Inspection of Hermetically sealed electronic components

Hermetically sealed electronic components such as MEMS, crystal oscillators, semiconductor devices are used in a wide range of applications.

Humidity and viscosity of filler gas significantly affect the performance of MEMS devices and hermetically sealed electronic components in which malfunction due to corrosion of internal circuit by humidity and change of gas viscosity affects performance and safety. Therefore, MEMS devices are in a vacuum state or enclosed and sealed by inert gas to maintain stable performance for a long term and to prevent malfunction. To ensure the reliability of the enclosure and sealing, high enclosing technology and highly accurate leak test to judge the existence of leak is indispensable. Normally, combination of two types of measurement, namely, gross leak measurement and fine leak measurement are necessary for MEMS inspection since single leak test for airtightness inspection of enclosed MEMS and other devices cannot cover a wide range of leak rate. Fukuda has automated complicated airtight test for MEMS and other devices and has been providing products to manufacturers in Japan and other countries that allow easier and prompt measurement compared to immersion leak test.

Leak testers for Hermetically sealed electronic components

For mass production

Completely automatic

High speed inspection



For test in development phase,etc. For inspection of small amount.

1ch semi-automatic



Tests ultra-fine leak




Test method by immersion and test method by Fukuda

The test method by immersion (Fluorinert + helium) and test method of Fukuda products (air + helium) are described in the diagram below.

The test method by immersion judges leak by immersing the work in Fluorinert and through generated bubbles. Since it is difficult to numerically express the leak amount from bubbles, the overlapping measurement range of helium leak test and Fluorinert cannot be checked and may have a range where it is not covered by either test. Therefore, it may create a range that cannot be measured and may not be able to identify defective products. On the other hand, Fukuda products will not omit defective products since they are able to overlap measurement ranges of helium leak test and air leak test to prevent uncovered measurement range.

Leak test by immersion

Gross leak measurement by visual inspection has a risk of human error and leak amount cannot be expressed numerically. Precise leak amount cannot be expressed numerically such as 5×10-5Pa・m3/s and 3×10-6Pa・m3/s with visual inspection. When leak amount value is not available, the limit of leak amount for removing unacceptable works is unclear with gross leak measurement in which helium gas exposure time cannot be decided. Helium gas exposure time is a standard to identify how much time it takes for the gas charged in the work to be discharged completely when the helium gas charged inside the product is at the minimum gross leak judgment value (the smallest leak amount that can be judged by the leak tester). There is a possibility to omit defective parts when the minimum judgment leak amount of gross leak cannot be measured by the method described in the figure above. Helium gas may be discharged and unacceptable work may not be detected when the internal volume is at a very low level such as 0.1mm3 with the process to measure works in several stages. Inspection by longer exposure time is possible when highly sensitive leak amount can be obtained by gross leak measurement in which airtightness inspection can be performed stably without omitting defective products.

Leak test by FUKUDA products

Gross leak measurement has a role to identify unacceptable work with large leak and ensure exposure time necessary for fine leak measurement. Fukuda products allow controlling of exposure time by numerically expressing the leak amount during the gross leak measurement since Fukuda products use air and gas for measurement. Secure and effective measurement is possible in whole leak range of large and small leak without the risk of human error since each process is performed in full automatic operation.
Gross leak test

Carry out gross leak testing using differential pressure type air leak testing. The leak rate of the work (tested component) is detected as values by placing work and master into small capsules and comparing the pressure. Leak testing of to 3×10-6Pa・m3/s(at 400kPa・G)(to 2×10-7Pa・m3/s Equivalent standard leak).

Fine leak test

Fine leak test is performed using helium gas to measure minute leak that cannot be detected by gross leak within the controlled exposure time. The measurement range of measuring devices of Fukuda is approx. 1×10-9~1×10-5Pa・m3/s(He)


Work size and exposure time

The exposure time differs according to internal volume of work. Let us examine the exposure time when the internal volumes of work are 2.0, 0.4 and 0.1mm3.
When the air leak amount is 1×10-6 Pa・m3/s(at 400kPa・G), He bombing pressure is 500kPa・G、and charging time is 3600 seconds, the exposure time will be 100 minutes for 2.0mm3 minutes for 0.4mm3 and 5 minutes for 0.1mm3 according to the internal volume of the product in which the helium gas will be completely discharged when the exposure time is extended further than the above time and accurate measurement will not be possible. Particularly, the smaller the internal volume of work, the smaller the helium amount to be charged in which severer time management is required since the exposure time will be shorter even when the leak amount is the same. Due to very small size of MEMS device, it is necessary to select a measuring instrument that can ensure controlling of precise exposure time and perform highly accurate gross and fine leak tests.

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