Institute of Circuit Technology Meriden Seminar, 2018
The Institute of Circuit Technology returned to Meriden, traditionally regarded as the centre of England, for its Annual General Meeting, which was followed by a technical seminar of five presentations, introduced as ever by Technical Director Bill Wilkie.
Steve Payne, ICT Vice-Chairman and Manager of European Operations for the International Electronics Manufacturing Initiative (iNEMI), gave an introduction and brief overview of the organisation in his presentation on future opportunities for PCB technology. He explained that iNEMI was a not-for-profit R&D consortium of leading electronics manufacturers, suppliers, associations, and government agencies, that encompassed all market sectors and technologies in electronics manufacturing, from design and modelling through to test, as well as recycling and sustainability issues. A principal objective was to roadmap the future technology requirements of the global electronics industry and to identify, prioritise and eliminate the gaps by engaging in timely R&D projects. The iNEMI roadmap represented the global collaboration of leading experts representing all aspects of the electronics industry, with a ten-year outlook that provided a perspective on technology trends and challenges. A unique characteristic of iNEMI projects was that they could leverage skills and resources across market sectors and throughout the supply chain.
Payne examined some of the issues associated with miniaturisation and high-density interconnect, embedded components, optical PCBs, flexible and stretchable circuits, and discussed the role of Industry 4.0 and the Industrial Internet of Things in the PCB fabrication sector. He commented that although most individual PCB fabricators had limited R&D resources, they could benefit from participation in collaborative projects to make the most of their collective expertise, and this would be a topic he would raise for discussion at the forthcoming PCB Fabricators’ Group meeting.
Dr Neil Chilton, Technical Director of Printed Electronics Ltd (PEL), gave a market overview of printed, conformal and flexible electronics, discussed PEL’s activities and areas of expertise, and introduced some novel techniques that used printing to create electronic devices or combined PCB technologies with printed electronics and additive manufacturing to produce “unconventional” circuitry and interconnects.
The market for “large area electronics,” a classification which included printed electronics and organic electronics, was expanding rapidly, particularly in the areas of displays and lighting. There was a substantial demand for printed sensors, predominantly mass-produced glucose test strips, but continued growth was forecast for non-biological sensors, principally photo-detectors, gas sensors and temperature sensors. In stretchable electronics, the key innovation areas were stretchable inks, flex-to-rigid connections, and sensor structures and materials.
Dr Chilton discussed opportunities for nano-metal inkjet printed circuits in stretchable and conformable electronics technologies, where a principal advantage was the elimination of conventional substrates by printing directly onto pre-existing surfaces. A limitation was that the circuitry was usually thinner, more fragile and more resistive than conventional electronics, and could not carry significant current. However, if inkjet was used to print a seed layer, more substantial conductors could be built up by electroless metal deposition. Screen printing was an alternative technique for the manufacture of sensors and ultra-thin flexible circuits and gave access to different materials and more robust structures. In aerospace applications, printed and large area electronics offered weight savings and opportunities for thin, long form factors.
Inkjet nano-particle inks were generally of very low viscosity and low metal content, and even on high quality substrates, conventional piezo-electric printers could not approach the resolution that could be achieved by photolithography. And it was difficult to print on curved surfaces. One of PEL’s innovations was their “3D Surface Printer,” with a programmable Z-axis, for non-contact digitally printing thicker deposits of viscous high-metal-content inks onto three-dimensional objects. And a multi-axis system had now been developed. Dr Chilton showed examples of printing on cylindrical pre-forms to create antennas for a defence application. It was also possible to use the technique for producing embedded electronics.
But at the other end of the resolution scale, a process for printing one-micron track and gap features was now available, known as “Super-Fine Inkjet,” with an electro-hydrodynamic system for generating drops in the sub-femtolitre range.
Dr Chilton stressed that printed electronics would not replace PCB technology but offered complementary production methods to enable new form factors, using a combination of new technologies and adaptations of established techniques.
ICT Chairman Professor Andy Cobley, leader of the Functional Materials Research Group at Coventry University, gave an introduction to the ‘MATUROLIFE’ project, funded under the Horizon 2020 programme, with over 20 collaborating organisations from across Europe. The project aimed to produce innovative assistive technology for older people, for example alarms and tracking devices, that would achieve better integration of sensors into fabrics and textiles, allowing designers to create high-added-value products that were not only functional, but also more desirable and appealing to older people as well as being lighter and more comfortable. Creative artists and fashion designers were included in the research team to facilitate design-driven innovation.
Conductivity and electronic connectivity in textiles could be achieved by encapsulating fibres with metal and prior work with the National Physical Laboratory had established a selective metallisation process, using a silver nanoparticle catalyst followed by electroless copper. The aim of current project work by the materials science collaborators was to replace the silver nanoparticle catalyst with a copper nanoparticle catalyst and establish a sustainable selective metallisation process for textiles. In parallel, the design management approach was to engage end users in the product design process with the aim to achieve aesthetically pleasing and fashionable assistive technology for older people.
The broader project objectives were to produce superior smart textiles and develop final finishes to improve their long-term electrical conductivity, to build a small-scale pilot line for the development of selective metallisation manufacturing concepts on textiles and fabrics, and to manufacture and validate assistive technology demonstrators in furniture, clothing and footwear.
Andre Bodegom, managing director of Adeon Technologies, discussed new developments in automated optical inspection (AOI), with particular reference to traceability. Commenting that the technology gap between IC substrates and PCBs was progressively narrowing, he listed the challenges to the developers of today’s AOI systems: maintaining design-embedded intelligence and key feature information, automatically attaching specific inspection parameters, and handling the data processing associated with high-mix quick-turnaround work, whilst maximising equipment utilisation by combining applications, and communicating inspection, measurement and traceability information to the outside world.
With the aid of a series of examples and screen-shots, Bodegom explained the concept of “parameterised” optical inspection, beginning with the software capability to read the original CAD data from any source and apply smart logic to filtering and zoning the attributes, identifying different materials and technology levels per layer, predicting magnification levels and automatic adjustment of greyscale and illumination with respect to the variety of track-widths, pad types and features, and identifying types of defects and their impact, enabling a straightforward and user-friendly error-free set-up for the operator.
Industry-leading equipment was capable of automatically identifying the particular layer of a particular job by barcode or QR code, and could set up, calibrate and register on-the-fly, with full automation an option, and scan and report defects according to pre-set technology levels and defect sizes, with on-line or off-line verification. Add-on metrology options could enable accurate dimensional measurement as well as height measurement and 3D profiling.
All results from inspection and verification could be collated in a central database, integrated into the factory IT system with open-platform logic, and accessed via any web browser on the same network, with the facility to maintain complete traceability and to let the customer generate any defect classification report he might need.
Graham Naisbitt, managing director of Gen3 Systems Ltd, presented a new approach to the ionic contamination testing of electronic circuit boards and assemblies. He discussed the limitations of the traditional method measurement of ionisable surface contaminants by resistivity of solvent extract (ROSE), which had originated back in the 1970s and is documented in IPC-TM-650, method 2.3.25. Although the technique had originally been intended for use as a process tool, it had been widely adopted as an acceptance test for cleanliness, in military and commercial standards. The requirement was to achieve better than the ionic equivalent of 1.56 micrograms of sodium chloride per square centimetre of extracted surface.
Naisbitt commented that the 1.56 micrograms limit was arbitrary, and did not correlate with environmental field reliability, especially considering the wide range of complexity of assemblies, the variety of components, feature sizes, number of solder joints, flux types and materials. Moreover, the test did not detect non-ionic contaminants which might contribute to reliability issues, and the conditions of test could extract ionic species from deeper within the material than the surface, which in real-life would never appear as free ionic material or affect reliability but could be interpreted as false defects.
Of more recent times, these limitations had been acknowledged and there had been a desire to change the approach to contamination testing, with the aim to use the dissolvable ionic material as a process indicator. A joint exercise by Robert Bosch and Gen3 Systems had demonstrated the validity of the process monitoring approach, and the consistency of measurement had been validated statistically by a gauge repeatability and reproducibility analysis across a number of sites world-wide. Sufficient flow rate, CO2 compensation and sensitive conductivity measurement had been shown to be necessary to achieve consistent performance. This test was of short duration and run at room temperature and was known by the acronym PICT (process ionic contamination testing). Naisbitt described in detail the work that had been done to optimise the PICT test process, and to compare it with the equivalent ROSE procedure.
The IPC ROSE working group had produced a white paper recommending that the technique should no longer be considered a cleanliness method but rather as a process indicator, and this recommendation would be included in Revision H of IPC-J-STD 001, classing PICT as a process control method. Naisbitt was leading the UK team working on the development of IEC 61189-5-504, which would similarly address previous difficulties and shift the emphasis from cleanliness assessment to process indicator.
Professor Andy Cobley wrapped up the proceedings, thanking participants, and the evening concluded with the customary convivial networking session.