Have you ever had electronics prove to be unreliable in the field and said, “But it passed cleanliness testing!” A common reason for this happening lies in the difference between product immersion/bulk resistivity testing (e.g. ROSE testing) and localized, steam extraction/electrical testing (e.g. C3 testing).

Industry standard non-destructive test methods (ref. IPC-TR-583) are based upon immersing the product in a solvent solution. The intent is to mobilize any ionic contaminants into the solution. ROSE testers measure the change in resistivity of the total solution – an average cleanliness reading for the entire tested product. Even when ion chromatography is used to analyze the extraction, the result is an evaluation of the average product cleanliness, over all the exposed surfaces.

The C3 (Critical Cleanliness Control) test method is based upon directing bursts of steam at a small surface area of the product (0.1 in2). Critical areas of the product, for example areas most prone to entrap contaminants or containing the most sensitive circuitry, are selected for C3 testing – multiple sites can be selected (multiple tests performed) on one product. An automated, electrical test is performed on the extracted sample from a site, resulting in an indication of the ionic cleanliness of that site. Frequently, test readings for one or more small areas will indicate a product reliability threat when the immersion test has indicated an overall, relatively clean product that should be reliable. Ion chromatography analysis of a C3-extracted sample identifies the specific contaminants and their concentrations on each tested product site – a site or sites deemed to be most critical to the performance and reliability of the product.

Collaborative testing by BAE Systems and Foresite has shown that the C3 produces results with improved correlation to SIR and reliability test results. The C3 is not dependent upon the presence of particular contaminants, but rather, indicates the conductivity and/or corrosivity of the contaminant mixture extracted from the product surface of interest.