There are a variety of known ways to secure a coaxial connector to an electrically conductive substrate such as a printed circuit board (PCB). One common way is soldering or bonding the two together. Proper alignment of the coaxial connector and the PCB is essential for optimal operation, and it is often difficult to align the coaxial connector properly with a signal trace on the PCB while bonding the coaxial connector. A series of connective and other problems can occur if there is misalignment or if the coaxial connector is not secured effectively.
FIG. 4 illustrates the electric field patterns of a coaxial device cross section. FIG. 5 illustrates a coplanar circuit with “ground under.” FIG. 6 illustrates the same coplanar circuit with a contact applied to the signal trace of the PCB for the purpose of launching the signal between the planar and coaxial devices. It is critical that the coaxial connector center contact be coplanar or nearly coplanar to the signal trace on the PCB for efficient signal transfer. Any disposition of the contact away from the PCB surface causes additional fringe capacitive effects and makes bonding more difficult to achieve. Excessive capacitance causes impedance error and signal loss in radio frequency (RF) circuitry.
There are several known approaches to keep the coaxial connector aligned and stationary for attachment to a PCB. For example, U.S. Pat. No. 5,404,117 discloses an electronic connector for connecting a coaxial cable to a microstrip transmission line or to a coplanar transmission line. To ensure proper alignment of the PCB and coaxial cable the optimal connection is detected with an electronic device before attachment, requiring time and adjustment.
Referring to FIG. 1, in this approach an end launch coaxial connector 14 has cooperating straight and parallel terminals 15a, 15b manufactured with a fixed separation gap 16 to receive a PCB. The gap 16 created between the signal side terminals and the ground side terminals is of a width equal to the thickness of the PCB thickness plus the appropriate tolerance buildup (typically 0.006″). FIG. 2 illustrates PCB 17 misaligned with center connector 18. If PCB 17 is soldered in the configuration illustrated in FIG. 2, the connection between center contact 18 and PCB 17 will be poor.
FIG. 3 illustrates a fixture 19 that can be used to hold in place the center contact 18 and the PCB 17. Fixture 19 is used to secure the coaxial connector 14 and PCB 17 during the bonding process to maintain coplanarity of center contact 18 to the PC trace. Fixture 19 is also needed to keep the axis of center contact 18 parallel to the PCB plane for proper alignment to mating connectors, electronic housing enclosure ports, and associated packaging hardware. Coaxial connector 14 and PCB 17 each have to be placed on fixture 19 and be properly aligned. If fixture 19 is moved or bumped before bonding occurs it can lead to misalignment of the center contact 18 and the PC trace on PCB 17.
It is essential and some times difficult to ensure proper alignment between the center contact and the PC trace on the PCB efficiently and on a consistent basis. Therefore, it would be beneficial to provide a coaxial housing that has the ability to align the center contact and PCB easily and hold in place until soldering or other bonding can occur. It would also be beneficial if the coaxial housing is manufactured at that same time as the coaxial connector and is part of the coaxial connector.
Besides misalignment, excessive soldering can create a poor signal so it is important to be precise when bonding the coaxial connector. Therefore, it would be beneficial to provide a system for fixing the PCB and the coaxial connector that does not involve the user doing anything else but applying the bonding material.