High purity helium mass spectrometer leak detection method for coarse and fine leaks
Helium, high-purity helium
In order to achieve higher sealing tightness testing of electronic components, a new type of stacked high-purity helium mass spectrometer leak detector has emerged internationally since the beginning of the 21st century. This instrument uses a cryogenic pump and a quadrupole mass spectrometer multiplier. The temperature inside the cryogenic pump can be reduced to 20K (-253 ℃), which can effectively absorb various gases other than hydrogen and helium.
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With this instrument, a combination of coarse and fine leakage detection can be performed. The coarse leak detection uses high-purity helium gas as a tracer gas. The coarse leak test piece pre filled with helium or pressurized helium is stored in air for a period of time. The internal high-purity helium partial pressure PHe should be equal to or higher than the high-purity helium partial pressure PHe0 in normal air. The equivalent standard leakage rate criterion for rejecting coarse leakage detection is L0, and the leakage rate criterion is measured using high-purity helium gas detected under vacuum in the form of molecular flow gas exchange (leakage).
Fine leak detection uses high-purity helium or other gases as tracer gases. The leaked tracer gases are passed through a cryogenic pump and then subjected to a period of stack detection using a mass spectrometer multiplier. Because cryogenic pumps can effectively improve the signal-to-noise ratio of high-purity helium gas to gases other than hydrogen, and through stack multiplication, greatly improve the sensitivity of high-purity helium gas leak detection. The Pernicke 700H CHLD from Inficon company currently has a minimum detectable high-purity helium gas leakage rate of 4 × 10-9Pa · cm3/s when sealed with copper gaskets in a small detection chamber. Using different detection chambers, the range of detectable high-purity helium gas leakage rate measurement criteria can be from 2 × 10-8Pa · cm3/s to 1 × 10-6Pa · cm3/s.
