The ionic cleanliness of printed circuit board (PCB) and printed circuit assembly (PCA) surfaces is important in electronics manufacturing and affects reliability of the product. The electronics industry has been interested in how ionic cleanliness correlates with corrosion, electrochemical migration, dendritic growth, and subsequent open circuits or leakage current during testing and in the field.
The most prominent, initial method for cleanliness evaluation is resistivity of solvent extract (ROSE) that measured the conductivity of a solution after flowing it over a surface of interest. A major disadvantage of this technique was its inability to detect specific ionic species generating conductivity.
Ion chromatography (IC) has become an important technique for the evaluation of ionic cleanliness. This technique, which detects individual ions, allows quicker trouble-shooting of contamination sources and better predictions about the detrimental effects of each ionic species by themselves. Ion chromatography is a form of high-performance liquid chromatography (HPLC) and works with aqueous sample solutions. It is able to measure concentrations of major anions, such as chloride and bromide, as well as major cations such as sodium, ammonium, and potassium in the parts-per-billion (ppb) and low parts-per-million (PPM) range. Concentrations of weak organic acids (WOAs) can also be measured through IC.