1. Visual inspection
The PCBA was observed using a magnifying glass (X5) or an optical microscope to evaluate the cleaning quality by observing the presence or absence of flux solid residue, tin slag tin beads, unfixed metal particles, and other contaminants. It is usually required that the surface of the PCBA be as clean as possible and that no traces of residues or contaminants should be visible. This is a qualitative indicator. It is usually targeted at the user's requirements, and the test criteria are set by itself, as well as the multiple of the magnifying glass used in the inspection. The method is simple and easy to operate. The disadvantage is that it is impossible to check the contaminants at the bottom of the components and residual ionic contaminants, which is suitable for occasions where the requirements are not high.
2. Solvent extraction test method
The solvent extraction test method is also called the ion contaminant content test. It is an average test of the content of ionic pollutants. The test is generally carried out by the IPC method (IPC-TM-610.2.3.25), which is to immerse the cleaned PCBA in the test solution of the ionic contamination tester (75%±2% pure isopropanol plus 25% deionized water), the ionic residue was dissolved in a solvent, and the solvent was carefully collected to determine its electrical resistivity. Ionic contaminants are usually derived from active materials of the flux, such as halide ions, acid ions, and metal ions generated by corrosion, and the results are expressed in terms of sodium chloride (NaCl) equivalents per unit area. That is, the total amount of these ionic contaminants (including only those that can be dissolved in the solvent), which is equivalent to the amount of NaCl, is not necessarily present on the surface of the PCBA or only NaCl is present.
3. Surface insulation resistance test method
This method measures the surface insulation resistance between the conductors on the PCBA. The measurement of the surface insulation resistance can indicate the leakage due to various temperatures, humidity, voltage and time conditions. The advantages are direct measurement and quantitative measurement; and it is possible to detect the presence or absence of flux in local areas. Since the residual flux in the PCBA solder paste is mainly present in the gap between the components and the PCB, especially the solder joint of the BGA, it is more difficult to remove, in order to further verify the cleaning effect, or to verify the safety of the solder paste used (electrical performance). The surface resistance in the gap between the measuring component and the PCB is usually used to verify the cleaning effect of the PCBA. The general SIR measurement conditions were 170 hours at ambient temperature 85°C, ambient humidity 85% RH, and 100V measurement bias.
4. Ion Contamination Equivalent Test Method (Dynamic Method)
5. Flux residue detection
