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The final session, on European needs for new technology, product safety and training, was introduced and moderated by EIPC board member Dr. Michele Stampanoni, vice president of strategic sales and business development at Cicor Group.
His first presenter was Emma Hudson, vice-chairman of EIPC and UL’s industry lead for PCBs in Europe, the Middle East, Africa, and Latin America, continuing in her campaign to help the PCB industry through the safety certification process, this time by advising how the solder limits for UL-Recognised PCBs required to be updated to reflect the realities of surface mount assembly soldering processes. She explained that solder limits represented the soldering processes the PCB would be exposed to during assembly, and that many PCB fabricators were using outdated values related to wave soldering, where the traditional solder float conditions did not represent current SMT soldering processes. It was clear there was a significant possibility that PCBs passing the solder float test would not pass when SMT soldering processes were used. Therefore, using inaccurate solder limits for safety testing was not acceptable and if the recognised solder limits were exceeded in production then the recognition, which was in effect the safety assessment, would be invalidated,
To help make implementation easier, UL would be offering standardised soldering profiles based on IPC-TM-650 2.6.27 T230 and T260, although it was acknowledged that many different product-specific soldering profiles were in use, and that fabricators could define their own limits if they meaningfully represented the conditions their boards would experience. Ms. Hudson gave comprehensive guidance on how to define and interpret solder limits, and described the procedures for updating them for different base materials and multilayer constructions, explaining where the CCIL Program could and could not be used. Similarly, for solder resists, with examples of when the permanent coating program could and could not be used.
She advised that, commencing in 2018, UL follow-up services would require evidence of the actual soldering profiles used for the PCB assembly, to confirm that the soldering processes to which the PCB had been exposed did not exceed the recognised solder limits and so invalidate the recognition. But UL were prepared to help, and she urged fabricators to get in touch and get their requalification programmes in progress without delay.
In his presentation on printed electronics for flexible and conformal applications, Dr. Neil Chilton, technical director at Printed Electronics Limited (PEL), grouped printed electronics, flexible electronics, plastic electronics and organic electronics under one collective heading: large-area electronics, meaning processes that could be employed on roll-to-roll substrates or those that were generally in larger format than PCB or silicon processes. He gave a background to the market, which was expanding rapidly in the areas of displays and lighting, power, and logic and memory. There was a substantial market in printed sensors, dominated by mass-produced glucose test strips, but sustained growth was forecast for non-bio sensors, principally photodetectors, gas sensors and temperature sensors. In stretchable electronics, the key innovation areas were stretchable inks, flex-to-rigid connections, and sensor structures and materials. And sportswear was leading the way in Smart clothing.
IDTechEx had forecast that the market for stretchable and conformable electronics would reach $600M by 2017, and Dr. Chilton explored the opportunities for nano-metal inkjet printed circuits in this technology area. The principal benefit was that circuits could be printed directly onto a pre-existing surface, so eliminating the substrate and its weight. Because the technique was digital, additive and direct, it gave the benefits of additive manufacturing. A limitation was that the circuitry was usually thinner, more fragile and more resistive than conventional electronics, and could not carry significant current. He considered that single layers of inkjet were more applicable to direct-printed sensors than to general circuitry. However, if inkjet was used to print a seed layer, more substantial conductors could be built up with electroless copper.
Generally, inkjet inks were very low viscosity, so they needed a high-quality substrate and could not achieve the same resolution as photolithography. Neither was it easy to print on 3D surfaces. But PEL had developed a system for printing viscous inks by digital 3D deposition, which gave thicker deposits and could be used for antennas. Dr. Chilton showed examples of printing on cylindrical pre-forms for defence applications. It was also possible to use the technique for producing embedded electronics.
Continuing the theme of printed electronics, Hortense Gaya, product manager for DuPont PVAM inks at CCI Eurolam, discussed the latest developments in materials for applications in wearables and in-mould electronics.
She began by describing the formulation of a conductive ink: The base polymer required good elasticity, good adhesion to substrates and the ability to withstand high temperatures. The solvent needed the ability to effectively solubilise the polymer to give good screen printing properties and to be compatible with printed circuit and graphics inks. The filler could be a dielectric, the choice depending on whether it was for an under-print or an over-print application, or a conductor, for example silver or carbon. The resulting functional ink should have a balance of conductivity and stretchability, and a balance of viscosity and good printing properties, as well as compatibility with substrates and graphic inks.
The market for wearable electronics was expanding rapidly, predominantly in sport and fitness and healthcare, but also in home and lifestyle, industrial, commercial and military applications. Smart sportswear could monitor heart rate, breathing and muscle fatigue, using for example silver paste as a conductor and silver/silver chloride as electrodes and dielectric, optimised for stretchability and adhesion to a thermoplastic polyurethane substrate to give a comfortable garment. Combination with active components could enable wireless communication, processing of data and intelligent feedback systems. In healthcare applications, parents and caregivers could get real-time information on vital signs of infants or the elderly. In military or emergency-response situations, real-time monitoring of vital signs could protect personnel, environmental sensors could let personnel know when safety limits had been reached, and location monitoring could coordinate responses and facilitate rescue.
DuPont had developed a family of stretchable base and cover films, silver and carbon conductor inks and encapsulants specifically for applications in wearable electronics. Ms. Gaya reviewed processing techniques: combinations of screen printing, die or laser cutting and hot lamination to fabric, and discussed the evaluation and measurement of performance in terms stretchability and elastic durability, washability and comfort.
Moving on to the topic of in-mould electronics, which she defined as printed electronic circuits that had undergone a thermoforming and injection moulding process, she explained that the technique combined film, graphics and electronics, and that the circuitry, with or without mounted components, remained functional as the conductor tracks followed the contours of the 3D shape of the mould. Typical applications were 3D circuits with capacitative switches, and LED lighting controls in automotive, avionics and domestic appliances. There was a substantial weight saving, and buttons and wires were eliminated. DuPont had formulated a complete suite of electronic inks designed to survive the intense stretching and heat of the thermoforming and injection moulding processes.
Christoph Bornhorn, managing director of FED (Fachverband Elektronik-Design), the German association for design, PCB and electronics manufacturing, described how FED had developed a four-stage training programme known as ZED (Zertifizierter Elektronik Designer)—Certified Electronic Designer—with the objective of increasing the professional competence and acceptance of PCB designers. Since the programme had begun in 2015, more than 500 people had participated in courses and seminars and gained basic and specialised knowledge of PCB design. A key principle of the programme was to involve designers in the entire electronics process and to gain an understanding of electrical engineering and physics, manufacturing technology and testing procedures, materials science, standards and regulations, and economic aspects, as well as studying PCB design from first principles.
At each of the four stages, participants who passed the exam received a qualification certificate for that ZED level. After passing the whole programme they were entitled to hold the title Zertifizierter Elektronik-Designer, ZED. So far, 22 people had passed the final exams at Level 4, and FED considered the ZED concept a major success. The intention was to intensify the marketing effort to bring the programme to the attention of a wider public and recruit more participants. At present, the programme was available only in German language.
The opening slide announced, “A New Era of Agile Electronics,” as Nano Dimension’s materials manager Robert Even explored the challenges of 3D-printed electronics and discussed how this disruptive technology would redefine PCB prototyping and shorten the design and test cycles of multilayer PCBs from weeks to days. “Testing new ideas is now quick and affordable—encourage your engineers to tinker!”
Nano Dimension’s technology was based on inkjet printing, and their DragonFly machine accepted standard Gerber and Excellon input formats. Nano Dimension manufactured their own inks: a dielectric photopolymer that served as both substrate and solder mask, and a conductive silver ink made by a patented process that controlled the size and distribution of the silver nanoparticles. The formulation was matched to that of the dielectric ink and optimised for the 3D printing of conductive traces, as well as for building via interconnects. The materials were inkjetted onto a hot substrate, causing the solvent to evaporate and the nanoparticles to become sintered as part of the print process, giving layer thicknesses of about 0.3 microns.
There were not yet any applicable IPC standards, but 3D printed circuits had been tested against the IPC specifications for conventional FR-4 copper circuits. Because the substrate had no fibre reinforcement, it had limited mechanical strength, and although the polymer had a high decomposition temperature, it had a relatively low glass transition temperature, and could only be soldered with low-melting alloys. It was possible to achieve 100-micron lines and 125-micron spaces, with vias down to 200 microns, through-holes down to 400 microns, signal layers greater than six microns thick and dielectric layers greater than nine microns thick.
Thin substrates were sufficiently flexible to be used in bend-to-fit applications and non-planar circuits could be fabricated. A notable additional feature was the capability to embed components, by laying down the initial layers, interrupting the printing process, placing the components, then resuming the printing operation.
The DragonFly had been awarded a productronica innovation prize in November 2017, and seven printers had been sold to date. A demonstration machine had been brought to the conference so that delegates had the opportunity to observe the 3D printing process in operation.
Alun Morgan brought an extremely successful EIPC Winter Conference to a conclusion, thanking all who had participated: speakers, moderators and delegates. Particular thanks went to the sponsors, and especially to Alstom Transport Information Solutions for their generous hospitality. And, as ever, to the EIPC staff: executive director Kirsten Smit-Westenberg and event manger Carol Pelzers, for their superb organisation and management of the event. Morgan closed by reminding all present that 2018 was the 50th anniversary year of EIPC and that there would be special celebrations at the summer conference in Germany in June.
I am again grateful to Alun Morgan for kindly allowing me to use his photographs.