The inspection after PCBA cleaning is mostly performed by visual inspection. For high-reliability products, special inspection equipment and standard methods are required to measure cleanliness. The standards for measuring cleanliness mainly include ion pollution and surface insulation resistance.
First, cleanliness standards
(1) Ionic pollution
At present, there is no clear standard for ionic contamination in SMT patch processing plants. Usually, it refers to the US military standard MIL28809 or the American Standards Association standard ANSI / J-001B.
(2) Surface insulation resistance (SIR)
Surface insulation resistance is usually measured using a comb circuit. This method is intuitive and quantitative, and has the highest reliability, but it is also the most difficult. It requires a comb circuit to measure. Usually requires the surface insulation resistance SIR ≥ 10 to the power of 10 / ㏀.
Second, inspection methods
The inspection of the cleaning process shall be carried out according to the cleanliness requirements of the product.
If it is a product with special requirements such as military products, medical treatment, and precision instruments, it is necessary to measure the Na ion staining degree with measuring instruments such as an omega (Ω) meter; in addition, a shape test piece is usually used to test the surface insulation resistance.
The method for measuring the cleanliness of an omega (Ω) meter is to immerse the printed circuit assembly (PCBA) in a clean standard solvent, dissolve the ionic contamination on the surface of the PCBA in the standard solvent, and then calculate the Equivalent sodium ion content to give the cleanliness of the part under test
Index For a required product, it can be inspected by visual inspection.
The visual inspection method needs to be inspected with a 4x microscope. The surface of the PCB and components should be clean and free of beads, flux residues and other dirt. The criteria for judging by the presence of contaminants.