The board authority live – the impact of green technology, 4 October 2005

Citation

Goosey, M. (2006), "The board authority live – the impact of green technology, 4 October 2005", Circuit World, Vol. 32 No. 2. https://doi.org/10.1108/cw.2006.21732bac.004

The board authority live – the impact of green technology, 4 October 2005

The board authority live – the impact of green technology, 4 October 2005

The Board Authority's second event in its “World Tour” was held on 4 October 2005, at the Taipei World Trade Centre and was timed to coincide with the Taiwan Printed Circuit Association show. “The Impact of Green Technology” aimed to cover a wide range of PCB technologies and processes that were more environmentally acceptable or which helped to address some of the increasing number of issues presented by forthcoming and potential legislation. The subject was clearly topical as the event was attended by approximately 130 people.

The conference began with an introduction from Steve Gold, editor of “The board authority”, in which he thanked the sponsors for their support and introduced the chairman, Bob Neves. Bob is President of Microtek Laboratories and he stated that the papers being presented at the current event, plus several more, were all being published in the forthcoming issue of “The board authority” (Volume 6, number 1, 2005). Attendees were given pre-production copies which contained 15 papers, all on the subject addressed by the conference.

The first formal presentation of the day was given by Mike Wood of MacDermid who covered for Don Cullen because not been able to attend the event. This paper was on the “Characterisation, functional performance, failure mode reduction and market trends of PCB surface finishes”. Mike outlined the environmental issues being faced by the industry and then detailed the wide range of surface finish alternatives to hot air solder levelling (HASL). The current usage of surface finishes was said to be as shown in Table I.

Table I

Finish	Percentage
HASL	25-40
Organic solderabilitypreservative	20-30
Electroless nickel/immersion gold	10-20
Immersion silver	10-15
Immersion tin	<10

It was stated that the preferred type of finish actually varied from region to region: OSP was popular in Japan, whilst Germany favoured immersion tin. In America, immersion silver was popular and immersion tin was not widely used in Scandinavia because of issues with thiourea.

Mike described the benefits and issues associated with each type of finish and also compared their fully burdened costs. He concluded that there was no single ideal alternative to HASL and hence there were many possible solderable finishes that were in use today.

The next paper was given by Sven Lamprecht of Atotech and his paper covered the implementation of green technologies at various stages of the PCB manufacturing process. He began by detailing the implications of the WEEE and RoHS Directives and stated that, because the RoHS Directive came into force on 1 July 2006, most PCBs would need to be lead-free by the end of 2005. He reported work carried out to evaluate the performance of various PCB manufacturing processes when subjected to typical lead-free soldering conditions. Examples included the ability of inner layer bonding systems to survive higher soldering temperatures and multiple soldering cycles. It was stated that conventional black oxide adhesion tended to be poorer with the newer high Tg materials that were increasingly being used in lead-free applications. After three lead-free solder cycles, the adhesion had been found to drop significantly. Atotech had developed a hybrid system which was claimed to show improved performance under similar conditions.

Sven then discussed the impact of using new laminates on the desmear and PTH processes. Halogen-free base materials contained new flame retardants as well as fillers and they also had higher chemical resistances. This could lead to insufficient smear removal, poor copper adhesion and bath contamination. Lead-free soldering also caused higher stress on plated through holes. Atotech were also aiming to remove cyanide, EDTA and formaldehyde from their products. Materials such as tartrate were being evaluated as alternatives to EDTA and hypophosphite was a possible replacement for formaldehyde. Work was also reported on the development of a new resin coated copper foil (RCF) manufacturing process that was claimed to be more environmentally friendly. The process used milled dry blended raw materials, extrusion and melt coating to make RCF without the use of solvents. This “Green RCF” had a coefficient of thermal expansion (CTE) in the region of 50-71 ppm/K and a Tg of between 145 and 155°C with good elongation.

The presentation then moved on to the subject of final finishes. It had been found that medium and high phosphorus ENIG deposits generally contained less than 0.1 per cent lead but work was underway towards the use of lead-free stabilisers. The benefits of using nitrogen inerting during reflow were described; a study of the effects of using nitrogen had been made by comparing the solderability of finishes both as received and after three reflow cycles either with or without the use of nitrogen. ENIG finishes performed best but it was found that all popular surface finishes could be used with lead-free as long as the conditions wee optimised. The importance of working with OEMs and assemblers was emphasised.

Yong Seng Boo of Cookson Electronics then presented a paper entitled “Selecting base materials for lead-free assembly” in which he discussed how the choice of laminate had an impact on subsequent reliability in lead-free applications. Conducting anodic filament formation was said to be laminate dependant. The decomposition temperature (Td), i.e. time to 5 per cent weight loss by TGA, of a laminate was also significant when moving to lead-free assembly. At 235°C most laminates had been found to lose virtually no weight after up to nine solder cycles. However, if the soldering temperature was increased to 260°C there was a very big difference in how individual laminates behaved. High Tg materials were not always the best choice for lead-free and, although conventional FR4 was generally acceptable, high Tg FR4 was not recommended. In choosing a laminate for lead-free it was important to consider a number of properties including Td, CTE and time to delamination; a suitable balance of these was required for success in lead- free assembly. Polyclad had produced a laminate selection guide for lead-free.

The fourth paper of the day was from Shikoku Chemicals and Koji Saeki presented “Next generation OSP for lead-free soldering”. An OSP solderable finish offered a low-cost solution that was compatible with the thinner PCBs that were increasingly being used in many applications. They offered a planar surface, with good reliability from a process that was aqueous based and VOC-free. A weakness was that they were transparent, which impacted reliability. The Japanese automotive industry was moving to OSP with lead-free solders. The predicted global usages of surface finishes in 2005 and for 2009 were said to be as shown in Table II.

Table II

Finish type	Percentageuse in 2005	Percentageuse in 2009
OSP	38	54
HASL	37	21
Gold, silverand tin	10	10
Rosin	15	15

It was also stated that there was increasing standardisation on the choice of lead-free solders being used on in Japan. Tin-silver-copper was the first choice at over 70 per cent with tin- copper being 10 per cent of the total. The remaining 20 per cent included, tin-silver-bismuth, tin-silver-indium, tin-zinc-bismuth and a small amount of tin-lead.

There then followed a description of how OSP process chemistries had been improved in recent years, such that some could survive five lead-free solder cycles without any copper oxidation being detected. New materials based on aryl phenyl imidazoles were said to be stable to temperatures in excess of 350°C. OSPs were now being used in BGA substrate fabrication which was a very demanding application. The BGA fabrication process required the OSP to be able to survive a longer exposure to heat stress as well as a plasma clean, baking, wire bonding and epoxy encapsulant moulding and curing.

Martin Goosey of Rohm and Haas Electronic Materials (Plate 6) then presented details of novel work undertaken to develop a more sustainable printed circuit board manufacturing process. In a paper entitled “Development of a sustainable PCB manufacturing process”, Martin described work to integrate novel metal capture technologies with the use of new organic absorbent resins and an advanced oxidation unit for destroying regenerated waste. The prototype process had been demonstrated and optimised in the laboratory and a pilot unit was currently being built. Installation at a UK PCB fabrication facility was planned for October 2005 and further in-service trials would be undertaken. The project had been partly funded by the UK Government's Sustainable Technologies Initiative and, in addition to Rohm and Haas Electronic Materials, also included two UK PCB fabricators and an equipment company.

Plate 6 Left to right: Happy Holden, Martin Goosey, Karl Dietz, Frank Bai

The final paper of the conference was presented by Happy Holden of Asian Pacific Materials, and this detailed work carried out to reduce the layer count of multilayer boards as part of the process for adapting to lead-free assembly. The work had been carried out in collaboration with Celestica and, in the particular case cited, it was thought that the move to lead-free would necessitate a change to polyimide with a concomitant five times cost penalty (This was said to be for a high layer count back plane requiring six solder cycles.). An alternative solution had been found in which the multilayer board was redesigned to make it thinner.

Happy stated that in Japan stacked vias were now used exclusively for mobile phones; as pitches had diminished the need for stacked vias and/or flip chip had grown. In 2004, 200 million mobile phones had been made on China using high density interconnect techniques (HDI). He then discussed the relative price and density trade-offs for a variety of HDI solutions for a range of inner layers and showed the advantages of reducing layer count and thickness in terms of cost. He also highlighted the benefits on EMI profile of using via in pad when compared to conventional designs. Specific reference was also made to the potential benefits of moving ground planes to the surface of a board. Twenty-three additional papers on this topic were available for download from www.asianps.net.

The final part of the conference was dedicated to a panel session in which the speakers answered questions from the audience and a lively interaction occurred before Steve Gold concluded the day's events. Overall, this was a most interesting and useful event, especially as it was designed to help manufacturers in the Far East come to terms with some of the many environmental issues that were increasingly impacting their businesses. The large attendance also confirmed how seriously environmental issues were being taken by Asian PCB fabricators. This was an excellent conference and the organisers are to be congratulated for organising this “World Tour”.

Martin GooseyTaipei World Trade Centre, Taiwan