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From the Editor:
The Lead-free Dilemma
December 31, 1969 |
Estimated reading time: 4 minutes
In his book on the modern state of agriculture and eating, The Omnivore's Dilemma, Michael Pollan states that few dominant products on the food market such as corn have risen to prominence wholly on their own; that federal policies often play a vital role. One could say the same for certain technologies, with the relationship between the EU's RoHS directive and X-ray fluorescence (XRF) analyzers being the most obvious example. Virtually every government body that performs compliance verifications uses XRF tools. And RoHS did not just set up the need for quick, simplified scanning capabilities to detect non-compliant materials, it also launched a host of other trends suppliers obsolescing components abruptly, parts numbering debacles, difficulty sourcing leaded components for high-reliability assemblies where XRF is a ready and able partner to the manufacturers.
XRF analyzers are equipment that many would not have considered adding to the manufacturing floor before the lead-free era, or more accurately the era of materials disclosure and regulation. With a mix of different systems available, it's useful to know what elements of elemental analyzers vary, and what will remain the same, essentially, across each system.
"The physics of these systems will not change," points out Sia Afshari, RMD Instruments. Virtually all XRF manufacturers agree that the process of obtaining a spectrum the first step in determining the composition of a product involves electron excitation from the X-ray source. Excitation is detected and the data is sent into proprietary algorithms that generate the materials composition and parts per million (ppm) calculations. This brings up the fundamental challenge to all XRF testing. "XRF assumes a homogeneous sample," as Monet MacGillivray, Innov-X Systems, puts it, and, Afshari adds "there is nothing homogeneous about electronics." RF shields, tiny components with closely spaced leads, coatings, plastics and metals comingled, stacked packages, embedded components, and the list goes on.
Different manufacturers conquer the homogeneous sample problem in different ways. MacGillivray recommends investigating the product you're testing. Historical clues to non-compliance can help testers gain accurate data. RMD's tool screens samples at a certain depth, which can eliminate fragmented elemental composition at the surface, particularly with solder samples. Oxford Instruments offers sample cups to gather quantities of small components, for example a suspect resistor, into a testable area, says representative Zach Dismukes. Collimated spot sizes allow users to adjust the sample size on NITON analyzers from ThermoFisher Scientific. Testing a single solder joint is feasible, says ThermoFisher's Peter Faulkner.
Once a test is performed with due diligence meaning the operator tested a homogeneous sample to the best of their ability the system interface comes into play. Any and all XRF systems will provide you with a spectrum analysis peaks and valleys at certain points that designate the presence of a certain element. The problem is that it takes a good deal of materials science knowledge and training to interpret a spectrum correctly, particularly with "sneaky" elements common to electronics. One of the features that matches XRF so well to screening components, testing assemblies, and verifying solder products is speed and ease of analysis. Users expect a low degree of training for accurate implementation, and suppliers responded with color-coded Pass/Fail displays, preprogrammed testing protocols and ppm limits, and margin-of-error guidelines. All these interface elements where the spectrum data becomes useable information is the "black magic of XRF," as Gary Effronson, Fischer Technology, puts it.
Another trend in XRF screening is benchtop conversion, where handheld devices are mounted for either rapid-fire scanning, or full-board scans that take a considerable amount of time. Benchtop stands also can increase accuracy in samples by removing the naturally wiggly human from the picture. The question with stands is whether you want the X-ray head mounted top-down (for better throughput) or bottom-up (a more economical option). Users also should decide whether they need to scan the board, creating a map, which is time-consuming but thorough, Fischer adds.
Lead-free isn't the only issue, nor is RoHS the end of the story. Trends in global markets are increasingly headed toward full-disclosure directives, incarnations of which can be seen in today's REACH legislation. Most XRF tools will scan for a full range of possible elements, but the interface will only display results for those pertinent to RoHS, or a user-defined set. If data on all elements is stored for later use, however, it can say manufacturers time and money when legislation or customer requirements change. "Storing REACH and full-disclosure data prevents an overhaul every time a new element is added to a product or shows up on a ban list," Faulkner summarizes. Be sure to find out what elements an XRF system can detect, what it will store, and what elemental groupings (for example, RoHS-5 and -6) are preprogrammed.
XRF systems have a few basic qualities that make them ideal for the full-disclosure environments of international electronics sales. All XRF tools provide non-destructive testing methods; they employ a relatively safe technology for handheld operation; their size and safety credentials make transportation around the facility or around the globe quite feasible. While XRF systems have been available for decades, this might be the first time you've looked into buying one. Choosing an XRF system comes down to an understanding of sample preparation, user interface, and expectations. Electronics assembly scanning is not the same as testing a pot of solder. Performing due diligence with XRF screening might not catch a leaded component that snuck onto a lead-free board, but it might prevent the governing body that banned lead from taking disciplinary actions. And XRF screening at inventory checkpoints can make up for a lack of support or flurry of confusion from suppliers dealing with leaded and lead-free versions of many components. Bringing a new piece of equipment into the manufacturing environment without introducing new waste products, without requiring extensive operator training, and without having to destroy product to discover information all this bodes well for manufacturers operating in the "trust but verify" mindset.
Meredith Courtemanche, managing editor