Abstract:
A needle-card adjusting device for planarizing needle sets on a needle card, in which the needle card is connected to a circuit board used as a contact interface to a test head. The needle-card adjusting device has a separate, dynamically operating adjusting unit for adjusting the needle-card.

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The present invention relates to a needle-card adjusting device for planarizing needle sets on a needle card (also referred to as a probe card) in relation to a wafer with which contact is to be made, in which the needle card is connected to a circuit board used as a contact interface to a test head. 
     Published, Non-Prosecuted German Patent Application DE 25 44 735 A1 discloses a test-head carrier with the aid of which the distance between individual test heads which carry test tips can be adjusted. This is intended to achieve adaptation of the test heads to the various shrinkages of ceramic substrates. 
     Furthermore, U.S. Pat. No. 5,861,859 describes an automatic planarizing system for test cards, in which a test card is adjusted with respect to a wafer surface. In which, first, three tips on the test card, of which two can be varied vertically, are aligned with the wafer surface. 
     As is known, needle sets on needle cards produce the electrical connection between individual contact pads or points on chips and a test head, in order in this way to check the serviceability of the chips on the wafer. In this wafer, the planarizing of the needle sets on the needle card in relation to the wafer with which contact is to be made, or the chips contained in the latter, becomes more and more complicated with the increasing number of the chips with which contact is to be made simultaneously. This is because the needle sets must be adjusted precisely to the contact pads respectively assigned to them on the chips, down to the order of magnitude of ¼ μm. 
     At the same time, it is to be noted that, in addition to the static adjustment of the needle card relative to the chips, dynamic components also have to be taken into account, these being caused, for example, by thermal expansion of the needle card during heating up or cooling down via a wafer holding device, also referred to as a “chuck”. Other dynamic components can be traced back to aging effects of the needle cards, on which the needle sets are mostly adhesively bonded. However, the dynamic components can also have very short time constants, such as in the case of vibrations. 
     In the case of needle sets that are adhesively bonded to the needle card, these have previously not been adjusted or have been adjusted only by a subsequent bending of each individual needle, which results in a considerable expenditure in time and money with the required accuracy down to ¼ μm. If the needle sets are fitted to so-called space transformers, then they can be adjusted with the aid of simple screws, with which, however, the indicated accuracy can barely be achieved. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a needle-card adjusting device for planarizing needle sets on a needle card which overcomes the above-mentioned disadvantages of the prior art devices of this general type, with which the needle sets on the needle card can readily be planarized in relation to a wafer with which contact is to be made. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a combination of a needle card assembly having a needle-card with a plurality of needle sets, a test head, and a circuit board functioning as a contact interface to the test head, with a needle-card adjusting device for planarizing the needle sets on the needle card in relation to a wafer with which contact is to be made. The needle-card adjusting device includes a separate, dynamically operating adjusting unit connecting the needle card to the circuit board. 
     In the case of the needle-card adjusting device of the type mentioned at the beginning, according to the invention the object is achieved by the needle card being connected to the circuit board via a separate, dynamically operating adjusting unit. The adjusting unit is preferably constructed from at least one piezoelectric element. However, it can also contain a multiplicity of piezoelectric elements, which act on the needle card in the edge region thereof. 
     With the needle-card adjusting device according to the invention, the planarity of the needle card can readily be produced on site by dynamic adjustment. Therefore maladjustments of the needle card, which has been brought about for example by thermal expansion of the needle card or by brief vibration, can readily be corrected. Because of the dynamic adjustability of the needle card, the parallelism between the needle card and the wafer can be corrected when contact is made via the wafer edge. 
     Since, using the separate, dynamically operating adjusting unit, via which the needle card is connected to the circuit board, even dynamic effects can readily be corrected, any requirement for additional adjusting devices is dispensed with. In addition, the adjustment can be performed with the aid of a contact test loop, that is to say a program for the verification of the contact between each needle and an associated pad. 
     The adjusting unit can act in directions that are essentially perpendicular to the plane covered by the needle-card surface and/or in directions that are essentially in this plane. 
     As a result of constructing the adjusting unit from piezoelectric elements, in particular, its adjustability can be implemented with high precision. 
     In accordance with an added feature of the invention, there is provided a sense line, an active line, and a control unit connected to the dynamically operating adjusting unit through the sense line and the active line for controlling the dynamically operating adjusting unit. 
     In accordance with a concomitant feature of the invention, there is provided a stiffening device disposed between the needle card and the dynamically operating adjusting unit. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a needle-card adjusting device for planarizing needle sets on a needle card, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, side-elevational view of a first exemplary embodiment of a needle-card adjusting device according to the invention; 
     FIG. 2 is a diagrammatic, partial, side-elevational view of a needle making contact with a pad on a chip; 
     FIG. 3 is a side-elevational view of a second exemplary embodiment of the needle-card adjusting unit; and 
     FIG. 4 is a plan view of a number of needle-card sets in a needle-card adjusting unit according to a fourth exemplary embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a needle card or probe card  1 , which is mounted by screws  4  between a circuit board  3  and a window in a stiffening device  2 . In this case, the circuit board  3  is used as a contact interface to a test head  5 , with the aid of which test signals can be supplied to individual needles  6  on the needle card  1 . 
     FIG. 2 shows the structure of such a needle  6 , the needle  6  here making contact with a pad  7  on a chip  8  of a wafer. 
     The electrical connection between the test head  5  and the circuit board  3  is indicated by connecting buses  9 , while connecting wires  10  are led between the circuit board  3  and the individual needles  6 . 
     The screws  4  constitute a mechanical adjusting unit, since their rotation can be used to effect approximate parallelism between the needle card  1  and a surface of the chip  8  with which contact is made by the needles  6 . 
     According to the invention, in addition to the screws  4 , piezoelectric elements  11  are also provided, which are in each case connected to a control unit  14  via a sense line  12  and an active line  13 . If a misalignment between the needles  6  on the needle card  1  and the wafer surface is determined by the piezoelectric elements  11 , the misalignment is reported to the control unit  14  via the sense line  12 . In the control unit  14 , for example a computer  14 , the corrections necessary to compensate for the misalignment are calculated, in order then to output appropriate signals via the active line  13  to the piezoelectric elements  11 . 
     Of course, all the piezoelectric elements  11  are connected to the control unit  14  via corresponding lines  12 ,  13 , although, in FIG. 1, this is shown for only one piezoelectric element  11 , for improved clarity. 
     Instead of piezoelectric elements, other components permitting dynamic adjustment can also be used. 
     The lines  12 ,  13  form, together with the control unit  14 , a contact test loop, with the aid of which the desired adjustment can be performed by appropriate dilation or contraction of the piezoelectric elements  11 . 
     After adjustment has been carried out, the zero position of the needle card  1  can be set by the screws  4 , so that the piezoelectric elements  11  only need to perform readjustments. 
     FIG. 3 shows a further exemplary embodiment of the invention, in which the needle card  1  with a set of the needles  6  is placed in a window in the stiffening device  2 . Here, the piezoelectric elements  11  are disposed between the stiffening device  2  and the circuit board  3 , so that the adjustment has to be performed merely via the piezoelectric elements  11  and not via additional screws  4 . 
     Otherwise, the exemplary embodiment of FIG. 3 is constructed in the same way as the exemplary embodiment of FIG.  1 : here, too, the piezoelectric elements  11  are connected to the control unit  14  via the corresponding lines  12 ,  13  (not shown separately in FIG.  3 ). 
     FIG. 4 shows an exemplary embodiment having a configuration formed of a number of the needle cards  1  which are fitted in a fixed frame acting as the stiffening device  2  and can be displaced laterally with respect to the frame  2  and with respect to one another by the piezoelectric elements  11 . 
     Such laterally acting piezoelectric elements  11  can also readily be combined with the vertically acting piezoelectric elements  11  of FIGS. 1 and 3 if they are fitted in a suitable way, for example, in FIG. 1, between the stiffening device  2  and the needle card  1 .