Abstract
Improved electrical connections to a probe head are provided by making electrical connections to a flexible circuit connected to the probes. Preferably these connections are solderless and made with a single ganged unit. Many advantages result compared to conventional approaches of making soldered connections to a flexible circuit, or coupling the flexible circuit to a printed circuit board (PCB) and making the connections from the PCB using semi-rigid coaxial cables.
Claims
1. A probe head for electrical testing, the probe head comprising: an array of probes; a flexible circuit interconnect structure electrically connected to the array of probes; and at least one connector configured to make two or more electrical connections between a corresponding two or more individual cables and a corresponding two or more contacts of the flexible circuit interconnect structure.
2. The probe head of claim 1, wherein the at least one connector is configured as a single ganged unit to make all of the two or more electrical connections.
3. The probe head of claim 1, wherein the at least one connector is configured as two or more discrete connectors to make all of the two or more electrical connections.
4. The probe head of claim 1, wherein an operation frequency of the probe head is 40 GHz or more.
5. The probe head of claim 1, wherein the flexible circuit interconnect structure includes two or more conductive transmission lines connecting the array of probes to the two or more individual cables.
6. The probe head of claim 5, wherein the two or more conductive transmission lines are selected from the group consisting of: coplanar waveguides, striplines and microstrips.
7. The probe head of claim 5, wherein at least one of the two or more conductive transmission lines is a coplanar waveguide.
8. The probe head of claim 7, wherein the coplanar waveguide includes a vertically separated ground structure.
9. The probe head of claim 8, wherein the vertically separated ground structure is configured as two auxiliary strips disposed beneath ground strips of the coplanar waveguide.
10. The probe head of claim 9, wherein the two auxiliary strips are connected to each other by periodically spaced ground straps.
11. The probe head of claim 8, wherein a termination structure of the coplanar waveguide includes two or more vias disposed to vertically connect a ground strip of the coplanar waveguide to the vertically separated ground structure.
12. The probe head of claim 1, wherein the two or more electrical connections are solderless.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] FIGS. 1A-C show exemplary embodiments of the invention.
[0064] FIG. 2 shows exemplary waveguide features of an embodiment of the invention.
[0065] FIG. 3 shows exemplary termination features of an embodiment of the invention.
[0066] FIGS. 4A-B show alternative waveguide types suitable for use in embodiments of the invention.
DETAILED DESCRIPTION
[0067] FIG. 1A shows an exemplary embodiment of the invention. This example is a probe head including an array of probes 110, a flexible circuit interconnect structure 108 electrically connected to the array of probes, and at least one connector 112 configured to make two or more electrical connections between a corresponding two or more individual cables and a corresponding two or more contacts of the flexible circuit interconnect structure. In operation, this probe head makes temporary electrical contact to device under test (DUT) 104, and the probe head typically includes a member 106 to provide mechanical support for flexible circuit 108. Connector 112 is in electrical communication with test equipment 102. In preferred embodiments, the electrical connections of connector 112 are solderless, which can be accomplished by clamping flexible circuit 108 between connector 112 and a support member 114 as shown.
[0068] FIG. 1B shows an example of a connector 112. Here connector 112 is a single ganged unit 120 configured to make all of the electrical connections, e.g., with a bed of nails formed by coaxial cable ends 122. Although it is often preferred to have a single connector as in this example, any number of connectors can also be employed. FIG. 1C shows an example where connector 112 includes two units, 124 and 126.
[0069] FIG. 2 shows exemplary waveguide geometry for the flexible circuit 108. Here waveguides 202 connect terminations 204 to terminations 206. The view of 208 is a cross section of one of these waveguides. Here M1 and M2 are the metal pattern layers, and are vertically sandwiched between polymer layers P1, P2, P3. The view of 210 is a top view of the M1 pattern, showing a coplanar waveguide with center conductor 216 and side conductors 214 and 218 (214 and 218 are also referred to as ground strips). The view of 212 is a top view of the M2 pattern showing auxiliary strips 220 and 222 connected to each other via ground straps 226. The purpose of the M2 pattern layer is to provide extra ground return and more signal shielding than one would have in a pure coplanar waveguide structure (i.e., if only the M1 pattern layer were present), without altering the impedance of the coplanar waveguide of the M1 pattern. The purpose of ground straps 226 is to prevent this structure from supporting undesirable higher-order modes. These RF (radio frequency) design considerations are known in the art, and so are not further described here. It is also well known in the art how to make structures as shown in the example of FIG. 2 in flexible circuit technology (e.g., in metal-polyimide multi-layer composite structures), so that is also not further described here.
[0070] FIG. 3 shows exemplary terminations for flexible circuit 108. Here view 302 is a top view of the circled termination of flexible circuit 108, and 304 is a schematic cross section view of the termination. V1 is a via that makes contact to center conductor 216 of the waveguide and extends to the surface of flexible circuit 108, as shown in the view of 304. The view of 306 is the M1 pattern at the termination, which includes a semicircular segment 308 joining side conductors 214 and 218. The view of 310 shows the M2 pattern at the termination, which is a metal ground plane 314 with a cutout 312 disposed below via V1. The view of 316 shows the pattern of vias V2 disposed to connect the grounded parts of the M1 pattern of this termination to ground plane 314. These vias are preferably present to improve shielding of the termination, suppress higher order modes and/or to avoid unnecessary resonance.
[0071] The preceding examples are implemented using coplanar waveguides but this approach can be extended to other transmission line types including microstrips and striplines. FIG. 4A shows a microstrip cross section and FIG. 4B shows a stripline cross section. Here 402 is the dielectric and 404, 406 are the conductors for the microstrip. Similarly, 408 is the dielectric for the stripline and 410, 412, 414 are the conductors for the stripline. In particular, 406, 412 and 414 are ground conductors, while 404 and 410 are signal conductors.
