Abstract:
An interface provides an electrical contact between test equipment and application equipment. The interface receives plural individual structures. At least one of the structures comprises at least one electrical path that provides the electrical contact. At least one of the structures is electrically isolated with respect to the interface and/or other structures and has a ground condition substantially independent of the ground condition of the interface and/or other structures.

Description:
This application is a Continuation of application Ser. No. 09/642,930 filed Aug. 22, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to interfaces between test and application equipments. 
     IC testers generate dedicated analog and/or digital signals that are supplied to a device under test (DUT) for analyzing the response thereof. Such testers are described in detail e.g. in the co-pending European Patent application No. 99105625.0 by the same applicant, EP-A-882991, U.S. Pat. No. 5,499,248, or U.S. Pat. No. 5,453,995. 
     In most cases, the provision of signals from the tester to a specific application site of the DUT has to be matched with the specific mechanical and electrical properties of the tester as well as of an application equipment handling the DUT. 
     FIG. 1 shows an example of a typical DUT application equipment such as a wafer prober  10  for transporting and positioning highly sensitive silicon wafers as DUTs. The wafers (not visible inside the wafer prober  10 ) are internally connected to a probe card  20  as interface of the wafer prober  10  towards a tester  25  (in FIG. 1 only symbolized as a general block). Wafer probers are generally applied for testing integrated circuit in the earliest possible production phase. 
     The probe card  20  is typically a device-specific printed circuit board (PCB), e.g. with high-density contact needles on the wafer side and gold-plated contact pads on the tester side (as the side visible in FIG.  1 ). The probe card  20  normally straddles the dense (needle) pattern form the wafer side to a wider pad pattern for contacting with the tester  25 . The size of the probe card  20  is generally limited by the hardware of the wafer prober  10 . The wafer prober  10  has to ensure a reliable electrical contact between the contact pads of the wafer and the probe card  20 . 
     A DUT board  30  represents the electrical and mechanical interface of the tester  25  towards the DUT. The DUT board  30  normally is a device specific printed circuit board (PCB) custom-built for the specific requirements of the DUT application equipment and can be exchanged dependent on the respective application. More details about the DUT boards  30  are described in particular in the aforementioned co-pending European Patent Application No. 99105625.0. In case that the DUT board  30  is provided as a custom-built exchangeable part, the DUT board  30  is often contacted within the tester  25  by means of spring-loaded contact pins (also called “Pogo™”) 
     While the DUT board  30  and the probe card  20  are electrically optimized (e.g. with respect to signal speed, signal purity, impedance, and transmission rate) regarding either the tester  25  or the DUT of the wafer prober  10 , a good electrical and mechanical matching between the DUT board  30  and the probe card  20  has to be achieved. This becomes in particular important with increasing signal transmission rates going up to two Gigabit per second. 
     In the example of FIG. 1, an interface tower  50  (also called “Pogo™ tower” ) is used as interface between the DUT board  30  and the probe card  20 . The interface tower  50  converts the pin pattern (normally rectangular arrangement) of the DUT board  30  of the tester  25  to the pattern (normally round and more dense) of the probe card  20 . In the example of FIG. 1, the interface tower  50  further has to bring signals from the tester  25  through a round-shaped hole in a head plate  60  of the wafer prober  10  and bridge the spatial distance between the DUT board  30  and the probe card  20 . 
     All the interfacing provided by the interface tower  50  has to be done with a minimum loss in performance for the entire test system provided by the tester  25  and the application equipment of the wafer prober  10 . That means that all parts in the electrical path of the interface tower  50  have to maintain a controlled impedance (normally 50 Ω) and a high contact quality for each provided tester channel (e.g. more than 1000 channels). 
     FIG. 2A shows in cross sectional view an embodiment of the interface tower  50  (product number E7017AA) as used for the Hewlett-Packard HP 83000. The interface tower  50  is of cylindrical shape with a central aperture  100 . A solid aluminum core  110  bears the electrical and mechanical contacts. The core  110  comprises a plurality of signal paths  120  and ground contacts  130 . In the representation of FIG. 2A, the top side of the tower interface  50  is to be directed towards the DUT board  30 , while the lower side of the interface tower  50  is to be directed to and to be contact with the probe card  20 . 
     FIG. 2B shows in greater detail the electrical paths of the interface tower  50  as depicted on the left side of FIG.  2 A. Each signal path  120  is provided by a double-sided spring-loaded contact (Pogo™) isolated by air within holes  140  drilled through the core  110 . Ground connection is performed by the ground contacts  130  provided by single-sided ground Pogos, which are arranged around the signal paths  120  and contacted directly with the aluminum core  110 . This arrangement of the ground contacts  130  together with the air-isolated holes  140  generates a 50 Ω environment, when a defined relation between the diameters of the electrical contacts of the signal paths  120  and the holes  140  is selected. Thus, the core  110  of the interface tower  50  provides a solid ground for all tester signals transmitted via the signal paths  120  and has to be isolated from a mechanical ground to avoid ground loops in the interface tower  50 . 
     The tower interface  50 , as shown in FIG. 2A, provides an excellent transmission of electrical signals between the DUT board  30  and the probe card  20 . The electrical configuration of the signal paths  120  and the ground contacts  130  ensures an almost loss-free signal transmission, even for very high transmission rates with bandwidths in the range of up to 7 GHz. 
     The provision of the holes  140  with a defined diameter over the entire length of the holes  140 , however, encounters severe mechanical difficulties. In case of the above described interface tower  50  with the product number E7017AA, holes  140  have to be provided with a diameter of  3  mm over a length of 50 mm. It is clear for the skilled person in the art that the provision of such holes is extremely difficult and costly and renders the interface tower  50  to be relatively costly. In this context, it has to be understood that each interface tower  50  normally is a specific custom-built part and usually only covers one specific pin-count (e.g. the number of individual electrical paths to be provided) for one specific tester arrangement. While, on one hand, the price of each interface tower  50  is relatively high (e.g. in the range of $ 30,000), a failure or breakdown of the interface tower  50 , on the other hand, can lead to significant costs until the testing procedure can be resumed. Thus, it will be required to keep relatively costly spare interface towers  50  in stock to reduce possible test stoppage times. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a lower cost interface between test and application equipment. The object is solved by the independent claims. Preferred embodiments are shown by the dependent claims. 
     According to the invention, an interface between test and application equipment (also referred to as tester/application interface or TA-interface) is provided with individual modular and exchangeable segments, i.e., structures. Each segment can comprise one or more electrical signal and/or ground paths or simply be a dummy segment in order to fill unused segment space with the TA-interface. 
     The modular arrangement of the segments allows to significantly reduce the testing costs, since the TA-interface, on one hand, can easily be adapted to a specific pin-count in a respective application. On the other hand, broken or malfunctioning segments can easily be exchanged without requiring to exchange the entire TA-interface. The TA-interface can thus be configured in accordance with the actual requirements and might also be upgraded on demand, thus allowing to distribute or shift costs until the actual moment of requirement. Furthermore, the modular segment configuration allows to limit stock costs from entire TA-interfaces to only less costly segments, in order to limit unavoidable stoppage time of the testing procedure. 
     In a preferred embodiment, all segments are substantially equal. In another embodiment, the TA-interface only comprises one or more different types of segments, whereby the segments of each type are equal. This further allows reducing costs due to an increased standardization and exchangeability within the segments of the same type. 
     In a further embodiment, one or more of the segments are electrically insulated or isolated, so that each of those one or more segments can be provided to be electrically independent with an individual electrical characteristics, such as an individual ground condition. This is in particular useful for testing DUTs with mixed analog and digital functionality. 
     In one embodiment, the ground condition of one or more of the electrically independent segments can be configured independently. 
     The invention thus provides a modular product structure allowing customer-specific configurations with lower price for lower pin-counts and rendering on site repair/exchange of segments (e.g. by the customer) possible. The invention further allows to provide segments with separated ground conditions, thus significantly increasing the flexibility of the entire test system and enabling testing of applications with mixed functionality (e.g. digital and analog). 
     In most cases, the TA-interface according to the invention is fully compatible with TA-interfaces already commercially available, such as within the Hewlett-Packard HP 83000 system. 
     In general, the TA-interface is applied for providing an electromagnetic link between test and application equipment. In most cases, however, the electromagnetic link is an electrical contact, an optical contact, or a combination of both. The test equipment preferably is an integrated circuit tester, and, accordingly, the application equipment preferably is an integrated circuit handling equipment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and many of the attendant advantages of the present invention will be readily appreciated and become better understood by reference to the following detailed description when considering in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to with the same reference sign(s). 
     FIG. 1 shows an example of a typical DUT application equipment, 
     FIGS. 2A and 2B show an embodiment of the interface tower  50 , and 
     FIG. 3 shows an embodiment of an interface tower  300  according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 shows an embodiment of an interface tower  300  as an example of a TA-interface according to the invention. The interface tower  300  is depicted in FIG. 3 in the same way as the interface tower  50  in FIG. 1, so that the shown upper side of the interface tower  300  is intended to be contacted with the DUT board  30 , while the lower side is intended to be contacted with the probe card  20 . The interface tower  300  according to the invention can be provided fully compatible with the interface tower  50  as shown in FIG. 1, so that the interface tower  300  can be applied in the same way as shown by and described for FIG.  1 . 
     The interface tower  300  comprises a frame  305  with a plurality of recesses  310   i  (with i=A, B, C, . . . ), each one adapted to receive a respective segment  320   i  (with i=A, B, C, . . .). In the-embodiment of FIG. 3, the interface tower  300  comprises eight recesses  320 A . . .  320 H, each filled with a respective segment  320 A . . .  320 H. In the explosive view of FIG. 3, the segments  320 A and  320 D are represented spaced off from-the interface tower  300 . As further apparent from FIG. 3, segments  320 A,  320 B,  320 E and  320 F are embodied as blank or dummy segments bearing no electrical contacts, while segments  320 C,  320 D,  320 G and  320 H are embodied as segments with a plurality of electrical contacts for establishing an electrical contact between respective contacts of the DUT board  30  and the probe card  20 . 
     Each segment  320   i  can be fixed to the frame  305  of the interface tower  300  e.g. by means of screws  330 . For that purpose, each segment  320   i  is provided on its upper side with a flange  340   i  laterally extending over a body  350   i  to be inserted into the respective recess  310   i.    
     Each flange  340   i  comprises holes  360 . For fixing the segment  320   i  to the frame  305 , the screws  330  are inserted into the holes  360  and screwed to the frame  305 . 
     On its upper side, the interface tower  300  further comprises rods  370  for adjusting and fixing the interface tower  300  to the DUT-boards  30  (cf. FIG.  1 ). 
     The arrangement of the signal paths  120  and the ground contacts  130  in the segments  320   i  is preferably provided in the same way as depicted in FIG.  2 B. Each ground contact  120  contacts directly with the solid core of the body  350   i . Preferably, the body  350   i , at least for the segments  320   i  with electrical contacts  120  and  130 , is provided by a solid aluminum core. 
     In a preferred embodiment, each segment  320   i  is electrically insulated from the frame  305  and/or other segments  320   i . For that purpose, an insulating layer  400  (preferably an epoxy layer) is arranged between the flanges  340   i  of the segments  320   i  and the upper side of the frame  305 . Between side walls  410   i  around each segment  320   i  and inner walls  420   i  of each recess  310   i , an insulation might be provided e.g. by a coating over the outside walls  410   i  and/or the outside walls  420   i  of the frame  305 . Alternatively or in addition thereto, an air gap (e.g. 0.5 mm) might be provided between the outside walls  410   i  and  420   i  of the segments  320   i  and the recesses  310   i . Further insulation might be provided with respect of the mechanical fixing of the segments  320   i  to the frame  305 . Preferably the head of the screws  330  will only come in contact with an insulating layer  500   i  (preferably an epoxy layer) provided on the top side of each segment  320   i  (cf. in particular FIG.  2 B), while the bodies of the screws  330  are spaced apart from the flange  340   i , so that no electrical contact will be provided by the screws  330  between the segments  320   i  and the frame  305 . 
     In the embodiment of FIG. 3, all segments  320   i  preferably have the same mechanical dimensions, but are capable of taking over different tasks. This allows configuring the interface tower  300  in accordance with the special applications. The interface tower  300  can e.g. be split into analog and digital areas comprised of one or more of the segments  320   i , whereby each area can have its own electrical ground condition. The segments  320   i  can be designed for different pin-counts and different performance requirements. Thus, the user of the test system will be able to upgrade the interface tower  300  when the pin count of the test system increases or if higher performance is required. 
     Mechanical and electrical contact between the interface tower  300  and the DUT board  30  as well as between the interface tower  300  and the probe card  20  is generally provided by mechanically pressing the components against each other. Contact might be provided manually e.g. using locking means such as screws, semi-automatically e.g. using bayonet slide locks or lever systems, or automatically e.g. using automatic loading mechanisms of the prober  10  and/or the tester  25 .