Ionic contamination occurs when ionic residues remain on a PCB which interferes with reliability and functionality. An ionic residue contains atoms or molecules that become conductors when they are in a solution. Exposure to moisture dissociates ionic residues into negatively or positively charged elements, altering the overall conductivity of the solution.
About 15% of PCBA failures are due to contamination. Testing for ionic contamination on a bare board before proceeding with assembly reduces the risk of defects caused by contaminants. The following guide will describe ionic contamination, the problems it causes, and how manufacturers perform ionic contamination testing:
Resistivity Testing in Batch-Format Aqueous Cleaning Systems: Systems used often to clean PCBs come from a built-in resistivity measurement tool. Although these results cannot be used to meet IPC standards, they can provide insight into the efficiency of the cleaning system.
1°: clean the PCB with an alcoholic solution
2°: test the resistivity of this solution
3°: by calculation, we estimate the contamination of the washing solution and we determine if there is ionic contamination. If this is the case, the solution will be more conductive
4°: from the abacus, we estimate the equivalent NaCl contamination
Machine : Metronelec CT100
The CT100 is designed to perform simple and accurate ionic contamination testing on printed circuit boards (PCBs) to obtain cleanliness measurements.
The measurements carried out on the ionic salts present are in full compliance with MIL-P-28809, MIL-STD-2000A, DEF-STD 10/03 IPC-TR-583, IES standards.
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