Isotropically conductive adhesives (ICAs) and inks are seen as suitable candidates for interconnecting components and for printed circuits. Silver (Ag) filled ICAs and inks are the most popular due to their high conductivity and good reliability. However, the price of Ag is a significant issue for the wider exploitation of these materials in low cost, high volume applications such as printed electronics. Copper (Cu) is considered as a more cost-effective filler with greater abundance. However, one of the major barriers to the implementation of Cu loaded ICAs is the poor oxidation resistance of Cu particles. The copper oxide is non-conducting and hence, the conductivity of untreated Cu loaded ICAs is limited. In this work, an efficient method for the removal of the copper oxide from copper powders and application of a protective organic coating to prevent re-oxidation was developed. The coating was found to be able to limit the re-oxidation of the copper before mixing and curing of the adhesive. The treated copper powder was combined with an adhesive resin and tracks were stencil printed onto glass substrates, and cured by heating under an inert atmosphere. The effect of different adhesive resins was investigated and the samples were characterised for electrical performance and microstructure. Tracks with electrical conductivity comparable to Ag filled adhesives were obtained. The cured materials showed good stability of resistivity during storage under ambient conditions, but when exposed to 85°C and 85% relative humidity, the resistivity of exposed tracks increased substantially after 12 hours storage and methods to reduce this were identified. Functional circuits were fabricated by printing a pattern of Cu paste, placing surface mount components into the wet paste and curing.

In this paper, positron annihilation measurements have been carried out on a-Si: H thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) at high and low rates by means of the variable energy positron beam Doppler-broadening technique. The depth profiles of microvoids in the films grown under different conditions have been determined. We found a smaller void fraction in the surface region of all films compared to the bulk, and a smaller void fraction in low rate than in high growth rate films. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature, although there appears to be a higher density of defects in the boron than phosphorus doped films. The depth profiles of the microvoid-like defects in the a-Si: H films are extracted by use of the vepfit program.

Glass is a promising substitute material for use as a high density substrate for electronic packaging due to its low cost, stability, similar coefficient of thermal expansion to silicon and transparency for optical interconnections. Electroless plating has been applied to deposit conductive tracks on this insulating substrate; therefore improving the plated layer adhesion is one of the most important considerations for development of the technology. Randomly rough surfaces do show improved plating retention compared to smooth untreated glass. However, it seems likely that controlling the surface texture would improve adhesion still further. Many studies have covered the relationship between surface roughness and adhesion performance, but few of them have considered the detail of surface topography in any depth. This paper reports on the use of excimer laser machining to produce controlled texture glass surfaces to improve the adhesion of electroless copper plating for interconnection tracks. As a major tool for the study the textures were characterised using non-contact areal/3D surface topography measurement, coupled with the new ISO 25178 areal surface texture parameters. The areal parameters in principle capture much more of the complexity of surfaces than traditional profile parameters such as Ra. Adhesion of the plated copper was quantified using scratch testing. The development of the experimental techniques for the study is described. From the initial results some potentially useful areal parameters for plating adhesion such as Sal, Str, Sdq and Vw have been identified. Their predictive value needs to be confirmed using statistical hypothesis testing with larger sample batch sizes.

A degree of surface contamination has been found to be beneficial for assembly quality of optoelectronics because it reduces the surface free energy of the ceramic substrates, therefore inhibits bleed of the epoxy adhesives used to assemble components to them. This study aimed to examine the implications for process control of current industrial practice where the control of ceramic surface free energy is not considered. This has been achieved by identifying and characterising the potential sources of the contamination found on ceramic sleds, which had passed through the optoelectronic supply chain, so that the variation in chemical composition and the degree of contamination could be determined.Two types of ceramic substrates, aluminium oxide and aluminium nitride were cleaned by plasma, then stored in commercial polymer waffle packs used for transportation and a variety of storage atmospheres for one month. XPS measurements to characterize the surface chemistry were subsequently carried out following the storage to identify the composition of contamination that had built up. Contact angle and bleed distance measurements were also made to quantify the effect of the contamination on the wetting properties of the contaminated surfaces.It was found that the composition of the contamination was not directly associated with the storage method or environment, but the quantity was. The highest degree of contamination occurred on samples stored using the industrial standard method of containment in polymer waffle packs with paper and polyethylene anti-static inserts, higher even than storage in open air. The major source of the contamination in this case was probably from the inserts, with a much smaller contribution from the waffle pack. The levels of contamination built up in such case produced apparent surface free energies only slightly lower than 30mJ/m2, the threshold for acceptable levels of bleed to occur during the assembly process. This has indicated that if storage were to be used as a method of controlling epoxy bleed, it is likely that episodes of epoxy bleed would occur in a random manner on the production line, due to variation in the sample storage conditions and tendency to adsorb contaminants.

The replacement of automotive wiring harnesses with large-area flexible printed circuits (FPCs) would help to reduce the vehicle weight and emissions. To help clarify what a future large-area FPC interconnection harness should be capable of, a detailed design exercise to meet the engineering specification of the instrument panel wiring harness of a specific midrange passenger car was carried out. To demonstrate the added value of using an FPC, intelligence in the form of active circuitry was incorporated in the designs.Two generic architectural concepts were pursued. The first, a single large-area FPC, supported the wire harness geometry, all point-to-point interconnections, and current ratings up to 4 A. However, the panel size was too large to be manufactured on existing automotive FPC process lines. The second, intended to be a collection of smaller FPCs that could be manufactured on existing automotive FPC process lines, was found not to be practical as originally conceived.A physical implementation of the single large-area FPC design was made in stages at different company sites using various pieces of equipment, some of which are not normally used for FPC or electrical circuit manufacture. Modified versions of the equipment could be used to create a large-area automotive FPC manufacturing line.

Chemical and physical variability in the as-received state of aluminium oxide and aluminium nitride ceramic substrate materials used in optoelectronic modules currently leads to a process yield less than 100% when adhesives are used for assembly and interconnection. The phenomenon of epoxy bleed is a contributing factor to this yield and steps are not yet taken in the industry to control or inhibit the undesirable wetting.Standard surface texture measurement techniques, XPS and contact angle measurements were implemented to characterise and compare commercial as-received samples. The quality controls currently in place are assessed and additional analysis methods in the QC stage are suggested for increasing yield. Commercially available conductive and thermally conductive adhesives, also used in optoelectronic module manufacture, were studied along with the surfaces.In this work the surface property measurements, wetting observations and shear failure modes are compared and discussed. It was found that varying as-received surface properties did not affect adhesion strength between the adhesives and ceramics enough to induce an undesirable failure mode, although epoxy bleed distance varies dramatically with varying surface conditions.

An increase in demand for miniature electronic devices with higher transmission rates and reduced power consumption has led to advances in science and technology. Optoelectronics can be defined as a coalition of optics and electronics. The communication, health care, and the defence sector all vastly benefit from the use of optoelectronics components in various devices such as lasers, optical fibres and imaging sensors. Components in the optoelectronics industry can be surface mounted on to the substrate materials. In this study aluminium oxide (Al 2 O 3 ) and aluminium nitride (AlN) have been laser micro machined in order to study the effects of laser machining on accuracy and repeatability. It was desirable to achieve features of sufficient quality as to be used as passive alignment features in the assembly process. A previous study carried out by Williams et al. (1) concentrated on limiting the epoxy adhesive flow, and demonstrated ways in which epoxy bleed could be successfully controlled. It highlighted excimer laser machining as a repeatable and capable process for producing precise geometries. However, it was concluded that further development was required before the features could be used in an optoelectronic assembly. In this study Al 2 O 3 and AlN ceramic substrates were surface micro-machined with KrF excimer laser. The objective of this work was to investigate the feasibility of producing accurate and repeatable micron scale feature designs (<;150μm in size) with laser ablation for use in the manufacture of optoelectronics components. Furthermore, the objectives of the research were to machine features with 90° side wall angles and to achieve surface average roughness (Ra) of less than 0.3μm within machined areas.

Lab-on-a-chip and microfluidic device technology is in the early stages of commercialization. A major market is medical point-of-care (POC) and other kinds of portable diagnostics. Such systems require assembly and fluidic interconnection among the microfluidic elements and other components. However, microfluidic chips have until now been produced in relatively small numbers. While the structuring methods to make the fluidic channels are based on well established micro-manufacturing techniques such as lithography and embossing and are in general suited to mass manufacture, packaging and assembly methods require development for larger manufacturing volumes. One problem is with reliable sealing of a capping layer to the microfluidic layer for large area polymer wafers. In conventional thermocompression bonding the high pressures and need to heat the whole thickness of the polymer stack leads to potential distortion of the microfluidic structures. We present results on trials on the use of low frequency induction heating to deliver heat directly to the bonding interface thus permitting the use of lower bond pressures. The selection and structuring of susceptor materials is reported, together with analysis of the dimensions of the heat affected zone. Acrylic plates have been joined using a thin(<10 mu m) nickel susceptor providing a fluid seal that withstood a fluid pressure of 590kPa. Another problem is how to provide support structures for connection of capillary tubing or for directly connecting microfluidic chips together to form systems. We propose the use of polymer overmoulding to create a mesoscale fluidic manifold, with anticipated advantages for manufacturing of ease of assembly and low part count. Results on the reliability of the fluid seal achieved by direct adhesion between overmould materials and glass are presented. A demonstrator overmoulded structure to connect a glass microfluidic chip to capillary tubing, using a compliant grommet for sealing, is also reported

Maintaining cleanliness of substrates for assembly in optoelectronic modules is important where surfaces will be subjected to further processes in which the surface properties can affect performance. Cleanliness is counter productive when considering epoxy bleed, since the carbon based contamination of surfaces has been seen to reduce surface free energy and inhibit the spread of epoxy material. The origin of this contamination can be from a number of sources including atmosphere, handling, surface treatments and outgassing from storage media. Whilst allowing contamination to remain on the surface can be an effective means of controlling the epoxy bleed, it is not a reliable solution through lack of controllability. Identifying and quantifying this contamination will be a useful step towards the understanding and control of epoxy bleed, whilst its removal will homogenise all surfaces allowing controllable solutions to be implemented. The substrate materials of interest were aluminium oxide and aluminium nitride, which are commonly used in the optoelectronics industry. Storage methods used in industry were recreated for the purpose of this study with storage of samples in tin foil used for comparison. Samples were stored in commercial polymer waffle packs in a variety of atmospheres which they might experience in industry, on an industrial site, for one month. XPS measurements were made following storage to identify the composition of the contamination and its source. Both the degree of carbon contamination and the functional groups of any adsorbed species are known to affect surface energy and epoxy bleed. Therefore narrow band XPS spectra for carbon were analysed for all samples. Of the many methods which could be employed to remove the surface contamination, solvent, plasma cleaning and firing were chosen for their suitability and due to their availability to industry. XPS was performed on samples following cleaning. It was found that the composition of the contamination on the surfaces was not linked to their storage method but the quantity of contamination was. Storing ceramics in polymer waffle packs does not protect them from build up of carbon contamination regardless of storage atmosphere. The use of tin foil for storage can reduce the degree of contamination presence significantly, but not prevent build up entirely. A high degree of bleed was seen in both samples cleaned but not stored as well as in samples cleaned after storage, showing the effects of storage contamination are easily reversed. While storing ceramics for an extended period of time will allow build up of sufficient contamination to stop bleed occurring, samples fresh from suppliers will not have built up sufficient contamination to reduce the surface free energy to a degree such that bleed will not occur.

PurposeMicrofluidic or “lab‐on‐a‐chip” technology is seen as a key enabler in the rapidly expanding market for medical point‐of‐care and other kinds of portable diagnostic device. The purpose of this paper is to discuss two proposed packaging processes for large‐scale manufacture of microfluidic systems.Design/methodology/approachIn the first packaging process, polymer overmoulding of a microfluidic chip is used to form a fluidic manifold integrated with the device in a single step. The anticipated advantages of the proposed method of packaging are ease of assembly and low part count. The second process involves the use of low‐frequency induction heating (LFIH) for the sealing of polymer microfluidics. The method requires no chamber, and provides fast and selective heating to the interface to be joined.FindingsInitial work with glass microfluidics demonstrates feasibility for overmoulding through two separate sealing principles. One uses the overmould as a physical support structure and providing sealing using a compliant ferrule. The other relies on adhesion between the material of the overmould and the microfluidic device to provide a seal. As regards LFIH work on selection and structuring of susceptor materials is reported, together with analysis of the dimensions of the heat‐affected zone. Acrylic plates are joined using a thin (<10 μm) nickel susceptor providing a fluid seal that withstands a pressure of 590 kPa.Originality/valueMicrofluidic chips have until now been produced in relatively small numbers. To scale‐up from laboratory systems to the production volumes required for mass markets, packaging methods need to be adapted to mass manufacture.

Polycrystalline aluminium oxide and aluminium nitride sleds were machined using a CO2 laser to explore the capability of the method to produce passive alignment and assembly features for use in optoelectronic assemblies. The geometry of machined features and surface texture of machined surfaces were characterised and found to be limited by the ablation method. Consequently, a KrF excimer laser was utilised in the trials for bulk machining of the ceramics but was observed also to be restricted by its slow ablation rate. However, the combined CO2 with KrF excimer laser were then employed to exploit the benefits offered by both, fast processing time of the CO2 laser and enhanced geometry and texture control with the KrF excimer laser. In this study, the geometry and surface texture generated by the individual and the combined methods are characterised and compared to identify the processing limitations. The ability for the machining methods to produce patterns of sufficient accuracy to act as passive alignment features is therefore discussed. The suitability to produce the various artifacts to enable adhesive flow control was also examined, which can be applied for micro-scale precise assembly of high density packaging. By considering the production of such features with desirable geometry and textures, the effects of the processing parameters on the bulk material and the substrate surfaces where the energy of laser beam directly interacted was particularly investigated. This will ultimately assist to establish optimum settings of processing parameters in association with the type, properties and thickness of the substrates.

Microfluidic systems are being used in more and more areas and the demand for such systems is growing every day. Hence, a cheap and rapid method for sealing these microfluidic platforms which can be used for mass manufacture is needed. In this paper low frequency induction heating (LFIH) is presented as technique for the packaging of polymer based microfluidic systems. Thin metal layers serving as susceptors are introduced between a stack of polymer slides and heated inductively. The generated heat melts the surrounding polymer and creates a bond. Preliminary work reported here has demonstrated such bonds are able to withstand a pressure of up to 590 kPa, that both ferro- and paramagnetic susceptors are suitable for the bonding process, and that even small metal features can be rapidly heated to a temperature of 200 °C. In addition simulations and validating experiments have been carried out to understand control of the heat dissipation in the workpiece.

The exponential growth in worldwide production and consumption of electronics, and the short operational lifespan of many products, has resulted in increasing amounts of electronics waste. There is enormous pressure on electronic product manufacturers to reduce the consumption of materials and their subsequent impact on the environment, especially at the end-of-life, through such measures as the EU Directive on Waste Electrical and Electronic Equipment (WEEE). Ideally any product should be separable into its constituent parts at end of life for subsequent reuse, recycling or disposal. However separation of a typical electronic assembly into its constituent parts is problematic because of the intimate nature of the bonding between the glass fibre/thermoset composite laminate, the laminated and embedded copper conductor layers and the soldered electronic components. To address these problems, an alternative processing route for manufacture of electronics assemblies is proposed, in which the electronic components and metal content can be easily separated out from the organic content at end-of-life. No separate printed circuit board is used to interconnect the components so the process may be termed as ldquosubstratelessrdquo. The route has the additional advantage that standard electronic assembly equipment can be used. In this work the process route is described and the implications of adoption for the electronics manufacturing industry considered. The results of initial proof of principle trials are described, and conclusions are drawn as to the development work required to allow adoption of the process by the industry.

Optoelectronics manufacturers are under continuous pressure for miniaturisation of optoelectronic modules. One route to further miniaturisation is to reduce the spacing between the optical and optoelectronic components in the optical path adhesively mounted to ceramic carriers. Flow control of the adhesives over the ceramic surface is then imperative. Uncontrolled wetting can lead to an excessive adhesive footprint which interferes in the application of other adhesives for subsequent components. However, insufficient wetting can lead to low strength bonds vulnerable to thermal fatigue and shear failure. This investigation focuses on determining the factors controlling the wetting of adhesives to ceramic surfaces, with the goal of minimising the potential for uncontrolled wetting while maintaining resistance to thermal fatigue and shear forces. In addition positional stability of adhered parts on cure and in-service must not be detrimentally affected. The first step in the investigation was to characterise the surface properties of alumina and aluminium nitride ceramic plates variously processed by commercial suppliers. The surface conditions included lapped, polished, etched and as-fired. The lubricants and abrasives used by the supplier companies for the mechanical surface treatments were not specified. Initial characterisation was performed by XPS, contact angle, SEM and surface texture analysis, amongst others. Commercially available conductive and thermally conductive adhesives were applied to the ceramics and their wetting behaviour linked to the surface properties observed. Finally, single lap joints were prepared with the ceramics and adhesives and were shear tested, and the shear failure modes identified. In this work the surface property measurements, wetting observations and shear failure modes are compared and discussed.

An existing process, droplet welding, has been proposed for the production of precision, high-temperature, lead-free electrical joints. A modified metal inert gas (MIG) welding plasma is used to produce molten metal droplets, which then fall on a part to make an electrical joint. The subject of the present paper is an investigation of the factors affecting successful welded joint formation for a given droplet material and target, with the goal of providing the basis of a computer model to enable rapid process set-up on a production line. It is found that a parameter space can be identified for good adhesion of a droplet to a target, characterized by droplet temperature and target thickness, for each droplet material/target material combination. Essentially adhesion can be viewed as determined by competition between the delivery of thermal energy from the droplet to the target immediately underneath the droplet, and the removal of the energy from the interface region to the rest of the target, with no role played by the droplet kinetics after impact. It is therefore concluded that a relatively simple thermal model could be used by production-line engineers to identify the parameter space for rapid process set-up with new material combinations and products. The conclusion is supported by evidence from high-speed video images of droplet impact. Such a simple thermal model is proposed and is found to be capable of predicting adhesion between droplet and target. The results are discussed in the context of the extensive literature on molten droplet impact and solidification.

Statistical data and information from industry interviews are used to build a picture of the implications of, and responses to, globalization in the key industry of electronics contract manufacturing in the UK. A comprehensive list of companies in the sector with associated employment and turnover data has been created from a variety of sources. Comparison of 2003 data with a 1997 dataset produces a unique longitudinal statistical picture of the industry over a period marked by the increasing influence of globalization. Total employment in the industry has decreased by 39 per cent from approximately 37 600 to 23 100 between 1997 and 2003. This breaks down into a decline in the printed circuit board (PCB) manufacturing subsector of 61 per cent, from 16 300 to around 6400, and a much smaller decline in the printed circuit board sub-contract assembly (PCBA) subsector of 22 per cent, from approximately 21400 to 16700. There has been a major shift in employment distribution away from large companies. Interview results indicate that the loss of large company capacity may have strategic implications for future technological capability. However, the UK is seen as a source of innovation and retention of strong engineering skills is key to bringing new products to the market.