Oxford Instruments
07 September 2006
One of the issues with the industry's move to lead-free is that of proof. Proof that your incoming components and boards are compliant, and proof that your (and your competitors) assemblies are lead-free as well. Neal Robson describes an instrument that fills this gap.
A common dilemma faced by companies when dealing with Waste Electronics, Electrical Equipment and Restriction of Hazardous Substances, (known collectively as WEEE/RoHS) legislation is what kind of equipment is best to invest in for identifying the presence of hazardous substances.
Whilst there is no individual technique that will test for all banned substances, X-Ray Fluorescence (XRF) analysis is often the technique of choice.
XRF works by sending X-Rays into a material, which excite and eject inner core electrons for each element in the sample. Another electron drops down to fill the hole left by the ejected electron, and a resulting secondary X-Ray, whose energy is characteristic for each element, is generated. A detector set at an angle to the surface being analysed then detects these secondary X-Rays. There are two types of XRF machines available to the WEEE/RoHS user: Portable XRF, a small rugged handheld device and benchtop Microspot Systems, where the X-Ray beam is collimated down to a tiny spot on the sample. Historically, portable XRF devices used a radioactive isotope source to excite the primary X-Rays sent into a material, but with recent advances these have mainly been replaced by miniature X-Ray tubes. The advantage here is that whereas isotope machines were always 'on', (always generating X-Rays), X-Ray tubes operate more like standard light bulbs - only generating X-Rays when the machine is switched on with all the interlocks made. This safety device means that the machine either is on or off so can be used, transported or stored with fewer problems. Safety is often a concern with portable devices. Oxford Instruments X-MET 3000 TXR has three safety overrides. Firstly a key is required to turn the machine on, an infra-red sensor requires the machine to be pushed up against an object before the X-Rays will turn on, and finally X-Rays are only generated when the trigger is pulled. Measuring times vary, but typically range from a few seconds for metal identification to two or three minutes for detailed soil analysis, with results and spectra displayed on a colour PDA screen. Results can be displayed in a number of ways and for RoHS analysis the software is normally configured with red/yellow/green colours showing if one or all of the elements are within specified limits, allowing a sample to be easily identified for RoHS conformance. Claims the company, one of the most appealing aspects of portable devices is the ability to measure all kinds of samples without having to create individual calibrations each time. This means that the machine does not have to be re-calibrated each time a different type of sample comes in the door. When used in the correct manner by a trained operator, instruments like the X-MET 3000 are safe and versatile. They can be used to screen incoming components of all sizes from packaging to computer parts and PCB boards to very small resistors and wires if used in a benchtop mode. Benchtop Microspot XRF systems, such as the Oxford Instruments X-Strata 960 have in the past been used as coating measurement systems. A typical example is the rapid non-destructive measurement of the gold layer on top of a nickel layer on a brass substrate, to allow optimisation of each layer in the manufacturing process resulting in reduced operating costs with no wastage. These instruments are now increasingly being used as basic RoHS analysers as well. They use a collimated X-Ray beam and by observing the sample on the in-built video camera allow the user to pinpoint specific spots on a board or component to be analysed. This allows users to go straight to the area of concern.
Contact Details and Archive...
Related Articles...
Most Viewed Articles...