PCBA cleaning is a critical step in the PCBA electronic placement process. As assembly density and complexity increase, it has become a focal point in the production and processing of high-performance products like military and aerospace components, garnering significant industry attention. To enhance the reliability and quality of electronic products, PCBA residues must be meticulously removed, and contaminants should be completely eradicated when necessary.
So, what are the detection methods for PCBA contaminants?
1. Visual Inspection
Use a magnifying glass (X5) or an optical microscope to inspect the PCBA and evaluate cleaning quality by checking for solid flux residues, tin dross, tin beads, unfixed metal particles, and other contaminants. The surface of the PCBA must be pristine, with no traces of residues or contaminants. This is a qualitative measure. Inspectors often use the user’s requirements as a benchmark to establish their own inspection standards and select the appropriate magnifying glass. This method is straightforward and easy to implement but cannot detect pollutants beneath components or residual ionic contaminants. It is best suited for electronic products with less stringent requirements.
2. Solvent Extraction Test Method
The solvent extraction test method, also known as the ionic pollutant content test, assesses the average content of ionic pollutants. This test typically follows the IPC method (IPC-TM-610.2.3.25). It involves immersing the cleaned PCBA into a test solution of the ion degree pollution analyzer (75%±2% pure isopropanol and 25% DI water). Residual ionic substances dissolve in the solvent, which is then collected and its resistivity measured. Ionic pollutants often originate from flux components, such as halogen ions, acid radical ions, and corrosion-induced metal ions. The result is expressed as the amount of sodium chloride (NaCl) per unit area, representing the total NaCl dissolved in the solvent. This measurement reflects the overall ionic contamination but may not exclusively indicate NaCl presence or surface contamination on the PCBA.
Comparison Before and After PCBA Cleaning
3. Surface Insulation Resistance Test Method (SIR):
The surface insulation resistance test method (SIR) measures the surface insulation resistance between conductors on the PCBA. It identifies leakage due to pollution under various conditions of temperature, humidity, voltage, and time. Its key advantages are direct and quantitative measurement, enabling detection of flux presence in localized areas. Residual flux, especially in BGA solder joints and gaps between devices and PCBs, is challenging to remove. To verify cleaning efficacy or assess solder paste safety (electrical performance), the surface resistance between components and the PCB is typically measured. SIR test conditions usually include an ambient temperature of 85°C, humidity of 85% RH, a bias of 100V, and a test duration of 170 hours.
So, what are the detection methods for PCBA contaminants?
1. Visual Inspection
Use a magnifying glass (X5) or an optical microscope to inspect the PCBA and evaluate cleaning quality by checking for solid flux residues, tin dross, tin beads, unfixed metal particles, and other contaminants. The surface of the PCBA must be pristine, with no traces of residues or contaminants. This is a qualitative measure. Inspectors often use the user’s requirements as a benchmark to establish their own inspection standards and select the appropriate magnifying glass. This method is straightforward and easy to implement but cannot detect pollutants beneath components or residual ionic contaminants. It is best suited for electronic products with less stringent requirements.
2. Solvent Extraction Test Method
The solvent extraction test method, also known as the ionic pollutant content test, assesses the average content of ionic pollutants. This test typically follows the IPC method (IPC-TM-610.2.3.25). It involves immersing the cleaned PCBA into a test solution of the ion degree pollution analyzer (75%±2% pure isopropanol and 25% DI water). Residual ionic substances dissolve in the solvent, which is then collected and its resistivity measured. Ionic pollutants often originate from flux components, such as halogen ions, acid radical ions, and corrosion-induced metal ions. The result is expressed as the amount of sodium chloride (NaCl) per unit area, representing the total NaCl dissolved in the solvent. This measurement reflects the overall ionic contamination but may not exclusively indicate NaCl presence or surface contamination on the PCBA.
Comparison Before and After PCBA Cleaning
3. Surface Insulation Resistance Test Method (SIR):
The surface insulation resistance test method (SIR) measures the surface insulation resistance between conductors on the PCBA. It identifies leakage due to pollution under various conditions of temperature, humidity, voltage, and time. Its key advantages are direct and quantitative measurement, enabling detection of flux presence in localized areas. Residual flux, especially in BGA solder joints and gaps between devices and PCBs, is challenging to remove. To verify cleaning efficacy or assess solder paste safety (electrical performance), the surface resistance between components and the PCB is typically measured. SIR test conditions usually include an ambient temperature of 85°C, humidity of 85% RH, a bias of 100V, and a test duration of 170 hours.
