Technology Update
By Richard D. Sarno, Ph.D.
The glass-ceramic method, which can be used to make hermetic seals in circular connectors, is a process by which crystalline ceramics are produced by the controlled crystallization of glasses. To accomplish this, a component that acts as a nucleating agent is added to the glass composition. Properly cooling the glass melt results in the formation of fine-grained, high-strength ceramics.
The crystalline phases produced, and the resulting microstructure, can be controlled by varying the nucleation and growth treatments during the connector sealing cycle. This makes it possible to produce glass-ceramics containing different crystalline phases, and therefore different physical properties, from the same initial glass composition. The most important of these properties in sealing applications is the coefficient of thermal expansion (CTE). By carefully controlling the time-temperature profile of the sealing cycle, and therefore the CTE, the same initial glass can be used to seal to a wide variety of conductor/housing material combinations.
The processing sequence for glass-ceramic-to-metal seals is much simpler compared to that of traditional ceramic-to-metal seals. For the latter process, the ceramic insulator must first be metallized by applying a refractory metal paint that is sintered in a wet, hydrogen atmosphere at temperatures above 1,400°C. Next, a wetable metal interlayer, normally nickel, is applied to the metallization. This is necessary because most braze alloys do not wet the metallization layer. The nickel layer can either be applied by plating (electroless or electrolytic) or by painting on a nickel oxide layer that is reduced in a hydrogen atmosphere. Finally, this metallized ceramic is brazed to the desired metal members (cap and conductor, or flange), either in vacuum or in an inert atmosphere, at temperatures between 850° to greater than 1,100°C.
For glass-ceramic-to-metal sealing, the process involves assembling the components — metal conductor(s) and housing, and a sintered glass bead or preform — and firing the assembly in an inert atmosphere at temperatures near 1,000°C.
By carefully controlling the time-temperature profile of the sealing cycle, the desired CTE of the glass-ceramic can be obtained and a hermetic seal results.
Ceramic-to-metal seals require having several dissimilar metals in contact (conductor, cap and braze alloy, or flange and braze alloy). This is a disadvantage when the assembly is to be used in a corrosive, aqueous environment. The galvanic cell set up by the dissimilar metals will lead to galvanic corrosion of the seal and seal failure. Glass-ceramic-to-metal seals do not contain dissimilar metals in contact because the conductor is directly joined to the housing by the glass-ceramic. Proper selection of the metal components and the glass-ceramic composition for the expected environment can eliminate galvanic corrosion.
RICHARD D. SARNO, Ph.D., is Research & Development Engineer, Ceramaseal, a division of CeramTec, U.S. Route 20, New Lebanon, NY 12125; (518) 794-7800; Fax: (518) 794-8080; Web site: www.ceramaseal.com.
Industrial Connectors
Han R23 Circular Industrial/Electrical Connectors are said to be suitable for use in measurement and automatic control systems, as well as fieldbus systems. They can reportedly be assembled from a range of inserts and housings, and mateability with other circular R23 types can be achieved. Features include up to 19 contacts, 25 V/60 V at 7.5 A; screw, solder or PCB solder termination; IP67-rated, corrosion-resistant housings; outer diameter of 26 mm; and a vibration-proof, screw-locking system. Harting Inc., Elgin, Ill.
Harsh Environment Connectors
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These Glass-ceramic Circular Connectors are high-density and high-temperature, and designed for extreme environments. The products include glass-ceramic hermetically sealed headers with up to 41 gold-plated pins and a standard plug on the air side. Three design options are available on the vacuum side: double-ended, straight-pin and solder-pin. The connectors have 304 stainless-steel shells, are UHV-compatible and are rated for temperatures from -269° to 400°C. Ceramaseal, a division of CeramTec, New Lebanon, N.Y.
Sealed Connectors
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One-Piece Circular Plastic Connectors (CPCs) are sealed and suitable for industrial applications. The one-piece design reportedly eases assembly. A wire-entry seal protects the rear of the connector and a peripheral seal protects the interface. The products have IP67 fluid protection and an operating temperature range of -50° to 125°C. They are housed in high-strength, impact-resistant thermoplastic housing, rated UL 94V-0. AMP, a part of Tyco Electronics Corp., Harrisburg, Pa.
Screw-clamp Connectors
CA Series Connectors feature an integrated strain-relief device and a screw-lock technique. They are adjustable through 90°, and adapt to a variety of cable diameters. Wrap-around seals are said to offer protection against dust and moisture. The products provide IP67 protection, and have VDE, UL/UR, SEV and CSA approval. Operating voltage is 250 VAC and operating current is 10 A. Silver- and gold-plated surfaces are available, as well as male, female, right-angle, straight, bulkhead and panel-mount configurations. Hirschmann Inc., Pine Brook, N.J.
Miniature Connectors
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M8 Circular Connectors are available with pin and socket contacts for free assembly or they come prewired. The miniature dimensions of the connectors are said to be suitable for sensor applications requiring smaller connectors. They are rated for operating voltages of up to 75 VDC (60 VAC) and for a maximum current-carrying capacity of 4 A. The prewired versions feature PUR cable in a variety of lengths (24 AWG). The free-assembly versions feature solder contacts. Both are available in three or four-position connections and are rated IP65/67 for industrial environments. Phoenix Contact Inc., Harrisburg, Pa.
DIN Connectors
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Circular DIN Connectors are IP67-rated, watertight and shielded for EMI protection. Available in 10 different pin configurations of up to 12 positions, the products are suitable for applications in medical instrumentation, measurement and control, and communications systems. With a rating of 60 to 250 V, the connectors offer low contact resistance and high current capacity of up to 5 A, depending on pin configuration. A threaded metal housing reportedly ensures self-seating alignment for reliable interconnection. Lumberg Inc., Midlothian, Va.
PCB Connectors
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ACP Series Connectors are designed for PCB and flex circuit applications. They are available in standard or low-profile receptacles, and are intermateable with MIL-C-26500, MIL-C-83723 and MIL-C-38999 connectors. Contacts are positively aligned and sealed in the insert, which reportedly eliminates floating, eases mounting and strengthens the assembly. The one-piece insert is permanently bonded into place. The bonding and sealing reportedly prevent wicking of liquid, vapor-deposited conformal coatings and cleaning fluids into the connector during assembly. Array Connector Corp., Miami, Fla.
Sealed Connectors
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Water-sealed JBX Connectors consist of panel-mount receptacles and cable plugs with rubber seals that provide high-sealing capability and meet the IP67 protection requirement. The high-endurance push-pull locking design is said to ensure protection against vibration, shock and accidental pulls on the cable. Twelve contact arrangements from two to 19 positions are available. Typical applications include medical and scientific instrumentation, global positioning systems, in-flight entertainment systems and speed-detection equipment. FCI USA Inc., Etters, Pa.
Miniature Connectors
Minisnap Miniature Circular Connectors are for instrumentation and medical OEM electronics. They feature a push-pull locking system, which is said to allow connector mating even in hard-to-reach places. The connectors can have solder PCB pins, solder cup or crimp contacts. They feature IP50 through IP68 protection and offer EMI performance. They are intermateable with industry-standard connectors. ODU-USA Inc., Camarillo, Calif.
Harsh Environment Connectors
CIR Bayonet and DSR Double Start Ratchet Connectors are multipin circular connectors that come in 12 shell sizes and over 250 insert arrangements. They are designed to provide high reliability in harsh environments with shock and vibration. Electrical contacts from size 20 to 4/0 or combinations of optical, pneumatic, coaxial, high-voltage and thermocouple contacts can be accommodated in the same connector. Veam, a division of Litton Industries Inc., Watertown, Conn.
Miniature DIN Connectors
Series MDS Circular DIN Connectors offer receptacles for surface mounting, right-angle mounting or conventional through-hole mounting. The connectors' RFI shielding and size reportedly make them suitable for high-density applications. The miniature plugs feature one-piece construction of the pin and crimping section for reported reliability and solderless assembly. Straight or side-entry types are offered in both molded and assembled styles. Mating receptacles accommodate six circuits. Current rating is 1 A AC/DC. Temperature range is -40° to 85°C. J.S.T. Corp., Waukegan, Ill.
Circular Connectors
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The Front Runner Series consists of circular connectors designed for high-performance, rugged applications. Two lightweight and noncorrosive package sizes of 11 and 19 are available, as well as 16 contact arrangements from three to 29 contacts. Contact sizes include 22, 20, 16 and 12. The connectors have hot-plug capability up to 25 A. Termination options include straight and right-angle board-mount, fixed flange-mount, and free cable. Environmental and EMI/RFI shielded options are also available. Positronic Industries Inc., Springfield, Mo.
Shielded Connectors
The design of HR10, HR10A and HR10B Snap Lok Circular Connectors reportedly makes them suitable for various applications. Three shell sizes are available: 7, 10 and 13 mm, with insert arrangements from four to 20 contacts. In-line receptacle jacks are also available with crimp and solder contacts. All of the metal connectors are shielded to eliminate EMI and RFI. Many models also have rubber boots to help reduce ESD. Another version offers a threaded-coupling locking mechanism. Hirose Electric (U.S.A.) Inc., Simi Valley, Calif.
Sealed Connectors
These Sealed Circular Connectors are designed for harsh environments. They intermate with unsealed counterparts, which is said to provide greater flexibility and success in specifying connectors that more accurately meet functional and cost targets. The connectors are rated at IP68, are highly chemical resistant and withstand operating temperatures of 200°C. Sealed plug versions are suited for use in moisture-laden or gaseous environments and provide protection from fuel, moisture, salt spray and severe weather. Fischer Connectors, a subsidiary of W.W. Fischer SA, Atlanta, Ga.
Miniature Connector
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Designed for harsh environments and RFI/EMI shielding requirements, this Circular Connecter is high-density and high-shock. Aluminum shells are "scoop-proof" with threaded couplings and five-key polarization with machined retention clips. The fluorosilicone rubber sealing provides fluid immersion protection, and the cadium-over-nickel shell finish provides corrosion resistance. Features include RFI/EMI shielding with no-gap grounding fingers and four sealing glands. Packard Hughes Interconnect, Irvine, Calif.
Aerospace Connector
The Model 893 Connector has been qualified on space shuttle missions, where it served as an umbilical to connect the inertial upper stage to airborn support equipment. Employing the company's nonexplosive actuator technology, the product is said to release within 15 ms after receiving a 5 A signal. It also employs a release lanyard backup feature that releases the connector upon 40 to 70 lb of pull from the lift-off thrust. G&H Technology Inc., Camarillo, Calif.
