In a remarkable development detailed in the article, “A Versatile Hermetically Sealed Microelectronic Implant for Peripheral Nerve Stimulation Applications,” published on the National Center for Biotechnology Information, unveils a groundbreaking neurostimulation platform. This platform introduces a fully implantable multi-channel neural stimulator designed for chronic experimental studies involving peripheral nerves in large animal models. Notably, the implant is hermetically sealed within a ceramic enclosure and encapsulated in medical-grade silicone rubber, ensuring both longevity and safety.

The stimulator’s microelectronics are implemented using advanced 0.6-μm CMOS technology. They incorporate a crosstalk reduction scheme to minimize cross-channel interference, ensuring precision in stimulation. Additionally, high-speed power and data telemetry enable battery-less operation, a significant advancement in the field. A wearable transmitter, equipped with a Bluetooth Low Energy radio link, and a customized graphical user interface, offer real-time and remotely controlled stimulation, adding to the device’s versatility.

This versatile implant comprises three parallel stimulators, each supporting independent stimulation on three channels. Each stimulator further facilitates six stimulating sites and two return sites through multiplexing. As a result, the implant can support stimulation at up to an impressive 36 different electrode pairs, enabling highly programmable and selective neural stimulation.

The article delves into the intricate details of the implant’s design, the method of hermetic packaging, and its exceptional electrical performance. Furthermore, in vitro testing with electrodes in saline solution underscores the device’s efficacy and safety.

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In the illuminating exploration titled “Die-Level Thinning And Integrating Route For Singulated MPW Chips Using Both Silicon Sensors And CMOS Devices” on Semiconductor Engineering.

The demand for ultra-thin silicon devices is surging across various applications, with flexible electronics standing at the forefront. To meet this demand, delves into a groundbreaking post-processing method that focuses on two silicon devices: an electrochemical impedance sensor and Complementary Metal Oxide Semiconductor (CMOS) die. Both these devices are sourced from a multi-project wafer (MPW) batch, and masterfully thins them at the die-level post dicing, ultimately reducing their thickness to an impressive 60 µm.

These finely thinned dies undergo a transformation, being flip-chip bonded to flexible substrates and hermetically sealed. The sealing is accomplished through two techniques: thermosonic bonding of Au stud bumps and anisotropic conductive paste (ACP) bonding. This strategic approach ensures that the thinned dies are not only compact but also possess impeccable reliability.

The thinned sensors are compared to their original counterparts, revealing advancements in both miniaturization and functionality. Importantly, the flip-chip bonded thinned sensors exhibit long-term reliability surpassing that of conventional wire-bonded sensors, underscoring the potential for game-changing innovations.

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In the insightful exploration titled “What is the Difference Between Hermetic and Non-hermetic Packaging” on, the profound disparities between hermetic and non-hermetic packaging methods come to light. 

The foundation of hermetic sealing rests upon the coefficient of thermal expansion alignment between glass and metal. A “matched seal,” characterized by this congruence, derives its structural integrity from the bond between glass and the metal’s oxide. Primarily utilized for low-intensity applications like light bulb bases, this glass-to-metal hermetic seal, albeit weaker, serves its designated purpose.

In contrast, the concept of “compression seals” materializes when glass and metal exhibit divergent coefficients of thermal expansion. This intricate dance results in the metal compressing around the solidified glass during cooling. The outcome is a robust seal capable of withstanding substantial pressure, finding its application across diverse industrial scenarios.

Glass-to-metal seals, surpassing epoxy alternatives, exhibit resilience at significantly elevated temperatures. Compression seals exhibit viability up to 250 °C, while matched seals endure up to 450 °C. Nonetheless, material choices are constrained due to thermal expansion considerations. The sealing process, executed at around 1000 °C in an inert or reducing atmosphere, safeguards components from discoloration.

Ceramic-to-metal hermetic seals introduce a transformative alternative to glass – co-fired ceramic seals. These ceramic marvels transcend the design limitations of glass-to-metal seals, excelling in high-stress environments demanding formidable hermetic performance. The selection between glass and ceramic hinges on the specifics of the application, encompassing weight, thermal dynamics, and material requisites.

Beyond metal applications, the article navigates into glassware sealing. These measures maintain high vacuum integrity, achieving impressively low air leakage rates. Emerging solutions like PTFE tape, PTFE resin string, and wax offer promising alternatives, necessitating careful handling during application for optimal hermetic outcomes.

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As highlighted in the article titled “Types of glass-to-metal hermetic seals” on Wikiwand, presents various methods crucial to diverse industrial applications. These seals ensure airtight integrity, offering distinct advantages based on their design and composition.

A pivotal classification in hermetic sealing is the “matched seal,” where glass and metal with identical coefficients of thermal expansion are bonded, relying on the connection between glass and the metal’s oxide. This type, while relatively less robust, finds utility in low-intensity scenarios like light bulb bases.

In contrast, “compression seals” address the challenge of varying coefficients of thermal expansion. In these seals, the metal compresses around the cooled solidified glass, making them capable of withstanding high pressure. This attribute positions compression seals as key players across a spectrum of industrial applications.

Glass-to-metal seals outperform epoxy counterparts in elevated temperature environments, with compression seals operable up to 250 °C and matched seals enduring temperatures as high as 450 °C. Nevertheless, material selection remains limited due to thermal expansion considerations. The sealing process takes place at approximately 1000 °C in an inert or reducing atmosphere to preserve component appearance.

Diversifying the field, ceramic-to-metal hermetic seals introduce co-fired ceramic alternatives to glass. These ceramic seals excel in demanding, high-stress environments, showcasing superior hermetic performance. The choice between glass and ceramic hinges on factors such as application, weight, thermal requirements, and material specifications.

Beyond metal, glass taper joints also feature in hermetic sealing, secured by PTFE sealing rings, encapsulated o-rings, or PTFE sleeves. Additional options like PTFE tape, PTFE resin string, and wax are emerging, offering airtight solutions without the risk of contamination caused by dissolvable substances like grease.

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In the article titled “Hermetic Sealing of Microelectronics Packages Using a Room Temperature Soldering Process,” a method utilizing a multilayered reactive foil is presented to achieve hermetic sealing in microelectronic packages. The foil consists of nanoscale layers of elements with negative heats of mixing, such as Al and Ni. By activating the reaction with a small electrical or thermal stimulus, the heat generated melts the solder layers and permanently joins the package lid to the base. This process eliminates the need for high reflow temperatures, offers low helium leak rates, and serves as a cost-effective alternative to methods like laser welding.

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In a patent titled “Method for hermetically sealing electronic devices,” a technique for creating hermetic seals in electronic device packages is described. The method involves the use of a stencil member with a closed loop opening, surrounded by web members, to secure the inner portion of the stencil. A glass slurry is forced through the stencil opening onto a substrate, forming a closed loop of glass. This loop is then glazed and bonded to the first substrate, which acts as a cover plate. The glass loop surrounds the electronic device and contacts the second substrate, creating a hermetic seal. Cooling solidifies the glass, ensuring isolation from the external environment.

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Metals with high strength-to-weight ratios such as Al and Ti are of considerable interest for niche applications, but electrical feedthroughs are challenging. Commercially available glass-to-metal seals in titanium were scaled to produce large thermal battery headers 38% lighter than conventional headers. The reliability of seals in titanium and stainless steel was investigated. Finite element modeling of conventional seals indicated that yielding in the pin results in crack-inducing axial stresses. Titanium seals with molybdenum pins are not susceptible to such yield, but a larger coefficient of thermal expansion difference in this glass-to-meal seal system results in very similar crack behavior. Microscopy supporting the results of the finite element modeling is presented. No cracks affecting seal hermeticity were predicted or observed.


Thermal batteries contain hygroscopic materials such as lithium that must be protected from exposure to the environment. The long shelf life expected in these reserve batteries (on the order of decades) demands hermetic packaging with leak rates on the order of 10-9 scc He/s. Leak rates this low cannot be achieved with polymer seals, which typically have leak rates two orders of magnitude higher. High quality elastomeric seals, such as Viton, can achieve such low leak rates, but these seals are quite expensive.

The only practical battery packaging for thermal batteries combined welded metal connections with insulator-metal seals for electrical feedthroughs. The predominant packaging for thermal batteries combines stainless steel cases with glass-to-metal (GTM) seals. A large number of sealing glasses and glass ceramics are available, but a common battery combination is 304L SS shells / Corning 9013 insulators / Alloy 52 pins. This combination is a compression seal on the SS / glass interface and a matched seal at the glass / pin interface. This combination has excellent reliability, good hermeticity, and relatively low cost. However, the strength-to-weight ratio for stainless steel is poor compared to common aerospace materials such as aluminum and titanium. Steel is nearly

Read more: Lightweight packaging for thermal batteries

The surface-mount T24 series consists of two devices, both 9 x 7.1 x 7.4mm (case code ‘C’).

33μF – 45V at 200°C (75V -55 to 85°C) 2.5Ωmax ESR (+25°C 120Hz)
10μF – 75V at 200°C (125V -55 to 85°C) 5.5Ωmax ESR (+25°C 120Hz)
Capacitance tolerance is ± 10% or ± 20% (standard).

In both cases, maximum leakage is 1μA at 25°C (5μA at 85/125°C).

Thermal shock tolerance is 300 cycles (MIL-STD-202, method 107, condition A – tested with MIL-PRF-39006).

“Featuring a glass-to-tantalum hermetic seal and a life rated to 2,000 hours [+200°C], it offers a smaller size and footprint than equivalent through-hole and over-moulded high temperature devices,” according to New Yorker Electronics, which is stocking the parts. “Vishay’s wet tantalum capacitors have been optimised for timing, filtering, energy hold-up and pulse power applications.”

Read more: 200°C wet tantalum capacitors are tough for the hard life

A specialist in power-protection systems, Schweitzer Engineering Laboratories (SEL), Pullman, Wash., recently avoided both costly redesign of its injection molds and boosted yield by opting to replace its pneumatic ultrasonic welder with a new ultrasonic servo welder.

SEL designs and builds digital products and systems that protect power grids around the world. The company offers a variety of fault indicators for use on subsurface or pad-mounted transformers, subsurface or pad-mounted switchgear and sectionalizing cabinets, junction boxes, and splices.

Recently, SEL was having difficulty assembling one of the many reset fault indicators it molds. The product is made of Makrolon 2607 PC from Covestro, Pittsburgh, and the project entailed welding the clear lens display screen to the body of assembly. Because the product is intended for harsh, submersed, and corrosive environments, the hermetic seal of the ultrasonically welded housing is tested to sustain temperatures ranging from -40 C (-40 F) to 65 C (140 F).

SEL was experiencing low yield from its pneumatic ultrasonic welding process. The welds were inconsistent, resulting in leaking, non-hermetic welds. SEL conducted several Design of Experiments over a three-year period, and the results always pointed to the same small welding process window with high down speeds and very short weld times. SEL engineers first suggested redesigning molds to get even flatter welding surfaces. However, before proceeding with this option, multiple sets of parts were taken to the Dukane Applications Lab in St. Charles, Ill.

There, Dukane’s 20 kHz iQ Series servo-controlled ultrasonic welding system with Melt-Match technology was used to perform tests on sample parts. iQ Servo welder graphs showed the part was acting like a spring because of a hollow area under the weld zone and was collapsing faster than the horn movement, resulting in inconsistent and leaking welds. As a result, it was necessary to use varying weld speeds.

Ken Holt, sr. application engineer at Dukane states, “Makrolon 2607 welds very well when the initial weld speed is slow and is gradually increased over the weld distance. Although old pneumatic systems are capable of varying the force during the weld, the rate of change
is restricted due to the time required to move air in or out of the air cylinder. However, the servo system is capable of accelerations of 50 in./sec2—equivalent to changing speed by 1 in./sec in 0.020 sec. Dukane’s patented Melt-Match technology further expands this capability by allowing 10 discrete velocity values during the weld process.”

Read more: Molder Gets Hermetic Seal, High Yield with Servo Welder

Numerous manufacturers are working to improve electric vehicle (EV) performance and economics. A major part of this effort is focused on improving battery technology; in particular, developing methods and materials to simultaneously bring down fabrication costs (especially reducing production cycle time) and also extend reliability. Can-to-cap welding of prismatic battery cells is a standout example of this work, and one in which recent developments in laser welding are addressed with great success.

Can-to-cap welding specifically refers to the process of sealing the lid on the casing (can), which contains all the electrode structures for the battery. This sealing is done after these internal parts have been assembled into the can. Since this occurs near the end of the production cycle—after most of the value has been built into the assembly—scrapping parts at this stage is particularly costly.

The sealing operation requires making a fairly long, continuous weld. A typical prismatic battery is around 20 mm wide by up to 300 mm long, and the weld goes around the entire battery perimeter. There are several key requirements for manufacturers to perform this process:

  • The weld seam must provide a hermetic seal with no gaps along the entire weld—even if the original part fit-up wasn’t perfect or isn’t consistent (especially at the corners).
    Welding must achieve adequate penetration depth and low weld porosity. This is necessary to create a seal strong enough to last the lifetime of the battery without cracking open, even when subjected to vibration and mechanical shock.
  • The welding process cannot create any spattered metal. Most importantly, spatter cannot occur inside the battery where it might create electrical short circuits. Spatter is especially a problem when welding aluminum, which is commonly used for battery cans. This is due to several factors, but primarily because of aluminum’s high reflectivity and low melting temperature. These may lead to keyhole instability, which causes weld spatter.
  • The heat input into the battery must be limited to avoid damaging internal parts.

Fiber lasers can deliver on all these requirements. As a result, they have already established themselves as useful production tools for prismatic battery can-to-cap welding. In the most common implementation, the beam focusing optics are gantry-mounted, and then moved around to follow the shape of the desired weld seam.

This gantry approach delivers highly precise mechanical alignment and great weld consistency. This is because the laser beam always hits the workpiece at the exact right place and the same angle of incidence. However, moving the optics (or alternately, the battery) makes a gantry system slow. This is an issue because slower speed translates directly into higher production costs.

Faster way to weld large areas
As manufacturers strive to dramatically increase their production capacity and also go to larger-sized prismatic batteries, the speed limitations of gantry-type welding systems become a significant issue (see Fig. 1). It’s well known that scanning systems can deliver higher weld speeds. This is because it is much easier to move the weightless laser beam using scanner mirrors than it is to physically translate the entire focusing optics assembly.

Read more: Advances in laser welding prismatic battery: Can to cap