Cleaning of printed circuit board
When cleaning printed circuit boards after mounting capacitors, select a solvent suitable for the cleaning purpose, e.g. removal of flux or dust .
Inappropriate cleaning solvent may cause blemishes of residual flux and other foreign substances or cause deterioration of coating resin. As a result, the electrical characteristics, especially insulation resistance, and the reliability of capacitors may deteriorate.
Cleaning conditions depend on the cleaning process and cleaning machines employed.
Confirm that the adopted condition does not affect the characteristics or the reliability of the capacitors.
Unsuitable, excessive or insufficient cleaning conditions may result in deterioration of the performance of a capacitor.
- Insufficient cleaning
- 1) Halogen in the residual flux may cause the corrosion of lead wires and/or terminal electrodes.
- 2) Halogen in the residual flux may cause deterioration of insulation resistance.
- 3) Water-soluble flux has a stronger tendency than halogen to cause the phenomena described in 1) and
- Halogen in the residual flux may cause deterioration of insulation resistance.
- 1) Some cleaning solvents may deteriorate the coated resin and may cause deterioration of performance of the capacitor.
- 2) When ultrasonic cleaning equipment is used, excessive ultrasonic power or direct vibration transfer to a printed wiring board may generate a resonant vibration in the board. This may cause a crack in a capacitor or its solder joints to the board and degradation in the terminal strength of the capacitor. In order to avoid this, the following cleaning conditions are recommended.
Power: ≦20 W/L
Frequency: ≦40 kHz
Duration: ≦5 min
NOTE The details is referred to JEITA ET-7405, and the bath size is 250 mm X 200 mm X 180mm(depth)
As the cleaning solvent becomes contaminated, the concentration of free halogen may become high. This may cause the same failures as Designs of land pattern.
NOTE When a water-soluble flux is used, sufficient cleaning with deionized water and drying are necessary as a finishing operation in the soldering process.
Insufficient cleaning and drying may deteriorate reliability of the capacitor.