Temporary connections for fast electrical access to electronic devices

Abstract: A given testing substrate (20) for fast-testing many integrated-circuit electronic devices (e.g., 10), one after the other, has a set of mutually insulated corrugated wiring areas (30) that can be aligned with solder-bump I/O pads (13) of the electronic devices. At the surface of each of the corrugated areas is located a layer (23) that is an electrically conductive durable oxide, or that is itself durable, electrically conductive, and non-oxidizable. During testing, the solder-bump I/O pads of the electronic device being tested are aligned with and pressed against the corrugated wiring areas of the given substrate. Alternatively, the electronic devices being of the electrically programmable variety, such as EPROMS, programming voltages can be delivered to each of the devices, one after the other, through the corrugated wiring areas of a single substrate.

Description: Technical Field This invention relates to methods of temporarily electrically connecting together a plurality of input-output (I/O) pads or terminals of an electronic device to that of another device, and more particularly to methods of thus connecting together such I/O pads for the purpose of relatively fast electrical testing of electronic devices, such as semiconductor integrated circuit chips--the term "fast testing" referring to testing of the order of typically one second of time duration--or for the purpose of programming electrically programmable electronic devices, such as electrically programmable read only memories (EPROMs). Background of the Invention Prior to bonding an electronic device, such as a semiconductor integrated circuit chip, into its final position in a package, for example, in a multi-chip module (comprising several chips), it is often desirable for economic reasons to test the chip electrically and discard it in case the test indicates that the chip suffers from an undesirable defect. In this way, further time and materials are not wasted in conjunction with processing and handling defective chips, such as packaging them. In one approach of prior art, such testing is performed by testing each semiconductor integrated circuit chip at the semiconductor wafer level--that is, by testing all the integrated circuit chips before they have been diced from the wafer into stand-alone individual chips. Each chip has input-output terminals or pads ("chip I/O pads") located on a major surface of the chip. Typically, these I/O pads are metallic and have surfaces, typically approximately 0.10 mm x 0.10 mm, typically comprising aluminum. The pads are typically spaced apart by approximately 0.10 mm. Each of the I/O pads can be devoted to receiving input signals or delivering output signals (or devoted to both), or devoted to receiving power or ground. In order to test a specific chip at the wafer level, the wafer and a testing circuit board are aligned, as by means of a step-and-repeat procedure. The testing circuit board has a set of probe wires, each typically made of tungsten or of beryllium copper. During testing, the probe wires are brought into good electrical contact with some or all of the chip I/O pads, including power and ground pads. Signals from probe circuitry are delivered through some of the probe wires to some of the chip I/O pads, while power and ground (voltages) are delivered to the chip power and ground pads. The resulting signal output voltages that are developed at other of the chip I/O pads are then detected by the probe circuitry via other of the probe wires. The time duration of each test for each chip is typically of the order of only a second ("fast testing"). The circuit board together with the probe circuitry are thereafter reused for testing other chips on the same wafer, as well as for other chips on other wafers. A problem with the foregoing fast testing procedure is that the testing signal frequency is limited to undesirably low values owing to the inductance of the probe wires and the capacitance of the testing circuit board. Therefore, high signal frequency testing --i.e., testing with signal frequencies as high as those to be handled by the packaged chip during subsequent normal operation, typically about 50 to 100 MHz or more--is not feasible at the wafer level but must await not only dicing of the wafer into chips but also proper packaging of the chips--that is, assembling each chip in a package. Each such package has a fan-out of the chip I/O pads into I/O pins that have surfaces of approximately 0.4 mm x 0.4 mm and that are spaced apart by approximately 2.5 mm. In this way, each thus packaged chip can be tested by plugging the package's I/O pins into a testing circuit receptacle that has electrical contacts which are aligned with the packaged chip pins, these contacts having wires connected to testing circuitry. However, such testing is costly in that it thus requires prior packaging of each chip: if a chip is fatally defective and thus is to be discarded, the packaging expenditure was wasted on such a chip. Therefore, it would be desirable to have a method of high signal frequency, fast testing of integrated circuit chips (or other electrical devices for that matter, such as laser chips) before they are packaged. U.S. Patent No. 4,585,991 discloses a multiprobe for electrically testing a microcircuit or integrated circuit on a semiconductor substrate. According to the present invention there is provided apparatus as defined in claim 1. This invention provides a method as set forth in claim 1. It is also advantageous that the method is further characterized as set forth in claim 2 or 3. It is also advantageous that the method is further characterized as set forth in claim 4. It is also advantageous that the method is further characterized as set forth in claim 5. It is also advantageous that the method is further characterized as set forth in claim 6 or 7. It is also advantageous that the method is further characterized as set forth in claim 8. It is also advantageous that the method is further characterized as set forth in claim 9. The substance (23) recited in claim 1 advantageously is durable and can be, for example, phosphorus-containing nickel, ruthenium, titanium nitride, or a noble metal such as platinum or gold. If a metal such as gold is used, the I/O pads of the electronic device should not be coated with gold or a gold-containing substance. The technical advantage of an embodiment of the invention resides in the fact that an insulating layer or skin unavoidably and inherently tends to grow on the surfaces of the solder bumps (13) or of the wiring layers (22), or of both--which interferes with the desired good electrical contact. This invention provides the desired good electrical contact by virtue of the durable corrugated exposed surface of the layer of substance (23)--whereby, during step (b) of claim 1, under pressure the corrugations bite into and break through the insulating skin, and in a nondestructive manner, so that good electrical contact is temporarily made between the I/O terminals (13) and the corrugated exposed surface, in such a manner that repeated (claim 3) tests of different electronic devices (10) using the same substrate device (20) can be performed. At the same time, the layer of substance (23), being electrically conducting or non-oxidizable, ensures good electrical conduction from the solder bumps to the wiring path on the substrate device (20). In this way, nondestructive and repeated testing can be performed, provided that the material of the corrugated layer of substance is properly selected. Brief Description of the Drawing FIG. 1 shows an elevational view, partly in cross section, of an electronic device and a testing substrate, useful in understanding a specific embodiment of the invention. Only for the sake of clarity, the drawing is not to scale. Detailed Description Referring to FIG. 1, an integrated-circuit electronic device 10 to be tested via a testing (wiring) substrate 20 has wiring layers 11, typically of aluminum. The electronic device 10 is typically a semiconductor integrated circuit or a laser. The wiring layers 11 are coated with localized foundation ("base") metal layers 12 which in turn are coated with bumps 13, such as solder or gold, at various areas where localized chip I/O terminals (or pads) are located. More specifically, base metal layers 12, each typically of tungsten having a thickness of approximately 0.1 µm, serve as foundation and barrier layers for bumps 13. Titanium layers (not shown), each having a thickness of approximately 0.1 µm, typically intervene between the base metal layers 12 and the wiring layers 11, in order to provide adhesion between the base metal layers 12 and the wiring layers 11, as known in the art. The bumps 13 typically are made of a solder material -- such as PbSn, SnAg, SnSb, In, InAg, InSn, InBi, or AuSn. The solder has been heated--after its formation as a preform on the base layers 12, typically by evaporation or sputtering--to form the shape of a solder ball, as indicated in FIG. 1. The testing substrate 20, typically monocrystalline silicon oriented (100) has wiring layers 22, typically of aluminum having a thickness of approximately 2.5 µm, that are connected to testing circuitry (not shown). The wiring layers 22 are separated from the testing substrate 20 by an insulating layer 21, typically of silicon dioxide having a thickness of approximately 0.5 µm. The wiring layers 22 are coated with a durable layer 23, typically phosphorus-containing nickel having a thickness in the approximate range of 1 to 2 µm. At areas of the top surface of the testing substrate 20 underlying each bump 13 and hence underlying each chip I/O pad of the device 10, the top surface of the testing substrate 20 has substrate I/O pads formed by localized (in the X-direction) corrugated wiring areas 30--i.e., localized portions of the top surface, each of which portions being corrugated with a set of parallel V-grooves separated by plateau regions located on the top surface of the durable layer 23. Each V-groove typically has a vertical depth of approximately 10 µm deep in the silicon substrate 20, and hence typically has a horizontal span of approximately 14 µm in the X-direction, and the distances between nearest neighboring vertices of the V-grooves are all typically approximately 16 µm in the X-direction, each of the plateau regions typically having a width of approximately 1 to 2 µm in the X-direction. The overall width in the X-direction of each corrugated wiring area 30 typically is approximately 100 µm, so that there is a total of typically six V-grooves associated with each localized corrugated wiring area 30 and hence with each substrate I/O pad. The overall width in the X-direction of each of these chip I/O pads is somewhat less than that of each of the localized corrugated areas, in order to have a safety margin. In order to perform the desired fast-testing of a given electronic device 10, all or at least some of its bumps 13 (i.e., chip I/O pads) are aligned with all or at least some of the respective corrugated wiring areas 30 (i.e., substrate I/O pads). These bumps 13 and these corrugated wiring areas 30 are then respectively mechanically pressed together into good electrical contact. The electrical tests are then performed by testing circuitry (not shown) connected through the corrugated wiring areas 30 of the testing substrate 20 to the chip I/O pads. More particularly, voltages are delivered by the testing circuitry--via some of the wiring layers 22, of the corrugated wiring areas 30, and of the chip pads--to the electronic device 10; and the electrical responses of the device 10 are measured by the testing circuitry--via other of the chip pads, of the corrugated wiring areas, and of the wiring layers. Finally, the electronic device 10 is mechanically pulled away from the testing substrate 20, whereby the chip I/O pads are pulled away from the substrate I/O pads. Immediately thereafter, the testing substrate 20 is capable of likewise being used for similarly testing many other electronic devices, one after the other. Although the invention has been described in detail in terms of a specific embodiment, various modifications can be made without departing from the scope of the invention. For example, instead of the vertices of adjacent V-grooves within a corrugated area 30 being spaced apart by approximately 16 µm in the X-direction, they can be spaced apart by distances in the approximate range of 1.0 to 20.0 µm--i.e., V-grooves having spatial periodicities in this range. Instead of V-grooves, other corrugation shapes (features) such as rectangles can be used, having spatial periodicities in this range. Moreover, it should be understood that if the testing circuitry (not shown) is ECL (emitter coupled logic) while the circuitry of the electronic device 10 is MOS (metal oxide semiconductor), an ECL-MOS translation device (not shown) can be connected between the device 10 and the testing circuitry, with a relatively small fan-out from the electronic device 10 to the translation device and a larger fan-out from the translation device to the testing circuitry. Instead of the aluminum wiring layer 22 extending into the corrugated areas, more durable metals (such as Mo or W) can be deposited and patterned so as to be present in these corrugated areas, while the aluminum wiring layer is then deposited and patterned so as not to be present in the corrugated areas but to come into contact with the patterned durable metal. In this way, the presence of the underlying relatively soft aluminum will be avoided at areas where the solder bumps 13 will strike during the fast testing. Also, as noted above, instead of phosphorus-containing nickel for the durable layer 23, ruthenium, titanium nitride, tantalum nitride platinum, or gold can be used. Finally, the electronic device 10 can be a programmable device, such as an EPROM, and the substrate 20 can be a wiring substrate suitably designed with wiring layers 22 and with localized corrugated areas 30 that are aligned for temporary electrical access to the I/O pads of the programmable device. In this way, a plurality of such programmable devices can be programmed, one after the other, using only one and the same wiring substrate--by means of applying programming voltages through the wiring layers 22 and the corrugated areas 30 to the I/O pads of each of the programmable devices while the I/O pads of each of the programmable devices, one of the devices after another, are pressed against the corrugated areas of the substrate 20.

Claims: An apparatus for providing temporary electrical connection of a plurality of I/O terminals (13) of a first device (10) to a plurality of I/O pads (30) of a substrate device (20), characterized in that said I/O pads (30) have an exposed top surface comprising a layer of substance (23) with a corrugated exposed surface, the substance comprising either a metal whose oxide is electrically conducting or a non-oxidizable electrically conducting material. The apparatus of claim 1, in which the corrugated surface has corrugation features that have a horizontal spatial periodicity within the range from approximately 1.0 µm to approximately 20.0 µm. A method for providing temporary electrical connection of a plurality of I/O terminals (13) of a first device (10) to a plurality of I/O pads (30) of a substrate device (20) according to claim 1, comprising the steps of (a) pressing together the terminals and the pads into electrical contact; (b) nondestructively pulling apart the terminals from the pads, whereby both the first and the second devices remain intact. The method in accordance with claim 3, for programming the first device, including the step, between the steps (a) and (b), of applying voltages through wiring layers (22) located on the second device and connected to the pads. The method, in accordance with claim 3, while the terminals and the pads are in electrical contact, the steps of: (c) applying test voltages to at least some of the I/O terminals through at least some of the set of I/O pads; (d) measuring the electrical responses developed at other of the I/O terminals through other of the I/O pads. The method according to claim 5 wherein steps (a) through (d) are performed with each of the plurality of the first electronic devices, one after the other. The method of claim 6 in which the plurality is at least one hundred. The method of claim 6 in which the plurality is at least one thousand. The method of claim 6 in which steps (a) through (d) span a duration of approximately ten seconds or less.

Inventors: FRYE ROBERT CHARLES, LAU MAUREEN YEE, TAI KING LIEN, FRYE, ROBERT CHARLES, LAU, MAUREEN YEE, TAI, KING LIEN
Applicants: AT & T CORP, AT&T CORP.
Application year: 1993
Main classification: G01R1
IPC codes: H01L21, H05K3, G01R1, G01R31, H01L27