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What’s in your product?

Or, why your quality-control department might want to zap your PCBs

Greenpeace has recently asserted that Apple’s iPhone uses a range of “potentially dangerous chemicals” in its construction, including compounds involving bromine. Directives such as RoHS (Reduction of Hazardous Substances) and WEEE (Waste from Electrical and Electronic Equipment) control the use and disposal of certain elements and compounds in electronic assemblies. The Greenpeace report stops short of alleging that Apple contravenes any of the regulations, noting only the presence of certain elements. In the case of bromine, an industry body (yes, there really is a chemical industry association just for bromine) was quick to jump in and say that Greenpeace could not know what actual compounds were used, and noted that certain brominated fire-retardent compounds are permitted under the regulations, and have few alternatives.
But how does Greenpeace – or anyone else – identify what an object or assembly is made of? The answer in this case is X-ray fluorescence spectroscopy, which these days can be a hand-held technique, for example with instruments such as the Niton analyser from Thermo Fisher Scientific. And it’s not just a technique for the analytical lab or for Greenpeace: while you are not likely to need it in the design lab, your company might want to check exactly what is in the goods it receives. You specify components that are lead free: is trusting the manufacturers’ data sheets enough to get you “off the hook” if it should happen that a supplier sends a batch that does contain lead? It is a largely untested legal area. Another example might be that you specify that your assembly sub-contractor must use lead-free solder: but rumours circulate that in some far-east locations, due to the rising cost of raw materials, old solder is reclaimed by melting it off scrap PCBs, and re-used – how would you verify what is on your PCB?
The Niton is a “gun” style device that emits a beam of X-rays. Any sample in its beam (you can set an 8-mm beam or a 3-mm spot), or at least, in the surface layer down to 100 or 200 microns, fluoresces, also in the X-ray spectrum, and the energies of the emitted X-rays are characteristic of the elements (you can only identify elements, not the compounds they are bound in) in the sample. The instrument is effectively an X-ray photon counter. It has a PIN diode detector: the amount of charge detected per event distinguishes the energy of the incoming X-ray, identifying the element species, and counting events of different energies tells you the relative abundance. A bit of processing allows the unit to present you with a list of elements found, and in what proportions: yours for around €30,000.