Testing for RoHS compliance

Introduction

In many respects the RoHS Directive is much better defined and easier to understand, in terms of compliance requirements, than the WEEE Directive. The RoHS Directive simply seeks to proscribe the use of certain materials in electronic equipment. These materials have been clearly defined and the levels above which they must not be present have been specified.

As long as none of proscribed materials are found to be present at levels above those stated the specific object under investigation will be RoHS compliant.

The key point from a producer perspective is that you need to be sure that none of the restricted materials is present in the products you put on the market.

Is my product or component RoHS compliant?

How can a producer be sure that a product or component is RoHS compliant?

A first step would be to seek assurances from suppliers that there are no RoHS proscribed materials present in the components they supply.

The electronics industry produces complex products comprising not just components but plastic mouldings, various metal parts, cables, screws, fixtures and fittings and a host of other individual items whose origin may not be easily traceable. The electronics industry has truly global supply chains and seemingly identical components from one company could often have originated from different factories in different parts of the world.

All this means that at some point many companies will need to test components and materials to ensure that they are indeed RoHS compliant.

RoHS compliance testing

From a basic analytical approach there is no great difficulty in testing for the presence of the RoHS proscribed materials. However, it is likely that most companies wishing to undertake such testing will have neither the resources, nor the finances to undertake what could ultimately be expensive and ongoing series of testing.

An initial low cost and relatively crude screening process is required. This can then lead to a more detailed and accurate analysis of those materials highlighted by the initial testing as being possibly non-RoHS compliant.

There has been much dialogue across the industry about the need to develop such unified test procedures for determining RoHS compliance and it seems likely that some degree of co-ordination will be achieved.

In the first instance it is quite often only necessary to know whether or not a component or part contains any of the RoHS proscribed substances. One very simple and inexpensive method for carrying out this initial analysis involves the use of an 'analytical pen' specific to the material to be analysed.

Test 'pens'

These 'pens' are in fact simply small cardboard tubes that enclose ampoules of specific chemicals that are able to give a reaction in the presence of the species to be detected. The presence of the materials can be indicated by, for example, a simple colour change.

The pad is applied to the sample to be tested e.g. a solder joint. It will colour if the material being tested fro is present. A range of 'pens' is available with reactants specific to the other RoHS proscribed metals.

XRF

One of the most economical instrumentation based analytical methods that has been proposed for initial RoHS compliance testing, utilises a technique known as X-Ray Fluorescence Spectrophotometry or XRF for short.

This method can be used initially to screen materials for cadmium, chromium, lead, mercury and bromine. It is a widely used technique that can give an accuracy of around 0.1% for the major elements and it has a detection limit of between 10 and 100 ppm for heavier elements. Portable detectors are now available which are easy to operate, reliable and require little maintenance.

It should be noted that XRF has a low sensitivity for cadmium, can also suffer from interferences between certain elements and uses a relatively large spot size for sampling which may cause problems with smaller items.

EDAX

Another rapid screening method which works well to give an initial indication of the presence of RoHS proscribed elements is Energy Dispersive Analysis by X-Ray (EDXA). This is a facility which is available on many scanning electron microscopes (SEMs) and which is capable of rapidly giving an indication of the elemental composition of a sample without the need for any elaborate preparation techniques.

It may not be suitable for smaller companies as the purchase of access time on an SEM could be expensive. As with XRF, EDXA only gives an initial indication of what elements are present and a further more detailed specific analysis would then be required for samples giving a positive indication for RoHS proscribed materials.

Other standard analytical test methods

For the metallic elements proscribed by RoHS, i.e. lead, cadmium, mercury and hexavalent chromium, their presence may be detected by a variety of standard analytical test methods.

• Lead
  In the case of lead and cadmium the suspect samples can be digested using acid and after filtration the solutions are analysed using Inductively Coupled Plasma Emission Spectroscopy (ICP-AES) or an Atomic Absorption Spectrometer (AAS).
  
  
• Mercury and Hexavalent Chromium
  Mercury and hexavalent chromium can also be analysed using these approaches, but for chromium the RoHS directive specifically proscribes hexavalent chromium and these 'tests' are unlikely to be able to give a clear indication of the oxidation state of the chromium in the sample.

  Fortunately, there are test methods available that are specific to the identification of chromium in the hexavalent oxidation state. For example, the reaction of hexavalent chromium with diphenylcarbazide is a well-established, common and reliable method for the determination of hexavalent chromium that has been solubilized using an alkaline digestate.

  The use of diphenylcarbazide is highly selective for hexavalent chromium and few interferences are encountered when it is used with samples that have been prepared alkaline media. Analysis of chromium using ion chromatography is also possible.

  For mercury analysis using an atomic absorption technique and both flame and cold vapour methods have been reported to be suitable.

• Brominated flame retardants
  For the brominated flame retardants banned by the RoHS Directive, the first and simplest test methods to use will probably be those that can simply detect the presence of bromine. This in itself is not proscribed and a positive indication for bromine would merely give an indication that one of the proscribed substances might be present - there are many other non-proscribed brominated flame retardants and so a subsequent more specific detailed analysis would then be required.

  An initial indication of the presence of bromine would normally be achieved using the methods outlined above or by analysis using other industry standard methods such as Gas Chromatography/Mass Spectroscopy (GCMS), Fourier Transform Infra-Red Spectroscopy (FTIR) or XRF. With a positive result from one of these methods, test samples would then need to be prepared for further analysis using techniques such as grinding and solvent extraction to obtain a material that could be analysed using High Resolution GCMS. Again, these techniques would be beyond the capabilities of many small companies and the services of a specialist chemical analytical service may be required.

Summary

There are many companies offering specialist analytical services and the number is likely to grow as concerns about the presence of RoHS proscribed materials increases. The specific techniques and sample preparation methodologies to be use will vary depending on the nature of the component or part to be examined.

In particular, the preparation of the sample for analysis is likely to be critical to then generation of valid data and it is recommended that the methodology is carefully developed and in collaboration with whoever is providing the analytical service.