Multiconductor transmission line probe

Abstract

A vertical transmission line probe is provided having alternating capacitive and inductive sections. These alternating sections can be designed to provide a desired transmission line impedance (e.g., 10-100 ohms, preferably 50 ohms). Probe deflection occurs primarily in the inductive sections, advantageously reducing bending stress on the dielectric of the capacitive sections.

Description

Technical Field

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[0001] The present invention relates to a vertical probe for temporarily making electrical contact with a device under test.

Background Art

[0002] Electronic devices and circuits are usually tested using a probe array configured to temporarily make electrical contact with a device under test. With the evolution of technology, the demand for probing devices under test at high frequencies (10 GHz or higher) has been increasing. Currently, high-bandwidth probe cards (10 GHz or higher) use very short probes such as membrane probe cards, or individual signal probes and ground probes are used in combination with each other.

[0003] Membrane probe cards are very short and hard, so they lack flexibility. As a result, the overtravel of the probes is limited and the contact force becomes very high. When the signal probe and the ground probe have separate structures, the signal probe and the ground probe cannot flex integrally as a monolithic unit. As a result, undesirable changes in impedance may occur during the test of the device. In addition, since the signal probe and the ground probe are separated, the method of ideally matching the impedance is limited due to mechanical constraints. Therefore, the provision of an improved high-frequency probe will advance the art.

Summary of the Invention

Means for Solving the Problems

[0004] This invention provides a vertical transmission line (e.g., ground-to-signal-to-ground) probe in which capacitive and inductive sections are arranged alternately. These alternating sections can be designed to provide a desired transmission line impedance (e.g., 10 ohms to 100 ohms, with 50 ohms being particularly preferred). The deflection of the probe during operation occurs mainly in the inductive section, advantageously reducing the bending stress on the dielectric of the capacitive section.

[0005] The length of these sections is preferably significantly shorter than the length of the probe (e.g., less than 1 / 10 of the total length of the probe), so that the alternating capacitive and inductive impedances can provide the desired RF transmission line impedance with sufficient accuracy.

[0006] This results in a multi-conductor probe that can achieve a transmission line effect because the individual conductors are spaced apart by a dielectric. Improved impedance matching enhances the overall frequency bandwidth of the probe structure. The blending of capacitive and inductive regions improves the mechanical integrity of the structure. Mechanical integrity is primarily achieved in the capacitive region of the probe, where flexibility is low. [Brief explanation of the drawing]

[0007] [Figure 1A] Exemplary embodiments of the present invention are shown. [Figure 1B] The overall configuration of an exemplary probe is shown. [Figure 2] This is an enlarged view of an exemplary embodiment. [Figure 3A] These are images of probes prepared at various magnifications. [Figure 3B] These are images of probes prepared at various magnifications. [Figure 3C] These are images of probes prepared at various magnifications. [Figure 4A] This figure shows probe images at two points in an exemplary manufacturing sequence. [Figure 4B]This figure shows probe images at two points in an exemplary manufacturing sequence. [Figure 5A] This diagram schematically illustrates variations in exemplary probe designs. [Figure 5B] This diagram schematically illustrates variations in exemplary probe designs. [Figure 5C] This diagram schematically illustrates variations in exemplary probe designs. [Figure 6] This figure shows an exemplary probe array according to one embodiment of the present invention. [Figure 7] This figure shows the reflection loss results for a conventional probe and a new probe. [Figure 8] This figure shows the insertion loss results for a conventional probe and a new probe. [Figure 9] This figure shows the results of measuring the termination impedance and time-domain reflectivity (TDR) of a conventional probe and a new probe. [Modes for carrying out the invention]

[0008] Figure 1A is a schematic diagram illustrating an exemplary embodiment of the present invention, which is an example of a vertical probe 112 for testing electronic equipment. The vertical probe 112 includes an alternating sequence of capacitive sections (102a, 102b, 102c, 102d) and inductive sections (104a, 104b, 104c) along the longitudinal direction of the probe 112, where 102 indicates a cross section across any of 102a, 102b, 102c, or 102d, and 104 indicates a cross section across any of 104a, 104b, or 104c. The probe 112 includes a signal conductor 106 and one or more ground conductors (108a, 108b) insulated from the signal conductor.

[0009] The capacitive sections (e.g., 102a, 102b, 102c, 102d) include a dielectric material 110 configured to hold the signal conductor 106 at one or more constant intervals by being placed in the space between the signal conductor 106 and one or more ground conductors 108a, 108b, as shown in cross-sectional figure 102. The inductive sections (e.g., 104a, 104b, 104c) are air bridge structures having the signal conductor 106 separated from one or more ground conductors 108a, 108b by an air gap, as shown in cross-sectional figure 104. Post 108c connects the ground conductors 108a and 108b to each other within the capacitive section, as will be described in more detail with reference to Figure 2.

[0010] The impedances of the capacitive and inductive sections provide a substantially uniform transmission path impedance of the probe. This is made possible by the approximate equivalence of the transmission path to known periodic LC structures. Therefore, in some embodiments, it is preferable that the alternating sequence of capacitive and inductive sections is periodic along the length of the probe. Preferably, the uniform transmission path impedance of the probe is substantially 50 ohms (i.e., 45–55 ohms). The lengths of these capacitive and inductive sections are preferably significantly smaller than the length of the probe (e.g., less than one-tenth of the total length of the probe), so that the resulting alternating capacitive and inductive impedances provide the desired RF transmission path impedance with sufficient accuracy.

[0011] Figure 1B shows an example of the overall probe configuration. This is a slightly more realistic overall probe configuration than the one shown in Figure 1.

[0012] Figure 2 is an enlarged view of an exemplary embodiment. This example relates to a preferred embodiment in which the vertical probe has a ground-to-signal-to-ground configuration. This ground-to-signal-to-ground configuration is also (more schematically) shown in reference numerals 102 and 104 in Figure 1A. Preferably, the ground conductors 108a, 108b of the ground-to-signal-to-ground configuration are electrically connected to each other within the vertical probe. A preferred method for providing this connection is shown in Figure 2. In this example, the capacitive section is configured as a layered post. This layered post includes a conductive core 108c connecting a lower ground layer 108a and an upper ground layer 108b to each other, an insulating shell 110 positioned around the conductive core 108c, and a signal conductor 106 positioned around the insulating shell 110.

[0013] Here, the signal conductor 106 is isolated from the conductive core 108c by an insulating shell 110. The insulating shell 110 sets the lower gap between the signal conductor 106 and the lower ground layer 108a. The insulating shell 110 also sets the upper gap between the signal conductor 106 and the upper ground layer 108b. The insulating shell 110 may have different radial thicknesses in different layers to facilitate setting the lower and / or upper gaps.

[0014] Figures 3A-3C show images of probes fabricated at various magnifications. Here, the inductive and capacitive sections of the probe can be clearly seen in the fabricated structure.

[0015] The above-described probe can be fabricated by MEMS (Micro-Electro-Mechanical System) manufacturing technology. Preferably, the above-described insulator is an organic dielectric material protected from damage by plasma or chemical processes by metallic encapsulation. The organic dielectric is exposed by selectively etching the protecting metal at the end of the process. For example, copper and other probe materials can protect the dielectric during a manufacturing process that may damage the dielectric, such as a plasma process. FIGS. 4A-4B show scanning electron microscope (SEM) images during fabrication of the same region. The dielectric is disposed inside the metal structure when appropriate. The images show before removal of the protecting metal (FIG. 4A) and after removal (FIG. 4B), as well as the resulting air bridge structure.

[0016] FIGS. 5A-5C are diagrams schematically showing variations of an exemplary probe design. The example of FIG. 5A shows a periodic probe having the same capacitance C0 in the capacitive section and each inductive section 502 having the same conductor width. In the example of FIG. 5B, the mechanical restoring force of the probe is determined by modulating the length and / or width of one or more inductive sections along the length of the probe. Here, the inductive sections 504, 506, 508 have different widths as shown in the figure. In the example of FIG. 5C, the capacitance of one or more capacitive sections is adjusted along the length of the probe. Here, different capacitances C1, C2, C3, C4 of the capacitive sections are shown. Thus, one way to adjust the capacitance is to have different values in each capacitive section by changing the spacing between the signal conductor 106 and the conductive core 108c of FIG. 2.

[0017] FIG. 6 is a diagram showing an exemplary probe array according to an embodiment of the present invention. Here, the probe array 602 includes two or more of the vertical probes (probes 602a, 602c, 602e) as described above, and is attached to the space transformer 604, and the obtained probe head assembly is configured to temporarily make electrical contact with the contact 608 on the device under test 606, as schematically shown by the arrow 610. When using a guide plate to define the probe positions of the probe array, it is possible to improve electrical grounding by utilizing the electrical contact between the metal (or metallized) guide plate and the ground conductor of the ground-to-signal-to-ground probe as described above. This is similar to prior research on multi-path probes having an external ground conductor combined with a metal or metallized guide plate. The number and arrangement of transmission line probes in the array are not important in implementing the present invention. Usually, the number and arrangement of probes are determined by the configuration of the device under test.

[0018] In practice, it is often preferable for the probe array 602 to further include one or more other vertical probes (602b, 602d) that may have any conventional vertical probe design. These probes may be used for connections where improvement of the electrical performance of the transmission line probe is not required and cost reduction and / or improvement of current capacity are more important issues. Therefore, a preferred probe head concept is to use transmission line probes only for electrical connections where improvement of electrical performance as described below is required. The remaining connections to the device under test may be made using conventional vertical probes.

[0019] The obtained probes exhibit excellent electrical performance. As an example, the reflection loss of the transmission line probe is better than -15 dB (i.e., -15 dB or less) at frequencies up to 60 GHz, as shown in FIG. 7, and is significantly superior to conventional probe designs where the reflection loss exceeded -15 dB at frequencies above 15 GHz. Also, the variation in reflection loss due to probe spacing and position was less for the transmission line probes than for conventional probes.

[0020] In another example, the insertion loss of the transmission line probe was good, less than 1 dB at frequencies up to 60 GHz, as shown in Figure 8, which is significantly better than conventional probe designs where the insertion loss exceeded 6 dB at frequencies up to 60 GHz. The variation in insertion loss due to probe spacing and position was also less with the transmission line probe than with conventional probes.

[0021] As a final example, as shown in Figure 9, the impedance time-domain reflectivity (TDR) measurement of the transmission line probe shows a significant reduction in ringing compared to conventional probes. The variability in impedance time-domain reflectivity measurements due to probe spacing and position was also less with the transmission line probe than with conventional probes.

Claims

1. A vertical probe for testing electronic equipment, The vertical probe has capacitive sections and inductive sections arranged alternately along its longitudinal direction, The vertical probe includes a signal conductor extending in the longitudinal direction and two ground conductors extending in the longitudinal direction and insulated from the signal conductor. The capacitive section includes a conductive core extending in a direction perpendicular to the longitudinal direction and connecting two of the ground conductors to each other, and a dielectric material disposed around the conductive core and positioned in the space between the signal conductor and the two ground conductors so as to maintain a constant distance between the signal conductor and the two ground conductors. The inductive section is configured such that the signal conductor is separated from the two ground conductors by an air gap. A vertical probe in which the impedances of the capacitive section and the inductive section provide a substantially uniform transmission path impedance.

2. The vertical probe according to claim 1, wherein the alternating arrangement of the capacitive section and the inductive section is configured to be periodic along the longitudinal direction of the vertical probe.

3. The vertical probe according to claim 1, wherein the uniform transmission path impedance of the vertical probe is configured to be substantially 50 ohms.

4. A vertical probe according to claim 1, having a ground-to-ground configuration for ground-to-signal.

5. The vertical probe according to claim 4, wherein the grounds of the ground-to-signal-to-ground configuration are electrically connected to each other within the vertical probe.

6. One of the two grounding conductors has a first grounding layer, and the other has a second grounding layer spaced apart from the first grounding layer. The aforementioned capacity section, It is configured as a layered post including the signal conductor arranged around the dielectric material, The signal conductor is configured to maintain a distance from the conductive core by the dielectric material, The dielectric material sets the distance between the signal conductor and the first ground layer. The vertical probe according to claim 1, wherein the dielectric material sets the distance between the signal conductor and the second ground layer.

7. The vertical probe according to claim 1, wherein the mechanical restoring force of the vertical probe is determined by adjusting the length and / or width of one or more inductive sections along the length of the vertical probe.

8. The vertical probe according to claim 1, wherein one or more capacitances of the capacitive section are adjusted along the length of the vertical probe.

9. A probe head comprising a probe array including two or more vertical probes as described in claim 1.

10. The probe head according to claim 9, wherein the probe array further includes one or more vertical probes.

11. The vertical probe according to claim 1, wherein the vertical probe is configured such that its reflection loss is -15 dB or less in the frequency range of 0 to 60 GHz.

12. The vertical probe according to claim 1, wherein the insertion loss of the vertical probe is configured to be 1 dB or less in the frequency range of 0 to 60 GHz.

Images