Abstract
Most of the physics pertaining to the flow of gases into packages are similar to the physics described in the flow of gases out of packages. The leak channels and conductances are identical; however, there is one important difference. The physics governing the difference between the high partial pressure and the low partial pressure of the leaking gas is very different. When a gas is leaking out of a package, the gas is usually leaking into a gaseous environment that does not change. Helium leaking out of a package into the air does not change the helium concentration of helium in the air, it remains at zero. One of the requirements for a gas to leak into a package is that the partial pressure outside the package be greater than the partial pressure of that gas inside the package. As this gas leaks in, the partial pressure of the gas inside increases until it equals the partial pressure outside. These gases will be flowing at different rates through the same leak channel(s) because of different partial pressure differences and different molecular weights. An additional gas flow is possible when there is a difference in total pressure. There are four important conditions when this can take place. They are: the forcing of helium into a package by subjecting the package to a helium pressure greater than that in the package (helium bombing); helium leak testing a package, the pressure outside the package is close to zero; packages that contain more than one atmosphere, leaking into the air; and packages sealed under vacuum or a reduced pressure.
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