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Emerald Group Publishing Limited
Copyright © 2004, Emerald Group Publishing Limited
European LEADOUT Project – Bob Willis, SMART Group
European LEADOUT Project – Bob Willis, SMART Group
Essentially an update from Bob Willis, Technical Director of SMART Group; he reminded the delegates of the 6th Framework Programme – covering low cost lead-free soldering technology to improve competitiveness of European SME. This is technical support for benchmarking, for joint reliability, for best practice guides, for assessment of the benefits of nitrogen processing, and for failure analysis. The programme involves several companies, and no less than 12 industry associations.
Angus Westwater of Rohm Electronics talked about how you control your components and discussed the impact of lead-free on component. Rohm Electronics are developing a lead-free roadmap, showing the transition to lead-free for components, with a cut-off date. He explained that the route can be easily managed, and how potential leaded component scrap is reduced or eliminated. But, he concluded, a lead-free road map must be implemented by anyone involved with component assembly NOW!
Chris Hunt of the NPL warned of the potential pitfalls on the path to lead-free, such as component suitability – there were concerns about softening of polymer mouldings, discoloration of LEDs. NPL had taken a look at the effect of lead-free soldering on LEDs, such effects including discoloration, melting of leg finishes. On polyester capacitors of wound construction could be problematic, temperatures of 215°C led to physical deterioration. With electrolytic capacitors, the extra heat needed for lead-free extra distorts the base, and there is a function loss on polyester capacitors due to high temperatures. With BGAs NPL were worried about out gassing of moisture, and possibly some delamination inside the component. You do need to watch out for components retaining their integrity.
Lead-free finishes gave acceptable results for solderability, process yields, moisture ingression, plating ductility – tin whiskers can either be solid, perforated or hollow, they can be straight but can come off in different directions, and he showed some typical examples.
Some devices nearing the end of their product life may not be converted to lead-free, cutting short their availability.
Solder joint reliability
SAC is the main alternative alloy to SnPb. But you do need to make comparisons, and global strain around component through thermal coefficient of expansion (TCE) mismatch is one of them; lead- free solder must be able to absorb global strain. Of all the lead-free solders, SAC gives the highest reliability in solder joint strains. For high strain tin/lead is better, for lower strain rate SAC is better. As you will not be able to use tin/lead, use bismuth on the alloy that is better for higher strains.
Lead contamination. NPL had looked at lead- free joint failure due to stress through thermal cycling, with SAC this had been in secondary reflow due to the LMP phase, and NPL are looking at this cause of failure.
There is quick test for lead, by the way, using a special pencil containing sodium rhodizonate.
Another potential problem with lead-free solder is the formation of Conductive Anodic Filaments
Martin Allison of Senju Manufacturing (Europe) looked at the status of lead-free manufacturing in Japan and compared it to lead- free manufacturing in mainland Europe. Japan have various laws in place for the restriction of lead in solder and recycling, and their Road Map is JEITA 2002. They started with components, which will be lead-free by the end of 2004. Equipment will be using lead-free solder from 2003 and they will be totally lead-free in Japan by 2005.
Solder alloys being used now are SAC 87 per cent, SnAg 7 per cent, SnAgBi 2 per cent for TV. Wave soldering is using 67 per cent SAC, 22 per cent SnCu, 7 per cent SnAgBi, BGA reflow is all lead-free.
In Europe, Matsushita are now lead-free, Fujitsu in Spain will be lead-free by 2004. Pioneer and Sharp aim for complete changeover by 2004 throughout Europe, Sony in Hungary, Spain and the UK are going lead-free by 2004. Hitachi will complete their move to lead-free in Europe by 2004. Sanyo and Canon already have products that are lead-free.
A look at non-Japanese companies in Europe and Scandinavia showed that in Norway there were trials under way; in Sweden there were some production and trials in medial and communication and automotive products. In Finland trials were taking place in communications, and automotive and security electronics, Estonia was heavily lead-free.
In Hungary, Epson are now lead-free. Germany is being a bit slow off the mark, but Italy has moved to lead-free in communications, and is trialling in other areas. France is at the trial stage for all fields, Portugal is trialling in the automotive and car hi-fi areas. In Spain, subcontractors to Japanese OEMs are already lead-free, and trials are taking place in white goods, automotive, CEMs, components, in Europe, as in Japan, SAC predominates for wave, reflow and BGA soldering.
Answering a question on costs, Martin said that lead-free is more expensive. Bob Willis wondered what it would take to get the UK industry moving over to lead-free? A mad panic?! He commented that the supply chain in the UK is a circle that has to be broken somewhere and he was surprised at the attitude of the UK SMT engineers towards lead-free.
For further information, visit the Web site: www.smartgroup.org/leadfree2004/name.pdf
John LingAssociate Editor