Surface electrical resistivity

The electrical surface resistivity and charge-decay time of most materials vaiy substantially with the relative humidity. It is important that materials be tested at the lowest RH expected in use. Items that are antistatic at 50 percent RH may not be antistatic at 20 percent RH. 

Table 8.10 Electrical Surface Resistance of the Layers from Different Acidic Baths at 60°C (99)...

The electrical surface resistance of the copper layers from different acidic baths after different depositions times is shown in Table 8.10. 

Surface Resistance For opaque substrates or very thick metal layers, measurement of the thickness optically is not feasible. For such materials eddy currents (induced current) are used to measure the electrical surface resistance of the metal layer and, consequently, the thickness of the metallized layer. The thinner the metal layer, the higher its resistance. Surface resistance is inversely proportional to the thickness of the layer (proportionality factor depending on the material). 

The surface preparation method must be carefully considered, especially if the completed weldbond is to have long-term durability to hostile environments. The surface preparation should provide an optimal surface for both adhesion and welding. Thus, the choice of surface treatment is crucial, and there can be a conflict of requirements. The spot welding process requires a low electrical surface resistance, and many adhesive surface preparation processes provide a high surface resistance because of oxide layer buildup. When it is impossible to harmonize on a surface treatment, current practice tends to favor treatments that yield good weld nuggets at the expense of the adhesive bond. 

Electrostatic spraying of powders is now a commercial reality. Golovoy (6) cites particle size, spherical particle shape, and electrical surface resistivity of the powder blend as important factors in deposition efficiency. 

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