Institute of Circuit Technology 41st Annual Symposium

Estimated reading time: 12 minutes

Dr. Donna Palmer introduced the new EPSRC Centre for Doctoral Training in Embedded Intelligence (CDT-EI) at Loughborough University, of which she was the manager. The centre, jointly sponsored by the Engineering and Physical Sciences Research Council, industry and the university, with funding of £13.6 million, was the first of its kind in Europe and focused on high priority areas such as autonomous complex manufactured products and systems, functional materials with high performance systems, data-to-knowledge solutions such as digital healthcare and digitally connected citizens, and engineering for industry, life and health. Research in embedded intelligence addressed the challenges posed by the technical needs and requirements of end-users. Challenge areas included design for embedded intelligence, manufacturing of embedded or on-bedded devices, packaging and interconnection, software for data collection, and hard-soft integrative technologies, all converging through applications engineering. CDT students were funded for four years and the programme included technical and transferrable skills training as well as a substantial research element. The centre brought together diverse areas of expertise to train engineers and scientists with the skills, knowledge and confidence to tackle evolving issues and future challenges, and provided a supportive and exciting environment for students, creating new working cultures, building relationships between teams within the universities and forging lasting links with industry.

ICT Chairman Dr. Andy Cobley, reader in sonochemistry and materials at Coventry University and director of the Functional Materials Applied Research Group, reviewed three research projects supported by the ICT.

The Eco-Innovation project MESMOPROC combined electrochemical reactor engineering with innovative ultrasound agitation to enable selective metallisation of microscale devices, components and printed circuit boards whilst eliminating repetitive photolithography. The conventional photolithographic method of patterning metal onto a substrate was a long, multiple step process, requiring many chemicals and a clean-room environment, and the mask could be used once only before it had to be stripped off. Electrochemical maskless patterning technology used a low metal concentration electrolyte and very small anode to cathode spacing. The ‘mask’ was placed on the anode, and ultrasound was used for agitation. The laboratory-scale reactor used in the initial stages of the project had been scaled up, plating trials were currently in progress at a PCB fabricator in the Czech Republic and a high-tech electroplating company in France, and the process was being demonstrated to potential customers and licensees.

A project for maskless metal patterning of non-conductive materials by electrochemical deposition in an external magnetic field was receiving pump-prime funding from Coventry University. The objective was to produce a disruptive, sustainable and cost-effective technology for the metallic patterning of non-conductive materials by selective electroless plating using template of magnetised iron rods mounted behind the substrate to attract metal ions.

e-MINDS was investigating electrochemical processing methodologies and corrosion protection for device and systems miniaturization, through a COST action, COST being an inter-governmental scheme to open the European research area to international cooperation in science and technology. Dr. Cobley explained that COST encouraged industry participation, and advised how small-medium enterprises could get involved.

Lunch was a less-than-formal event, which involved a walk to the museum’s High Street and queueing for traditional fish and chips, cooked in authentic beef dripping by Hobbs and Son, served in newspaper with salt and vinegar and consumed while standing in the street!

Chip wrappers ecologically disposed of and greasy fingers washed clean, delegates returned to the conference room for the afternoon session, which began with an authoritative guide to the selection of PCB materials for LED lighting applications by Les Round, technical sales manager at Spirit Circuits.

The PCB was an integral part of a modern LED luminaire, providing a convenient base for assembly and subsequent fixing of LEDs into the luminaire, thermal management of the LEDs, and an aid to power and light efficiency. LED applications fell into three main categories: low wattage/low density, mid power and high power, each of which required a substrate that balanced cost against performance. A typical low power/low wattage application was in ceiling-tile lights, accounting for large numbers of large-area single-sided PCBs on which there was a relatively low thermal demand. Low cost, flatness and high reflectance were fundamental requirements and these could be met by CEM1 material, which cost less than equivalent single-sided FR-4 and had better flatness, although it needed to be selected carefully to ensure reflow compatibility. The finished surface required high reflectivity to maximise luminaire efficiency. This had opened up a market for specially formulated white solder resists and Round described test methods developed at Spirit for qualifying reflectivity

For mid- to high-power applications, the main requirement of the PCB was effective thermal management in order to improve efficiency and longevity. A wide range of IMS materials was available to meet most thermal demands. Materials could be selected based on cost versus performance, although customers sometimes specified particular proprietary grades. Spirit had evaluated more than 70 commercially available IMS material using their own testing procedures, and had produced a league table of thermal performance. A simulated down-lighter test was used to compare high-specification IMS, traditional IMS, branded Chinese IMS and unbranded Chinese IMS. Only the unbranded Chinese material gave unsatisfactory results, and Round advised caution in selecting this type of product from data sheet values alone, without doing practical testing. He strongly recommended that the materials and panel sizes were selected as early as possible in the design cycle, and that designers used their PCB suppliers’ product knowledge to best match materials to the specific requirements of the application: thermal performance, flatness, solderable finish and solder resist.Page 2 of 3

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