Pull It, Seal It, and Forget It
With the invention of the incandescent light bulb and vacuum tubes more than a century ago, the vacuum became a major tool in manufacturing. Today, the lowly light bulb is being challenged for supremacy by CFLs and LEDs. And thanks to the cost-effectiveness, compact size, and improved efficiency and reliability of digital electronics and semiconductors, vacuum tubes are largely a thing of the past (aside from a few niche applications).
Yet, the process of creating a vacuum atmosphere is still very much alive — in fact, it’s a vital part of electronic component manufacturing.
Repeated vs. one-time production of a vacuum atmosphere
There are a number of applications in which a vacuum is repeatedly pulled in order to accomplish a task. Some examples include vacuum metalizing coils used in coating product surfaces; a scanning electron microscope (SEM), which operates in a vacuum; pumping systems used to move fuel or other liquids; and even the common vacuum cleaner, although since it typically produces only enough suction to reduce air pressure by about 20%, it is only a partial vacuum, at best.
However, there is another use of the vacuum atmosphere — specifically, the various manufacturing processes where you want to pull a vacuum once, seal it, and never have to give it a second thought. This one-time production of a vacuum atmosphere is used in applications that require a sealed glass construct with no entry or exit points.
Vacuum chambers and linear vacuums
A vacuum atmosphere is generally created one of two ways — using either a vacuum chamber or a linear vacuum device. With a vacuum chamber, a pump is used to remove air and other gases from a rigid (usually metal) enclosure, resulting in a low-pressure environment inside the chamber. This type of vacuum atmosphere is commonly used for physical experiments and testing of devices that need to function in an airless environment (such as outer space), as well as for processes such as vacuum deposition and vacuum drying. It also provides an air- and contaminant-free environment that is essential for the fabrication of semiconductors.
In addition, as we mentioned in our last blog, a vacuum chamber can be used in the one-time potting (encapsulation) process to create a void-free seal around electronic components, such as the semiconductors used in solid state relays. One-time hermetic sealing of power semiconductor devices can also be accomplished by positioning a semiconductor die in the cavity of a package, pulling a vacuum, and then sealing the package with a ceramic or metal cap.
This brings us to the linear vacuum, in which a vacuum is pulled using an external vacuum pump connected to a device via capillary tubing, which is then sealed. This type of vacuum atmosphere is responsible for the thermal insulation layer in the thermos you used to carry to school. In the world of HVAC, the fabrication of a heating or cooling system uses a linear vacuum to form a thermal barrier, as well as to purge the unit of air and other gases, moisture, and contaminates that could compromise system operation and performance. (In addition, air conditioning or refrigeration systems that have been opened to the surrounding environment during installation or service must also be properly evacuated, using vacuum pumping to degas and dehydrate the system.)
The use of capillary tubing for a vacuum atmosphere
Capillary tubing can provide the very thick wall and small inside diameter (ID) required for the process of pulling a vacuum atmosphere. For this purpose, the metal chosen for the capillary tubing must be soft enough to be easily heat-formed and capable of being crimped to form a tight, leak-free seal. In addition, you need to be sure the capillary tubing has:
- A very clean ID, with no burrs, debris, or blockages that could clog the tube or contaminate production
- No outside diameter (OD) leaks
- No ID leaks after the vacuum is pulled
- The ability to be metallurgically joined to itself to form a leak-free self-seal
Combining good design and careful inspection of parts goes a long way in assuring that a vacuum atmosphere is air tight. Working with the right partners also helps to ensure that parts and processes are tested all along the supply chain, to meet your manufacturing needs, production deadlines, and quality standards.
For tips on how to choose the best partners for your electronic parts requirements, download a free copy of our guide, 7 Secrets to Choosing a New Contact Partner: Technical Guide to Outsourcing Your Precision Metal Fabrication.
