PCBA cleanliness detection method

Publish Time: January 05,2019

Visual inspection

Use a magnifying glass (X5) or an optical microscope to observe the PCBA, and evaluate the cleaning quality by observing the presence of solder solid residues, tin slag, beads, unfixed metal particles and other pollutants. It is generally required that the surface of PCBA must be as clean as possible, and traces of residues or pollutants should not be seen. This is a qualitative indicator. It usually takes the user's requirements as the goal, and develops its own judgment criteria and multiples of the magnifying glass used during inspection. The characteristic of this method is simple and easy to implement, but the disadvantage is that it is not possible to check the pollutants at the bottom of the component and the residual ionic pollutants, which is suitable for occasions with low requirements.

2. Solvent Extraction Test Method

The solvent extraction test method is also called the ionic contaminant content test. It is an average test of the content of ionic pollutants. The test generally uses the IPC method (IPC-TM-610.2.3.25). It is to immerse the cleaned PCBA in the test solution of the ionization pollution analyzer (75% ± 2% pure isopropanol plus 25% DI water), dissolve the ionic residue in the solvent, carefully collect the solvent, and measure its resistivity.

Ionic contamination usually comes from the active materials of the flux, such as halogen ions, acid ions, and metal ions generated by corrosion. The results are expressed in terms of sodium chloride (NaCl) equivalents per unit area. That is, the total amount of these ionic pollutants (including only those that can be dissolved in the solvent), which is equivalent to the amount of NaCl, does not necessarily exist on the surface of PCBA or only NaCl exists.

3. Surface Insulation Resistance Test (SIR)

This method measures the surface insulation resistance between conductors on PCBA. The measurement of surface insulation resistance can indicate the leakage of electricity due to pollution under various temperature, humidity, voltage and time conditions. Its advantages are direct measurement and quantitative measurement; and it can detect the presence of flux in local areas. Since the residual flux in PCBA solder paste mainly exists in the gap between the device and the PCB, especially the BGA solder joints, it is more difficult to remove. In order to further verify the cleaning effect, or to verify the safety (electrical performance) of the solder paste used In general, the surface resistance in the gap between the component and the PCB is used to check the cleaning effect of the PCBA.

General SIR measurement conditions are 170 hours at 85 ° C ambient temperature, 85% RH ambient humidity, and 100V measurement bias.