SEM/EDS analysis is a useful technique for characterizing contamination on contact surfaces.  

The figures below show EDS spectra of contamination on a gold-plated connector contact.  The contamination was causing intermittent high contact resistance.

The EDS spectrum in this case shows C, O, Na, Mg, Al, Si, Au, S, K, Ca, Ni, & Cu.  Au is the only element that should appear in the spectrum.  The contamination appears to be a combination of “dirt”, ionic compounds, and corrosion product (i.e. of Ni & Cu).

The EDS spectrum in this case shows C, O, Zn, Mg, Al, Si, Au, S, K, Ca, & Fe.  Between these two spectra we see 10%+ of the elements on the periodic table of elements, where we should only detect gold.

  • Oxygen (O) – mostly as corrosion product, i.e. oxidation 
  • Iron (Fe) – unknown source, possible corrosion product 
  • Magnesium (Mg) – likely as oxide mineral or glass constituent 
  • Aluminum (Al) – likely as oxide mineral or glass constituent 
  • Silicone (Si) – likely as oxide mineral or glass constituent 
  • Chlorine (Cl) – corrosive, likely a chemical contaminant 
  • Sulfur (S) – corrosive, likely a chemical contaminant 
  • Potassium (K) – likely as oxide mineral or glass constituent 
  • Calcium (Ca) – likely as oxide mineral or glass constituent 
  • Copper (Cu) – possible corrosion product 
  • Nickel (Ni) – possible corrosion product 
  • Zinc (Zn) – possible corrosion product

Dirt, ionic compounds, and corrosion product are likely to cause high contact resistance for a connector like this one.   The EDS spectra provide a good basis for understanding the nature of the contact resistance problem.

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