MEMS probe with separate electrical and mechanical designs

Abstract

MEMS probes have a separation of electrical and mechanical design. In these probes, electrical conduction is primarily through one or more conductive rails, while mechanical compliance against vertical compression is provided by a coil. This separation of electrical and mechanical design allows for a combination of electrical and mechanical properties that is not possible with conventional probes, where the probe body is subject to both electrical and mechanical design constraints.

Description

[Technical Field]

[0001] The present invention relates to a vertical probe for testing electrical equipment. [Background technology]

[0002] Test fixtures containing vertical probe arrays are commonly used in testing electrical equipment. Vertical probes make temporary electrical contact with the device under test. These vertical probes (as opposed to cantilever probes) are positioned within the probe head so that they are substantially perpendicular to the device under test. Vertical probes are often preferred when the device under test has a large number of contacts (e.g., wafer-scale probing) because they can provide more contacts within a given probe head area than cantilever probes. In traditional vertical probes, the probe body is "all-inclusive," in the sense that it provides both the electrical path and mechanical compliance and mechanical contact force. This combined functionality in the probe body creates undesirable design trade-offs between current carrying capacity (CCC), contact force, overtravel (the vertical distance the probe compresses upon contact), and electrical signal / power integrity.

[0003] At higher electrical frequencies (e.g., above 5-10 GHz), the electrical and mechanical design requirements for vertical probes significantly conflict. Electrical design considerations at these frequencies tend to lead to shorter probe designs with undesirable mechanical properties, such as extremely limited vertical deflection range and increased susceptibility to particulate damage.

[0004] It would therefore be an advancement in the art to provide a vertical probe with improved electrical and mechanical design. Summary of the Invention [Means for solving the problem]

[0005] This work addresses the above problem by providing vertical probes with separate electrical and mechanical designs. The basic idea in some embodiments is that each probe comprises a mechanically elastic coil and an electrically conductive rail, where the coil provides the desired mechanical elasticity and the rail provides the primary current path. The coil is in electrical contact with the rail at the base and tip of the probe. This electrical contact at the probe base is achieved by attaching the rail to the coil at the probe base. The electrical contact between the rail and coil at the probe tip may be a sliding electrical contact. Even if the rail and coil are made of the same material (or the same multilayer stack), the more direct current path provided by the rail may allow current to flow preferentially through the rail, if desired.

[0006] Two main variants of this design are envisioned, differing in the geometric relationship between the rails and the MEMS layer stack. The deposition direction of the probe is defined here as the deposition direction of the MEMS multilayer stack, which is perpendicular to the vertical axis of the probe, and the "horizontal" direction is defined herein as the direction perpendicular to both the deposition direction and the vertical direction.

[0007] In a side rail variation, two rails are configured to sandwich the coil horizontally. In a side rail variation, the rails and coil may have the same multi-layer stack structure or different multi-layer stack structures.

[0008] In the rail-on-back variant, the MEMS layer structure has two distinct parts along the deposition direction: a first part defining the coil and a second part defining the rail, where the rail and the coil are formed from different layers of a multilayer stack. [Brief explanation of the drawings]

[0009] [Figure 1A] FIG. 1 illustrates an exemplary embodiment of the present invention. [Figure 1B] FIG. 1 illustrates an exemplary embodiment of the present invention. [Figure 2A] FIG. 10 is a diagram illustrating a first example of a tension protection function. [Figure 2B] FIG. 10 is a diagram illustrating a first example of a tension protection function. [Figure 3A] FIG. 10 is a diagram illustrating a second example of a tension protection function. [Figure 3B] FIG. 10 is a diagram illustrating a second example of a tension protection function. [Figure 3C] FIG. 10 is a diagram illustrating a second example of a tension protection function. [Figure 4A] FIG. 10 is a diagram illustrating a first example of scrub operation control. [Figure 4B] FIG. 10 is a diagram illustrating a first example of scrub operation control. [Figure 4C] FIG. 10 is a diagram illustrating a first example of scrub operation control. [Figure 5A] FIG. 10 is a diagram illustrating a second example of scrub operation control. [Figure 5B] FIG. 10 is a diagram illustrating a second example of scrub operation control. [Figure 5C] FIG. 10 is a diagram illustrating a second example of scrub operation control. [Figure 6A] FIG. 10 is a diagram illustrating a third example of scrub operation control. [Figure 6B] FIG. 10 is a diagram illustrating a third example of scrub operation control. [Figure 7A] FIG. 10 illustrates a second embodiment of the present invention. [Figure 7B] FIG. 10 illustrates a second embodiment of the present invention. [Figure 7C] FIG. 10 illustrates a second embodiment of the present invention. [Figure 7D] FIG. 10 illustrates a second embodiment of the present invention. [Figure 8A] 1A-1C are schematic diagrams of several probe array configurations. [Figure 8B] 1A-1C are schematic diagrams of several probe array configurations. [Figure 8C]1A-1C are schematic diagrams of several probe array configurations. [Figure 8D] 1A-1C are schematic diagrams of several probe array configurations. [Figure 9A] FIG. 10 is a diagram showing an example of two guide plates. [Figure 9B] FIG. 10 is a diagram showing an example of two guide plates. [Figure 9C] 10A and 10B are diagrams showing examples of two other guide plates. [Figure 9D] 10A and 10B are diagrams showing examples of two other guide plates. [Figure 10A] FIG. 10 is a diagram showing an example of three guide plates. [Figure 10B] FIG. 10 is a diagram showing an example of three guide plates. [Figure 10C] FIG. 10 is a diagram showing an example of three guide plates. [Figure 11A] FIG. 10 shows a first example of angled guide plate holes. [Figure 11B] FIG. 10 is a diagram showing a first example of guide plate holes arranged at an angle. [Figure 12A] FIG. 10 is a diagram showing a second example of guide plate holes arranged at an angle. [Figure 12B] FIG. 10 is a diagram showing a second example of guide plate holes arranged at an angle. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1A and 1B illustrate a first embodiment of the present invention, which is an example of the rail-on-back variant described above. FIGS. 1A and 1B show front and side views, respectively, of a probe 102 including a mechanically resilient first member 106 (i.e., the aforementioned "coil") and a conductive second member 108 (i.e., the aforementioned "rail"). The probe 102 also includes a probe tip 110 configured to make temporary electrical contact with a device under test and a probe base 104 configured to make electrical contact with a test fixture. Mechanical compliance between the probe tip and the probe base is primarily determined by the mechanically resilient first member. The current path between the probe tip and the probe base is primarily through at least one conductive second member. The conductive second member is attached to the mechanically resilient first member at the probe base, as shown. As described above, the coil and rail designs are separate. For example, the coil may be optimized for compliance, contact force, and short vertical length (mechanical characteristics), while the rail may be optimized for current carrying capacity and bandwidth (electrical characteristics). Another design improvement is to provide a retention mechanism for the rail 108 to engage with the guide plate hole. In this embodiment, these retention mechanisms are formed by flexures 108a and 108b on both sides of the rail 108. This effectively prevents the probe from falling out of the guide plate hole.

[0011] The coil may be (and in fact usually is) made of a conductive material, but this does not change the fact that the current flows primarily (i.e., 80% or more) through the rail. One reason for this is that the current path through the coil is much longer than the current path in the rail, resulting in increased resistance. The typically larger cross-sectional area of ​​the rail compared to the coil also exacerbates this resistance difference. The current between the probe base and the probe tip flows primarily through the rail, which is the path of least resistance.

[0012] In this embodiment, the probe 102 is a multilayer MEMS (microelectromechanical systems) probe having a MEMS deposition direction (left-right direction in FIG. 1B), and as shown in FIG. 1B, the conductive second member is arranged above or below the mechanically elastic first member in the MEMS deposition direction.

[0013] In one exemplary design of the rail-on-back variant, a probe measuring 85 x 50 x 1600 μm had the following probe performance parameters: contact force 1.2-1.8 grams at 75 μm overtravel; probe current capacity 0.8 A (uncoated) / 1.2 A (with 1 μm gold coating); bandwidth 10-25 GHz depending on plate material and dB reference (-15 dB vs. -10 dB); stress at 100 μm overtravel 1.02 GPa; sidewall retention force 0.68 grams; pincer grip force 0.25 grams.

[0014] The electrical contact between the probe tip and the conductive second member is preferably provided by a slidable mechanical contact in which the probe tip comprises a tip structure 112 that mechanically engages a corresponding rail structure 114 on the conductive second member. Embodiments of the present invention are not limited to any particular shape of the sliding contact.

[0015] In a preferred embodiment, the tip structure mechanically engages with the rail structure to provide protection against unintentional pulling forces that could cause the probe tip to be inappropriately pulled out of the probe. Figures 2A-2B and 3A-3B show two examples of such structures.

[0016] The example in Figures 2A-2B shows a structure in which rail structure 208 engages tip structure 206 to provide tension protection. Here, Figure 2A shows a probe, and Figure 2B shows a close-up of the probe tip. The probe is positioned within guide plates 202 and 204. Rail 108 is provided with a hook (on the left side of the figure) to provide this protection. Protrusion 210 on rail 108 engages the guide plate, flexibly engaging rail structure 208 with tip structure 206. In operation, tip 110 in Figure 1B can move upward until tip structure 106 engages slot bottom 212 to accommodate probe overtravel, but downward movement of tip 110 is prevented by rail structure 208.

[0017] Figures 3A-3C illustrate another way of providing this functionality. Here, Figure 3A shows a probe, Figure 3B shows a close-up of the probe tip when the probe is not positioned in a guide plate hole, and Figure 3C shows a close-up of the probe tip when the probe is positioned in a guide plate hole. In this example, a rail structure 302 forms a flexible pincer, and deformation of the rail closes the pincer when the probe is positioned in the guide plate hole. The tip structure includes a ridge 306 and a motion stop 304. The motion stop 304 engages the pincer 302, preventing significant downward movement of the tip 110, as shown in Figure 3C. Probe overtravel is accommodated by the slidable engagement of the ridge 304 with the pincer 302.

[0018] The tip and rail structures are also used to determine the scrubbing motion of the probe tip when it contacts the contact pad of the device under test. Here, the scrubbing motion of conventional probes is lateral (i.e., movement in the x-y plane), where the z-direction is the normal to the probe array. Such motion is provided by embodiments of the present invention. Furthermore, some embodiments of the present invention may provide a rotational scrubbing motion (i.e., rotation of the tip about the z-axis) in addition to or instead of the lateral scrubbing motion. Some examples are provided below.

[0019] 4A-4B show a first example of defining a scrubbing motion. Here, scrubbing structures 402 and 404 (the rail and tip portions, respectively) are asymmetric. The left-right asymmetry in FIG. 4B defines a primarily lateral scrubbing motion. The example shown in FIG. 4B also has front-to-back symmetry, which may result in a rotational scrubbing motion.

[0020] Figures 5A-5B show a second example of defining a scrubbing motion. Here, the rail and tip scrubbing structures 502 and 504 engage to achieve a "back-and-forth" scrubbing motion (with the backward movement being approximately half the forward movement). The left-right asymmetry shown in Figure 5B defines a primarily lateral scrubbing motion. Alternatively, the example shown in Figure 5B may have front-to-back symmetry, resulting in a rotational scrubbing motion. The goal here is to achieve a maximum scrubbing distance with approximately 50 μm of overtravel, followed by a scrubbing motion that moves backward approximately half the distance with 75 μm of overtravel. The rail 108 structure 502 is tuned to be stiff enough to push the tip and scrub, yet slightly flexible enough to prevent rigid binding or locking when the tip is fully shifted. In one implementation of this approach, the lateral scrubbing motion was 4 μm of movement in the X and Y directions and 7 rotations around the probe axis.

[0021] 6A-6B show a third example of defining a scrubbing motion. Here, scrubbing structures 602 and 604 (rail and tip, respectively) engage to achieve a "back and forth" repetitive scrubbing motion. The left-right asymmetry in FIG. 6B defines a primarily lateral scrubbing motion. The example shown in FIG. 6B also has front-to-back symmetry, which may result in a rotational scrubbing motion.

[0022] Practice of the present invention is not limited to these three examples: any manufacturable shape may be used to define the scrubbing action, which would allow unprecedented freedom in designing a scrubbing action suitable for various test applications.

[0023] 7A-7D illustrate a second embodiment of the present invention, which is an example of the side rail variant described above. FIGS. 7A and 7B are front and side views of a probe 102 including a mechanically resilient first member 106 (i.e., the aforementioned "coil") and conductive second members 702 and 704 (i.e., the aforementioned "rails"). The probe 102 also includes a probe tip 110 configured for temporary electrical contact with a device under test and a probe base 104 configured for electrical contact with a test fixture. Mechanical compliance between the probe tip and the probe base is primarily determined by the mechanically resilient first member. The current path between the probe tip and the probe base is primarily through the rail. The rail is attached to the mechanically resilient first member at the probe base, as shown. FIG. 7C is a perspective view of the probe of FIGS. 7A and 7B. FIG. 7D is a perspective view of the probe of FIGS. 7A and 7B. FIG. 7D shows the probes shown in FIGS. 7A and 7B positioned within guide plates 202 and 204.

[0024] In this example, the probe 102 is a multilayer MEMS (microelectromechanical systems) probe with a MEMS deposition direction (left-to-right in FIG. 7B ), and the rails 702 and 704 are arranged to sandwich the mechanically resilient first member 106 in a horizontal direction perpendicular to the MEMS deposition direction, as shown in FIG. 7A . Side-rail variants are typically easier to fabricate than rail-on-back variants. Again, optional features may be provided to prevent the tip from being pulled out of the probe due to excessive tension. In this example, the tip structure 706 engages with the rail feature 708 to provide tension protection. Although not shown in these examples, the scrubbing action of side-rail probes can also be controlled by adding appropriate scrubbing features to the tip and / or rails.

[0025] For an exemplary design of the side rail variant, for a probe array with a grid pitch of 150 μm and probe size of 120 × 50 × 1200 μm, the following performance parameters were obtained: contact force of 3.3 grams ± 50% at 75 μm overtravel; probe current capacity of 1.05 A ± 20% A; maximum overtravel of 100 μm; bandwidth of 60 GHz at -10 dB; sidewall retention force of 1.4 grams.

[0026] 8A-8D are schematic diagrams illustrating multiple probe array configurations. FIG. 8A is a schematic diagram illustrating an example in which a probe array 802 is arranged within a single guide plate 804. FIG. 8B is a schematic diagram illustrating an example in which a probe array 802 is arranged within two guide plates 804 and 806. FIG. 8C is a schematic diagram illustrating an example in which a probe array 802 is arranged within three guide plates 804, 806, and 808. Any number of guide plates may be used. To better understand this aspect of the present invention, it should be noted that conventional vertical probe arrays often include two thin guide plates spaced well apart near the base and tip of the probe array. The spacing between the guide plates provides space for lateral deflection when the probes are compressed vertically, and the use of thin guide plates minimizes friction as the probes pass through holes in the lower guide plate to accommodate overtravel.

[0027] Attaching the rail to the coil at the probe base has the advantage that probe overtravel is strictly limited to coil compression. This eliminates the need for relative motion between the probe and guide plate. As a result, guide plate arrangements such as those shown in Figures 8A-8C are possible, which were previously not possible with conventional probe arrays. The advantage of completely or nearly completely surrounding the probe with guide plates is that it at least protects the probe from mechanical damage during handling. The vertical spacing between guide plates is preferably narrow enough to prevent undesirable buckling of the probe between the guide plates. In some probe designs, a guide plate spacing of 250 μm or less has been found to be sufficient, but the preferred guide plate spacing will vary depending on the details of the probe design. Note that this design principle is the opposite of traditional vertical probe array designs, which traditionally required probe buckling between the guide plates during operation.

[0028] Another variation on probe head design employs angled guide plate holes, as shown schematically in FIG. 8D. Here, a probe array 812 is arranged in a single guide plate 814 with angled holes. The key parameter is the angle of deviation from vertical, θ. The angle (tilt), θ, can be selected to define the scrubbing motion of the probe tips of the probe array. The following figures show some examples of these ideas.

[0029] 9A-9B show an example of two guide plates, where probe 902 is the probe of FIGS. 1A-1B and is positioned within two guide plates 804 and 806.

[0030] 9C-9D show another example of two guide plates, where probe 904 is the probe of FIGS.

[0031] 10A-10B show an example of three guide plates, where probe 902 is the probe of FIGS. 1A-1B. Probe 902 of FIGS. 1A-1B is disposed within three guide plates 804, 806, and 808.

[0032] 11A-11B show a first example of a guide plate with angled holes. Probe 902 is the probe of FIGS. 1A-1B and is positioned within two guide plates 1102 and 1104. Here, θ is 1.2 degrees, which is large enough to allow vertical alignment of the probe base and probe tip with appropriate probe design (e.g., slight lateral offset of the tip and base contact points).

[0033] 12A-12B show a second example of a guide plate with tilted holes. Probe 902 is the probe of FIGS. 1A-1B and is positioned within two guide plates 1202 and 1204. Here, θ is 5 degrees, which was found to be a suitable tilt for providing maximum scrubbing action in one design. With such a large tilt, it is typically not possible to vertically align the probe tip and probe base.

Claims

1. 1. A probe for use in a vertical probe array, comprising: a first member having mechanical elasticity; at least one second member having electrical conductivity; a probe tip configured to make temporary electrical contact with a device under test; a probe base configured to make electrical contact with the test device; the mechanical compliance of the probe tip and the probe base is determined primarily by the first member having mechanical elasticity; a current path between the probe tip and the probe base passing through at least one second member that is primarily conductive; A probe, wherein at least one second electrically conductive member is attached to the first mechanically resilient member at the probe base.

2. 2. The probe of claim 1, wherein the probe is a multilayer MEMS (microelectromechanical system) probe having a MEMS deposition direction, and the at least one second member having electrical conductivity includes two members arranged to sandwich the first member having mechanical elasticity in a horizontal direction perpendicular to the MEMS deposition direction.

3. 2. The probe of claim 1, wherein the probe is a multi-layer MEMS (micro-electro-mechanical system) probe having a MEMS deposition direction, and the at least one second member having electrical conductivity includes a member arranged above or below the first member having mechanical elasticity in the MEMS deposition direction.

4. 10. The probe of claim 1, wherein the probe tip includes a tip structure that mechanically engages a rail structure of the at least one conductive second member to provide both electrical contact and slidable mechanical contact between the probe tip and the at least one conductive second member.

5. 5. The probe of claim 4, wherein the tip structure mechanically engages with the rail structure to provide a protective function that prevents the probe tip from being pulled out of the probe by an unintentional pulling force.

6. The probe of claim 5 , wherein hooks on the rail structure engage with the tip structure to provide a pull protection function.

7. The probe of claim 5 , wherein a pincer in the rail structure engages with the tip structure to provide pull protection.

8. 5. The probe of claim 4, wherein a scrubbing action of the probe tip upon vertical compression of the probe is determined by one or more scrubbing structures of the probe tip and / or the at least one conductive second member.

9. The probe of claim 8 , wherein the scrubbing motion comprises a rotation of the probe tip about a vertical axis of the probe.

10. The probe of claim 8 , wherein the scrubbing motion comprises a lateral motion of the probe tip over a contact pad of the device under test.

11. one or more scrubbing structures of the probe tip and / or the at least one conductive second member, a sliding engagement of at least one electrically conductive second member with the asymmetrical shape of the probe tip; and 9. The probe of claim 8, wherein the probe is configured as selected from the group consisting of: sliding engagement of at least one second member having electrical conductivity with a shape that defines a reciprocating motion of the probe tip.

12. Two or more probes according to claim 1; and one or more guide plates having guide plate holes in which the two or more probes of claim 1 are disposed.

13. The vertical probe array of claim 12 , wherein the guide plate holes are angled relative to the vertical direction of the vertical probe array.

14. 14. The vertical probe array of claim 13, wherein the inclination of the guide plate holes is selected to define a scrubbing motion of the probe tips of two or more of the probes of claim 1.

15. 1. A method for probing a device under test with one or more vertical probes, comprising: a) providing at least one probe comprising the configuration (a1-a4); b) probing the device under test with the at least one probe; The configurations (a1 to a4) are: a1) a first member having mechanical elasticity; a2) at least one second member having electrical conductivity; a3) a probe tip configured to make temporary electrical contact with the device under test; and a4) a probe base configured to make electrical contact with a test device; a mechanical compliance between the probe tip and the probe base is determined primarily by the first member having mechanical elasticity; a current path between the probe tip and the probe base passing through at least one second member that is primarily conductive; A method wherein at least one said second member having electrical conductivity is attached to said first member having mechanical resilience at said probe base.

16. the at least one probe is a multi-layer structure probe having a MEMS (micro-electro-mechanical system) structure with a MEMS deposition direction; 16. The method of claim 15, wherein the at least one second electrically conductive member comprises two members arranged to sandwich the first mechanically elastic member in a horizontal direction perpendicular to the MEMS deposition direction.

17. the at least one probe is a multi-layer structure probe having a MEMS (micro-electro-mechanical system) structure with a MEMS deposition direction; 16. The method of claim 15, wherein the at least one second electrically conductive member comprises a member disposed above or below the first member that is mechanically resilient in the MEMS deposition direction.

18. 16. The method of claim 15, wherein the probe tip includes a tip structure that mechanically engages a rail structure of the at least one conductive second member to provide both electrical contact and slidable mechanical contact between the probe tip and the at least one conductive second member.

19. 20. The method of claim 18, wherein the tip structure mechanically engages with the rail structure to provide a protective feature that prevents the probe tip from being pulled out of the at least one probe by an unintentional pulling force.

20. 20. The method of claim 19, wherein hooks on the rail structure engage the probe tip to provide pull protection.

21. 20. The method of claim 19, wherein a pincer at the rail structure engages the tip structure to provide tension protection.

22. 20. The method of claim 18, wherein a scrubbing action of the probe tip upon vertical compression of the at least one probe is defined by one or more scrubbing structures of the probe tip and / or the at least one conductive second member.

23. 23. The method of claim 22, wherein the scrubbing motion comprises rotation of the probe tip about a vertical axis of the probe.

24. 23. The method of claim 22, wherein the scrubbing motion comprises a lateral motion of the probe tip on a contact pad of the device under test.

25. one or more scrubbing structures of the probe tip and / or the at least one conductive second member, a sliding engagement of at least one electrically conductive second member with the asymmetrical shape of the probe tip; and 23. The method of claim 22, wherein the at least one second member is configured as selected from a sliding engagement between the at least one second member having electrical conductivity and one or more reciprocating features provided on the probe tip.

26. The method of claim 15 , further comprising providing one or more guide plates having guide plate holes in which one or more of the probes are disposed.

27. 27. The method of claim 26, wherein the guide plate holes are disposed at an angle relative to the vertical direction of the vertical probe array.

28. 28. The method of claim 27, wherein the angle of the guide plate holes is selected to define a scrubbing motion of the probe tips of the two or more probes of claim 1.

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