This month’s analysis: SEM and EDX.

Ed.: This continues a four-part series on typical analysis techniques and their pros and cons in regard to understanding electronics residues.

Energy dispersive x-ray spectroscopy (also known as EDS or EDX) is an analytical technique used for elemental analysis or chemical characterization. The elemental matter is hit with charged particles, and EDX analyzes the x-rays emitted. There are four primary components of the EDX setup: beam source, x-ray detector, pulse processor and analyzer. Most often, EDS is part of scanning electron microscope or electron microprobe (Figure 1). A SEM comes with cathode and magnetic lenses to create and focus a beam of electrons. (It also has elemental analysis capabilities.) A detector converts x-ray energy into voltage signals; this information is sent to a pulse processor, which measures the signals and passes them on to an analyzer for data display and analysis.¹


Applications and limitations. The use of SEM identification of metal elements with only gross high levels of ionic elements. The EDX scan of this contact brush on a motor (Figure 2) shows carbon, oxygen, copper, silver, aluminum (part of the detector), silica, gold (sputter coating to protect and test sample), but it does not show the chloride and succinic acid from a water-soluble flux used to solder wires on the motor and let it flow into the motor.


The SEM/EDX analysis shows elemental information, but quantification is difficult. Because EDX uses a single electron beam to release the elemental shell and bounces this shell to the detector, it will burn through a thin film of organic and ionic residues on the surface of whatever is cut up and placed into the vacuum chamber. Because SEM/EDX is a destructive test – requiring either cutting, coating or scraping – it must be the last test run on the area of investigation. Thin-film materials, such as chloride and sulfate, can be volatilized under sublimation where the thin materials will be carried away in the vacuum and not detected.

References

1. Wikipedia.

Terry Munson is with Foresite Inc. (residues.com); tm_foresite@residues.com. This column appears monthly.