Tag: Hermetic Sealing

Some kinds of packaging must maintain a seal against the flow of gases, for example, packaging for some foods, pharmaceuticals, chemicals and consumer goods. The term can describe the result of some food preservation practices, such as vacuum packing and canning. Packaging materials include glass, aluminum cans, metal foils, and gas impermeable plastics.

Some buildings designed with sustainable architecture principles may use airtight technologies to conserve energy. Under some low energy building, passive house, low-energy house, self-sufficient homes, zero energy building, and superinsulation standards, structures must be more air-tight than other lesser standards. Air barriers are not effective if construction joints or service penetrations (holes for pipes, etc.) are not sealed. Airtightness is a measure of the amount of warm (or cool) air that can pass through a structure. Mechanical ventilation system can recover heat before discharging air externally. Green buildings may include windows that combine triple-pane insulated glazing with argon or krypton gas to reduce thermal conductivity and increase efficiency. In landscape and exterior construction projects, airtight seals may be used to protect general services and landscape lighting electrical connections/splices. Airtight implies both waterproof and vapor-proof.

Applications for hermetic sealing include semiconductor electronics, thermostats, optical devices, MEMS, and switches. Electrical or electronic parts may be hermetic sealed to secure against water vapor and foreign bodies to maintain proper functioning and reliability.

Hermetic sealing for airtight conditions is used in archiving significant historical items. In 1951, The U.S. Constitution, U.S. Declaration of Independence, and U.S. Bill of Rights were hermetically sealed with helium gas in glass cases housed in the U.S. National Archives in Washington, D.C. In 2003, they were moved to new glass cases hermetically sealed with argon.

Types of epoxy hermetic seals
Typical epoxy resins have pendant hydroxyl (-OH) groups along their chain that can form bonds or strong polar attractions to oxide or hydroxyl surfaces. Most inorganic surfaces—i.e., metals, minerals, glasses, ceramics—have polarity so they have high surface energy. The important factor in determining good adhesive strength is whether the surface energy of the substrate is close to or higher than the surface energy of the cured adhesive.

Certain epoxy resins and their processes can create a hermetic bond to copper, brass, stainless steel, specialty alloys, plastic, or epoxy itself with similar coefficients of thermal expansion, and are used in the manufacture of hermetic electrical and fiber optic hermetic seals. Epoxy-based seals can increase signal density within a feedthrough design compared to other technologies with minimal spacing requirements between electrical conductors. Epoxy hermetic seal designs can be used in hermetic seal applications for low or high vacuum or pressures, effectively sealing gases or fluids including helium gas to very low helium gas leak rates similar to glass or ceramic. Hermetic epoxy seals also offer the design flexibility of sealing either copper alloy wires or pins instead of the much less electrically conductive Kovar pin materials required in glass or ceramic hermetic seals. With a typical operating temperature range of −70 °C to +125 °C or 150 °C, epoxy hermetic seals are more limited in comparison to glass or ceramic seals, although some hermetic epoxy designs are capable of withstanding 200 °C.

Read more: Hermetic seal

At advanced nodes and in the most advanced packages, physics is no one’s friend. Escalating density, smaller features, and thinner dies make it more difficult to dissipate heat, and they increase mechanical stress. On the flip side, thinner dielectrics and tighter spaces make it more difficult to insulate and protect against that heat, and in conjunction with those smaller features and higher density, it makes them more prone to failure due to thermal runaway or accelerated aging.

This becomes even more complicated in heterogeneous designs, where different combinations of materials with varying coefficients of thermal expansion can result in die shift, warpage, and failure to make connections between die. That, in turn, can affect performance and power. Consequently, rather than just relying on the silicon substrate to remove the heat in a planar device at established process nodes, thermal effects need to be identified early, analyzed, and then addressed.

“Co-planarity and warpage are key concerns as we assemble multiple chips — sometimes 7 to 12 on a single organic substrate,” said Ingu Yin Chang, senior vice president at ASE Group. “Localized thermal management is also a concern, because a certain area will have hotspots. That’s something we are working on with our suppliers or customers to identify in the early stages so that we know what to do in terms of overall thermal management.”

These kinds of problems are cropping up everywhere, from PCBs — which are becoming increasingly dense, as well — all the way into the most advanced packages. Consider copper balance, for example, which is a way to symmetrically distribute copper traces in every layer of the PCB stack. Chip Greely, vice president of engineering at Promex, said that balance is necessary to avoid board twisting, bowing, or warpage. While copper balance was defined decades ago at the board level, it now has made its way to the chip level. “Copper balance has turned into a problem at the individual package level, where I’m putting in 7, 10, or 12 different devices, flipping them, or die-attaching them onto a substrate at different temperatures.”

Read more: Managing Thermal-Induced Stress In Chips

The art of working with glass dates back millennia, but innovative technology is pushing the glass industry into the modern era. One of the companies at the vanguard of glass-to-metal sealing technology is Yamamura Photonics. Founded in 1949, the company has grown into an industry leader and its core Glass To Metal Seal (GTMS) technology has applications ranging from X-ray devices to high-voltage railroads.

Sealing glass to metal is a complicated process. Yamamura’s GTMS technology has enabled the company to develop a wide range of products such as the TO-Cap, a flat window or lens cap with high hermeticity used in LD and PD hermetic packages, and the Glass LID used in thinner packages such as LEDs or lasers.

These products have been developed through Yamamura’s own take on monozukuri. Company president Tomoyuki Taguchi explains that “the most important thing is to manufacture and provide products which can cater to customers’ needs. This is a process of continuous improvement.”

Yamamura recently exhibited its Low Temperature Co-Fired Ceramics (LTCC) green sheets for substrates, which are lead-free and have been developed for 5G applications, having a lower dielectric loss compared to conventional sheets. This understanding of the developing needs of the market comes from the company’s dedication to communicating with its customers, which Mr. Taguchi says differentiates Yamamura from its competitors. The company’s customer-centricity has been key to its expansion into the Asian market, and Mr. Taguchi reveals plans to grow in North America and Europe as well.

Read more: Glass ceramics and optical parts supporting next generation industries

SMA feedthroughs are constructed using a basic coaxial configuration and are perfect for high-frequency signal transmission applications like microwave and radio communications systems.

SMA coaxial feedthroughs excel in high and ultra-high vacuum (HV/UHV) systems due to their low electrical impedance (50Ω) and low noise capacities.

While vacuum feedthrough connectors fulfill various functions in HV/UHV applications, they must first adhere to several key requirements. The connector must be guarded from electromagnetic interference and must be hermetically sealed.

In the construction of the feedthrough, the materials used must be rated for superior performance in extreme temperatures (as low as the cryogenic regime) and vacuum compatibility. The part should also allow for signal transmission at the frequencies required in the system.

What is an SMA Feedthrough?
Also called subminiature version A connectors, SMA feedthroughs were initially created in the 1960s, integrating a minimalistic screw-type interface with a coaxial cable.

With a single thread coupling and low electrical impedance, SMA connectors were the ideal choice for antenna connections because of their inherent compatibility with radiofrequency.

SMA feedthroughs are most effective for signals in the range of DC to around 18 gigahertz (GHz) and are mainly used for signal processing in this bandwidth in HV/UHV applications.

The robust physical construction of SMA feedthroughs empowers their electronic performance, consisting of high durability metal units in either floating or grounded designs.

Read more: Vacuum Applications for SMA Feedthroughs

One of the most promising new materials for photonic integrated circuits (PICs) is lithium niobate on insulator (LNOI). This platform offers a variety of unique optical characteristics, including a high electro-optic (EO) coefficient, high intrinsic 2nd and 3rd order optical nonlinearities, and a large transparency window (350 to 5500 nm).

The purpose of this project is to expand CSEM’s expertise in various aspects of the value chain, including PIC design, simulation, fabrication, photonics packaging, testing, and the creation of a functional experimental demonstration.

With the maturity of the technology, it is now possible to integrate a detector for carrier-envelope frequency offset, which is crucial for stabilizing femtosecond lasers. The successful completion of this demonstration will validate CSEM’s ability to deliver a fully packaged and competitive PIC-based solution, from design to final product.

This project utilizes CSEM’s multidisciplinary expertise in Photonic Integrated Circuit (PIC) design and fabrication, packaging, system engineering, laser stabilization, and metrology to construct a full demonstration of a Carrier-Envelope Offset Frequency (fCEO) detection unit.

The fCEO detection unit, based on Lithium Niobate on Insulator (LNOI) waveguide technology,1 requires a lower optical pulse energy and results in a smaller, more cost-effective solution compared to the traditional approach utilizing highly nonlinear fiber and frequency doubling crystal.

These advantageous characteristics have the potential to greatly enhance the use of optical frequency combs in various industrial and space applications by reducing costs, size, and power consumption.

The demonstration unit is constructed using a low-loss etching technique for Lithium Niobate on Insulator (LNOI) waveguides, which have proven to be reliable under femtosecond pulse illumination1 and have exhibited low loss levels of less than 0.2 dB/cm.

Currently under development, a two-level waveguide etching process will enable the creation of a double-inverse taper necessary for efficient light coupling between the optical fiber and the LNOI waveguide. The goal is to achieve a loss of less than 1 dB per facet, with current results showing a loss of 4 dB per facet.

In addition to the fiber and LNOI waveguide, the demonstration unit includes a photodiode placed at the waveguide output to detect the fCEO signal.

As shown in the CAD design presented in Figure 1, the components can be housed within a standard butterfly 14-pin package, which is mounted on a Peltier element serving as a micro-bench. The unit is also designed for hermetic sealing.

Read more: Lithium Niobate on Insulator (LNOI) – A Promising Material for Photonic Integrated Circuits (PICs)

Hermetic sealing is the encapsulation of electronic components into an airtight metal or ceramic housing using either parallel gap resistance seam welding or opposed electrode projection resistance welding. It is a key manufacturing process utilized in assembling micro-electronic packages for communication, aerospace and medical device manufacturing.

Uses of hermetic sealing
Microelectronic devices are commonly used in industrial commercial communications, transportation, military, and aerospace industries and include optical sensors, pressure sensors, communications devices, thermal and laser imaging and power amplifiers. By sealing these electronic packages, external contaminants – like moisture – are kept out preventing degradation of the electronic components inside and extending lifetime usefulness.

Implantable medical devices, like pacemakers and defibrillators, also require careful hermetic sealing to protect both the device and the patient.

Microelectronic package types
There are two primary types of packages: metallic tub and ceramic.

The preferred material for metallic tub base packages is Kovar, which has a similar Coefficient of Thermal Expansion (CTE) as glass; the use of this material prevents the metal-to-glass seals of the feedthrough connectors of the package from leaking due to material expansion from heat generated during the welding process.

Ceramic packages are made of a ceramic substrate with a brazed metal seal ring. Kovar is also used in ceramic packages; the Kovar is brazed onto the ceramic base as a seal ring to which the lid is welded.

Parallel gap resistance seam welding
Parallel gap seam welding is one way to execute a hermetic seal. A seam welder with rolling wheel electrodes is connected to a power supply, which is responsible for delivering electric current across the electrodes, through the lid and the package. The seam welder delivers multiple overlapping weld spots, thus creating a continuous weld (Figures 2 and 3).

Read more: Hermetic sealing technologies enable reliable welds, protect electronic devices

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.

Platinum resistance temperature detectors (Pt-RTDs) have a near-linear change in resistance with any temperature changes. Pt-RTDs maintain a significant and uniform rate of resistance change over a much wider operating temperature range than a thermistor. Pt-RTDs are excellent for measurement and control applications with temperatures ranging from -70° C to 500° C.

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

Subassemblies, modules, and components developed for various military applications, such as avionics, ground vehicles, and portable electronics, all need to operate in a variety of harsh environments, which range from extreme temperatures to high shock and vibration. At the same time, lighter and smaller designs are critical for space- and weight-constrained systems, and durability and reliability are at the top of the list of big concerns. These stringent demands translate into big challenges for connector makers to ensure that the interconnects provide highly reliable and fast connections over extended use and in harsh conditions.

Connector makers also need to consider a multitude of design requirements such as mating cycles for long life, ingress protection and ease of use. High-speed data transmission capability also is becoming a bigger factor in new communication designs. While component manufacturers need to meet specific military standards and specs, many connector manufacturers are developing their own advanced technologies and processes to provide a higher level of reliability and usability.

Addressing the need for watertight products in harsh environments, Cinch Connectivity Solutions, a Bel group company, recently released its Cinch Mil/Aero Circulars’ DMS-TP series. These connectors are waterproof when temporarily immersed up to 300 meters, and they are resistant to corrosion. They are also designed for ease of use with scoop-proof shells. The nickel-plated brass shells allow the connectors to withstand prolonged use in the presence of oil, gas, sand, mud, hydrocarbons, and salt.

The Cinch circular connector series offers a full range of frequencies, insulation resistance, dielectric withstanding voltage, operating voltage or capacitance. They also are available in hermetic sealing in any circular connector configuration. These glass, ceramic or epoxy-sealed packages can be used in components or assemblies in harsh environment applications that demand no leakage even under extreme changes in temperature, pressure, humidity and intense vibration, said the company.

A new circular connector from ITT Cannon also addresses ingress protection. Cannon’s Nemesis II CBA 20+ meters is a high-speed, high-mating and quick-termination interconnect that has been tested for water submersion to 20+ meters (65.6 feet). The miniature circular interconnects, designed for soldier-worn applications, operates in extreme and harsh environments so it can be used in battlefield communication devices and applications. It provides power, signal and data in a smaller integrated design to deliver reliable communications in a reduced weight solution. In addition, the breakaway functionality allows soldiers to quickly disconnect/reconnect their cables and equipment if they become caught, and the connector easily terminates to wire, PCB and flex circuits.

Read more: Building a Better Rugged Connector for Military Products

Hermetic sealing is the encapsulation of electronic components into an airtight metal or ceramic housing using either parallel gap resistance seam welding or opposed electrode projection resistance welding. It is a key manufacturing process used in assembling microelectronic packages for communication, aerospace, and medical device manufacturing.

Uses of Hermetic Sealing

Microelectronic devices are commonly used in industrial commercial communications, transportation, military, and aerospace industries and include optical sensors, pressure sensors, communications devices, thermal and laser imaging, and power amplifiers. By sealing these electronic packages, external contaminants—like moisture—are kept out preventing degradation of the electronic components inside and extending their lifetime.

Implantable medical devices, like pacemakers and defibrillators, also require careful hermetic sealing to protect both the device and the patient.

Microelectronic Package Types

There are two primary types of packages: metallic tub and ceramic.

The preferred material for metallic tub base packages is Kovar, which has a similar Coefficient of Thermal Expansion (CTE) as glass; the use of this material prevents the metal-to-glass seals of the feedthrough connectors of the package from leaking due to material expansion from heat generated during the welding process.

Ceramic packages are made of a ceramic substrate with a brazed metal seal ring. Kovar is also used in ceramic packages; the Kovar is brazed onto the ceramic base as a seal ring to which the lid is welded.

Read more: Want Reliable Welds? Hermetic Sealing Can Help