Lead-Free Testing for RoHS Compliance

Richard Boyle, European Technical Services Manager (Soldering Products), Electronics group of Henkel, UK and Nick Hoo, B.Eng., Materials Technology Division Manager, Tin Technology, UK

Already in these columns, there has been much discussion about compliance with the RoHS Directive, and the need for electronics manufacturers to gather information about the composition of components and assembly materials from their suppliers. While it represents another administrative burden on all of those involved, it is nevertheless an accepted part of performing the exercise in 'due diligence' that the directive requires. But what do you do when that information is not readily available - perhaps because the original source in the supply chain is, as yet, unaware of the necessity to provide it?

One answer is to arrange testing of the parts in question with an independent laboratory - specifically, one that is equipped with the necessary equipment and, most importantly, the analytical expertise to assess materials for RoHS compliance. At the electronics group of Henkel, such a service has been used for some time, both to supplement our own research and development work on lead-free solders and materials systems, and, on occasions, as a value-added service for our customers. In our case, this work is sub-contracted to Tin Technology (formerly ITRI), a company probably best known in the electronics industry for its activities under the Soldertec banner. Recognising the need for rapid testing and informed interpretation of the results, Tin Technology has grouped together certain test routines to provide a 'RoHS screening service'.

Why do I need a screening service?
So who should use such a service, and why? This was an oft-heard enquiry when Tin Technology launched its RoHS screening service at Nepcon in Brighton earlier this year, making it available to large electronics corporations and one-man enterprises alike - literally anyone that needs to provide evidence that they have carried out the necessary degree of due diligence in complying with the directive. Talking to people at the event, it was apparent just how little most people know about the true content of their components and materials - not surprising really, as they've probably never had to worry about it before, as long as the item conformed to specification and passed QC.

This experience is confirmed from a materials supplier's point of view; some customers know very little about the products that they supply, although it's often not for want of trying to find out. Lack of information and support from the supply chain, especially when it extends back to countries that are not actively pursuing a lead-free or other environmental improvement policy, is one of the major customer concerns reported with respect to RoHS compliance. That's where specialist knowledge comes in - a suitably-equipped and expertly-staffed laboratory will know where each of the banned substances can reasonably expect to be found in an assembly, and will be able to specify a suitable combination of non-destructive surface testing and more vigorous treatment as necessary to reach and identify the inner contents.

What should be tested, and how?
Having established who needs to have their products screened and why, how does one decide what should be tested and which method(s) should be used? There is no standard answer to that question, rather it should be a decision based on advice from the customer's screening service provider. The myth persists in some circles that all that is needed is to crush the whole product and have the residue analysed, but the reality is very different, and your screening technicians will be happy to advise you on your specialised requirements, based on their knowledge and experience of the component parts of your assembly. In general terms, tests are carried out on anything from bare PCBs and individual components through to complete assemblies, including casings, wiring and fasteners, using an array of test techniques.

Lead screening
By way of example, the usual approach to lead screening is to start the process with energy-dispersive x-ray fluorescence spectrometry (ED-XRF), a qualitative and quantitative process in which the interaction of x-rays with the test piece causes secondary (fluorescent) x-rays to be generated. Each element present in the test piece produces x-rays with different energies, which are detected and displayed as a spectrum of intensity against energy; the position and height of each peak identifies the element present and its concentration in the sample. ED-XRF is accurate and fast, but only sensitive enough to measure concentrations down to about 0.1%. One limitation of the technique is that the depth to which the surface is penetrated will vary according to the nature of the material being analysed. On plated or painted metals, the surface layer may need to be mechanically or chemically removed before analysis to ensure that the radiation reaches the substrate to be tested, while other materials may allow the radiation to reach beyond the desired depth, giving a misleading result. The skill of the equipment operator and the intelligent interpretation of results are therefore critical to the accuracy of the findings. Wavelength-dispersive x-ray fluorescence (WD-XRF) may be used in a similar fashion to ED-XRF; although this method offers higher sensitivity, it is less cost-effective and therefore not as commonly used for routine analysis.

Verification of banned substance content
Once the initial screening has identified the presence of a banned substance, further verification takes place. Using lead once again as an example, the precise concentration present is determined using inductively-coupled plasma atomic emission spectrometry (ICP-AES) or atomic absorption spectrometry (AAS). Both give similar results, the difference being in the principle of operation - as the names suggest, the former utilises energy radiation, and the latter energy absorption to produce results. It is perhaps worth mentioning that despite our focus on lead for this discussion on screening, your chosen laboratory should of course be able to carry out testing for all substances banned by the RoHS directive, although the actual screening and verification techniques for each may vary.

Worrying trends
One thing is ominously clear to both the materials supplier and the test-house - many companies are lagging behind in making their preparations for the RoHS directive, and some may leave it too late to make the deadline. From the materials side, we see many wave-soldering machines that still need to be converted to suit the lead-free process - can they all be made ready in time? And from the testing side, it is only recently that there has been an upsurge in the number of companies investing in screening of their components and assemblies, a trend that is expected to continue. Tin Technology is so concerned at the level of industry tardiness that it has embarked upon a retraining programme for several of its laboratory staff, to ensure that additional resource will be available to cope with a potential last-minute rush for testing.

Cover yourself!
At the time of writing, nobody knows for sure how rigorously the aftermath of the RoHS directive is to be policed, nor whose shoulders this responsibility will settle upon. The crucial message is that advance planning can prevent headaches later on. If you don't have certification from your suppliers to cover all of the component parts of your assemblies, and you are unlikely to receive this in good time, consider getting some independent tests done. Make sure too that you take advice from your chosen test-house on the parts of your assemblies that need to be analysed. Don't just assume that because you have had the obvious items screened, you're in the clear - those banned substances can be found lurking in the most unexpected materials and places! You'll have the peace of mind that if your process is ever scrutinised in the future, you can prove that due diligence was undertaken… and you'll be in the best possible position to keep your products in the market, while vendors that were less far-sighted have to watch theirs being withdrawn.

About the authors:

Richard Boyle
Richard Boyle joined Multicore Solders in 1985 and has fulfilled a variety of technical and commercial roles during his twenty years with the company, which is now a part of the Henkel Electronics Group. While his role involves participation in a multitude of projects with customers around the world, at present his major focus is on providing technical support for customers implementing lead-free processes within Europe.

Nick Hoo
Nick Hoo graduated from the University of Surrey, UK with an honours degree in Metallurgy, and has subsequently worked in research in the UK, USA and Luxembourg. Since joining Tin Technology in 1999, he has undertaken research in soldering and other fields of study within materials science, lectured widely on the subject of lead-free soldering, and presented several papers at international conferences and seminars.