Northern UK Circuit Group (NUKCG) Spring Seminar

Citation

Goosey, M. (2005), "Northern UK Circuit Group (NUKCG) Spring Seminar", Circuit World, Vol. 31 No. 4. https://doi.org/10.1108/cw.2005.21731dac.003

Northern UK Circuit Group (NUKCG) Spring Seminar

Northern UK Circuit Group (NUKCG) Spring Seminar

Keywords: Electronics industry, Seminar

Lead – free and Digital Technologies, Alba Centre, Livingston, 14 April 2005

This one day seminar on lead-free and digital technologies was opened by the NUKCG's Chairman, Peter Dalglish, who outlined the seminar's themes and content. The meeting began with a key note presentation from David Kynaston on the recently completed DTI Electronics Innovation Growth Team's (EIGT) report. David outlined the findings of the report and stated that the objective was to develop a vision for UK electronics to the year 2015. He highlighted that traditional definitions of the electronics industry were radically and rapidly changing. The EIGT project was undertaken for a number of reasons such as the increasing degree of outsourcing and off-shoring, the growth of electronics manufacturing in China and the UK's inability to commercialise innovation. There has also been a paradigm shift in global electronics manufacturing. The EIGT had found that the electronics industry was poorly represented, yet there were a large number of trade associations. Only 20 per cent of UK electronics companies were members of such an association. The EIGT had specific working groups covering innovation, sectors and global regions, supply chain, government and industry issues and skills. A large amount of market research was carried out and numerous in-depth interviews with senior personnel from industry were also used to validate the information. The EIGT had also sought to identify the key policy challenges faced by the industry. In the UK there were now few large traditional electronics companies and science and technology teaching had been found to be poor in terms of the needs of the industry. The EIGT had made a large number of recommendations. These included the need for the formation of an Industry/ Government Electronics Leadership Council (ELC) and this had now been endorsed by Government. There was also a need to review the SIC codes that were used to define the industry. Another recommendation was that public procurement and technical roadmaps should also be created by all government departments. A toolkit was being produced to provide the industry with a single access point for information pertaining to all supply chain decisions. Copies of the EIGT report are available at www.dti.gov.uk/industries/electronics/eigt/html.

The next presentation was from Dr Martin Goosey of Rohm and Haas Electronic Materials, who gave an update on the current state of the RoHS Directive and its impact on lead-free assembly. Martin highlighted the current problems around the adoption of the RoHS Directive due to the procedural errors made by the commission in approving the list of RoHS exemptions and the maximum concentration values. He then covered the implications of the RoHS Directive in terms of the transition to lead-free assembly. The key alloy choices for lead-free were described and these had melting points significantly higher than for tin-lead. Martin then focused on the materials related issues associated with the transition to lead-free and he highlighted the impact of higher soldering temperatures on the materials choices and process assembly parameters. He also detailed some of the other lead-free solder related problems such as tombstoning and fillet lifting. Lead-free solder was already used in volume production and had been for some time. The key for success was to understand the issues and to make allowances for them. With lead-free becoming mandatory by July 2006, it was also important not to leave it until too late to begin the transition.

The next presentation of the morning was from Stephen Mainwaring who described “Lead-free assemblies in Solectron”. In this presentation Stephen related the experience of moving to lead-free assembly and he outlined many issues involved in maintaining high quality, reliable product output. Stephen stated that there had been a lot of development work on lead-free pastes and they were now almost drop in replacements for tin- lead pastes. Solectron was encouraging its customers to get everything ready for compliance by the end of 2005 rather than to wait any longer. The component suppliers to Solectron were all adopting different approaches to component identification and yet the best route would be to change part numbers. Changing reflow processes had proved to be more straightforward than converting wave soldering. Wave soldering equipment would probably need to be modified in some way, especially as lead-free solders were quite aggressive to solder pots and related stainless steel components. Cast iron solder pots resisted erosion quite well, although existing parts could be nitride coated if a lower cost alternative was required. Tin-silver-copper alloy bar could be up to three times the price of tin-lead alloy bar, although the Sn100C alloy (Sn 0.7 Cu 0.1 Ni) was only around twice the price. Some alloys were available that contained a small quantity of lead (e.g. 0.35 per cent), which could cause problems with RoHS compliance if any further accidental additions of lead occurred. A key challenge with lead-free wave soldering was to achieve good hole filling without causing secondary reflow on the top side and without exhausting the flux. As wetting times were significantly slower than for tin-lead, wave conveyor speeds would have to be slowed down. Stephen also demonstrated typical joint quality issues and defects seen with lead-free solders. Examples included shrinkage cracks and dull joints. Some SMT adhesives had been found to be unable to withstand the lead-free soldering temperatures. During the lead-free transition period, the possibility of lead contamination was a serious concern and monitoring was important. Dissolution of copper into lead-free alloys was also a concern, especially in minipots used for repair where longer heating periods were typical. For some products it may not be possible to convert them to lead-free wave soldering and other solutions would be needed.

The final presentation of the morning was from Stewart McCracken of Materials Consultancy Services Ltd, who covered the analysis and reliability of lead-free assemblies. In this presentation Stewart focused on the impact of solder joint microstructure on reliability and he emphasized how joint metallurgy was determined by the soldering process conditions. The most critical parameters were alloy combinations, material condition and reflow profiles. The differences and similarities between SAC and tin-lead alloy joints were contrasted and compared. The occurrence of hot tearing in SAC alloy joints was shown, but it was also demonstrated that this was concentrated mainly in the surface of the joints and was not considered to be a major reliability issue. Stewart stated that the type of intermetallic formed in a solder joint was heavily influenced by the metal on the substrate, e.g. whether it was with copper or nickel. Since tin took part in the growth of intermetallics, they were the same for both tin-lead and SAC alloys, although they tended to be slightly thicker for SAC as the processing temperature was higher.

The main theme for the afternoon session was Digital Printing and its applications in the electronics industry. The first paper was given by Dr Steve Jones, Chairman of Circatex, and his presentation was entitled “Total Digital Printing of PCBs”. Steve gave an overview of the technology and he argued that adoption of the technology was vital for UK companies developing a business model based on enhanced services. In his presentation he discussed current PCB manufacturing technologies and he highlighted that most boards were now made in the Far East. It was predicted that by 2010 Europe would have only around 100 fabricators left. High volume PCB production had been lost from Europe and the technology would also rapidly drain to Asia. Asian pay rates and hours worked in China would be illegal in Europe. However, most OEMs and CEMs would like to procure locally and were currently doing so, at least for prototyping. Quality was now given, irrespective of where the goods were made. Steve then went on to detail the importance and potential benefits of maximizing the area utilisation on a PCB panel. He emphasized the dimensional changes in warp and weft directions of a laminate during chemical processing and how they were considered to affect yields and the area of a board that could be utilized. Circatex had collected huge amounts of data that had been used to develop algorithms that were now employed in a predictive modelling approach. This had been developed far enough to allow it to be used to make compensations on the shop floor. However, the process was still too long and too complicated. Inkjet printing had been identified as a potential alternative, which could avoid the need to use the traditional three-photo imaging stages used in PCB fabrication. Inkjet printing could apply ink directly to where tracks were required. Alternatively, the possibility of depositing conductive tracks directly was even more exciting. Steve then described the basic inkjet deposition process and how ultimate resolution was achieved. Currently, laser direct imaging was the only robust digital printing method available, but it used conventional etch/solder resists/masks, etc. Inkjet offered far more possibilities, in addition to tracks, a whole range of other components might be deposited, e.g. sensors, batteries, photonic circuits and batteries. Circatex had the ambition to take inkjet technology into commercial reality and were working with a number of customers and suppliers to achieve this.

The next presentation was from Robert Harvey of Xaar and was entitled “Digital Printing of Electronics”. Digital printing could offer auto-correction for substrate distortion, direct CAD to manufacture and the possibility for depositing embedded passive components. Currently, track and gap limitations were around 100 μm, but this would reduce in the next few years. Digital imaging could also offer higher yields, fast turn manufacturing, faster product development and a range of other benefits. Seiko Epson announced in November 2004 that it had produced a 20 layer circuit board using the technology approach. Xaar was developing its own technology and was looking for the UK and the European companies to use its technology. Examples of equipment including an etch resist printer and a solder mask printer were shown and these would be commercially available in the next few months. Micrographs of a Rohm and Hass developed etch resist mask were shown. Robert also demonstrated how a grey scale could be achieved using a range of ink drop sizes to achieve finer resolution and smoother angled lines.

The third presentation on Digital Printing was from Scott Mulligan of Zot and he gave an overview of direct legend printing in a PCB fabrication environment. Scott introduced the major equipment manufacturers and detailed how the process had been commissioned within the Zot manufacturing facility. Zot had been using this approach for 3 years and had found that it offered a lot of additional opportunities for traceability. The resolution could be set to as high as 720 by 720 dots per inch but, the higher the resolution used, the longer it took to print the image. At these levels the image quality was very close to that of the photo-imageable approach. Minimum line widths were claimed to be 100 μm with a stated accuracy of 5 μm and a resolution of 10 μm. The quality conformed to IPC standards. There were some consumable parts for which costs needed to be allowed, e.g. print heads had to be replaced every 12 months at a cost of nearly £600 and UV lamps cost around £3,900. A matt or semi-matt legend was applied to the part-cured solder mask and then a final cure was applied. Overall, the process could be 82 per cent faster than silk screen printing and could cost around 87 per cent less; for some companies the machine costs could be recovered in approximately 12 months. Interestingly, only four companies in the UK were currently thought to be using this approach.

The final digital printing paper was entitled “Laser Direct Imaging – How it works” and it was given by Andrew Norton of Peplertech Ltd. Peplertech were the UK and Scandinavian agents for Orbotech, the Israeli company with 1,500 employees in 30 countries. Laser direct imaging (LDI) was an enabling technology that offered more functionality per square metre, higher yields, and defect reduction. The technology also meant that no artwork was required and both LDI UV resists and solder masks were now available. The equipment used a Coherent 2 kW solid state laser operating at 355 nm and every panel was measured individually. Panel exposure was achieved via an electro-acoustic beam modulator, a rotating polygon and a fixed optical system. Up to 120 24" by 18" panels could be exposed per hour and minimum line widths of 40 μm could be achieved. Orbotech had now installed over 100 LDI units, with 21 being in Europe and several in the UK. Examples of features produced using the Shipley (now Rohm and Haas) 720 LDI resist were shown and these had excellent side wall profiles. The presentation concluded with a video commercial for the Orbotech Paragon 8000 LDI unit.

The meeting closed with a further presentation by Dr Martin Goosey, in which he gave an introduction to the possibilities for end-of-life electronics recycling. Martin described the opportunities for combining mechanical and chemical methodologies for recovering valuable materials from automotive electronics. Results from the analysis of various automotive electronic assemblies were given and the materials content was defined in terms of recovered material value. The need for a sustainable approach to chemical recovery of metals was emphasized, since traditional chemical treatment methods had typically generated large quantities of undesirable waste. The presentation concluded with an outline description of a new chemical recycling process that had been developed by Imperial College and which was being evaluated for use in automotive electronic scrap recycling.

Overall, this was a very interesting seminar with two important and topical themes that generated a lot of interest, questions and interactive dialogue.

Martin Goosey