BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a diagram illustrating an apparatus of the invention employed with a space transformer.
FIG. 2 is an isometric view of two probes that can be used in accordance with the invention.
FIG. 3 is an isometric view of another probe that can be used in accordance with the invention.
FIG. 4 is a three-dimensional view of other probes with non-linear portions.
FIG. 5 is a three dimensional view of still other probes with non-linear portions.
FIG. 6 is a three-dimensional view illustrating an array of probes held in a retention arrangement.
FIG. 7 is a three-dimensional view illustrating the operation of a scrubbing protrusion on a contacting tip of a probe from the array of FIG. 6.
FIG. 8 is a three-dimensional view illustrating the array of probes and retention arrangement of FIG. 6 attached to a space transformer in accordance with the invention.
FIG. 9A is a plan cross sectional view illustrating a method of attaching probes held in a retention arrangement of FIG. 9 to a space transformer.
FIG. 9B is a plan cross sectional view illustrating the operation of probes in the retention arrangement of FIG. 9A when the holder is not removed.
DETAILED DESCRIPTION
The present invention will be best understood by first reviewing an apparatus 10 of the invention as shown in the diagram of FIG. 1. Apparatus 10 can be employed in a probe card or other electrical testing equipment for testing a device under test (DUT) 12. Frequently, DUT 12 is an integrated circuit on a wafer that requires testing prior to dicing. Alternatively, DUT 12 is an electronic device or circuit that is already mounted. The functionality of DUT 12 is verified by applying test signals to a number of its bumps or pads 14.
Apparatus 10 has a number of probes 16 arranged in an array and designed for establishing electrical contact with pads or bumps 14. Typically, the number of probes 16 is large and their spacing or pitch is very small, e.g., on the order of several microns. For clarity, only three probes 16A, 16B, 16C are illustrated. The construction of all probes 16 is analogous and will be explained by referring explicitly to probe 16A.
Probe 16A has a connect end 18A for applying the test signal, a retaining portion 20A and two arm portions 22A, 24A. Arm portion 24A terminates in a contacting tip 26A for making electrical contact with a corresponding bump 14A of DUT 12.
Apparatus 10 has a retention arrangement 28 for holding each of probes 16 below its retaining portion 20 and just above arm portions 22, 24. More precisely, retention arrangement 28 has a plate 30 with openings 32. Preferably, plate 30 is a ceramic plate. Openings 32 are provided for receiving and guiding retaining portions 20 of probes 16. To ensure accurate placement of probes 16 in retention arrangement 28 openings 32 are precision machined. Preferably, openings 32 are laser-machined openings.
Further, retention arrangement 28 has a holder 34 for holding probes 16 by their contacting tips 26. Holder 34 can be made of various materials, but in the present case it is made of polyimide. A series of holes 36 in holder 34 is designed to retain contacting tips 26. Holes 36 preferably have a suitable structure or cross-section to ensure that, once inserted, contacting tips 26 stay in holes 36 unless intentionally removed. A frame 38 keeps holder 34 in the appropriate position with respect to plate 30 to ensure that probes 16 are all well-aligned and their contacting tips 26 maintain a high level of planarity.
Retaining portions 20 of probes 16 are potted with a potting agent 43 in a potting region 40 defined above plate 30. A lateral enclosure 42, here in the form of a lateral barrier mounted on top of and about the perimeter of plate 30 defines potting region 40. A person skilled in the art will recognize, that lateral enclosure 42 is especially useful for containing any low-viscosity potting agent 43 prior to curing or when a significant thickness of potting agent 43 needs to be employed. A suitable potting agent 43 is an epoxy that exhibits proper wetting with respect to plate 30 and retaining portions 20 of probes 16 and hardens upon contact with atmospheric oxygen. Potting agent 43 may be poured into potting region 40 from above once probes 16 are properly aligned both horizontally and vertically. As potting agent 42 cures and hardens, probes 16 are retained in their proper positions.
Apparatus 10 also has a space transformer 44 with probe contacts 46 on its bottom surface 48 for contacting probes 16 at their connect ends 18. Specifically, space transformer 44 is employed for establishing electrical connections between test signal leads 50 from a testing device 52, e.g., a testing circuit on a printed circuit board, and probes 16. In contrast to signal leads 50, probe contacts 46 on bottom surface 48 are densely spaced and can be directly connected to probes 16. For example, in the case of probe 16A, its connect end 18A is assigned to establish electrical connection with contact 46A. In practice this is preferably done by providing a soldering ball on contact 46A and soldering connect end 18A thereto. Other alternatives, such as a side friction connector between connect end 18A and contact 46A can also be used to establish electrical connection.
Space transformer 44 allows the user to convert relatively sparsely spaced leads 50 to an array of much more densely spaced or high pitch probe contacts 46 for accessing very densely spaced probes 16. Probes 16, in turn, require tight spacing in order to access very densely packed and small pads or bumps 14 of DUT 12. Various types of space transformers and routing strategies are known to those skilled in the art. Any of those can be applied in apparatus 10. In addition, testing device 52 can generate test signals directly, receive external instructions for generating test signals or simply receive some or all of the test signals and assign them to signal leads 50.
During operation, probes 16 of apparatus 10 are placed in physical contact with bumps 14 to establish electrical contact. Electrical contact is not only due to physical contact, but also due to a scrubbing motion executed by contacting tips 26 of probes 16 while engaging with bumps 14. The scrubbing motion removes surface oxidation from bumps 14 and thus ensures a low-resistance electrical contact so that the test signals are efficiently delivered to bumps 14.
Apparatus 10 can employ probes of various types and geometries, including probes with two or more arm portions. FIG. 2 is an isometric view of two exemplary probes 60A, 60B that can be used in apparatus 10. Each one of probes 60 has a retention portion 62A, 62B and two arm portions 64A, 66A and 64B, 66B, respectively. More precisely, arm portions 64A, 64B are base arm portions extending away from center axes AA, AB of probes 60A, 60B, and arm portions 66A, 66B are reverse arm portions extending back toward center axes AA, AB. Base and reverse arm portions 64A, 64B and 66A, 66B inflect at corresponding joints or knees 68A, 68B. This geometry lends probes 60A, 60B a measure of mechanical flexibility that allows contacting tips 70A, 70B of probes 60A, 60B to perform effective scrubbing movements when brought in contact with pads or bumps 14 of DUT 12.
Probes 60 have round cross-sections and are spaced at a pitch Δ. In a preferred embodiment, contacting tips 70A, 70B are located on reverse arm portions 66A, 66B distal from knees 68A, 68B with a non-zero offset δ relative to center axes AA, AB, respectively. Non-zero offset δ further improves the scrubbing behavior of probes 60.
Apparatus 10 can use other probes that have non-circular cross-sections. FIG. 3 illustrates in an isometric view a probe 80 that has a generally rectangular and varying cross-section. Probe 80 has a retention portion 82, a base arm portion 84, a reverse arm portion 86, a knee 88 and a contacting tip 90. Once again, contacting tip 90 has a non-zero offset δ relative to a center axis AA of probe 80 to achieve improved scrubbing motion.
In still other embodiments, apparatus 10 uses probes that have one or more non-linear arm portions. FIG. 4 illustrates an array of probes 100 each having a retention portion for being potted in retention arrangement 28 and a contact end 104. Each probe 100 has a non-linear arm portion 106 with a knee 108. Arm portion 106 terminates in a contacting tip 110. Note that contact end 104 of each probe 100 is designed for making side friction connections rather than a soldered connection. In other words, contact end 104 is designed to be placed into a metallized hole of a ceramic plate located above retention arrangement 28 and contact is established by sliding the ceramic plate sideways to ensure mechanical contact with contact end 104. In this case space transformer 44 establishes electrical connections with contact end 104 via a soldered connection to the ceramic plate. Alternatively, space transformer 44 may itself be provided with metallized holes for receiving contact end 104 of each probe 100. Also note, that in this embodiment there is no offset between contacting tip 110 and the center axis of probe 100.
FIG. 5. shows an array of probes 120 each having a retention portion 122 terminated in a contact end 124. A stop 126 is provided at the lower end of retention portion 122 to help align probes 120 in a retention arrangement and aid in maintaining their planarity. The presence of stop 126 also aids in keeping the potting agent in the potting region during assembly.
Each probe 120 has a non-linear arm portion 128 with a joint or knee 130. Non-linear arm portion 128 has a varying degree of curvature along its length and terminates in a contacting tip 132. Tip 132 is offset from the center axis of probe 120 in order to provide for improved scrubbing behavior.
FIG. 6 is a three dimensional view illustrating an array of probes 140 each having a non-linear arm portion 142 and a contacting tip 144. Probes 140 are mounted in a retention arrangement 146 and extend out from plate 148 through openings 150. The holder for holding probes 140 at contacting tips 144 has been removed in this embodiment. Arrangement 146 is fully assembled and probes 140 are potted in the potting agent in the potting region (not visible) of arrangement 146.
FIG. 7 illustrates contacting tip 144 of a particular probe 140 in more detail. The bottom surface of tip 144, which is the surface that comes in contact with a pad or bump 154, is provided with a scrubbing protrusion 152. Protrusion 152 is a raised, rectangular portion of the bottom surface of tip 144. Although other geometries are possible, this type of protrusion 152 is preferred. During operation, as a contact force is applied, tip 144 comes in contact with bump 154 and executes a lateral scrubbing motion, as indicated by arrow S. The scrubbing motion helps to remove oxide from bump 154 and establish a good electrical contact.
Terminating the tips with scrubbing protrusions in any apparatus of the invention is preferred, since it improves the scrubbing behavior of the probes. It should also be noted, that due to the improved hold of the probes achieved by potting them in the potting enclosure, as well as any axial offset of their tips, all of these measures cooperate to produce a very effective scrubbing movement.
FIG. 8 is a three-dimensional view of the array of probes 140 in retention arrangement 146 attached to a space transformer 156. In this embodiment connections to space transformer 156 contacts are soldered connections 158. Once completed, connections 158 can be capped with an epoxy or adhesive for protection.
FIG. 9A is a plan cross sectional view illustrating a set of probes 160 in a retention arrangement 162 that employs plate 164 and holder 166. Plate 164 has openings 168 for holding probes 160 below their retaining portions 170. Holder 166 has openings 172 for keeping contacting tips 174 of probes 160. A potting region 176 is defined above plate 164. Potting region 176 does not include any lateral barriers for containing a potting agent 178. In this embodiment, agent 178 is a sufficiently viscous epoxy to not require containment prior to curing. In addition, epoxy 178 may be applied and cured in layers to build up to the required thickness without the need for lateral containment.
In the view shown by FIG. 9 probes 160 are already potted in potting agent 178 and are being attached to a space transformer 182. To establish the electrical connection, connect ends 184 or probes 160 are brought in contact with and soldered to pads 186 of transformer 182 by re-flowing solder balls 188. Preferably, an underfill 180 (see FIG. 9B), typically of an epoxy or other stable dielectric is provided in order to strengthen the mechanical connection between transformer 182 and retention arrangement 162.
FIG. 9B is a plan cross sectional view illustrating the use of probes 160 mounted in retention arrangement 162 with holder 166 left in place over contacting tips 174 rather than removed. Due to the presence of holder 166 the motions and scrubs, as indicated by arrow S, of probes 160 are mechanically coupled. Thus, as contacting tips 174 engage with contact pads or bumps 200 of a DUT 202 they will tend to execute more concerted scrub motion. Of course, a person skilled in the art will recognize that the decision to remove or keep holder 166 can be made on a case by case basis and depending on planarity, scrub length and contact force requirements when dealing with any particular DUT 202.
Any of the above-described embodiments can be implemented in a full-fledged testing system or probe card. The retention arrangement of the invention provides excellent mechanical characteristics to the probes it holds. In particular, even in very dense arrays that address densely packed probe pads or bumps the probes are held securely while offering requisite mechanical properties such as resilience, compliance and reliable scrub motion to remove oxide from the contact pads or bumps.
Many other embodiments of the apparatus and method are possible. Therefore, the scope of the invention should be judged by the appended claims and their legal equivalents.
Patent Application
20080088327
