Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-10-10
2003-10-28
Cuneo, Kamand (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C361S794000, C361S780000, C174S051000, C174S262000, C439S063000, C324S1540PB, C324S095000
Reexamination Certificate
active
06639154
ABSTRACT:
BACKGROUND OF THE INVENTION
A thorough test of a high-speed digital system typically includes a procedure for sampling signals from hardware components of the system (e.g., circuit boards, interconnects, silicon devices, etc.) to determine how these components affect signal integrity. To access these signals, an engineer or technician typically connects specialized measurement equipment to the system hardware. In some configurations, such equipment includes a measuring device (e.g., a Time Domain Reflectometer or TDR) that connects to a circuit board which is either (i) part of the high-speed digital system under test, or (ii) a specialized assembly (e.g., a daughter card) that closely integrates with the system under test (e.g., through high-density connectors). Typically, the engineer solders a coaxial radio frequency (RF) connector to a specialized feature of the circuit board called a signal launch. The engineer can then attach a coaxial cable (e.g., a 50 ohm cable) from the measuring device to the soldered RF connector in order to access signals of the system under test.
One type of signal launch, which is hereinafter referred to as an edge mount signal launch, resides along an edge of a special type of circuit board called a microstrip, or microstrip line, which has an exposed signal conductor on one side of a dielectric substrate and an exposed ground conductor on the other side. Both the signal and ground conductors typically run to the edge of the circuit board. An engineer typically attaches an edge mount coaxial RF connector having outer soldering posts and an inner soldering post to the circuit board. In particular, the engineer solders the inner soldering post of the connector to the signal conductor and the outer soldering posts to the ground conductor. The engineer can then access signals of the system under test by attaching a coaxial cable from a measuring device to the connector.
Another type of signal launch, which is hereinafter referred to as a surface mount signal launch, resides on the surface of a circuit board rather that along an edge in order to receive a connector that mounts perpendicularly relative to the circuit board surface. A circuit board having multiple surface mount signal launches may position these signal launches in a circular fashion around a component mounting location (e.g., an array of vias for a high-density connector) such that etch lengths from the mounting location to the signal launches are of equal lengths for signal matching purposes. A conventional surface mount signal launch typically includes a large centrally-located signal via (i.e., a plated-through hole) and four large ground vias that are equidistant from the signal via. An engineer typically places a surface mount coaxial RF connector having a thick centrally located signal post and four thick surrounding ground posts over the surface mount signal launch such that each post inserts into a respective via (the signal post in to the signal via and the ground posts into the ground vias). The engineer then solders the posts to the surface mount signal launch. The engineer can then attach a coaxial cable from the connector to the measuring device in order to access signals of the system under test using the measuring device.
SUMMARY OF THE INVENTION
Unfortunately, there are deficiencies to the above-described conventional types of signal launches. For example, in connection with the conventional edge mount signal launches, it is difficult to position multiple edge mount signal launches in a circular fashion around a component mounting location (e.g., an array of vias for a high-density connector) such that etch lengths from the mounting location to the signal launches are equal for signal matching purposes. Circuit boards are typically rectangular in shape (i.e., have straight edges rather than circular edges) thus making it difficult to position edge mount signal launches in a circular manner. Additionally, a typical circuit board has a relatively small amount of perimeter length (vis-à-vis surface area) thus limiting the number of edge mount signal launches that can be conveniently placed on that circuit board when compared to the number of surface mount signal launches that can be placed on a circuit board. Furthermore, edge mount signal launch connections are highly susceptible to damage and fatigue over time due to there location along the circuit board edge. For example, a relatively a small amount of torque on an edge mount connector can stress the connector, solder joints and circuit board in that area to a point that causes a fracture in the solder joint or perhaps physical damage to the connector and/or the circuit board.
In connection with conventional surface mount signal launches, such launches are typically not well impedance-matched with their coaxial surface mount RF connector counterparts, and are thus a source of signal distortion. In particular, the centrally-located signal via and surrounding ground vias are typically made large for improved manufacturability (simpler drilling and plating) and soldering (more room to accommodate the thick connector posts and promote solder flow during the soldering process). Unfortunately, the large size of the centrally-located signal via reduces the amount of clearance between the signal via and surrounding ground conductor within the circuit board (i.e., ground planes) thus providing a high capacitance effect between the signal via and the ground conductor. Additionally, the large size of the signal via forces the ground vias to be placed substantially away from the center of the signal launch, the distance being uncharacteristically greater than the distance between the inner conductor and the outer conductor of standard coaxial cable (e.g., 50 ohm cable) thus creating inductance loops within the surface mount signal launches. The high capacitance effect and created inductance loops tend to distort signals through the surface mount signal launches thus degrading signal integrity.
Unfortunately, for the conventional surface mount signal launch, it would be difficult to counteract the above-described transmission line effects by changing the size of the signal via or positions of the ground vias. In particular, it would be difficult to decrease the size of the signal via because the conventional surface mount signal launch must accommodate soldering of a thick signal post of the coaxial RF connector. Furthermore, it would be difficult to move the ground vias closer to the signal via since the conventional surface mount signal launch solders to the RF connector, and an adequate amount of clearance is required between the ground vias and the signal via to prevent mechanical mounting problems and soldering problems.
In contrast to the above-described conventional signal launches, the invention is directed to techniques for forming a connection between a circuit board and a connector using a signal launch having multiple sets of ground vias. One set of ground vias enables the connector to mount securely to the circuit board (e.g., using solder, screws and nuts, etc.), while another set of ground vias provides electrical pathways that more closely match conductor clearances of a coaxial cable which can connect the connector to a measuring device (e.g., a TDR). Such pathways decrease signal distortion through the signal launch and the connector (e.g., keep any inductance loops small) thus improving the accuracy of signal measurements from the circuit board.
One arrangement of the invention is directed to a connection system having a circuit board that includes (i) a section of circuit board material having a signal conductor, a ground conductor, and dielectric material that physically separates the signal conductor and the ground conductor, and (ii) a signal launch. The signal launch includes a signal via that physically contacts the signal conductor and the dielectric material of the section of circuit board material. The signal launch further includes a first set of ground vias and a second set of ground vias, each of whi
Cartier Marc
Gailus Mark
Alcala José H.
Chapin & Huang , L.L.C.
Huang, Esq. David E.
Teradyne, Inc.
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