Compressed air, as the second largest power source after electricity, has been recognized by the business community. Many users often only pay attention to the configuration, equipment selection, and subsequent installation and use of smt patch proofing or processing production line. The choice of main equipment (for example: placement machine, solder paste printer, wave soldering machine, etc.) ignores the reasonable selection and investment of aerodynamics, leaving long-term hidden dangers to the production line.

The compressed air used in the smt production line is not only required to provide stable and sufficient air pressure and flow, but also the compressed air used must be dry and clean (the manufacturer’s instruction manual also emphasizes it). Next, the editor of Zhongyan Electronics will give an introduction.

1. Impurities in compressed air
The impurities in compressed air mainly include oil, solid particles, water, dust and so on.
The oil in the compressed air mainly comes from the mechanical movement process inside the air compressor, and the lubricating oil necessary for the air compressor to perform work. Oil-free air compressors are undoubtedly the best choice, but due to the extremely high price of oil-free air compressors, most users can only choose ordinary screw compressors. Therefore, it is inevitable to mix part of the oil in the compressed air. Dust particles, oil and moisture in the air can be removed with high efficiency filters and dryers.
2. Principle of compressed air

REFLOW SOLDERING OVEN MACHINE INFRARED REFLOW SOLDERING OVEN/REFLOW SOLDERING OVEN SMT HOT AIR CONVECTION 8 HEATING ZONE

The solid particles in compressed air are mainly removed by precision filters. There are three principles:

1) "Directly capture" the larger and heavier particles moving in a straight line;

2) "Inertial collision", used to capture particles that are smaller, lighter, and change direction slightly with the airflow;

3) As for very small particles, they are filtered out due to "Brownian motion". Once the particles collide with the fiber, they will be firmly absorbed due to van der Waals force, electrostatic attraction and vacuum attraction.

3. Selection principle of compressed air

The following principles should be followed when selecting models:

1) According to the compressed air source and the use requirements of the production equipment (for example: equipment requirements for compressed air quality, gas pressure, flow, etc.), select the filter level;

2) When filters of different levels are used in combination, they should be configured in order from low level to high level, and can not skip arbitrarily;

3) The pressure drop between the inlet and outlet of the filter should be as small as possible.
The water in the compressed air is mainly filtered through refrigeration dryers and adsorption dryers, and the filter can also remove part of the liquid water. The refrigerated dryer mainly separates part of the liquid water by cooling high-temperature compressed air, but it cannot completely solve the problem of water in the compressed air. Generally, its pressure dew point is greater than 15°C. The adsorption dryer mainly absorbs the water molecules in the compressed air on its surface through molecular sieve, and discharges the water through the pressure swing method, so as to completely remove the water in the compressed air. Generally, the air pressure dew point after passing through the dryer is less than -20℃.
The oil in the compressed air is mainly filtered by a filter. If the oil content is high, it is best to configure an activated carbon filter. When smt patch processing plants choose filters, they should not only consider the price factor, but also pay attention to the filter quality and effect.