Ionic Cleanliness Testing
Ionic cleanliness test is used to measure the conductivity (or resistivity) of a sample which can be related to the amounts of ionic materials present. The resistivity of the solution decreases as the level of ionic contamination increases. There are two types of contaminants – ionic and nonionic. Ionic contaminants are typically flux residues or harmful materials that are picked up or left behind during the process. They are generally water-soluble organic or inorganic acids or salts. They contain molecules or atoms that are conductive when in solution which can disassociate into either positively or negatively charged species and increase the overall conductivity of the solution. These ionic contaminants can degrade the reliability of the electronic components and assemblies as they contribute to current leakage between the circuitry, promote dendrite growth, and increase the risk of corrosion.
Shown in Figure 2 is a typical contamination vs. time plot. As per IPC-TM-650 Method 2.3.25 (ROSE Method), ionic residues are expressed as equivalents of sodium chloride (NaCl) in micrograms per unit surface area. The sample passes the test if the conductivity (or resistivity) is less than or equal to the target conductivity (or resistivity) value, and fails otherwise.
Figure 2. Contamination vs. time graph.
Applicable Specifications & Standards:
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