The Institute of Circuit Technology Winsford Evening Seminar
February 1st 2011
Winsford in Cheshire, towards the north-west of England, proved a popular new venue for The Institute of Circuit Technology’s series of evening technical seminars. The inaugural Winsford event, kindly sponsored by C C Electronics Europe, brought together a fifty-strong group of PCB professionals including that stalwart of the industry Dennis Price, returned to health after serious illness, to the delight of all present. Introduced by ICT Chairman Professor Martin Goosey, the programme covered a broad topic range and included papers on applications of ultrasonics, embedded RFID, automatic panel handling and via filling.
Dr Andy Cobley, Head of Materials at Coventry University’s Sonochemistry Centre, reported the progress of a study of the use of ultrasound to enable the permanganate desmear process, which traditionally involves high temperatures, long process times and hazardous chemistry, to be successfully carried out at lower temperatures and concentrations. Initially supported by the Innovative Electronics Manufacturing Research Centre, work had continued with funding from the Technology Strategy Board. Dr Cobley explained the principles of ultrasonic cavitation and the phenomenon of microjetting, which on a microscopic scale could produce extreme temperature and pressure effects at surfaces, capable of breaking chemical bonds and generating free radicals which, together with a mechanical scrubbing and cleaning action, could result in significant surface modification of materials. Moreover, ultrasonics could destroy boundary layers and facilitate the movement of reactants and by products to and away from the surface. Initial work using water alone had demonstrated and quantified the principal parameters: frequency, intensity and temperature, and provided a technology platform as a baseline for further development and eventual commercialisation. Recent work, directed at the desmearing of drilled multilayer test pieces, had examined the effect of ultrasound at various temperatures and permanganate concentrations, and had indicated that smear removal was generally better with ultrasound and that using ultrasound. It had been possible to produce samples free from interconnection defects with full strength and half strength permanganate at 60 ºC. Funding was currently being sought to enable further process validation, to scale up from laboratory to process demonstrator and to explore the applicability of sonochemical principles to other process areas.
Axel Bindel, a Research Associate at Loughborough University, was working on a collaborative research project involving PCB fabricators and assemblers, avionics and automotive OEMs, and recyclers, directed at the development of a product and process monitoring system for electronic assemblies using embedded radio frequency identification (RFID). The objective was to reduce the lifecycle costs of manufactured products by embedding intelligent information which would increase the observability and traceability of the product through the whole electronic manufacturing supply chain: PCB fabrication and assembly, original equipment manufacturing and recycling. The project partners were examining techniques for embedding RFID devices within the PCB, and developing software for selecting and handling the product information stored on them. Bindel gave an overview of the principles of RFID and its advantages over optical systems such as bar codes, particularly that no line-of-sight was required, then described the additional processes required at the lay-up and bonding stages of multilayer circuit board manufacture. The physical dimensions of an RFID chip were relatively small, typically about 450 microns in X and Y, but additional area was required within the circuit pattern to accommodate the antenna. No internal power supply was required: the chip was energised by electromagnetic induction from the reader. Manufacturing considerations included the number of plies of prepreg to use, the size and shape of the recess required, and the temperature and pressure of the bonding process. Interconnection could be achieved using conductive adhesives or solder paste. Although early trials had given poor yields, with problems of chips breaking, yields were continuing to improve and were now better than 70-80%, with chips maintaining their functionality through the thermal shocks of hot-air solder leveling and reflow. Good progress had been made with software development and applications were being evaluated in electronics manufacturing and recycling. Potential end-users had shown great interest, particularly in the automotive industry.
Leon Benmayor, from Gabriel Benmayor SA in Spain explained the benefits of automatic panel handling in PCB processing: reduced labour costs, reduced scrap and increased productivity, and went on to describe a range of proprietary equipment which included loader-unloaders, conveyors, angle diverters, turning and rotating devices. He used video to illustrate their principles of operation and special features designed to maintain direction, sense of flow and spacing between panels, to handle thin and flexible material, and safety devices to avoid damage to the work in case of malfunction. Particularly fascinating to watch in action was a loader specially developed to automate the workflow through a laser direct imaging machine. To achieve the complex motion required, the loader was equipped with a six-axis robot arm, together with a double manipulator to reduce cycle time. It could handle panels from 50 microns to 3.2 mm thick, carrying them from an input cassette, aligning them on the LDI machine then removing them to an output cassette after exposure. An additional benefit was that the machine could be programmed either for normal series operation or, if a first-off or prototype batch was required to be fast-tracked through the system, to feed layers sequentially to expose for example sides 2 and 3, 4 and 5, 6 and 7 in succession.
Final presentation came from Martin Bunce of MacDermid, who posed the question “Why fill via holes?” then went on to explain the reliability benefits of filling blind microvias with electrodeposited copper. Many PCB designs included blind microvias and plated through-holes on the same panel, creating a market demand for an electroplating process that would fill vias and plate through-holes simultaneously. MacDermid had responded by developing a proprietary acid copper chemistry with deposit properties meeting IPC specifications for tensile strength elongation and solder shock, whilst offering a through-hole distribution of 87% on 4:1 aspect ratio. Bunce explained the mechanism of via filling. The process flow was standard except for a predip prior to the copper bath designed to enhance bottom-up plating. The predip uniformly coated the panel with an accelerator, which was removed from outer surfaces by mild rinsing, but not from the bottom of the microvias. The plating bath itself contained a suppressor, which was absorbed on to the outer surface but was prevented by the accelerator from absorbing on the base of the microvias. The accelerator promoted the selective deposition of copper and as the via began to fill, deposition speed was enhanced as the curvature within the hole decreased. As the plating in the via approached the outer surface, a leveller displaced the accelerator and inhibited further plating, leaving a near-planar surface. Microvia geometry influenced filling efficiency: undercut profiles and exposed glass fibres could present difficulties, and quality of primary metallisation was critical. Extensive qualification tests had been carried out both by MacDermid and their customers, and physical properties had exceeded customer expectations. No extraordinary equipment set-up was needed to operate the process and it had a wide capability range, whether in panel plate or pattern plate format.
Professor Goosey brought the seminar to a close and thanked all who had attended, and particularly CC Electronics Europe for their support. He commented that the membership of the Institute continued to grow at an encouraging rate and that regional seminars clearly provided good opportunities for circuit technologists to get together, learn about new developments, and network and share opinions and experiences with their counterparts in the industry.
Pete Starkey
ICT Council
6th February 2011
