SMART Group 6th European Surface Mount Conference

SMART Group 6th European Surface Mount Conference

Keywords: Conferences, Europe, Soldering, Surface mount technology

SMART Group held their 6th European Surface Mount Conference in November,once again at the Old Ship Hotel in Brighton. It got off to a flying start with a “Lead-free, Ask the Experts” question and Answer session. Concoat MD Graham Naisbitt took the chair, and Clive Simmonds of BAe Systems, Jim Vincent of Bookham Technology, David Hillman and Doug Pauls of Rockwell Collins responded to questions from a large audience (Plate 1).

 Plate 1The panel from the question and answers session

Comment was invited on the likelihood of continued availability of tin-lead solder after July 2006. Then consensus was that the natural rules of supply and demand would prevail: tin- lead would be made available for as long as people were prepared to pay for it. Inevitably, as the requirement became smaller and more specialised, the price would increase. For aerospace and military applications, a demand for tin-lead solders would remain until lead-free alternatives had been proven to be as functional and have long-term reliability. Doug Pauls of Rockwell commented that his company could move over to lead-free soldering tomorrow, but that they would not be able then to guarantee product reliability.

Response to the question of how WEEE and RoHS compliance would be policed revealed that the UK Government had yet to make any meaningful provision and that responsibility would nominally fall upon local trading standards departments. In reality the supply chain would become self-policing. Relying upon audit trails and declarations of compliance and there was no doubt that competitors would be carefully monitoring each other's products.

The need for cleaning lead-free assemblies after soldering, and potential difficulties that might be encountered, was the subject of a lively discussion. It was agreed that unless the cleanliness of incoming components was assured, it might be a good practice to clean anyway, although lead-free fluxes could require more aggressive cleaning processes. The cleaning challenge had not yet been comprehensively addressed; lead-free flux formulations were still in a state of evolution and optimisation, and cleaning experience was limited. One certain conclusion was not to use a no- clean flux if any requirement to clean an assembly was anticipated.

There was some debate as to whether in principle the industry should continue to apply for exemptions from lead-free legislation. It was not necessarily too late to make a case for exemption, but the response time can be lengthy. More realistically, the industry should be lobbying for extensions to cut-off dates,particularly where long-term reliability investigations had not yet been concluded. Whatever the merits of qualification procedures, it was impossible to look with certainty from 15 to 20 years into the future.

Bare board considerations such as halogen-free laminates and lead-free finishes were discussed. It was generally agreed that currently available halogen-free laminates only marginally pass UL flammability testing, and the additional temperature stresses of lead-free assembly processes would probably cause further degradation of properties. There was a need for some fundamentally new development, but none was emerging.

Lead-free hot-air solder-levelling had been demonstrated to be practicable,but was not considered to be the preferred finish for the future. Electroless-nickel/immersion-gold was falling out of favour. Immersion tins,immersion silvers and organic solderability protectives were expected to become the mainstream finishes in the longer term.

The value of such a question and answer session cannot be underestimated.

Over the 2 days there were nine workshops. In one, entitled “Lead-free introduction for consumer and automotive applications” Hans-Jürgen Albrecht came over from Berlin to talk about how Siemens are introducing lead-free technology, and since he has been working on lead-free since 1997, he knows a thing or two about it. He looked at the composition of lead-free solder alloys, and the preferred solders for some of the major organisations and OEMs,and all of them are different; in Germany it will be different again. There are about 100 different lead-free solders, and in his opinion that's 99 too many. He listed the components that are compatible with various finishes, and SAC seems the common denominator, especially for chip scale packages. It was interesting to note that he had contacted some 110 suppliers, and only 45 of them responded they are on the time schedule for the changeover to lead-free. Amongst his conclusions from a detailed presentation was that international co-operation and consolidation is required, and he is spot on the mark there.

Professor Bill Plumbridge of the Open University and Angus Westwater of Rohm Electronics put together an excellent workshop looking at components and solder joint reliability in a lead-free world. After a good look at the problem caused by using lead, they moved on to the problems of lead contamination of solder joints, solder machine erosion, inventory control, BGA placement in a lead-free process, the parameters encouraging whisker growth in component tin plating,amongst other things. They said that if you looked long and hard at the subject,you would be bound to conclude that ever decreasing component termination solder joint surface area, and reliability demands, the industry would have had to adopt a mechanically improved and durable lead-free solder, irrespective of environmental legislation.

Jean-Paul Clech is with EPSI Inc. in New Jersey, and his workshop provided an overview of reliability trends for popular lead-free alloys such as SAC. He put the performance of lead-free and mixed assemblies into perspective with that of SnPb assemblies, and identified common risk areas. He presented detailed data on material properties and fatigue curves, also accelerated test results, and went through the effects of common PCB and component finishes in workshop bristling with experience.

Dave Hillman and Doug Pauls both work with Rockwell Collins in the USA, and as a double act they were singularly successful in putting together, over two workshops, the way in which to establish a sound lead-free manufacturing process. Covering the range of materials and process considerations, they gave many practical examples, and put down all the data that must be considered for reliable lead-free assemblies.

Phil Zarrow (Plate 2) was on for a double-whammy, and one could see why. He took his workshop delegates through an understanding of how to identify and correct most SMT assembly problems, including vendor and design related ones. Phil went through a step-by-step investigation of the reflow soldering process,including solder paste deposition, and highlighted some of the problems, and some of the remedies. In this high-tech age good workmanship still remains a vital ingredient in the manufacture of SMT circuit boards assemblies.

 Plate 2Phil Zarrow

Alan Brewin of NPL is someone you can listen to all day. His chatty style of presentation made his workshop on interpreting reliability data a source of great interest to the many who attended, and the work done at NPL on lead-free reliability must be amongst the finest in the world. Alan explained how one could make sense of reliability data, not just for solder joints, but also for laminates and fluxes, and how to make intelligent use of this in approaching ones own lead-free trials, and subsequent design or material choices.

Not having Bob Willis at a lead-free conference is like having a lion missing in Trafalgar Square. Like all good lions, Bob roared his way through the immense subject of trouble-shooting the lead-free wave soldering process. Given the daunting size of the subject, it was appropriate that someone like Bob could tackle it, covering as he did the detailed examination of the process, in all its aspects. It is the wave soldering process that is the most affected by the change in materials, so it was important to consider the cost increase in the alloy, the solder bath and copper erosion, and impact of the increased temperatures, in a most demanding process.

David Bernard of DAGE and Nick Hoo of ITRI chatted about the application of or appropriate test and inspection procedures, the merits of different inspection methods. Some test parameters are no longer valid with lead-free solders, so implementing lead-free solder into production raises questions as to the acceptability and adequacy of a company's existing test methods. The use of X-ray equipment was discussed, and how it can be used for optical inspection of BGAs.

Quite apart from the nine workshops, there were three further focus presentations, the first on WEEE and RoHS legislation for anyone who is not yet fluent in this language. Next came one on SMD placement, which covered the implications of miniaturisation, and the impact of “new” processes. There followed a talk on the experience gained on the complete lead-free production facility run at Nepcon in May this year, which had provided some invaluable feedback on the various board finishes, solder alloys, reflow technologies and rework options that were available.

In the first of two Keynote Addresses, Mark Hutton from BPA Consulting came to talk about developing 5-year forecasts. We all abide by forecasts, he said,so we need to understand them, as in the end it is down to the individual to judge their value. At BPA they specialise in short-, medium- and long-term forecasting, with their key competence focused on the electronic manufacturing sector. They know the supply chain of the EMS field, and cover PCBs, IC packaging, MCMs, advanced materials, connectors and system architecture; they also devote time to liasing with investors who are looking at emerging technologies. How accurate are they? No one is that accurate, said Mark, but BPA have an enviable track record.

Forecasting meets three needs – short-term, which is essential for utilising resources, capital equipment, raw materials, labour. Medium-term– adjusting resources to meet future requirements, and long term, where you have to determine capital resource requirements to meet the long term growth strategy.

Forecasting techniques include – qualitative – judgmental, market research, and Delphi. Quantitative – time series and explanatory methods. BPA have been successful with their proven methods, and Mark then went on to illustrate how to read data, why 12/12 curves are used, how to understand growth curves and how to create a centred curve. Good data comprehension can give you 3-6 months early warning.

Be assured that any forecast from BPA is based upon the latest sophisticated and scientific techniques available. Or, as Mark said, they combine quantitative decomposition and regression with qualitative judgmental forecasting. Quite.

Phil Zarrow of ITM Consulting then came on to talk about lead-free implementation – the other 90 per cent. He set the scene by establishing that SAC is the main usable alloy, acceptable production processes have been made, and now it is implementation and logistics that involve significant efforts – the other 90 per cent.

He went through the reasons for going lead free, the moral convictions, the technical advantages, the higher temperatures and the reliability, the competitive advantages of requirement, and the legal mandates. But what about costs? Lead-free solder joints cost 400 per cent more, claimed one industry observer. A claim that is unsubstantiated. Prismark estimate that costs will rise from 4-15 per cent for assembly, with production costs up by 5 per cent. Phil said that it was remarkable to note that whereas Japan had had JEITA in place since 1998, in the USA official regulations and roadmaps are still pending. Forty-eight per cent of companies surveyed in the USA have no plans to use lead-free, 24 per cent says that they will get round to it in about a years time, and only 12 per cent use it now.

Phil emphasised that the key area is product reliability and functionality. In the move to lead-free be aware that “drop-in” replacements do not exist. There are many factors to consider, such as higher temperatures; material requirements including surface finishes; higher temperatures affect upon plastics and laminates; repair materials; hardware; components and PCBs. Moisture damage in IC packages is a concern. He looked at other aspects to consider, including printing, solder paste powder, lead-free will impact on equipment, and processes; and, yes, there is a greater propensity for voiding.

IPC Standard 610D is now awaited, the essential criteria have been identified, so hang on for it. In the move to lead-free, remember that quality training comes into it, too. However, it is logistics that is the most complicated portion. The wisdom of going partial lead-free was discussed, this is not a sound idea, as it costs more in the long run. You do need to maintain two separate processes.

Lead-free will affect design, procurement, manufacturing and support, but approach it all as a team, and plan your implementation logistics. And do it now. What are the advantages? You can maintain market share, and gain a competitive edge. And the disadvantages? Higher material costs, equipment conversion, training costs.

In his closing comments, Phil said that we would all be much stronger for it. Hopefully the same may be said for the solder joints.

The whole subject of lead-free is fraught with uncertainty, beset with difficulties, carries a vast burden of added cost, and has been implemented by people who will have had little or no idea of the implications of their ideology. Those who attended the SMART Group Conference in Brighton are amongst those sound and excellent people now dealing with those implications, and the organisers are to be congratulated on putting together a very full programme that covered the subject in huge depth.