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Ultraminiature Coaxial Connectors for SMT Applications

A new generation of surface-mount technology (SMT) coaxial connectors that further miniature interconnects and provide cost savings

September 1, 2000
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Ultraminiature Coaxial Connectors for SMT Applications

RF Interconnect Products
Radiall Inc.
Stratford, CT


The ever-increasing demand for miniaturization in microwave communications systems and equipment continues to require components that are both smaller and less costly. One of the determinants of size has traditionally been interconnect devices. A new generation of surface-mount technology (SMT) coaxial connectors have been introduced that further miniaturize interconnects and provide cost savings as well. The patented Micro Miniature Pressure Contact (MMP) product line consists of the Ultra Miniature Pressure (UMP) series and the Interconnect Miniature Pressure (IMP) series. The innovative pressure contact concept makes it possible to utilize one coaxial connector where normally two or three are required. The UMP is designed for board-to-board cable link connectors, and the IMP series features board-to-board adapters.

UMP SERIES CONNECTOR DETAILS

The UMP receptacle requires only 15.8 mm2 (4.4 x 3.6 mm) of board area and 2 mm in height when mated, thus providing an extremely high density and low profile solution to RF PCB interconnects. As a result, the UMP series connectors can be mated after integration of the PCB in the subsystem since only 2 mm of clearance are required. The new coaxial connectors, at a weight of 0.03 g for the receptacle and 0.08 g for the plug, are also among the lightest RF connector pairs that exist today. Figure 1 shows the UMP connector's unmated and mated profiles. Figure 2 shows a comparison of the UMP mated pair with other, more standard, RF coaxial interconnect devices.

The UMP connectors feature a wide DC to 6 GHz frequency range, thus permitting the connector series to be used in various communications equipment such as 900 and 1900 MHz mobile phone service or 5.8 GHz for laptop use. They are also a competitive alternative to cable terminations or direct soldering, while offering more flexibility (possibility to disconnect). The connectors offer very low SWR performance that includes 1.02 at 900 MHz, 1.06 at 1800 MHz and 1.16 at 5 GHz. Typical SWR vs. frequency for a mated connector pair is shown in Figure 3 . In addition, as a result of their lateral connection, the UMP series connectors may be used in either on-board or on-edge applications.

A positive locking feature ensures that the plug is correctly mated with the receptacle. Furthermore, a mechanical coding eliminates any risk of introducing the plug upside down. The plug is assembled on the cable with soldering operations on the center and outer contacts that provide a minimum cable retention of 20 N. The connection is 100 percent secured, and an easy-to-use extraction tool is required to disengage the mated pair. The connector supports loads on all three axes without disconnection.

This series is particularly well adapted to high volume applications thanks to an innovative and fully automated cabling process.The packaged receptacles are fully compatible with pick-and-place equipment and are delivered in reels of plastic-embossed tape containing either 100 or 4000 UMP receptacles. The cavity geometry is designed for perfect component positioning. The straight plugs are delivered as pigtails or cable assemblies. Standard range is designed for 1 mm/50 W cable. Connectors for other cable types can be offered upon request.

The UMP mated pairs have been fully tested for vibration and shock performance based on the CECC 22 000 specification. Dielectric withstanding voltage is 350 V RMS and the working voltage is 100 V RMS. Contact resistance is rated at 60 and 10 m for the center and outer contacts, respectively. Insulation resistance is 1000 M (min) and RF leakage at 2 GHz is ?40 dB. Maximum insertion loss is rated at 0.2 x "F (F = frequency in gigahertz).

The connector plug body is fabricated in brass and the receptacle is beryllium copper, while the center and outer contacts are brass and beryllium copper, respectively. All metallic parts are gold plated. The insulator is LCP.

CONCLUSION

The new MMP series RF coaxial connectors represent the smallest SMT interconnects available today for PCB use. The ultra low profile will enable highly dense PCB subassemblies to be assembled without the need to have the RF connections made prior to integration. The connectors will provide new levels of space and cost savings without sacrificing reliability or performance.

RF Interconnect Products,
Radiall Inc.,
Stratford, CT (203) 380-9800.

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