Due to its softness and compressibility, indium is ideal for use in creating a seal.
Let's get right into it:
Indium preforms are commonly used to create seals. The preforms are made into an endless variety of shapes and sizes to fit the application. Crucial to the seal is the thickness of the preform, because, if the volume of indium is insufficient, the seal will eventually fail – due to lack of indium to fill in the gaps.
Indium wire is also a form used in the creation of 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, 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.
Indium metal 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.
Not all seals require the same level of performance. A purity of 99.99% indium is adequate for a vacuum, hermetic or cryogenic seal, but higher purities are also available if needed. Some seals need to maintain their integrity for many years while others only need to hold for a short period of time. Develop your design based on what you know about the application.The more critical seals will need to be made following the procedure outlined below to insure that the integrity requirements are met.
- アセトンでインジウムの脱脂を行い、シールを妨げる可能性のある表面の有機物を除去する。
- 表面の酸化物を除去するため、インジウムを10%塩酸に約1分間浸漬する。
- HClを除去するため、脱イオン水で十分にすすぐ。
- アセトンで洗い流し、水を除去する。
- ドライ窒素でブロー乾燥するか、自然乾燥させてください。
Please see our Application Note on Etching Indium to Remove Oxides, and watch this video to see how it's done.
注意：
Indium will cold weld to itself, especially after the surface oxides have been removed. See exactly what I mean. 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.
インジウムの使用準備が整ったら、プリフォームまたはワイヤを密封対象表面に適切に配置するよう注意を払う必要がある。インジウムを所定位置に配置した後、シール形成に必要な圧力は用途によって異なる。必要なシールを形成するのに最適な圧力を決定するまで、数回の試行が必要となる場合がある。これらの試行は、使用するインジウムの厚さを調整する良い機会でもある。
Feel free to tap into our experience and knowledge to help you shorten the time to get your seal process ready for implementation.
ポール・ソチャ
23 October 2012
