PCBA Tech - About SMT surface mount board after welding

Organic solvent cleaning process for SMT surface assembly board after welding

Organic solvent cleaning means that only organic solvents are used for cleaning and rinsing. After cleaning, the organic solvent on the surface of the workpiece evaporates quickly without a drying process. The cleaning mechanism is mainly dissolution. This method is suitable for cleaning printed circuit boards that are sensitive to water and whose components are poorly sealed.

General organic solvent cleaning or ultrasonic cleaning gas technology, which is the most widely used high cleaning in SMT chip processing, and the effect of high cleaning efficiency technology ultrasonic cleaning. Ultrasonic technology can clean contaminants at the bottom of components, between component companies, and in small gaps. It is suitable for post-weld cleaning of high-density, narrow-pitch, surface-mounted boards and SMA with serious pollution. Ultrasonic vibration will produce a large impact force and has a certain ability to penetrate components. It can penetrate into the packaging material layer by layer to block access to the inside of the device and damage the internal connection of the IC. Therefore, military products are generally not recommended. Use this method.

1. The principle of ultrasonic cleaning

The cleaning agent produces pore structure and diffusion effects under the action of ultrasonic waves. The hole will produce a strong impact force to clean up the contaminants attached to the surface; ultrasonic vibration will cause the liquid particles in the cleaning agent to diffuse and accelerate the speed of the cleaning agent to dissolve the contaminants. Since the cleaning agent liquid can be washed into the smallest gap of the workpiece, creating gaps and diffusers in any part of the cleaning liquid, the bottom member can be cleaned, and there are small gaps between the chip processing elements and contaminants.

The number of holes generated during ultrasonic cleaning, the size of the holes, and the strength of the vibration of the cleaning agent are related to the vibration power and frequency of the piezoelectric vibrator. The greater the density of the holes and the size of the holes, the higher the cleaning efficiency. The density and size of the holes should be adjusted to the greatest possible extent.

Second, the selection principle of cleaning agent

1. It has good wettability and low surface tension, so that the contaminants on the surface during the SMT patch processing process can fully improve the wetting and dissolution.

2. Medium capillary action, low viscosity, can penetrate into the gaps of the circuit board components to be washed, and easy to discharge.

3. High density, which can slow down the speed of solvent volatilization. Can reduce costs and reduce environmental pollution.

4. The high boiling point is conducive to vapor condensation. Disinfectants with high boiling points are safe, and can improve cleaning efficiency by continuously increasing the temperature at the same time.

5. Dissolving ability. Solubility is also known as the Kauri Butanol value (Kauri Butanol, KB value), which is a characteristic parameter of the solvent for the ability to dissolve contaminants. The larger the KB value, the stronger the ability to dissolve organic pollutants.

6 Less corrosive (corrosion). The components of the PCB solder package, and the corrosion effect occurs. After cleaning, the characters and marks on the surface of the components and the printed circuit board can be kept clear.

7. Non-toxic (or low toxicity), harmless, and less environmental pollution.

8. Good safety, non-flammable and explosive.

9. Low cost.