This special feature focuses on the latest trends of sealing inspections and leak testing. One comprehensive report along with 7 technical introductions will enhance the knowledge of users and manufactures of the sealing inspections and leak testing.

Sealing inspections have been carried out to ensure the reliability of the sealing products in various industrial fields. The methods include waterproof tests based on ingress protection (IP) code, environmental testing at high temperature and humidity condition, babble testing, leak testing with pressure difference method (air leak test), helium leak testing, and so on. This overview article summarizes the latest trends of these testing methods. Recent requirements on the accountability for sealing inspections in the medical field and the activities using reference test peaces in the field of measuring instruments are also introduced.

Many electronic devices with internal cavity are sealed in a vacuum state or filled with inert gas to protect the internal elements and circuits for stable operation over a long period of time. Hermetic tests using air, helium gas, or liquid are used to inspect the sealing performance and ensure their quality. In general, there are two main types of tests : gross leak tests to detect large defects and fine leak tests to detect minute defects. The gross leak test is mainly performed by immersion testing using fluorine-based inert liquid. However, in recent years, alternative test methods have been sought due to deterioration of availability and consideration of environmental impact. In this paper, we introduce the appropriate condition setting method for air leak test, which is one of the alternative tests, and fine leak test to avoid overlooking any defects.

Helium leak tests utilized in automotive components are described in this paper. First, the method for determining the leak thresholds for automotive components that use fuel liquids or hydrogen gas is described. An overview of the helium leak tester used for in-line testing is then provided. The leak test method for resin parts with high gas permeability, and check valves that generate leaks when tracer gas is introduced are then described, as a leak test method tailored to the characteristics of the unit under test. Finally, authors development of a leak tester. The following topics are introduced : Helium gas recovery and purification system to solve the problem of helium gas depletion, the development of leak tester using alternative helium gases (N₂, Ar, Air, etc.), and the development of high-pressure liquid leak tester for high-pressure automotive parts to avoid the risk of rupture of high-pressure components due to high-pressure gases.

The helium leak testing market continues to expand, especially in the next-generation automotive market. In recent years, helium leak detectors have been increasingly upgraded from general-purpose equipment to specialized equipment. This paper introduces the market trend of helium leak testing and leak testing methods using helium leak detectors.

Operando hydrogen microscope (OHM) is an original hydrogen visualization equipment using electron stimulated desorption (ESD) method. In the equipment, permeated hydrogen atoms through the sample membrane are ionized by incident electron on the sample surface, desorbed into UHV environment and detected. By using the electron source of a scanning electron microscope (SEM) as the excitation source for ESD, we visualize the surface hydrogen distribution from the hydrogen desorption position. In the paper, we used OHM to visualize hydrogen leak position in standard conductance element (SCE), which is a filter of open type standard leak. As an example of measurement, we also identified the location of a leak in a sealing device.

Leak testing is one of the important nondestructive testing methods to get the conformance of the product quality. Helium leak testing is the most sensitive nondestructive testing method in the industrial field, and it is usually done by helium leak detector. On the contrast, from basic to more complex leak testing can be done by the partial pressure gauge which is categorized as a quadrupole mass spectrometer. This article explains the basic method of leak testing by the quadrupole mass spectrometer, and also mentions the ultrafine leak testing technique for the vacuum sealed MEMS sensors.

Toward the Sustainable Development Goals (SDGs) announced by United Nations, several developments are undergoing in the world. One of the great interests of the development is the primary and secondary battery. The others are the development of the refrigerant of low global warming potential. One of the interesting techniques in vacuum science and technology field toward SDGs is leak testing. In this article, we introduce the technique of the leak testing method for lithium-ion battery, hydrogen fuel cell and refrigeration and air conditioning. Now a days, several types of battery and refrigerant were developed toward the SDGs. To answer the technical difficulty of the leak testing for each field, we have also developed several leak testing method/methodologies.

In this article, we will explain the classification of detection methods using tracer gas, typical leak testing methods, and introduce the latest trends in leak detector.