Surface Insulation Resistance

07 March 2003

Surface Insulation Resistance (SIR) testing, is a non-destructive methodology used to evaluate electronic assembly materials and processes as one measure of reliability.

The goal of SIR testing is to catch dangerous propensities for electro-chemical failure mechanisms, such as unacceptable electrical leakage under humid conditions, corrosion and metal migration, before they can occur on produced assemblies.

Three factors need to be present for electro-chemical failures to occur: electrical potential, moisture and an ionic residue. Electrochemical failure can best be visualised using the VENN Diagram. Increasing and decreasing these factors can be thought of as increasing and decreasing the diameter of the circles.

In SIR testing, temperature and humidity levels are artificially elevated to accelerate the moisture factor. A voltage is applied to provide a power source. If the test substrate has a low ionic content, then the measured SIR will remain "acceptable". If the ionic content is high, such as from improperly cured solder resist or from flux residues, then "unacceptable" leakage currents, corrosion and metal migration will occur.


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