In the electrical and electronic industries, leak detection methods such as the injection method, the suction method and the pressurization method are often used according to the sealing requirements of different products.

1. Back pressure leak detection

Back pressure leak detection is to put the tested part with tracer gas under a certain pressure into the leak detection fixture, and then connect it to the leak detector to evacuate it. The tracer gas leaks out through the leak hole and is detected by the leak detector. total leakage.

Small electronic devices should use this leak detection method. First, adjust the instrument, and then put the device into the pressurized tank and press helium gas into it. The helium gas enters the inside of the device with leaks, and the device without leaks only absorbs helium on the surface. The device pressurization pressure and time are determined according to the GB2423, 2328 documents. After the device is taken out from the pressurized tank, the helium gas adsorbed on the surface is blown off, and then put into the leak detection fixture to be evacuated. After the vacuum is pumped to the set value, it will automatically The fixture is connected to the measuring system of the instrument. At this time, the helium gas pressed into the leak hole device leaks out and is detected, and its leak rate is displayed on the leak rate meter. Generally, the exclusion method is used in the leak detection of the back pressure method. Put a certain number of devices in the fixture, and the total leak rate of this batch does not exceed the predetermined value for scrap, indicating that this batch is qualified; if the total leakage rate exceeds the predetermined value for scrap, half can be taken out, and the remaining half can continue to be leaked, and this half is qualified Indicate that the leaky device is in the half taken out, and check for leaks until the leaky device is detected.

This leak detection method sometimes also misses detection. This is because the helium gas has been exhausted for those devices with large leak holes before they are put into the leak detection fixture, so a rough inspection of the device is usually required before the back pressure leak detection method.

At present, electronic product supervision and inspection departments and manufacturers widely use helium mass spectrometer leak detectors for product quality supervision, and have established their own standards and methods.

2. Leak detection by injection method

Leak detection by injection method is to connect the inspected part to the detection port of the leak detector, and continuously spray tracer gas to the suspicious leak hole with a spray gun. The tracer gas enters the leak detector through the leak hole and is detected. The casing of electronic devices, high-voltage switch tubes, zinc oxide, arresters, etc. should all use this method to detect leaks.

Depending on the product, it is necessary to select fixtures of different sizes or auxiliary tools such as leak detection of the tube shell. After the leak detector works normally, use the standard leak hole to calibrate the leak rate, and then the tube shell can be sprayed for leak detection. First, fix the fixture to the leak detection port, and place the tube shell to be tested on the rubber plate above the fixture to assist The pumping system will automatically connect it to the measuring system of the instrument after pumping it to a predetermined vacuum. Then use a spray gun to continuously spray helium to the tube shell for 1 to 3 seconds. When there is a leak in the tube shell, the helium gas will enter the mass spectrometry part of the instrument through the leak hole, and the amount of leakage will be directly displayed on the leak rate meter. , this method can not only judge the location of the leak, but also measure the size of the leak. The entire detection cycle only takes one minute.

3. Inhalation leak detection

The suction method leak detection is opposite to the injection method leak detection. The sniffer gun is connected to the detection port of the leak detector, and the test piece is filled with the tracer gas of the specified pressure, and the leaked helium gas is sucked into the leak detector by the sniffer gun detection. It is very uneconomical to use a spray gun for leak detection of large containers or containers with a large number of internal vent pipes, and the leak detection speed is slow. Generally, a sniffer gun is used for leak detection. At present, there are no mature methods and standards for leak detection of large containers in the electronic watch industry. For example, for a container as large as a high-voltage capacitor, the key to quality control is welding technology, and the air-tightness supervision method adopts bubble leak detection, so the rejection rate is controlled at a few thousandths.

Before leak detection, the sniffer sensitivity of the instrument must be calibrated, and then the container is filled with helium gas with a pressure higher than one atmosphere. Some containers are of thin plate structure. It is recommended to make a clamp outside the container to prevent deformation and damage to the device under high pressure. When the suction gun moves along the welding seam, the speed should not be too fast, and it should be about 1mm away from the surface to ensure the suction sensitivity. It is better to make the probe into a bell mouth shape. At present, the leak detection results of such large-scale electrical devices show that their leak rates are generally in the range of 10-6 to 10-7Pa.m3/S.

We believe that with the widespread and intensive use of helium mass spectrometer leak detectors in this field, the industry's leak detection standards and methods will soon be established.

No matter which leak detection method is used, the operator is required to have careful observation ability and a high sense of responsibility, because false detection and missed detection will cause losses, and the operator's alertness and proficiency in discovering unknown things are also very important.

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