Due to its softness and compressibility, indium is ideal for use in creating a seal. Generally 99.99% indium is adequate for a vacuum, hermetic or cryogenic seal, but higher purities are also available if there is a requirement. Regardless of the end use, Indium Corporation can provide the correct purity, form and shape to do the job.
Indium preforms are commonly used to create a seal. The preforms can be made into an endless variety of shapes and sizes to fit the needs required in the application. Crucial to the seal is the thickness of the preform because, if the volume of indium is not sufficient, the seal will eventually fail due to lack of indium to fill in the gaps. A Technical Support engineer from Indium Corporation is only a phone call away to give experienced help in this important area in designing a seal application.
Indium wire is also used to create a vacuum, hermetic, or cryogenic seal. Care must be taken to insure that the correct diameter of wire is used to make the seal. Too small of a diameter and the gap will not be adequately filled - leaving the seal area vulnerable to leaks. Too large and the indium, when compressed, will exit the seal area and may interfere with other electronics in the area.
When using wire, care must be taken to have the wire centered in the area to be sealed. If the wire is off-centered, it may not create an adequate seal when compressed, due to non-uniformity. In some cases, it is beneficial to make a small groove in the seal area so the wire can be placed using the groove as a guide for accurate placement.
Not all seals require the same level of attention. Some seals need to maintain their integrity for many years while others only need to hold for a short period of time. The end users should know what is required in their case. The more critical seals will need to follow the procedure outlined below to insure that the integrity requirements are met.
Indium is self-passivating and will form about 80-100 Angstroms of oxide on its surface, at room temperature. In more critical seal applications, it is essential that this oxide layer be removed prior to creating the seal because, if the oxide is present during the compression of the indium, the oxide will be pushed below the surface and could create a path for leakage.
The following oxide removal procedure should be followed and applies to both indium preforms and wire:
- Degrease the indium in acetone to remove any surface organics that could interfere with the seal.
- Place the indium in 10% HCl for about 1 minute to remove the oxide on the surface.
- Rinse thoroughly in DI water to remove the HCl.
- Rinse in acetone to remove the water.
- Blow dry with dry nitrogen or allow to air dry.
Please see our Application Note on Etching Indium to Remove Oxides
Caution:
Indium will cold weld to itself, especially after the surface oxides have been removed.Care must be taken that the indium is not allowed to touch other freshly-etched pieces of indium as they will stick together similar to Contact Cement.Separation is difficult, if not impossible, without damaging the indium piece.
Please see our Application Note on the Cold Welding of Indium
After the indium is ready to use, care must be taken in the proper placement of the preform or wire on the surface to be sealed. Once the indium is in place, the amount of pressure required to make the seal is dependent on the application. A few trials may be required until just the right amount of pressure is determined to form the seal that is needed. These trials are also a good time for adjustments to be made in the thickness of the indium used.
Please contact Indium Corporation if you need help with any portion of your seal requirement. We have the experience and knowledge to share, which will help shorten the time to get the seal process ready for implementation.
Paul Socha
15 October 2012