Universal multicontact connection between an EWS probe card and a test card of a "test-on-wafer" station

Abstract: An universal connector employing a plurality of double female contacts installed with a certain clearance in receptacles of a body which may be suspended in a coupling position with a plurality of male contacts arranged on the top face of an EWS probe card and with a plurality of male contacts arranged on the bottom surface of a test card in a test-on-wafer station, provides a multicontact universal connection for any pair of so equipped cards of the inventories of probe cards and of test cards of the station. The connection is easily to set up and exibits excellent stability and uniformity characteristics of the electrical couplings, while reducing sensibly the time necessary for the setting-up and debugging of the test station for initiating a certain cycle of testing-on-wafer. The stability and reproducibility of the electrical couplings provided by the connection increases the precision of the measurements of critical parameters of the integrated devices with a positive effect on the production yield.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to an universal multicontact connecting system fixture between an EWS probe card and a test card for a "test-on-wafer" station of a production line for semiconductor devices. 2. Description of the prior art Test stations for carrying out quality control testing on wafers of integrated semiconductor devices being fabricated are installations of basic importance for controlling the quality of microelectronic productions. These test stations are rather complex as they are equipped with sophisticated apparatuses for the automation of the testing operations in order to permit high levels of productivity in performing quality control tests on all the pieces being fabricated. Commonly, each test station has an inventory of interchangeable EWS probe cards and an inventory of interchangeable test cards. Basically, each card is- specifically constructed for testing a specific product. In particular an EWS probe card is the means by which a plurality of minute conducting probes are placed in contact with respective metal pads fromed on the front surface of each integrated device being fabricated on the wafer. The electric contact between the point of each probe and the respective contact pad is established by elastic pressure and it is evident that the uniformity and reproducibility of the contact pressure are critical factors for the regularity and precision of the measurements of the electrical parameters which must be carried out on the single integrated device being fabricated. Conversely, a test card is a card which contains the appropriate circuitry for implementing predetermined biasing conditions and detecting functions of electrical parameters through the plurality of contacting probes, as well as control, compensation, and data processing functions in order to present the results of the tests in a most appropriate form to a variety of analytical equipments which determine whether the tested device fits the design specifications. The electrical connection of the various circuital nodes of the integrated device being tested and which are contacted by means of the probes of the EWS card, to the respective outputs and inputs of the test card are normally arranged by means of a plurality of cables, provided with end male connectors to fit female sockets present in the two cards. The cables used are often single-conductor cables. Notwithstanding the fact that these cable connections must be made when preparating the test station for testing a particular type of device, they are tedious to make and above all they are a source of problems, in consideration that the number of single-conductor cable connections may be extremely high (from 60 to 180 wires). Documents DE-U-8500168.6 and DE-A-3721312 disclose multicontact probe assemblies for electrical testing. The assemblies include a connector body having a plurality of resiliently assembled contacting needles. The cable connections between the probe card and the test card, nothwithstanding the fact that they may not introduce any appreciable load asymmetry or disuniformity on the pressure held contacts established with the pads of the device on the wafer, which could severely affect the contact resistance, which for a load variation of ± 10 gr may vary by 10-20 milliohm, still cause a problem because the reciprocal spatial disposal of the connecting cables is hardly stable and reproducible at every setting up of the station. This causes changes of capacitive and inductive couplings among signals which make necessary time consuming compensation interventions with the deployment of RC networks or with other means, which must be performed during a phase of "debugging" of the test station set-up, before the station can start functioning. These preliminary set-up operations are time consuming and are very critical as often, an imperfect trimming may cause instability of the measurements of particularly critical parameters of the integrated device which may lead to a virtual loss of production. Vis-à-vis this state of the art, it has been found now that these problems and drawbacks of these known fixtures, may be overcome, while greatly reducing the time necessary for setting up the test station when installing a different EWS probe card and/or a different test card in preparation for the testing of a new type of integrated device. SUMMARY OF THE INVENTION These objectives and advantages are accomplished by employing a special connection system which utilizes a special multipolar connector having substantially universal characteristics and by which it is possible to quickly and easily connect any EWS probe card to any test card, chosen among the respective card inventories of the test station, and operatively installed in the test station in predisposition of the station for the testing on wafer of a certain semiconductor device. According to an embodiment of the present invention, the system of electrical connection between an EWS probe card and a test card installed in a test station comprises subtantially three cooperating parts, two of which are represented by a plurality of male contacts, permanently fixed according to a predetermined arrangement, on a face of each EWS probe card and on a face of each test card, respectively, usable by the test station for performing test-on-wafer of semiconductor devices being fabricated. The male contacts are operatively fixed on the faces of the two types of cards which oppose each other when the cards are mounted on a card supporting structure of the test station. A third part is advantageously unique and universally usable with any pair of probe card and test card and is quickly and easily installed for connecting the various male contacts present on one card to the various male contacts present on the other card. This element of interconnection between the two cards installed in the test station, is constituted by a flat and preferably annular body provided with a plurality of doublefemale contacts held in a nonrigid manner inside respective receptacles which extend across the thickness of the body. The body into which the plurality of doublefemale contacts is set is preferably made with an electrically insulating material, such as a plastic material. The arrangement on a plane of the double female contacts is "specular" to the arrangement on a plane of the male contacts present on the interchangeable EWS probe cards and test cards, in order to accomplish a reciprocal coupling among all male contacts of a card with correspondent male contacts of the other card in an univocal mode, through the double female contacts of said universal connector. The body of the universal connector with double female contacts may be permanently joined to (or provided with) a supporting flange in order to be autonomously supported by the same supporting structure of the cards, in a coupling position which is intermediate to the position of the two cards and such as not to bear on the normally underlying EWS probe card, which is generally suspended in the lowest portion of the card support structure of the test station. BRIEF DESCRIPTION OF THE DRAWINGS The different aspects and advantages of the invention will become more evident through the following description of a preferred embodiment and reference to the attached drawings, wherein: Figure 1 is a schematic elevation view of a card support structure of a test station for on-wafer testing of integrated devices, which is equipped with the "universal" multi-contacts connection system object of the present invention; Figure 2 is a partial plan view on the sectional plane II-II indicated in Fig. 1; Figure 3 is a partial, exploded, cross-sectional view of the connection system of the invention; and Figure 4 is a partial cross-sectional view of a detail showing one coupling of the connection. DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the Figures, wherein the same parts are indicated with the same numbers, a typical tooling of a test-on-wafer station, comprises a card carrier frame 1 , which may be solidly fixed on a support structure 2 of the test station. Commonly, the card carrier 1 supports an EWS probe card 3 in a lowermost frame of the card carrier body 1 . The probe card 3 may be blocked in its seat by means of several turning latches 4 . Notably, from the bottom face of the EWS probe card 3 projects a plurality of minute elastically cantilevered conducting probes terminating with suitably bent coplanar contact points, as indicated, as a whole, with 5 in the schematic illustration of Fig. 1 . An automatic handling apparatus (not shown in the Figure) provides to position a wafer under the probes 5 and, after alignment of one of the integrated devices present on the wafer, the latter is raised to a predetermined height for establishing contacts with the points of the elastic probes 5 for the time necessary to the performance of the test measurements on the integrated device. These last steps are automatically repeated for each device of the wafer. On the top face of the probe card 3 is arranged a plurality of male contacts, in the form of cylindrical pins 6 parallel to each other and rigidly mounted on the card. Each male contact is electrically connected to one of the probes 5 projecting from the bottom surface of the card. Normally these male contacts are arranged in a regular manner with an uniform spacing along one or more circumferences or arcs of circumference, though other geometrical arrangements in the assembly plane may be used. In- the example shown, the arrangement of the contacts is on a single circumference having a diameter of about 100 millimeters for a total number of 60 contacts, each formed by a male pin having a diameter of 1.5 millimeters. This arrangement is shown schematically in the plan view of Fig. 2 . Normally, the pins of the male contacts 6 pass through the thickness of the printed circuit card 3 in order to establish electrical continuity with the respective probes 5 . A universal connector 7 is provided with a number of double female contacts equal to the number of male contacts (60) present on the top surface of the EWS probe card 3 . The double female contacts are arranged on the respective assembly plane in a "specular" manner in respect to the male contacts . The double female contacts of the universal connector 7 are mounted in a nonrigid manner inside respective receptacles which extend across the thickness of a toroidal shaped body, which is in turn assembled into the bore of a support flange 8 , capable of being suspended into a suitable seat of an immediate, ring-shaped, support shelf 9 of the card carrier body 1 , in order that the coupling between each female end of the double female contacts of the toroidal universal connector 7 with the respective male contact 6 of the EWS probe card 3 , is established with a certain mechanical clearance in order to prevent that the weight of the universal connector 7 be borne in any substantial way by the probe card 3 . A test card 10 , containing the specific test circuitry (schematically shown as a whole by means of the dash line profile 21 in Fig. 1 ) is similarly provided, on its bottom face, with a plurality of male contacts arranged in a mirror-like fashion as the male contacts on the top face of the probe card 3 . This second plurality of male contacts couples with the plurality of top female sockets of the double female contacts of the universal connector 7 , for establishing an electrical continuity between pairs of male contacts of the probe card 3 and of the test card 10 , respectively. Of course, in case of an arrangement of the contacts in a nonunivocal manner (as in the case of a uniform distribution on a circumference), the two male portions of the universal connection system and the universal connector (i.e. all three parts of the connection) may be provided with a visual index or with a mechanical dovetailing joint in order to ensure an univocal way of connecting together of the three parts. In the partial, exploded, sectional view of Fig. 3 , the peculiar features of the universal multicontact connection system of Fig. 1 are clearly shown. The male contacts 6 of the probe card 3 , are set into a circular channel formed by the two concentrically spaced vertical walls 6b and 6b' of an annular body of an insulating material. The stems 6a of the male contact pins 6 emerge from the bottom surface of the probe card 3 and are soldered to a respective conductive track of the printed circuit card. The male contacts present on the bottom face of the test card 10 are entirely similar to the male contacts of the probe card 3 . Also in this case, the pins 12 are provided with stems 12a, whose extremity project from the top surface of the card 10 where they are soldered to a respective conductive track of the printed circuit of the test card. The plurality of male contacts 12 is set into a circular channel formed by the lateral concentric walls 12b and 12b' of an annular channel of electrically isolated material through the base of which the male contacts are held. The universal connector 7 with double female contacts employs a plurality of contacts, each having two female socket ends 7a and 7b connected together by a stem 7c . The socket ends of each double female contact are housed with a certain clearance GG into cylindrical cavities formed in two toroidal bodies of insulating material 7e and 7d , provided with coaxial holes 7h and 7h' for the passage of the respective male contact pins. The two toroidal assembly bodies 7c and 7d are in turn assembled between two coaxial annular spacer bodies 7f and 7f ', which may be made of metal. The outer annular spacer 7f is provided with a circular ridge or flange 7g for fitting with an assembly flange 8 ( Fig 1 ). In the particular shown in Fig. 4 , the coupling between a male contact and the respective female socket terminal of the universal connector is shown to have a mechanical clearance GG' in order to ensure that the intermediate universal connector assembly does not bear on the EWS probe card 3 . The male contact arrays with which the plurality of cards of the whole card inventory of a test station are furnished, are of relatively low cost. Therefore to equip all the probe cards and all the test cards with such a plurality of male contacts, does not imply a major expenditure. By contrast, the universal connector equipped with the double female contacts is advantageously unique and may be used for coupling together any EWS probe card and any test card. The female contacts are preferably of a type suitable to ensure a low contact resistance, a high reliability and durability under the conditions of use of the universal connector. Of course it is also possible to mount permanently female type contacts on all the cards and to equip the universal connector with mating double-ended male contacts. However this alternative embodiment may be less preferable than the preferred embodiment described above in terms of the greater cost of equipping all the cards with more expensive and cumbersome female sockets. Preferably, the female contacts have a socket formed by a plurality of wires tensioned between two axially spaced rings and normally held at a certain inclination in respect to the socket axis to form an hyperboloid-shaped sleeve, as the female contacts marketed in Italy by the firm Connei S.p.A. Connettori Elettrici Industriali, under the trade name of HC contacts and the trade mark HYPERTAC ®. The metal wires have the property of stretching for accommodating a coupling male pin inserted in the socket thus "wrapping" themselves around the pin and providing a number of linear contact paths. The mechanical clearance with which the double female contacts are assembled inside the receptacles of the universal connector and the mechanical clearance which is purposely ensured between the "suspended" universal connector and the underlying EWS probe card, together with the intrinsinc stability of the contact resistance ensured by the female contacts used for forming the universal connector, confer to the complete connection a remarkable stability, uniformity and reproducibility of contact conditions while greatly simplifying the preliminary set-up operations when prearranging the station for a certain test cycle. Above all the greatly improved stability and reproducibility of the conditions of electrical couplings of the various bias and measurement signals afforded by the electrical connection system of the instant invention, has been found to have a remarkably positive effect on the production yield. This unsuspectable result may be attributed to the increased reliability and precision in testing particularly critical electrical parameters of the integrated devices.

Claims: A test-on-wafer station (2), including a card support structure (1), an EWS probe card (3), a test card (10) and a multicontact connection device (7) for connecting said test card and said probe card, comprising a first plurality of contacts (6) permanently mounted on a top surface of said probe card (3) and individually connected to a respective probe (5) elastically cantilevering from the bottom surface of said probe card, a second plurality of contacts (12) permanently mounted on a bottom surface of said test card (10), said multicontact connection device being in the form of a universal connector (7) provided with a plurality of double ended contacts (7a, 7b, 7c), capable of operatively mating with the contacts of said first (6) and second (12) pluralities of contacts, and wherein said double ended contacts are mounted with a certain clearance inside respective receptacles formed in a retaining and electrically insulating body (7e, 7d, 7g) of the universal connector; said pluralities of contacts (6, 12) being arranged on their respective assembly planes in a substantially specular manner in order to make possible a reciprocal coupling among said contacts (6) of said probe card with respective contacts (12) of said test card through said double ended contacts of (1) universal connector (7); means (8, 9) in said card support structure (1) for supporting said electrically insulating body (7e, 7d, 7g) in a coupling position between the top end contacts (7a) of said universal connector (7) and the contacts (12) of said test card and between the bottom end contacts (7b) of said universal connector (7) and the contacts (6) of said probe card (3), without substantially bearing on said probe card (3); said first (6) and second (12) pluralities of contacts being male contacts and said double ended contacts (7a, 7b, 7c) of said universal connector (7) being female contacts, or viceversa. The universal connector (7) of claim 1, having double ended female contacts and wherein said double female-ended contacts (7a, 7b, 7c) are mounted with a certain axial (GG') and lateral (GG) clearance within said receptacles and said means (8, 9) for supporting said body (7e, 7d, 7g) are capable of suspending said body in said coupling arrangement with a predetermined vertical clearance (GG'). The universal connector (7) of claim 1, having double ended female contacts and wherein each of said double female contacts has two female end sockets (7a, 7b) formed by a plurality of metal wires tensioned between two axially spaced rings at an inclination angle in respect to the socket's axis and capable of stretching for accommodating a coupling male pin. The universal connector (7) of claim 1, wherein said pluralities of male and female contacts are disposed in at least an arc of circumference on respective planes. The universal connector (7) of claim 4, wherein an indexing means is present on each coupling part for ensuring an univocal way of coupling together. The universal connector (7) of claim 5, wherein said indexing means is a mechanical dovetailing joint.

Inventors: LIBRETTI GIUSEPPE, LIBRETTI, GIUSEPPE
Applicants: ST MICROELECTRONICS SRL, STMICROELECTRONICS S.R.L.
Application year: 1991
Main classification: H01L21
IPC codes: H01R31, G01R31, H01L21, H01R11, G01R1