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.