubble. For the first time the dependence of these effects has been observed on the surface of a plastic material as a function of ultrasonic frequency.

Controlled protein release from microcapsules with composite shells using high frequency ultrasound—potential for in vivo medical use

The possibility of protein release from polymeric microcapsules by means of low-power (up to a maximum of 3.2 W) high-frequency (850 kHz) ultrasound was studied. The release efficiency using these ultrasonic parameters that are close to those currently used in medical diagnostic and ultrasound treatment was compared to that achieved with a conventional 20 kHz 70 W ultrasonic probe. Microcapsules were made by polyelectrolyte multilayer assembly on 3–5 µm calcium carbonate particles with co-precipitated fluorescently labelled protein. Ultrasound induced protein release was monitored by supernatant fluorescence increase after sonication. The release efficiency is improved by the presence of gold nanoparticles in the microcapsule shell. The amount of gold nanoparticles in the shell was found to play an important role in release efficiency. The irradiation was carried out at several intensities and exposure times and evidence of microcapsule rupture after treatment was obtained by confocal and scanning electron microscopy.

Review of effect of ultrasound on electroless plating processes

Abstract When an electrochemical process is performed in an ultrasonic field, a number of well known effects occur as a result of acoustic cavitation, including enhanced mass transport, thinning of the diffusion layer and localised heating. Sometimes described as sonoelectrochemistry, applying simultaneous ultrasonic irradiation with electrochemistry has proved beneficial in a range of applications that include electrodeposition, electrosynthesis and electroanalysis. Many studies of electroplating in an acoustic field have been carried out and reviews have been published. Electroless plating is also an electrochemical process with great importance to a number of industries including aerospace, electronics, photovoltaics and automotive. Among a range of benefits that have been found as a result of introducing ultrasound to these processes are improved plating rates, coverage and adhesion of the coatings. With modern demands for high speed plating, reduced manufacturing times and the plating of nanomaterials, it is timely to review the influence of ultrasound on electroless deposition processes.

The use of insoluble anodes in acid sulphate copper electrodeposition solutions

SUMMARY The use of insoluble anodes in horizontal acid copper electroplating machines is becoming the industry standard. Despite this fact there appears to be little published work on the optimisation of the anode material for this application. Although titanium coated with iridium dioxide is widely used for its long lifetime under oxygen evolution conditions, it appears that no consideration has been given to the effect of this oxide on other electroplating parameters, for example the oxidation of additives, pulse plating etc. This paper reviews the materials that have been employed as insoluble anodes in acid sulphate electrolytes including those used for electrodeposition, electrowinning operations, and other electrochemical processes. It considers the factors that affect the materials performance under oxygen evolving conditions and collates values from the literature for the oxygen evolution potential and Tafel slopes for this reaction that have been obtained for various metal oxides. From these data, a set of criteria is established which an insoluble anode material should meet if it is to be successfully employed in an acid copper horizontal electroplating machine.

The sonochemical surface modification of materials for electronic manufacturing. The effect of ultrasonic source to sample distance

Purpose – To build on the results detailed in the previous paper where it was shown that sonochemical surface modification could be achieved in water. This paper aims to look at one of the factors affecting sonochemical surface modification, namely the ultrasonic source to sample distance.Design/methodology/approach – Ultrasound was applied through deionized water for the surface modification of three materials: a high Tg PCB laminate (Isola 370HR), a polyphenylene ether – polystyrene polymer (Noryl HM4025) and an acrylonitrile‐butadiene‐styrene/polycarbonate (Cycolac S705). The efficacy of the treatment was determined by weight loss, scanning electron microscopy, contact angle, roughness and tape testing after electroless copper plating.Findings – The study confirmed, and extended the previous findings, that a range of substrates could be sonochemically surface modified in water, even though in this work the ultrasonic horn had a larger tip size and produced a different ultrasonic intensity. Although the...

Methods for achieving high speed acid copper electroplating in the PCB industry

Significant reductions in the cycle time for the desmear, “making holes conductive” and imaging stages of the printed circuit board manufacturing process have been achieved by the use of horizontal conveyorised techniques. If these savings in time are to be fully realised, it is also necessary to have a high‐speed acid copper electroplating process that, by implication, must be capable of operating at very high current densities. This paper outlines the fundamental electrochemical principles of acid copper electroplating and explains how these impact on high speed electroplating in terms of the electrolyte chemistry, the construction of the plating cell and the method in which the current is delivered (i.e. DC or pulse).

Electroless deposition of nickel-boron coatings using low frequency ultrasonic agitation: Effect of ultrasonic frequency on the coatings

&NA; The effect of ultrasound on the properties of Nickel‐Boron (NiB) coatings was investigated. NiB coatings were fabricated by electroless deposition using either ultrasonic or mechanical agitation. The deposition of Ni occurred in an aqueous bath containing a reducible metal salt (nickel chloride), reducing agent (sodium borohydride), complexing agent (ethylenediamine) and stabilizer (lead tungstate). Due to the instability of the borohydride in acidic, neutral and slightly alkaline media, pH was controlled at pH 12 ± 1 in order to avoid destabilizing the bath. Deposition was performed in three different configurations: one with a classical mechanical agitation at 300 rpm and the other two employing ultrasound at a frequency of either 20 or 35 kHz. The microstructures of the electroless coatings were characterized by a combination of optical Microscopy and Scanning Electron Microscope (SEM). The chemistry of the coatings was determined by ICP‐AES (Inductively Coupled Plasma ‐ Atomic Emission Spectrometry) after dissolution in aqua regia. The mechanical properties of the coatings were established by a combination of roughness measurements, Vickers microhardness and pin‐on‐disk tribology tests. Lastly, the corrosion properties were analysed by potentiodynamic polarization. The results showed that low frequency ultrasonic agitation could be used to produce coatings from an alkaline NiB bath and that the thickness of coatings obtained could be increased by over 50% compared to those produced using mechanical agitation. Although ultrasonic agitation produced a smoother coating and some alteration of the deposit morphology was observed, the mechanical and corrosion properties were very similar to those found when using mechanical agitation. HighlightsUltrasound did not bring significant modification of the hardness or wear behaviour.Ultrasonic agitation generates a significant increase of the plating rate.When ultrasonic agitation was employed the coating thickness increased by over 50%.Ultrasonic agitation generates a smoother and less porous morphology.

The use of ultrasound to enable low temperature electroless plating

Purpose – Electroless plating is an important process in printed circuit board and electronics manufacturing but typically requires temperatures of 70‐95°C to give a suitable deposition rate. This is becoming problematic in industry due to the rising price of energy and is a major contribution to production costs. Previous studies have noted beneficial effects of ultrasonic irradiation upon electroless plating processes and it has been reported that sonication can increase the plating rate and produce changes to the chemical and physical properties of the deposited coating. The purpose of this paper is to reduce the operating temperature of an electroless nickel bath by introducing ultrasound to the process.Design/methodology/approach – The deposition rate of an electroless nickel solution was determined by two techniques. In the first method, test coupons were plated in an electroless nickel solution at temperatures ranging from 50‐90°C and the plating rate was calculated by weight gain. In the second ap...

Ultrasound Sonochemistry – A more sustainable approach to surface modification?

The electronics and metal finishing industries have always had a requirement for adhesion promotion on a vast array of di-electric substrates and with the emergence of printed electronics the choice of substrate will increase still further as, theoretically, anything that can be printed could become an electronic device. The surface modification of polymers and plastics is important in the traditional manufacture of printed circuit boards (PCBs) (i.e. the desmear process) and moulded interconnect devices (MIDs), but will become even more so for polymer electronics, printed electronics, Radio frequency identification (RFID) technology etc. The metallization of glass and ceramics is critical to the success of all WiFi equipment (the ceramic aerials and waveguides must be metallised), Flat Panel Displays, Organic Light Emitting Diodes (OLEDs) and Light Emitting Polymers (LEPs) as well as solar panels. In addition the etching of silicon and the newer semiconductor materials such as silicon-germanium, gallium arsenide and indium phosphide is an essential step in the processing of these substrates.

Ultrasound assisted dispersal of a copper nanopowder for electroless copper activation

This paper describes the ultrasound assisted dispersal of a low wt./vol.% copper nanopowder mixture and determines the optimum conditions for de-agglomeration. A commercially available powder was added to propan-2-ol and dispersed using a magnetic stirrer, a high frequency 850 kHz ultrasonic cell, a standard 40 kHz bath and a 20 kHz ultrasonic probe. The particle size of the powder was characterized using dynamic light scattering (DLS). Z-Average diameters (mean cluster size based on the intensity of scattered light) and intensity, volume and number size distributions were monitored as a function of time and energy input. Low frequency ultrasound was found to be more effective than high frequency ultrasound at de-agglomerating the powder and dispersion with a 20 kHz ultrasonic probe was found to be very effective at breaking apart large agglomerates containing weakly bound clusters of nanoparticles. In general, the breakage of nanoclusters was found to be a factor of ultrasonic intensity, the higher the intensity the greater the de-agglomeration and typically micron sized clusters were reduced to sub 100 nm particles in less than 30 min using optimum conditions. However, there came a point at which the forces generated by ultrasonic cavitation were either insufficient to overcome the cohesive bonds between smaller aggregates or at very high intensities decoupling between the tip and solution occurred. Absorption spectroscopy indicated a copper core structure with a thin oxide shell and the catalytic performance of this dispersion was demonstrated by drop coating onto substrates and subsequent electroless copper metallization. This relatively inexpensive catalytic suspension has the potential to replace precious metal based colloids used in electronics manufacturing.