Compressed air quality analysis standard for precision electronics industry

Conclusion first

the precision electronics industry has extremely high requirements for the cleanliness of compressed air. It mainly refers to the two sets of standard systems of ISO 8573 and GB/T 13277. The core is to control five things: solid particles, moisture, oil, microorganisms, and harmful gases. Among them, particles, oil and water are required for daily inspection, and microorganisms and harmful gases are selected for inspection according to product risks. If the factory uses a water-lubricated air compressor, the two most troublesome problems of oil and waste water will disappear directly, and it will be much easier to reach the standard.

To what extent should the five major testing items be controlled respectively

the first is solid particles

the line width on precision electronic products has been as small as nanometer level, and a dust that is invisible to the naked eye may cause short circuit or open circuit. Therefore, the standard requires that the particles in the air must be very few. Generally, particles with a particle size of 0.1 microns or more are required, and no more than one thousand particles per cubic meter are required. Tighter scenarios require even 0.01 micron-level particles to be controlled.

The detection uses a laser particle counter. The principle is to let air pass through a beam of laser, and the particles will scatter the light. The instrument counts the number and size of the particles according to the intensity and number of scattered light.

The second is moisture.

The water in the air has two forms, one is visible liquid water droplets, and the other is invisible water vapor. The amount of water vapor is expressed by dew point temperature, and the lower the dew point, the less water. The precision electronics industry usually requires a dew point below minus seventy degrees Celsius, meaning that the air is dry to contain almost no moisture.

If the dew point is not low enough, water vapor will condense into a water film on the surface of the chip, causing corrosion or abnormal electrical performance. The cold mirror dew point meter is used for detection. Air is allowed to contact a mirror. The temperature at which dew begins to form on the mirror is the dew point.

The third is oil.

Oil is the most taboo pollutant in the precision electronics industry. Oil mist will adhere to the circuit board, affect the quality of welding, and even lead to product failure. The standard requires the total oil content to be controlled below 0.001 mg per cubic meter, which is close to the limit of the detection instrument.

The detection method mainly uses the photoionization detector, which can sense the extremely small amount of hydrocarbon molecules in the air, that is, oil vapor. Gas chromatography can also be used for more accurate analysis.

The fourth is microbes.

In the clean workshop, bacteria and fungi in the air will fall on the surface of the product and cause pollution. It is usually required that the number of viable bacteria per cubic meter of air does not exceed one. The detection method is to collect the microorganisms in the air on the culture medium with a floating bacteria sampler, and then count the colonies after 48 hours of incubation in a constant temperature box.

The fifth is harmful gas.

Including carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxides of these. The carbon monoxide in the compressed air mainly comes from the high temperature cracking of the air compressor lubricating oil, and the carbon dioxide may come from the ambient air. Although these gas concentrations are not as strict as the first four, they should be monitored in high cleanliness scenarios.

How to do the test is reliable

the sampling point should be selected at the end of the pipeline close to the gas equipment, not more than 5 meters away from the equipment, avoiding elbows and valves downstream, because these places are easy to accumulate pollutants. Before sampling, the valve should be opened to let the air blow for a few minutes to drain the stored air in the pipeline, otherwise the measured data does not represent the actual gas quality.

In terms of detection frequency, the newly installed system is recommended to be inspected every three months, and the mature system with stable operation can be inspected once every six months to once a year. However, if there is a quality problem with the product, it should be inspected immediately.

Water-lubricated air compressor makes it easier to reach the standard.

The biggest trouble of traditional oil lubricated air compressor is oil. During the compression process, lubricating oil will become oil mist and oil vapor mixed into the air. It is difficult to completely remove the oil vapor after filtering. Moreover, the discharged condensed water contains oil, which belongs to oily wastewater and has high treatment cost.

The water-lubricated air compressor uses clear water instead of lubricating oil, and there is no oil in the compression chamber, so the air discharged does not contain oil, and the oil content test is easy to pass. The condensed water discharged is clean water, which does not need to be separated from oil and water, nor does it need to treat oily wastewater, thus saving a lot of subsequent maintenance.

One sentence summary

the compressed air standard for the precision electronics industry is that the particles should be few to almost no, the moisture should be dried to almost zero, the oil should be clean to almost undetectable, and the microorganisms should be controlled to almost non-existent. Because the water lubricated air compressor does not use oil, the two largest pollution sources of oil and oily wastewater are directly eliminated, which is the most convenient choice in this industry.