A hermetic seal is an air tight seal that is used to prevent contaminants such as solids, liquids, or gases from entering a package. Hermetic seals used in a wide range of applications including semiconductor electronics, thermostats, optical devices, MEMS, and switches. Electronic parts can be hermeticly sealed to ensure water vapor, dust particles or other particles do not enter package to ensure proper operation of the component. Many Semiconductor devices and components require hermetic seals to be used in High Reliability (Hi-Rel) applications.

Some RF and Microwave Parts that are often available with Hermetic Seals are:

Coaxial Connectors: Hermetically sealed RF connectors are used in a wide range of applications where entry of liquid, air or gas has to be avoided.

RF Semiconductors: Many Hi-Rel Applications like Space, Military and Critical communications require semiconductors ICs to be Hermitically Sealed.

Hermetically Sealed Relays: The device is sealed into a metal cover via welding to ensure zero intrusion of any form of materials. This is done to make the relay free from the impact of ambient conditions such as harmful gas, humidity, dust, etc.

Hermetically Sealed MEMS: To secure the operations of MEMS devices, it is advised to design a hermetically sealed package which protects the device from wet environments. There are multiple ways in which MEMS devices can be hermetically-sealed. In the one show below, a lid (metal) is placed on a ceramic package which is hermetically sealed via seam welding.

How do you Test the Hermeticity of a Seal?

The most common method used to determine the hermeticity of a seal is to measure the rate at which helium escapes from a package that has been pressurized with helium. As stated by MIL-STD-883C, a hermetic package is one in which the leak rate of helium after pressurization is below a rate specified with reference to the package size (refer to Table 1). The sealed package is placed in a chamber which is pressurized with helium (helium bomb) to a level depending on the package volume.

Read more: What are Hermetically Sealed Packages?

It’s a 50-cent word that we commonly associate with food packaging, but what is a “hermetic seal,” or what does “hermetically sealed” really mean?

The simple definition is that it means the container is airtight. Originally, the term applied to glass jars and other rigid containers, but now its use has been extended to plastics that do not let air pass through them.

Most of us are conditioned to check the lids of products in glass jars to confirm that there is a slight curvature present. This indicates that there is a vacuum in the container that is formed when the product is hot-filled into the container. Once the lid is put on the jar and the contents begin to cool, the air in the headspace at the top begins to contract. It is the shrinking of this volume of air that provides the vacuum and draws the centre of the lid downwards to create the dimple effect. When you open the container, the sudden inward rush of air releases the vacuum and causes the lid to make the distinctive “pop” that we like to hear.

Non-rigid containers made of composite plastic materials can also be airtight, but there is not the noticeable curvature to the lid, nor the popping sound when the container is first opened.

Hermetic seals are important in providing safe food for us as consumers. Most spoilage microorganisms require oxygen from the air to survive. Let’s use the example of cooked strawberry jam to explain things. When it is made, the jam is heated to its boiling point, which creates the rich flavour, dissolves the sugar, and kills off the microorganisms that may have been present on the strawberries. While it is still hot, the jam is poured into clean glass jars and the lids are applied. The sealed jars are inverted in some processes to ensure that the underside of the lids are heated sufficiently to destroy any potentially lingering microorganisms.

After cooling, the jam jars can be stored at room temperature for a prolonged period of time, while still remaining safe to consume. However, once the container is opened and the airtight seal is broken, it’s a whole new ball game.

In our example, when you open the jar of jam, air from your surroundings can enter it. Now, the clock starts ticking and it’s all downhill from there in terms of quality and food safety. Airborne microorganisms can enter the jar, so you need to take steps to prevent them from growing. Of course, the simplest thing to do is keep the opened jar of jam in the refrigerator, which did not need to be done before you broke the hermetic seal.

Jam is a very interesting product since it has a certain level of resistance to microbial growth. This is due to the sugar in the jam, as well as the pectin, binding the water that is present so tightly that it is not available for microorganisms to use to support their growth. Unfortunately, all that can change.

As more and more jam is used, the volume of air in the jar increases and undesirable things start to happen. Each time you open the jar, you allow moist warm air to flow into it. When you put the lid back on the jar and place it back in the refrigerator, or even leave it at room temperature, the moisture in the trapped headspace air can condense and cause water droplets to form on the surface of the jam. There is also what is called a “dynamic equilibrium” set up between the jam and the trapped air above it. With time, some of the moisture from the jam may escape into the headspace air as water vapour. Just like the water vapour in the air that entered the jar when you opened it, this vapour will also condense.

Read more: What the heck does hermetically sealed really mean?

[Eric Strebel] is no stranger to pressure and vaccum tanks, regularly using them for all manner of resin casting jobs for his product design business. However, sometimes it becomes necessary to run equipment within a pressure tank, such as for rotomoulding or other similar jobs. In order to get power into a tank under pressure, [Eric] built a special plug with a hermetic seal to do the job. (Video, embedded below.)

The build starts with a large metal plug which screws into the pressure vessel, into which a square recess is machined. For the electrical passthrough, [Eric] selected GX-16 aviation connectors, in this case packing six conductors. The connectors are hooked up back-to-back through the hole in the metal tank plug, using bare copper wire. This is to avoid insulation on wires acting as a channel for gases to pass through. With the connectors wired up and an acrylic disc in place to stop overflow, the metal plug is filled with resin to create the hermetic seal.

Results are good, with the connectors functioning electrically and the resin acting as a perfect seal. There’s a small risk of short circuit with the exposed copper conductors, but [Eric] is exploring some easy solutions to avoid issues. We’ve seen his work before, too – like this great discussion on cardboard as a design tool. Video after the break.

Read more: HOW TO CREATE HERMETICALLY SEALED ELECTRICAL CONNECTIONS

You’ll need sensors to complete your new appliance, building automation product or automated manufacturing system. You may need customization for a specific sensor assembly. While price and delivery are critical decision factors, other considerations determine a successful sensor selection. Here are some essential facts about sensor choices and four crucial questions whose answers should carry significant weight in your decision process.

Magnetic detection sensors for proximity detection, positioning and control
Reed switches have two ferromagnetic blades (reeds) hermetically sealed in a tubular glass envelope. The contacts on each reed have a thin layer of precious metal to provide a low resistance electrical connection. The glass envelope is filled with nitrogen gas to eliminate oxygen and prevent contact oxidation. Reed switches can be activated by either a permanent magnet or an electromagnet. The relative stiffness of the reed blades, the small gap and the overlap between the two contacts determine the switch’s sensitivity, defined by the intensity of the magnetic field required to change the state of the contacts. Unlike an integrated circuit sensor, a reed switch does not require power to operate. Thus, a reed switch is an excellent control element in battery-powered products.

Hall effect sensors generate a voltage when exposed to a magnetic field intensity and when supplied by a source current. The sensor is a semiconductor-based material. Hall voltages are microvolt and millivolt levels; thus, a Hall effect sensor requires signal conditioning. In addition, the semiconductor element requires temperature compensation and EMC/ESD protection. Hall effect sensors monitor proximity and provide continuous rotary or linear positioning.

Reed relays combine a reed switch and control coil. As with other relays, this provides galvanic isolation between the coil control circuit and the controlled load. The reed relay’s small size and high magnetic efficiency enable lower coil drive power than other relay types. Other advantages include high insulation resistance, low contact resistance and long contact life.

TMR switches integrate tunneling magneto resistance (TMR) and CMOS technology to provide a magnetically triggered digital switch with high sensitivity and ultra-low power consumption. It contains TMR magnetic sensor and CMOS signal processing circuitry within the same package, including an on-chip TMR voltage generator for precise magnetic sensing, a TMR voltage amplifier and comparator plus a Schmitt trigger to provide switching hysteresis for noise rejection. An internal bandgap regulator provides a temperature compensated supply voltage for internal circuits, permitting a wide range of supply voltages.

Temperature sensors
Thermistors are thermally sensitive resistors whose resistance is a function of their temperature. Negative temperature coefficient (NTC) thermistors decrease their resistance when the temperature rises, and positive temperature coefficient (PTC) thermistors increase their resistance when the temperature rises. Thermistors provide high accuracy over a narrow range of approximately -50° C to 100° C. Thermistors have highly predictable characteristics and excellent long-term stability; they’re ideal sensors for temperature measurement and control applications.

Read more: Common sense about sensors: 4 questions to ask before selecting sensors for your next design

From March 12 to March 16, 2022, NASA’s airborne Lunar Spectral Irradiance, or air-LUSI, flew aboard NASA’s ER-2 aircraft to accurately measure the amount of light reflected off the Moon.

Kevin Turpie, air-LUSI’s principal investigator, said the Moon is extremely stable and not influenced by factors in Earth like climate to any large degree, according to a statement issued by NASA. He said that the Moon becomes a very good calibration reference, using which researchers can set their instruments and see what is happening on Earth.

NASA makes comprehensive satellite calibration and validation efforts, and the air-LUSI flights are part of these efforts.

How Moonlight Improves Accuracy Of Satellites
With the help of NASA’s Earth-observing satellites, researchers get a global perspective on the interconnected Earth system. Many of these satellites measure light waves reflected, scattered, absorbed, or emitted by Earth’s surface, water, and atmosphere. The light includes visible light, ultraviolet and infrared wavelengths, and all wavelengths in between.

The individual satellite instruments need to be “in tune” with each other, like musical instruments in an orchestra, for researchers to obtain maximum information. Scientists can use the Moon as a “tuning fork” to easily compare data from different satellites to look at global changes over long periods of time, the statement said.

How air-LUSI Telescope & ER-2 Aircraft Work
The air-LUSI telescope measures how much light is reflected off the lunar surface to assess the amount of energy Earth-observing satellites receive from moonlight.

The air-LUSI telescope was mounted aboard the ER-2 aircraft managed by NASA’s Armstrong Flight Research Center in Palmdale, California.

The ER-2 is a high-altitude aircraft which flies at 70,000 feet, above 95 per cent of the atmosphere, and can scatter or absorb the reflected sunlight. As a result, the air-LUSI telescope could collect very accurate measurements that are analogous to those a satellite would make from orbit. The air-LUSI telescope measured the Moon for four nights just before a full Moon, during the March flights.

Due to this airborne approach, scientists can study moonlight during different phases of the Moon and can also bring the instrument back between flights for evaluation, maintenance, and repair, the statement said.

The air-LUSI spectrometer is constantly at sea level temperature and pressure as it is hermetically sealed. A spectrometer is a device used for measuring wavelengths of light over a wide range of the electromagnetic spectrum. It is typically used to measure wavelengths of electromagnetic radiation that has interacted with a sample.

The telescope collects light, which enters an integrating sphere. After this, the light is directed to the spectrophotometer.

Read more: How NASA Is Using Moonlight To Improve Accuracy Of Satellites Observing Earth

Cornell Dubilier has introduced the world’s only hermetic aluminum electrolytic capacitor with a glass-to-metal seal and it is now available through franchise distributor New Yorker Electronics.MLSH Slimpack: World’s first hermetically sealed aluminum electrolytic capacitor from Cornell Dubilier

The new Cornell Slimpack, type MLSH, is the first in a series of hermetically sealed aluminum electrolytic capacitors that the company plans to introduce over the next several months. It is poised to replace banks of costly wet tantalum capacitors.

With its glass-to-metal seal that prevents dry-out and high capacitance retention at low temperatures, this capacitor technology has extraordinarily long life in order to meet the most demanding military and aerospace applications. The hermetic Slimpack is a spin-off of the non-hermetic Flatpack series that New Yorker Electronics has been supplying to military and aerospace end-users for more than 20 years.

Cornell Dubilier expects this technology to replace parallel and series banks of wet tantalum capacitors for new and existing designs, especially where bulk storage is paramount. According to the manufacturer, the MLSH Slimpack (measuring 1.0 x 1.5 x 0.5 in.) will weigh less and have more capacitance than a parallel bank of three or more wet tantalum capacitors as if at -55° C. High capacitance at low temperature is a key requirement for power supplies used in military and aerospace applications.

In addition to its performance advantages, the technology is expected to have a significantly lower cost than a comparable bank of wet tantalum capacitors.

Read more: World’s First Hermetically Sealed Aluminum Electrolytic Capacitor Now Available through New Yorker Electronics

SCHURTER has improved the packaging of its space fuse series MGA-S, with an enhanced dissipative structure on the outer layer of the ESD bag. The outer layer of the old packaging was aluminum with abrasion-resistant coating. The material of the outer layer of the new packaging is a static-dissipative polyester.

The MGA-S is hermetically sealed and robust. It has a small construction with a rated current range of 0.14 – 3.5A, and a high breaking capacity of up to 300A. Its small dimensions in a popular 1206 footprint [3.2 mm by 1.55 mm] make the MGA-S the smallest SMD fuse qualified for use in equipment for space. Rated voltage range is 32 – 125 V AC, 125 V DC, this non-resettable fuse is qualified according to ESCC Generic

Specification 4008 and associated detail specification 4008/001.

The MGA-S with its thin film technology (metal sputter process) increases the long-term stability of the fuse through the homogeneous crystal structure of the metal layers. Applications include equipment that is launched into orbit, with a specific focus on satellite power system architectures. This includes protection of power supplies, batteries and solar arrays.

The MGA-S is built according to UL 248-14 and CSA 22.2 no. 248-14 and carries UL and CSA recognition. It is also tested according to MIL-STD 202, Method 108A, 103B, 106E, 107D, 211A & 215A.

Read more: New MGA-S Fuse Is Hermetically Sealed and Robust