Tag: package leak testing

All About Leak Detection

As with almost every facet of vacuum systems, there is no single method which fulfills every situation and every criterion. This is certainly the case with leak detection, with four main methods being employed: the bubble test; pressure decay test; pressure rise test; and helium sniffer mode/helium vacuum mode tests.

These four tests roughly correspond to the “simplistic” bubble test (for low-vacuum pressures), through to the “high-tech” helium tests (for high-vacuum pressures). There are many companies that provide several types of package leak tests.

The bubble test is best illustrated by placing a punctured bicycle tube underwater and marking where the bubbles come from, or placing washing-up liquid around the joint of an active water/gas pipe and observing whether the liquid forms a froth. Both are reliable ways of detecting a low-pressure leak. The bubble test is employed up to vacuums of 10-4 mbar.

The pump-down test is conducted by evacuating a closed vacuum vessel until a certain pressure is obtained, then closing the pump’s inlet valve. After a pre-determined period of time, the inlet valve is again opened, and the time is recorded for the pump to return the vacuum to the original evacuated level. This process is repeated a number of times.

If the time to return the vacuum to the original level remains constant, then a leak is present. If this time period decreases, this indicates reduced gas liberation (out gassing) on the inside of the system (i.e. a “virtual” leak), however, it does not exclude a leak from also being present.

Alternatively, the pressure rise test is made by plotting the vacuum level against the time after a vacuum level has been achieved, and after isolating the system, the curve will be a straight line if a leak is present. However, if the pressure rise is due to gas liberation from the system walls, the rise will gradually taper off to reach a final, stable value.

Residual Gas Analysis For Leak Detection In Sealed Devices

Quality or failure analysis is a very critical step that needs to be performed on products before they are finally launched in the market. Here products are checked under various parameters and test conditions such that it turns out perfect for use. One of the steps in this regard is to test hermetically sealed devices for any trace gases that might have crept inside it while manufacturing. 

It is a very critical step as such gases, especially the moisture content in them can cause serious problems in the functioning of the device. It can cause corrosion, fogging, leakage, current bit errors and other lubrication issues. To keep control on these trace elements various package leak testing devices are used.

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Some of the instruments that are being utilized for trace gas detection are known as residual gas analyzers. These instruments operate by creating a beam of ions from the sample of gas being analyzed. Here the resulting mixture of ions thus produced is separated into individual species through their specific charge to mass ratios. 

To determine these ratios, a typical RGA consists of three major parts, namely an ionizer, mass analyzer and an ion detector. The output of these gas analyzers shows the relative intensities of different species present in the gas. This output is also known as a mass scan or mass spectrum.

It is a very innovative method and produces accurate results. It is a very useful technique for industries that produce sealed devices or utilize them in their products. Application of residual gas analysis apply to a range of industries including Microelectronics, Hermetic modules manufacturers, Metals, Ceramics, Telecommunication, Food, Medical devices, Pharmaceutical, Packaging and in the Illumination segment.