PROBE DISK AND ASSOCIATED ASSEMBLY APPARATUS

Abstract: Apparatus (10) for fabricating probe disks (12) including means for mounting a disk shaped substrate (16) and a sample of an integrated circuit (18) on a platform (14) and means (48) for positioning probes (40) on the surface of the substrate. Also disclosed is a fabrication method wherein the positioning means (48), guided by an operator, picks up a probe from a loading station (54) and positions it on the substrate with the contact end (42) of the probe protruding through an opening (28) in the substrate and touching a contact pad (44) on the sample circuit (18). The operator uses a microscope (60) during this process to visually align the contact end of the probe with its corresponding contact pad. Once properly positioned, each probe is adhesively bonded to the substrate. After a sufficient number of probes have been so positioned, a ring (64) is adhesively bonded to the assembly. Another embodiment of probe disk adds a second level of probes to permit probing of double rows of contact pads.

Description: Specification "Probe Disk And Associated Assembly Apparatus" BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to electrical interfaces for testing electronic devices, and more specifically to a probe disk with cantilevered probes for contacting integrated circuits to be tested. Description of the Prior Art During the course of manufacturing integrated circuits, testing for circuit functionality is a key- step. Typically, circuit testing occurs after the circuitry is fully formed on a wafer, but before the wafer is separated into individual dice. Each of the circuits on the wafer is individually tested by a cir¬ cuit tester in a step-and-repeat process. The circuit tester is electrically connected to the circuit through an array of probes that are oriented to con¬ tact appropriate portions of the circuit under test. To facilitate cirύcit testing and subsequent packaging, contact pads are formed on the surface of each integrated circuit and serve as access points to the circuitry. These contact pads are distributed over the surface of the integrated circuit in various patterns depending on the individual constraints of the circuit. Commonly used patterns include in-line single rows or staggered double rows of uniformaly spaced pads arrayed about the periphery of the circuit. Although the wafers are normally quite flat, the probes must have some vertical compliance to com- O PI pensate for any uneven or warped surfaces . In order to maximize the utility of circuit testers, probes are arrayed on removeable probe cards. Each probe card is fabricated for one specific integrated circuit, and is installed in the circuit tester for testing that circuit. To enable the circuit tester to be capable of testing a differ¬ ent integrated circuit, a corresponding probe card is fabricated according to that circuit's contact pad array and is installed in the circuit tester. It is, therefore, known in the prior art to mount probes on removeable probe cards. It is also known in the prior art to position a probe on a probe card by soldering one end of the probe to a conductor on the probe card, with the cotact end of the probe protruding through an opening in the probe card. U.S. Patent No. 3,930,809, issued to Evans is typical of the above approach. Evans also discloses a robot mechanism for positioning probe holders on a probe card prior to mounting by soldering. One disadvantage to this design is that the contact force between the probes and the corresponding circuit under test is limited by the peal strength of the conductive traces on the probe card. Another disadvantage is that restrictions on the positioning of the probe holders prohibit interfacing to contact pads on a staggered double row pattern. SUMMARY OF THE PRESENT INVENTION Accordingly, it is a primary object of the present invention to provide a circular probe disk utilizing resilient wire probes for providing electrical connection to the contact pads of a circuit under test. OMPI Another object of the present invention is to provide a circular probe disk with wire probes mounted thereto that is capable of accurately contacting double rows of contact pads. Still another object of the present invention is to provide means for improving the vertical force capability of mounted probes . A further object of the present invention is to provide apparatus for facricating a probe disk that may be used to interface to a corresponding integrated circuit. A still further object of the present invention is to provide a method for fabricating a probe disk that may be used to interface to a corresponding inte- grated circuit. These and other objects, which will hereinafter become apparent, are accomplished in accordance with the illustrated preferred embodiments of the present invention by providing a particular fabrication appar- atus and a method for fabricating novel probe disk assemblies. The fabrication apparatus includes means for mounting a disk shaped substrate and a sample of an integrated circuit on a platform, and means for positioning wire probes on the surface of the sub- strate in alignment with the contact pads of the inte¬ grated circuit. According to the fabrication method, the sub¬ strate and sample circuit are mounted to the platform with the circuit visible through an opening in the center of the substrate. Under operator control, a positioning mechanism picks up a wire probe from a loading station and positions it on the substrate with the contact end of the probe protruding through the opening in the substrate and touching a contact OMPI pad on the sample circuit. The other end of the probe is positioned to touch one of several conductive strips disposed about the periphery of the substrate. The operator uses a microscope during this process to visually align the contact end of each probe with its corresponding contact pad. Once properly positioned, each probe is adhesively bonded to the substrate. After a sufficient number of probes have been so positioned, each probe is soldered to its corresponding conductive strip and a ring is adhesively bonded to the assembly to permanently fix the probes in position. The now completed probe disk may be soldered to a printed circuit board to form a probe card having edge contacts electrically connected to the probes by circuit board traces. Another embod¬ iment of the probe disk adds a second level of probes to permit the contacting of double rows of contact pads. One advantage of a probe disk fabricated accord- ing to the present invention is that it is a sturdy and di ensionally stable assembly. Another advantage of such a probe disk is that the probes are electrically connected by soldering rather than by holders and thereby reduce electrical resistance. These and other objects and advantages of the present invention will no doubt become apparent to those skilled in the art after having read the follow¬ ing detailed description of the preferred embodiments which makes reference to the several figures of the drawing. IN THE DRAWINGS Fig. 1 is a perspective view of an assembly apparatus according to the present invention. Fig. 2 is a perspective view of a partially assembled probe disk that includes a substrate and various probes installed thereon by the assembly apparatus of Fig. 1. Fig. 3 is a perspective view of a ring that is to be installed on top of the probes and substrate of Fig. 2 to form a probe disk assembly. Fig. 4 is a cross-sectional view of a probe disk assembly, according to the present invention, and is taken along the section lines 4-4 shown in Fig. 2. Fig. 5 is a plan view of the probe disk assembly of Fig. 4 installed on a printed circuit board to form a probe card. Fig. 6 is a cross-sectional view of an alterna¬ tive embodiment of a probe disk assembly having longer points and a ring with a smaller inside diameter. Fig. ' 7 is a cross-sectional view of another alternative embodiment of a probe disk assembly that utilizes a flat substrate. Fig. 8 is a cross-sectional view of still another alternative embodiment of a probe disk assem¬ bly that utilizes a flat substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In Fig. 1, there is shown an assembly apparatus 10 according to the present invention for fabricating a probe disk assembly 12. Assembly apparatus 10 includes a platform 14 upon which a circular substrate 16 and a sample of the integrated circuit to be tested 18 are positioned. Sample circuit 18 is held in position by a vacuum chuck (not shown) , while sub¬ strate 16 is positioned over two dowel pins 20 and 22 that are affixed to the platform and extend through alignment apertures in the substrate 16. A turntable 24 attaches the platform 14 to a base 26 and permits the platform to be rotated about its vertical axis. Turning for the moment to Fig. 2, a closer view of the probe disk assembly 12 reveals that the sub¬ strate 16 is generally disk shaped with an opening 28 centered about its axis. While the bottom surface of the substrate is flat, the top surface 30 is conically concave. As a result, the thickness of the substrate is thinner at the opening 28 than it is at the peri¬ phery 32. The combination of a mounting hole 34 and a mounting slot 36 allow substrate 16 to be disposed over the dowel and be accurately positioned thereby relative to the sample circuit -18. Note that the apertures and dowel p ns are positioned along a non- diametrical chord of the disk 12 so that they serve to both orient and position the disk. Dispersed around the periphery 32 of the substrate are conduc¬ tive strips 38 of copper or other electrically con- ductive material. Each strip 38 is electrically insulated from each other since the substrate is composed of a non-conductive material such as ceramic, for example. The main purpose of the assembly apparatus 10 is to facilitate the accurate positioning of probes 40 on substrate 16 so that a contact end 42 of each probe touches a contact pad 44 on the sample circuit 18, and so that a mounting end 46 of each probe touches a conductive strip 38. Toward this end, assembly apparatus 10 includes a positioning mechanism 48 that is controlled by an operator either manually or through a control panel 50. Positioning mechanism 48 is moveable in translation along three orthogonal axes and in rotation about a vertical axis, in a man- ζ E A^r OMPI ° ner well known in the art. In operation, the operator manually places a probe 52 on a loading standard 54, then guides the grasping jaws 56 of the positioning mechanism 48 to grasp the mounting end 46 of the probe. The operator then guides the positioning mechanism and probe 58 toward the probe disk and carefully positions the probe on the substrate 16. During this phase of the operation, the oprator uses a microscope 60 to insure that the contact end 42 of the probe is properly touching its corresponding contact pad 44, and that the mounting end 46 is touching its corresponding conductive strip 38. With the probe 40 properly posi¬ tioned, it is adhesively bonded to several points 62 to the surface 30 of the substrate 16 with an appropr¬ iate adhesive which may be, for example, cyanoaσrylate After the adhesive has set, the grasping jaws 56 release the probe and are moved to be loading station 54 to grasp another probe. Before the new probe is positioned on the substrate, the turntable 24 is rota¬ ted to orient a different conductive strip 38 toward the positioning mechanism 48. After all of the probes have been bonded to the substrate in the above-described manner, the ring 64 is adhesively bonded to the top of the probes and the substrate. The adhesive may be, for example, epoxy. Ring 64, shown in Fig. 3, is composed of a non- conductive material such as ceramic and includes two notches 66 and 68 in its outer perimeter to position it with respect to the dowel pins 20 and 22. After the adhesive cures, the mounting ends 46 of the probes are soldered or otherwise electrically connected to their corresponding conductive strips 38. At this point, the fabrication process of the probe disk 12 f OMPI is complete and the disk may be removed from the assembly apparatus. In Fig. 4, a cross-sectional view of the probe disk shows that the contact end 42 of each probe 40 is extended in cantilevered fashion and predetermined distance into the opening of the substrate 16. Ring 64 acts as a strain relief to react against any upward force transmitted from the contact ends of the probes as the contact a circuit under test. The probes are composed of an electrically conductive, adequately stiff material, such as beryllium-copper or tungsten wire, for example, and may be plated with a higher conductivity material such as gold to increase effective conductivity and solderability. Note that by carefully selecting the stiffness of the probe wires and the diameter of the disk opening, and thus the length of the cantilevered segments of the probes, the contact force can be accurately predeter¬ mined. In order to use the probe disk 12 with a circuit tester, the disk must be packaged in a suitable form. One such form is shown in Fig. 5 wherein the probe disk is attached to a printed circuit board 70 to form a probe card 72. Probe card 72 includes circuit traces 74 which electrically connect the conductive strips 38 of the probe disk to the card edge contacts 76. By soldering the conductive strips of the probe disk to the traces of the printed circuit board at their contact points 78, low-resistance, continuous electrical paths are established from the contact ends of the probes to the card edge contacts. The probe card 72 thus fabricated may be used with circuit testers for testing integrated circuits in ways commonly known in the art. SZEX OMPI - WIPO " When the contact pads 42 of an integrated circuit are spaced closer together than those shown above, an alternative embodiment of the probe disk may be utilized, as shown in Fig. 6. A ring 80 with a smaller diameter opening 82 permits longer probes 84 to be used while maintaining the desired probe stiffness . When the contact pads 42 of an integrated cir¬ cuit are in double rows, another alternative embodi- ment of the probe disk may be utilized which provides double layers of probes, as shown in Fig. 7. In this case, the first layer of probes 40 are installed as described above to contact the outermost contact pads. upon completion, a ring 86 is bonded to the top of the first layer of probes as was ring 64. Ring 86 permits a second layer of probes 88 to be installed by adhesive bonding. The upper probes 88 contact the inner contact pads of the integrated circuit and are soldered to a second layer of conductive strips 90. Atop the second layer of probes 88 is placed a second ring 92 which is adhesively bonded in place. As a result, this embodiment can interface to integrated circuits with double rows of contact pads. Another embodiment of a probe disk according to the present invention is shown in Fig. 8. This parti¬ cular probe disk 94 uses a flat substrate 96 and proves 98 with longer tips. Alternatively, the probes can be formed as indicated at 99. In a manner similar to that described above, the probes 98 (and 99) are soldered to conductive strips 100 around the periphery of the substrate 96 and a ring 102 is adhesively bonded to the tops of the probes to provide a strain relief. As will be clear to those skilled in the art, alterations and modifications may be made to the disclosed embodiments without departing from the inventive concepts thereof. The above description is therefore intended to be illustrative and informative rather than limiting in scope. Accordingly, it is intended that the following claims be interpreted as covering all such alterations and modifications that reasonably fall within the true spirit and scope of the invention. What is claimed is:

Claims: CLAIMS 1. A probe disk for enabling electrical connec¬ tion to be made to the contact pads of an integrated circuit to be tested, said probe disk comprising: e a disk-shaped substrate formed of an electri¬ cally insulative material and including an opening centered at its axis and conductive strips dispersed in spaced-apart relationship about its periphery; a first array of probes each including a contact ■ n end and a mounting end, each said probe being disposed on the top surface of said substrate such that its mounting end is electrically coupled to one of said contact strips and its contact end protrudes into and through said opening to a location corresponding to ■ __ the position of one of the contact pads of an integra¬ ted circuit to be tested; and a first ring formed of an electrically insula¬ tive material and affixed to the top of said first array of probes and said substrate such that said 20 first array of probes is sandwiched between said first ring and said substrate. 2. A probe disk as recited in claim 1 wherein each probe of said first array of probes is adhesively bonded to the surface of said substrate and the mount- 25 ing end of each probe is soldered to one of said con¬ ductive strips . 3. A probe disk as recited in claim 2 wherein the top surface of said substrate is conical in shape to form a generally concave upper disk surface. 4. A probe disk as recited in claim 1 wherein said probe disk includes locating holes to aid in positioning said probe disk with respect to said integrated circuit to be tested. 5. A probe disk as recited in claim 1 and further comprising: a second array of probes with each probe dis¬ posed upon the top surface of said first ring such that its contact end protrudes into and through said opening to a location corresponding to one of said contact pads of said integrated circuit to be tested; and a second ring of an electrically insulative mat¬ erial affixed to the top of said second array of probes and said first ring such that said second array of probes is sandwiched between said first and second rings. 6. A method for assembling a probe disk for use in making electrical connection to the contact pads of an integrated circuit to be tested, said probe disk having a disk shape with an axially centered opening therethrough and also having several contact strips dispersed about the periphery thereof, said method comprising the steps of: positioning said probe disk and a sample of said integrated circuit on a mounting fixture with said integrated circuit visible through said opening; positioning and attaching probes on and to the surface of said disk with one end of each probe pro- truding into and through said opening and contacting one of said contact pads, and with the other end of each probe electrically connecting to one of said con- 1PO tact strips; and attaching a ring over said probes to sandwich said probes between said ring and said disk. 7. A method for assembling a probe disk as recited in claim 6, wherein said attaching step inclu¬ des adhesively bonding said probes to said disk and soldering said probes to said contact strips. 8. A method for assembling a probe disk as recited in claim 6, wherein said step of positioning said probes is assisted by observing said integrated circuit and said probes through a microscope for accu¬ rately positioning said probes . 9. A method for assembling a probe disk as recited in claim 8, wherein said step of positioning said probes is accomplished by a positioning mechanism controlled by the operator. 10. Assembly apparatus for installing probes on a substrate to form a probe disk, each of said probes including a contact end disposed for electrically con- necting a test point of a test device, said fixture comprising: a base; a platform rotatably mounted to said base, said platform including means for mounting the substrate and test device; positioning means for moving the probes from a loading station to said substrate, and for positioning the contact ends of said probes at the test points of said test device, said positioning means being under control of an operator; and a microscope focused on said substrate and said, test device to assist the operator in controlling said positioning means for positioning said probes. 11. Apparatus as recited in claim 10, wherein said positioning means includes jaw means for grasping said probes and also includes displacement means for moving said jaw means between said loading station and said substrate.

Inventors: GARRETSON OLIVER R, WATSON GORDON W, GARRETSON, OLIVER, R., WATSON, GORDON, W.
Applicants: TRI GAMMA CORP, TRI-GAMMA CORPORATION
Application year: 1982
Main classification: G01R31
IPC codes: G01R1