Design engineering working on a mobility device
by Sara McCaslin Sara McCaslin No Comments

Canted Coil Springs and SWaP: A Mechanical Answer to Mobility Device Design Constraints

Modern mobility devices demand a constant balancing act: adding capability without adding size, weight, or power draw. Canted coil springs, however, offer a simple mechanical answer to problems that might otherwise require bulkier, power-hungry systems. This article explores how they support SWaP goals across mobility device design.

Canted Coil Springs

A canted coil spring is a type of coiled spring where the individual coils are tilted (canted) at an angle relative to the spring’s axis, rather than sitting perpendicular to it as in a standard coil spring. Unlike most conventional springs, canted coil springs are also wound with an elliptical (oval), rather than round, cross-section, which is a structural detail that, combined with the coil angle, produces their signature load-deflection behavior.

Canted geometry gives these springs a distinctive load-deflection curve: they can provide a nearly constant force over a wide range of deflection. This is unlike conventional springs, where force rises roughly linearly with compression. Because each coil deflects independently, the spring also compensates for wear, misalignment, and tolerance stack-up over its service life rather than losing contact force as mating surfaces change.

Because of this near-constant-force property, their ability to conform to irregular surfaces, and their independent-coil construction, canted coil springs are widely used for fastening and latching, electrical connectors, and EMI shielding. They’re typically manufactured in 300-series stainless steel, Hastelloy, Inconel, Elgiloy, or copper alloys, with Elgiloy generally specified where extreme temperatures or corrosive media are a factor, and can be gold-, silver-, or nickel-plated for electrical or semiconductor applications.

SWaP and Mobility

SWaP stands for Size (or Space), Weight, and Power, three critical constraints engineers must optimize when designing modern electronic and mechanical systems, including mobility devices.

A mobility device is any tool or piece of equipment engineered to help someone move around, maintain balance, or perform physical activities they would otherwise have difficulty with due to injury, disability, illness, or age-related limitations. There are a wide variety of such devices, including canes, crutches, walkers, wheelchairs (manual and powered), mobility scooters, gait trainers, and stairlifts.

For mobility devices, optimizing SWaP means engineers are working to build lighter, more compact equipment that maximizes battery life and maneuverability without sacrificing performance.

Canted Coil Springs and SWaP

Canted coil springs, which feature individual coils set at a slanted angle, are versatile components that may help reduce size, weight, and/or power draw in certain mobility-device subassemblies. The examples below are candidate applications based on the springs’ established engineering behavior. They illustrate where the technology’s known strengths are likely to translate well to mobility hardware, not documented case studies specific to this market.

Impact on Size

Canted coil springs support the Size constraint in SWaP because their compact radial cross-section can deliver meaningful force in a much smaller envelope than many conventional springs or actuators. They can also be integrated directly into joints, connectors, or latch mechanisms without a separate housing.

Candidate applications include compact latch mechanisms for folding wheelchair frames or walkers, where available hardware space is highly constrained; miniature multi-point electrical contacts in joystick-style controllers; space-constrained connector interfaces between battery packs and drive systems in mobility aids; and small-envelope detent mechanisms for adjustable cane or crutch height-locking pins.

Impact on Weight

Canted coil spring solutions are lightweight (and generally less complex) compared to hydraulic or motor-driven mechanisms that might otherwise be needed to achieve similar constant-force behavior.

There are several candidate applications where canted coil springs could help reduce weight. As the detent element in a stepped seat-back recline lock for manual wheelchairs, a canted coil spring could provide reliable, wear-compensating engagement at each locking position. This is a lighter-weight alternative to a heavier ratchet mechanism, though a spring alone is not a substitute for a hydraulic damper where controlled, velocity-dependent recline motion is required for safety. 

Canted coil springs may also be well suited as the detent spring in wheelchair quick-release axles, where their independent-coil design could better compensate for wear and tolerance changes over repeated cycles than a conventional single coil spring, improving reliability without adding weight or part count. Finally, they can provide lightweight EMI shielding in onboard electronics for power scooters, potentially replacing heavier shielding gaskets.

An older woman on a mobility scooter
An older woman on a mobility scooter

Impact on Power

Canted coil springs are purely mechanical, passive components: they draw no power of their own. In electrical-contact applications, such as spring-energized connector contacts between battery and motor interfaces, the only associated loss is minor resistive (I²R) loss at the contact interface, which is negligible compared to the power draw of an active switching or motor-driven alternative. Because the constant-force characteristic requires no active control system or feedback loop to maintain consistent pressure or engagement, canted coil springs can serve locking mechanisms, seating adjustments, and connector contacts without consuming any of a device’s power budget.

Because of this, canted coil springs can enable passive constant-force seating-pressure adjustment, avoiding motorized actuators in cushioning systems. They can also support mechanical (non-electric) locking pins for folding walkers and rollators, preserving battery life for onboard electronics. As spring-energized electrical connector contacts in battery-to-motor interfaces, they maintain reliable contact without active control circuitry. And when used as passive brake or wheel-lock engagement springs in manual wheelchairs, they require no power source to maintain holding force.

There’s also an indirect power benefit: because canted coil solutions are lighter than the hydraulic or motorized systems they can replace, they reduce the overall mass a powered mobility device has to move to improve battery efficiency and range.

Secondary SWaP-Adjacent Benefits

The ability of canted coil springs to conform to irregular or moving surfaces reduces the need for precision-machined mating parts, simplifying manufacturing and reducing part count. Their independent-coil design also means individual coils continue to compensate for wear and misalignment throughout the product’s service life, which can reduce the maintenance burden in applications like wheelchair wheel-lock and brake engagement points.

This durability is directly tied to material selection: canted coil springs made from 300-series stainless steel, Hastelloy, or Elgiloy are engineered to resist a wide range of temperatures and corrosive or humid conditions, which is relevant for mobility devices such as outdoor scooters and rollators that see regular exposure to the elements.

Conclusion

Canted coil springs can offer a low-complexity way to help meet SWaP objectives. Their passive operation, small footprint, and durable, self-compensating design make them a strong candidate for replacing motorized or hydraulic solutions in specific mobility-device subassemblies (provided the application doesn’t require the velocity-dependent damping or continuously variable control that only an active system can provide). These springs are well worth considering in the next mobility device design. If you’d like to learn more about Advanced EMC FlexForce canted coil springs, contact us today! 

Semiconductor
by Daniel Mays Daniel Mays No Comments

Meeting SEMI Standards for Seal Purity, Outgassing, and Chemical Resistance

Semiconductor fabrication facilities are among the most demanding environments for seal materials on the planet because a single contamination event can scrap a wafer batch worth hundreds of thousands of dollars. And every polymer, lubricant, and elastomeric material contains residual volatiles. SEMI standards deal with how to take these residual volatiles into account when designing components, such as seals, for wafer fabrication environments. The purpose of this blog post is to discuss what SEMI standards actually require and how engineers select bearings to meet them.

The SEMI Standards Landscape

SEMI standards serve as the common language of the global semiconductor supply chain. For example, SEMI standards define fitness for use by establishing minimum thresholds (e.g., outgassing limits, contamination levels, chemical compatibility requirements) that a component must meet to be considered safe for use in semiconductor manufacturing environments. These standards also protect the wafer from contamination that can destroy device yield and make suppliers accountable. 

By referencing a SEMI standard in a procurement specification, a fabrication engineer can require documented, third-party-verifiable compliance rather than relying on a supplier’s marketing claims. These standards also enable global interoperability: tools, chemicals, and components built to SEMI standards can move across fabrications and geographies without extensive re-qualification. This serves as a major economic benefit in a highly globalized industry.

SEMI F-Series (Facilities and Materials)

The SEMI F-series serves as the most relevant category for seals. Standards like SEMI F57 govern polymeric components and wetted surface materials used in UHP (ultra-high purity) gas distribution systems, covering surface finish requirements, material qualification, and cleanliness protocols. SEMI F2 addresses test methods for metallic contamination on wetted surfaces. These are the specs a seal or bearing supplier is most likely to be asked to demonstrate compliance with.

SEMI C-Series (Chemicals)

The SEMI C-Series of standards defines purity grades and acceptable contamination levels for process chemicals such as acids, solvents, and oxidizers. While these standards primarily govern the chemicals themselves, they are also critically important for material selection. If your seal is sitting in a bath governed by a C-series chemical specification, that specification indirectly defines the chemical resistance your seal must demonstrate. Engineers selecting materials for wetted components need to understand what chemical grade they are designing for.

SEMI S2 (Safety Guidelines for Semiconductor Manufacturing Equipment)

S2 is a broad equipment safety standard with direct implications for materials selection. It addresses chemical containment, materials of construction for chemical-wetted components, ventilation requirements, and labeling. It’s often the standard a tool OEM must satisfy as a condition of fab entry, making it a gateway document that touches bearing and seal design.

Purity: Metallic Contamination and Ionic Cleanliness

When it comes to cleanliness in fabrication environments, the core concern when it comes to contamination is the presence of trace metals (Fe, Na, K, Ca) as killer defects in semiconductor devices. Both dynamic seals are going to shed particles, and this includes wear debris, surface oxides, and manufacturing residues. Among the key material considerations are the use of PTFE bearings and seals, while other options include ceramic bearings (Si₃N₄, ZrO₂) as the go-to for ultra-pure applications and surface treatments (e.g., electropolishing, passivation, and their limits).

Outgassing: The Invisible Contamination Problem

Through outgassing, volatile organic compounds (VOCs) deposit on wafer surfaces and disrupt lithography, deposition, and etch processes. Two standards commonly apply: SEMI F10 and NASA ASTM E595, serving as the benchmarks engineers reference. And there are two key metrics that matter: ML (Total Mass Loss) and CVCM (Collected Volatile Condensable Materials). The general targets used by engineers are TML < 1.0% and CVCM < 0.1%. And remember that a material can pass TML and fail CVCM. Bearings and seals must comply with both. However, CVCM is the one that matters most because it captures what actually re-deposits on a cooler surface.

In seal assemblies, the vast majority of problems come from lubricants and greases (silicone-based greases are particularly problematic in vacuum) and adhesives, polymer cage materials, and elastomeric seals. This includes nylon and acetal bearing cages and standard elastomeric seals with curative that can volatize under heat and vacuum. To avoid these issues, industry best practice is to use …

  • PFPE-based dry film lubricants
  • PTFE lip seals (which are known for their high purity and self-lubrication)
  • Perfluoroelastomers (FFKM)

Bake-Out Procedures

As already discussed, every polymer, lubricant, and elastomeric material contains residual volatiles that may include trapped solvents from manufacturing, absorbed moisture, unreacted monomers, and plasticizer fractions. At room temperature, these substances release slowly over weeks or months. Elevated temperature, however, drives that same process in hours, forcing the material to shed its residual volatiles before it is ever installed. This process is known as bake-out and must be accomplished for a material to be safe to use in a high-purity environment.

Chemical Resistance: Surviving the Process Chemistry

The process chemistry involved with semiconductor manufacturers includes chemicals such as HF, H₂SO₄, HCl, H₂O₂, IPA, NMP, ozone, and aggressive plasma environments. And although a material may be listed as chemically resistant on a data sheet, that does not account for critical variables such as concentration, temperature, and exposure time. Swell, extraction, and stress cracking are the failure modes that tables consistently miss.

The material compatibility hierarchy for seals is:

  • FFKM (Kalrez®, Perlast®): broadest chemical resistance, low extractables
  • PTFE: excellent passive resistance but poor dynamic sealing performance
  • EPDM / FKM (Viton®): acceptable in some applications, disqualified in others (HF is a hard no for FKM)

Conclusion

SEMI compliance is not just a checklist, but rather a systems-level engineering discipline. Material selection, outgassing qualification, and chemical resistance validation must work together to result in a fully SEMI-compliant seal. Engineers who treat these as a system rather than separate line items build better products. If you are looking for a SEMI-compliant sealing solution, contact the engineers at Advanced EMC today.