Standards and inspection methods for PCBA cleaning process

Standards and inspection methods for PCBA cleaning process

The inspection after PCBA cleaning is mostly carried out by visual inspection. For products with high reliability, special testing equipment and standard methods are required to measure cleanliness. The standards for measuring cleanliness mainly include ion contamination and surface insulation resistance.

The inspection after PCBA cleaning is mostly carried out by visual inspection. For products with high reliability, special testing equipment and standard methods are required to measure cleanliness. The standards for measuring cleanliness mainly include ion contamination and surface insulation resistance.

1、 Cleanliness standard

(1) Ionic contamination

At present, there is no clear standard for ion contamination in SMT chip processing plants, which usually refers to MIL28809 or ANSI/J-001B of American Standards Institute.

(2) Surface insulation resistance (SIR)

The surface insulation resistance is usually measured by a comb circuit. This method is intuitionistic and quantitative, and has the highest reliability, but it is also the most difficult, which requires the design of comb circuit to measure. It is generally required that the surface insulation resistance SIR ≥ 10 to the 10th power/㏀.

Standards and inspection methods for PCBA cleaning process

2、 Inspection method

Cleaning process inspection shall be carried out according to the cleanliness requirements of the product. For products with special requirements such as military products, medical treatment, precision instruments, etc., it is necessary to measure the Na ion contamination with an omega (Ω) meter and other measuring instruments; In addition, shaped test pieces are usually used to test the surface insulation resistance.

The omega (Ω) meter measures cleanliness by immersing the tested printed circuit assembly (PCBA) in a clean standard solvent, dissolving the ionic contamination on the PCBA surface into the standard solvent, and then calculating the equivalent sodium ion content of the standard solvent, so as to give the cleanliness index of the tested piece. For a required product, it can be inspected by visual inspection.

The visual inspection method needs to be checked with a 4x microscope. The surface of PCB and components should be clean and free of beads, flux residues and other contaminants. The judgment standard is to see each contaminant.