What are Carbon Contacts On PCB?
Carbon contacts refer to electrical contacts used in printed circuit boards (PCBs) that utilize carbon materials. As PCBs have become increasingly prevalent across industries from consumer electronics to aerospace, there is a growing need for more robust and reliable electrical connections on boards. Carbon contacts provide superior performance compared to traditional metal alloy contacts due to certain unique properties of carbon.
Carbon materials used in contacts include graphite, carbon black, graphene, carbon nanotubes (CNTs), and diamond-like carbon (DLC). Contacts made from these materials demonstrate excellent electrical conductivity, low contact resistance, high thermal conductivity, and resistance to arc erosion and material transfer. As such, carbon contacts outperform metal contacts in applications requiring high numbers of mating cycles, high temperatures, high voltages/currents, and/or corrosive environments.
Benefits of Carbon Contacts
Carbon contacts offer the following key advantages over traditional metal alloy contacts:
Highly Conductive
Carbon materials like graphene and CNTs can demonstrate electrical conductivity comparable or superior to metals like copper. This allows for reliable connections with low contact resistance.
Resists Arc Erosion
Carbon's high melting point and heat tolerance prevents material loss due to electrical arcing during contact mating/breaking. This allows carbon contacts to endure more mating cycles.
Low Contact Resistance
Carbon contacts can achieve lower contact resistance compared to metals, especially when coated with small amounts of precious metals like gold or silver. This reduces power losses through connections.
High Thermal Conductivity
The high thermal conductivity of carbons like graphite and graphene prevents excessive heating at contacts under high currents. This maintains connection reliability and integrity.
Anti-Sticking
Carbon materials like graphite create dry lubricant surfaces that reduce friction and prevent metal transfer between contacts during mating/breaking. This preserves contact surfaces.
Table: Key benefits of carbon contacts over traditional metal alloy contacts
Carbon Contact Materials
Various carbon materials are leveraged to create electrical contacts, with the most common being graphite, carbon black, graphene, carbon nanotubes (CNTs), and diamond-like carbon (DLC).
Graphite Contacts
Graphite is a crystalline form of carbon with excellent electrical conductivity and thermal conductivity. In addition, graphite acts as a solid lubricant, providing low friction surfaces. These properties make graphite useful as an electrode, brush, and contact material. Graphite contacts demonstrate reduced contact resistance and material transfer (anti-sticking), allowing them to withstand more mating cycles versus metal contacts.
Carbon Black Contacts
Carbon black is a product of incomplete combustion of hydrocarbon materials, consisting of finely divided particles of amorphous carbon and some hydrogen content. It has high electrical conductivity as well as anti-sticking properties. Carbon black is widely used as a conductive additive in polymers and rubbers. When incorporated into contact materials, carbon black improves conductivity and lubricity to reduce friction and wear.
Graphene Contacts
Graphene is a single layer of graphite with remarkable electrical, thermal, and mechanical properties. Graphene has very high electrical and thermal conductivities, allowing it to function well as a contact material. In addition, graphene has tremendous strength despite being extremely thin. Coating metal or carbon contacts with graphene can significantly improve properties and lifespan.
Carbon Nanotube (CNT) Contacts
CNTs are tiny cylindrical carbon structures with diameters on the nanometer scale. But despite their small size, CNTs have extremely high electrical conductivity, thermal conductivity, and tensile strength. CNT arrays/films can be fabricated into conductive coatings or free-standing mats to create contacts. The high conductivity and strength of CNTs impart performance advantages over metals.
Diamond-Like Carbon (DLC) Contacts
DLC refers to amorphous carbon material that displays some diamond-like properties, such as high hardness. DLC coatings provide very hard, durable, and electrically conductive surfaces. Applying ultra-thin DLC coatings onto base contact materials imparts greatly improved wear resistance and lifespan to electrical contacts.
Table: Common carbon materials utilized in electrical contact applications
Manufacturing Carbon Contacts
Several techniques exist to fabricate the carbon materials described above into electrical contact form factors and integrate them onto PCBs.
Molding & Compaction
Fine carbon powders, like graphite or carbon black powder, can be mixed with binder materials, molded into contact shapes, and compacted via processes like isostatic pressing. This allows manufacturing complex contact geometries with net shape or near-net shape.
Screen Printing
Carbon-loaded conductive inks and pastes containing materials like graphite, carbon black, and silver can be screen printed onto PCB substrates in precise contact pad shapes and sizes. Screen printed carbon contacts provide high conductivity and can endure repetitive mating cycles.
Physical Vapor Deposition (PVD)
PVD methods like sputtering or thermal evaporation can deposit ultra-thin films of carbon materials such as graphene or DLC onto contact surfaces. PVD enables excellent control over deposit thickness, uniformity, and integrity to tailor contact properties.
Chemical Vapor Deposition (CVD)
CVD processes facilitate growth/deposition of carbon materials directly on contact surfaces. CVD can produce carbon films like CNTs or graphene on contacts by exposing hydrocarbon precursors to high heat. This imparts greatly enhanced conductivity, wear resistance, and lifespan.
In most cases, carbon contact materials require integration with base metals like copper, silver, or noble metals on PCBs using the above manufacturing processes. This optimizes electrical performance while leveraging the unique advantages of carbon contacts.
Table: Overview of major techniques for fabricating carbon contacts
Applications of Carbon Contacts
The superior lifetime, reliability, and performance of carbon contacts in demanding conditions make them well-suited for the following applications:
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High Temperature Electronics
Carbon's high melting point allows carbon contacts to withstand extremely high temperature environments (>500°C) found in aerospace systems, nuclear reactors, automotive sensors, and oil/gas logging equipment. This imparts improved reliability over traditional metal contacts.
High Power Connectors
The high electrical and thermal conductivity of carbon materials enables reliable transmission of very high currents and voltages in power electronics connectors found in electric vehicles (EVs), wind turbines, solar panels, etc. Carbon handles high power loads better than metals.
Low-Voltage High Frequency
Low contact resistance and excellent conductivity characteristics of carbon contacts maintains signal integrity across low-voltage (<60V) high frequency connections encountered in computing, telecom systems, and consumer electronics. This supports high data rates.
Electromagnetic Interference (EMI) Shielding
Carbon materials like carbon black composites or CNTs function as effective EMI absorbing materials due to electrical conductivity. They can shield sensitive contacts from electromagnetic interference when applied as gaskets, shielding tapes, or directly integrated into connectors.
Corrosive Environments
The inherent corrosion resistance and impermeability provided by diamond-like carbons (DLCs) allow carbon contacts to reliably operate in highly oxidizing or saline environments found in oil/gas exploration, chemical processing, wastewater systems, etc. where metal contacts would rapidly degrade.
Dry Circuit Applications
Carbon's solid lubricating properties creates low friction wiping contacts for sensitive electronics with low wettability requirements. The anti-sticking properties prevent material transfer, ideal for very low current (pA-μA) medical sensors, aerospace avionics, lab instrumentation etc. prone to failure with applied lubricants.
In summary, rugged carbon contacts outperform metal counterparts across the above challenging applications by sustaining reliable connections over longer lifetimes with lower maintenance. Their unique electrical, thermal, and mechanical attributes impart performance advantages unachievable using conventional contact materials.
Comparative Analysis of Carbon Contacts
A high level comparison of important electrical contact properties and characteristics for conventional metals versus carbon allotrope materials is provided below:
Table: Comparison of electrical contact properties - metals vs. carbon allotrope materials
Key Takeaways
The comparative analysis highlights carbon materials match or improve upon the performance capabilities of high conductivity metals for virtually all major contact properties and metrics. The carbon contacts provide simultaneously high electrical & thermal conductivity, mechanical strength, and robustness against arcing, corrosion, fouling, and material transfer.
Future Roadmap for Carbon Contacts
While carbon contacts have recently begun penetrating the electronics market for demanding applications, wider adoption across additional industries is expected over the next 5-10 years as next-gen carbon enhanced connectors and contacts increase availability.
Manufacturing Scale-Up
Scaled manufacturing and increased commercial availability of molded carbon composites and carbon coatings applied via processes like CVD and PVD will reduce costs and promote broader implementation.
Hybrid Metal-Matrix Composites
New metal-matrix composite formulations embedding nano-scale carbons like graphene and CNTs into copper or silver matrices will provide mass producible, cost effective next-gen conductive contacts.
3D Printing/Additive Manufacturing
3D printing of specialty carbon and carbon-composite powders into net shape contact components using industrial binder jetting, SLS, and extrusion AM processes will enable on-demand fabrication of geometrically complex carbon contacts.
High Data Rate Applications
The excellent conductivity, signal integrity, and RF performance characteristics of carbon will drive adoption into short contact length connectors for high frequency communication systems supporting 5G rollout.
Commercial Aerospace Systems
Stringent demands of the aerospace industry in terms of reliability, safety, and maintenance intervals will incentivize qualification and integration of carbon contacts into major aircraft systems over the next decade.
In summary, as material and manufacturing innovations continue improving the cost, quality, and availability of high performance carbon contacts, adoption rates across diverse connectors, PCBs, and electronic components are projected to grow rapidly. Carbon possesses inherent advantages over conventional metals that will position it as an increasingly strategic material for global electronics over the coming decade.
FQA
What are the main advantages of carbon contacts over traditional metal alloy contacts?
The key advantages of carbon contacts include:
Why are carbon nanotubes (CNTs) suitable materials for electrical contacts?
CNTs have an extremely high electrical conductivity (10^7 - 10^9 S/m) equaling or exceeding that of most metals. In addition, they demonstrate excellent thermal conductivity along with high strength and hardness. These properties make them ideal contact interface materials.
What manufacturing process allows deposition of graphene directly onto contacts?
Chemical vapor deposition (CVD) enables direct growth and deposition of graphene films onto base contact materials. The process facilitates coating components with precisecontrol of graphene thickness, uniformity, and integrity.
What industry applications are carbon contacts best suited for?
The extreme environment tolerance and reliability of carbon contacts makes them ideal for high temperature electronics, high power connectors, aerospace systems, automotive sensors, nuclear energy applications, and other challenging segments.
How are diamond-like carbon (DLC) coatings able to improve contacts performance?
Ultra-thin DLC coatings significantly enhance contact hardness and wear resistance, reducing debris formation. The durable DLC layer also imparts excellent corrosion resistance while maintaining high electrical conductivity. This extends operational lifetimes.