Abstract:
Disclosed is a test head assembly for a test system, comprising a test head having a plurality of test head contact areas for providing electronic signals to one or more devices under test (DUT) and/or for receiving electronic signals therefrom. The test head assembly further comprises fastening means for fastening one or more individual, physically separated DUT boards to the test head, each DUT board being provided for holding one or more of the DUTs and adapting electrical contacts thereof to at least one of the plurality of test head contact areas. In order to provide a flexible and modular test head arrangement allowing an easy exchange of different DUT boards with different seizes, the arrangement of the fastening means and the plurality of test head contact areas is commensurable, so that one or more DUT boards with same and/or different lateral dimensions are attachable to the test head.

Description:
FIELD OF THE INVENTION 
     The present invention relates to test head assembly for a test system. 
     BACKGROUND OF THE INVENTION 
     Electronic devices, such as integrated circuits (ICs), are normally tested after production and before use. As an example of a test system generally applied for testing purposes, automatic test equipment (ATE) is designed to conduct analysis of functional or static parameters to evaluate the degree of performance degradation and may be designed to perform fault isolation of unit malfunctions. The decision making, control, or evaluative functions are normally conducted with minimum reliance on human intervention. 
     FIG. 1A illustrates, in a generalized cross sectional view, a typical test system as known in the art, such as the Hewlett-Packard HP 83000 or HP 95000 series. For testing a device under test (DUT)  20 , the test system  10  comprises a tester  30  and a test head assembly  35 . The test head assembly  35  represents the mechanical and electrical interface between the DUT  20  and the tester  30 . The tester  30  generally comprises test electronic for generating test signals and evaluating signals received from the DUT  20 . 
     The test head assembly  35  comprises a test head  40  and at least one DUT board  60 . The DUT  20  might be fixed directly or via a socket  50  to the DUT board  60 , which, again, is normally mechanically fixed to the test head  40  by means of a fixture  70 . 
     The DUT board  60  represents the mechanical and electrical interface between the DUT  20  and the test head  40 . The DUT board  60  is also employed to adapt electrical contacts from the DUT  20  to electrical contacts at the test head  40 . In particular with respect to miniaturized ICs, the necessity of such an adaptation of the miniaturized contacts of the DUT  20  to larger contacts of the test head assembly  35  becomes readily apparent. 
     The fixture  70  is employed for mechanically holding and fixing the DUT  20  via the DUT board  60  to the test head  40  and to allow exchanging the DUT board  60 . 
     FIG. 1B illustrates, in an explosive side view, a typical principle for fixing the DUT board  60  to the test head  40 , as employed e.g. in the Hewlett-Packard. HP 83000 or HP 95000 series. The DUT board  60  can be mechanically affixed to the test head  40  by means of a plurality of screws  80 , whereby a stiffener- 90 , as part of the fixture, can be arranged therebetween. When the DUT board  60  is mechanically affixed to the test head  40 , one or more contact areas  95 A,  95 B and  95 C of the test head  40  electrically couple to contact areas  100 A,  100 B and  100 C of the DUT board  60 . 
     The contact areas  95 A,  95 B and  95 C comprise a plurality of pins (not shown in detail), such as spring loaded pins, which will be forced/pushed against respective contact pads  110  (shown in FIGS. 2) of the.contact areas  100 A,  100 B and  100 C of the DUT board  60  for providing a good electrical contact. Since the DUT boards  60  are generally formed of flexible plastic material, the stiffener  90  is employed for avoiding bending of the DUT board  60  under the influence of the contact pressure. 
     While the DUT board  60  in FIG. 1B is affixed to the test head  40  by means of mechanical connecting means such as the screws  80 , FIG. 1C illustrates another principle wherein the DUT board  60  is affixed to the test head  40  by means of negative pressure means as employed e.g. in the Teradyne Integra series J750. The top part of FIG. 1C shows a cross sectional view, while the lower part depicts a worm eye&#39;s view from the direction of arrows A. Vacuum slots  120  in the test head  40  are arranged close to the contact areas  100 A and  100 B for-removing air. Rubber seal lips  130 A and  130 B are provided for establishing a negative pressure between the DUT board  60  and the test head  40 , thus attaching the DUT board  60 . 
     It is to be understood that, in general, for each different DUT  20  a specific and thus different DUT board  60  has to be provided for adapting the specific layout of contacts of the respective DUT  20  to the contact areas  95  provided from the test head  40 . Employing exchangeable DUT boards  60  renders the test system  10  capable for testing a plurality of different DUTs  20 . It is clear that different test algorithms may have to be provided by the tester  30  for any different DUT  20 . 
     FIGS. 2A to  2 D show examples of DUT boards  60  as known in the art. The one or more DUTs  20  are generally located in the center of the respective DUT board  60 . It is clear that number of DUTs  20  on one respective DUT board  60  is limited by the sizes and/or pin counts (i.e. the number of pins or other individual electrical contacts) of the respective DUTs  20 , the pin count (channels) of the test head  40 , and the available area in the center of the DUT board  60 . Each DUT board  60  comprises one or more contact areas  100  comprising a plurality of individual contact pads  110  electrically coupled to the (one or more) DUT  20 , preferably via strip conductors of the DUT board  60 . 
     When the DUT board(s)  60  is/are fastened to the test head  40 , individual contact areas  95  of the test head  40  couple to the respective contact areas  100  for providing an electrical contact between the test head  40  and the DUT(s)  20 . Spring-loaded cable assemblies designed in accordance with the respective contact areas  100  couple thereto for establishing the electrical contact, between the respective DUT boards  60  and thee test head  40 . 
     Changing between different DUTs  20 , however, generally requires a change in the hardware, of the test head assembly  35  adapted to the specific arrangement of DUTs  20  and their respective contact areas  100 . In most cases, however, only the respective DUT boards  60  have to be exchanged. FIGS. 2A and 2B illustrate center arrangements of the DUT board  60 . The DUT board  60  in FIG. 2A comprises four contact areas  100 A,  100 B,  100 C and  100 D substantially arranged around the DUT  20 . An example of an embodiments according to FIG. 2A can be found e.g. in the Hewlett-Packard HP 83000 Series. In FIG. 2B, only one contact area  100  is provided which substantially encircles the DUT  20 . An embodiment according to FIG. 2B can be found e.g. in the Teradyne J971 or Schlumberger S9000 series. The center arrangements of FIGS. 2A and 2B are mainly used for optimizing timing delay requirements in that the contact area  100  is designed in a way that the individual contacts thereof are located as close as possible to the corresponding contacts of the DUT  20 . 
     FIG. 2C shows a device-specific arrangement for a plurality of individual (i.e. physically separated) DUT boards  60 . Each DUT  20  is located in the center of a respective DUT board  60 , whereby only one DUT  20  is applied on each DUT board  60 . The contact area  100  of each DUT board  60  is device-specific and may substantially correspond to the centered arrangement according to FIG. 2A, An example of an embodiment according to FIG. 2C can be found in the Hewlett-Packard HP 95000 Series. The device-specific arrangement according to FIG. 2C in particular fits the requirements of short timedelay and multi-site testing. 
     FIG. 2D shows a DUT board  60  designed for the specific requirements of the negative pressure attachment systems as depicted in FIG.  1 C. One or more DUTs  20  are arranged in a row between parallel contact areas  100 . 
     It has to be understood and it is expressly noted that the different attaching systems as depicted in FIGS. 1C and 1D require entirely different solutions for the design of the, DUT board  60 . Whereas the mechanical connecting system according to FIG. 1B allows to arrange a plurality of individual DUT boards  60  as shown in FIG. 2C, the negative pressure attachment system of FIG. 1C requires that all DUTs  20  have to be located on one single. DUT board  60  since the negative pressure applied through the vacuum slots  120  requires an uninterrupted space between the contact areas  95  and  100 . A separation into individual DUT boards  60  would require a modification of the negative pressure applying means arranged in the test head  40 . Such modifications at the test head  40 , however, are normally very expensive and would require a detailed knowledge of the spatial dimensions of the specific arrangement of individual DUT boards  60 . 
     Each of the designs of the DUT boards  60  in the FIGS. 2A-2D requires a specific design of parts corresponding to the DUT boards  60  of either or both the fixture  70  and the test head  40 . This limits the exchangeability of different DUT boards  60  or requires costly modifications of corresponding parts at the test head site. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a more flexible test head arrangement allowing an easy exchange of different DUT boards. 
     According to the invention, a test head assembly for a test system comprises a test head having a plurality of test head contact areas, each with one or more individual contacts, for providing electronic signals to one or more devices under test—DUT—and/or for receiving electronic signals therefrom. The test head assembly further comprises fastening means for fastening one or more individual, physically separated DUT boards to the test head, each DUT board being provided for holding one or more of the DUTs and adapting electrical contacts thereof to at least one of the plurality of test head contact areas. 
     In order to provide a flexible and modular test head arrangement allowing an easy exchange of different DUT boards with different seizes, the arrangement of the fastening means and the plurality of test head contact areas is commensurable, so that one or more DUT boards with same and/or different lateral dimensions are attachable to the test head. 
     In a first preferred embodiment, the arrangement of the fastening means and the plurality of test head contact areas is commensurable in (only) one dimension (e.g. in the direction of the breadth of the DUT boards), so that one or more DUT boards with same and/or different seizes in that dimension can be attached to the test head preferably in a longitudinal row. Accordingly, the arrangement can provide and support more than one longitudinal rows, preferably arranged as substantially parallel rows, so that in each row one or more DUT boards with same and/or different seizes (e.g. breadths) in that dimension can be attached. 
     In the first embodiment the fastening means and the plurality of test head contact areas are preferably arranged in one or more longitudinal rows. Preferably, each DUT board comprises at least one DUT contact area having one or more individual contacts electrically coupled to the one or more DUTs of that respective DUT board. Each DUT contact area can be electrically coupled to at least one of the plurality of test head contact areas for providing an electrical contact between the respective DUT board and the test head, and each DUT contact, area is arranged substantially parallel to the one or more longitudinal rows. 
     In a second preferred embodiment, the arrangement of the fastening means and the plurality of test head contact areas is commensurable in two dimensions (e.g. in the direction of the breadth and the length of the DUT boards), so that one or more DUTT boards with same and/or different seizes in one or both of that two dimensions can be attached to the test head. 
     In the second preferred embodiment the fastening means and the plurality of test head contact areas are preferably arranged in accordance with the first embodiment. The second preferred embodiment, however, further comprises adapting means for adapting the test head contact areas to be coupled to a respective DUT board to the lateral dimensions of each DUT board. Preferably, the adapting means allow/s to either withdraw one or more test head contact areas from contacting the respective DUT board, or to couple only one or more test head contact areas to the respective DUT board. 
     The second preferred embodiment preferably provides a certain redundancy of fastening means and test head contact areas, so that a great variety of DUT boards with different lateral dimensions can be coupled to the test head. 
     It is clear that the respective DUT boards according to the invention have to be adapted to the test head assembly to be coupled to, so that the respective DUT contact areas are adapted to match with corresponding ones of the plurality of test head contact areas. This can be preferably accomplished by arranging the DUT contact areas in a predefined way, e.g. only in one or more parallel rows with defined distances between those rows, whereby the arrangement of the DUT contact areas substantially corresponds with the arrangement of the plurality of test head contact areas, e.g. with defined distances substantially match with defined distances between one or more parallel rows of the plurality of test head contact areas whereby the distances between the rows of the DUT contact areas and the test head contact areas substantially match. 
    
    
     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 or can be built up substantially equally or similarly are referred to with the same reference sign. 
     FIGS. 1A to  1 C illustrate a typical test system as known in the art, 
     FIGS. 2A to  2 D show examples of DUT boards  60  as known in the art, and 
     FIGS. 3A to  3 C show embodiments of test head assemblies according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3A shows, in a three dimensional explosion view, an embodiment according to the invention of a test head assembly  35  and four DUT boards  60 A,  60 B,  60 C and  60 D, each carrying one or more DUTs  20 . The DUTs  20  are not shown in FIG. 3A since the DUT boards  60 A- 60 D are depicted in a worm&#39;s eye view, i.e. from the side to be attached towards the test head  40 . The DUT boards  60 i (with i=A . . . D) are mountable onto the stiffener  90  (also shown in FIG. 3A from the side to be attached to the test head  40 ). The stiffener  90 , again, can be mounted onto the test head  40  via the fixture  70 . 
     It is to be understood that the stiffener is only required for applications in which the DUT boards  60 i might be bent or otherwise deformed under the influence of the contact pressure applied for providing a good electrical contact between the contact area  95   a  of the test head  40  and the contact areas  100  of the DUT board  60 . In case that the DUT boards  60 i are sufficiently stiff and/or the applied contact pressure is low enough, the DUT board  60 i can be directly mounted onto the test head  40 , preferably by means of screws or the like. 
     For mounting the DUT board  60 i onto the test head  40 , either directly or via the stiffener  90 , respective mechanical connecting means, such as screws or the like, can be applied. However, any other means for mounting the DUT board  60 i onto the test head  40  are applicable for the purposes of the invention, as long as those mounting means allow individually attaching and detaching each individual DUT board  60 i to and from the test head  40 . In case that negative pressure means are applied, it has to be made sure that each DUT board  60 i can be individually attached by means of the negative pressure means. That means that, in contrast to the example shown in FIG. IC, the vacuum slots  120  have to be provided individually for each DUT board  60 i and cannot cover more than one DUT board  60 i. In other words, the embodiment of the DUT board.  60  shown in FIG. 1C could also serve the purpose of the invention. For testing more than one DUT boards  60 , however, a plurality of DUT boards  60 i according to FIG. 1C have to be aligned in a longitudinal row as shown e.g. for FIG.  3 A. The provision of individual negative pressure means for each individual DUT board  601 , on the other hand, might render the whole test head assembly  35  too expensive, so that mechanical connecting means are used preferably. 
     For allowing an easy exchange of DUT boards  60 i with different breadth (in the direction of arrow A), the respective contact areas  100 Aj (with j=1 . . . 8) are aligned in a longitudinal row  100 A. Accordingly, the contact areas  100 Bj are aligned in a longitudinal row  100 B. Each DUT board  60 i comprises one or more contact areas  100 Aj at one end and one or more contact areas  100 Bj at the opposing end, all contact areas  100  being arranged on the lower side (generally the opposed side where the DUT(s) is/are located) of the DUT board  60 i. In the embodiment of FIG. 3A, the DUT board  60 A comprises contact areas  100 A 1  and  100 A 2  at one end and contact areas  100 B 1  and  100 B 2  at the opposite end. Accordingly, the DUT board  60 B comprises contact areas  100 A 3  and  100 A 4  at one end and contact areas  100 B 3  and  100 B 4  at the opposite end, and so on. 
     In accordance with the alignment of the contact areas  100 Aj in the line  100 A and the contact areas  100 Bj in the line  100 B, the test head  40  provides a line  95 A of contact areas  95 Aj to be coupled to the corresponding contact areas  100 Aj of line  100 A, and contact areas  95 Bj in a line  95 B to be coupled to the corresponding contact areas  100 Bj of line  100 B. In the embodiment of FIG. 3A, the alignment and arrangement of the contact areas  100 Aj substantially matches with the alignment and arrangement of the contacts areas  95 Aj. Accordingly, the alignment and arrangement of the contact areas  100 Bj substantially matches with the alignment and arrangement of the contact areas  95 Bj. 
     The advantage of the invention becomes readily apparent with respect to the embodiments illustrated in FIGS. 3B and 3C which substantially correspond to the embodiment of FIG. 3A, however, with exception of the DUT boards  60 i. Instead of four individual DUT boards  60 A . . .  60 B shown in FIG. 3A, the embodiment of FIG. 3B only has two individual DUT boards  60 E and  60 F, whereby the DUT board  60 E covers substantially the same breadth as the DUT boards  60 A and  60 B, and DUT board  60 F covers substantially the same breadth as DUT boards  60 C and  60 D. In the embodiment of FIG. 3C, only one DUT board  60 G is employed which substantially covers the same breadth as the DUT board  60 E and  60 F or, accordingly, the DUT boards  60 A . . .  60 D. 
     For attaching the embodiments of FIG. 3B or FIG. 3C onto the test head  40 , the stiffener  90  as shown in FIG. 3A, or a correspondingly modified one, can be employed, as far as the stiffener is required. The arrangement according to the invention allows to use all the DUT boards as shown for the embodiments of FIG. 3A to FIG. 3C for the same test head  40  (as shown in FIG. 3A) without any hardware modification. This arrangement significantly distinguishes in particular from the device specific arrangement e.g. according to FIG. 2C in that the invention allows to more flexibly employ different DUT boards with different breadths, all using the same hardware design of the test head  40  in FIGS. 3A-3C. Whereas a change in the lateral dimensions of the DUT boards  60  is not possible in FIG. 2C without changing the respective contact area design of the test head  40 , the invention allows to vary the breadths of the DUT boards without any hardware modification required. 
     It is to be noted that the one or more DUT boards  60 i (with i=A . . . G), as shown in the FIGS. 3A and 3B, lined up in a row do not have to cover the full applicable breadth of the test head  40 , i.e. where contact areas  95  are provided. Instead of employing four DUT boards  60  as shown in FIG. 3A, only one, two or three of such DUT boards could be used not covering the fully applicable breadth for aligning DUT boards. Accordingly, only one of the DUT boards  60 E or  60 F in FIG. 3B could be used. On the other hand, a mixture of DUT boards  60  with different breadths is also applicable. As an example, one DUT board  60 E according to FIG. 3B could be employed together with one or two of the DUT boards  60  according to FIG.  3 A. 
     It is noted that in the embodiments of FIGS. 3A-3C, the individual contacts of the contact areas as well of the DUT boards  60 i as of the test head  40  are respectively aligned substantially perpendicular to the alignment of the contact areas. However, it is clear that the alignments of the individual contacts can also be in parallel to the alignment of the contact areas, e.g. as shown in FIG.  2 D. 
     The arrangement according to the invention not only allows to flexibly (ex)change and arrange DUT boards  60 , but also to modularly arrange the test head  40 . In the latter case, the user can choose the pin count, i.e. the number of individual contacts and contact areas, of the test head  40  within the same mechanical casing/frame  200  of the test head  40 . For cost reasons, or in case that only a low pin count is required, the user might choose a reduced test head with, for example, only the contact areas  95 A 1 - 95 A 2  and  95 B 1 - 95 B 2 . For a medium pin count, the user might choose a test head with the contact areas  95 A 1 - 95 A 4  and  95 B 1 - 95 B 4 . For a high pin count, the user will choose the full arrangement of contact areas  95 Aj and  95 Bj as shown in the lower part of FIGS. 3A-C. The modularity of the arrangement according to invention further allows to simply upgrade from the low pin count version to the medium or the high pin count version by simply adding the respective contact areas (and corresponding test electronics) to the test head  40 . Preferably, the test electronics corresponding to respective contact areas is arranged/located underneath the respective contact areas, thus allowing a higher degree of modularity. 
     In another embodiment, the test electronics and contact areas can be modularly employed for different casings  200  with different lateral dimensions. That means that the user can reuse the test electronics and contact areas when upgrading from a smaller casing  200  to a larger one. 
     It is to be understood that the invention is not limited to the arrangement of individual DUT boards  60  in one row, but also that-more than one (preferably parallel) rows are applicable. Accordingly, the invention is not limited to DUT boards  60  with two contact areas. DUT boards with either only one contact area or more than two contact area can also be employed for the purpose of the invention. 
     The stiffener  90  has to be designed to provide sufficient mechanical stability and stiffness to the DUT boards, and might comprise a base frame plate, guiding bushings for positioning, cam bearings, and/or mounting holes for the DUT board(s). 
     With the solution according to the invention it is possible to use the same DUT board  60  on a test head  40  with a low pin count, a medium pin count (e.g. double pin count) or a high pin count (e.g. four times). The advantage for a user might be that in a start phase for testing only singular DUTs  20 , only a small and thus cheap DUT board  60  is required. In a volume phase for testing a plurality of DUTs  20  in parallel, the small DUT board  60  (of the start phase) only has to be complied and can be used e.g. on the medium pin count test head  40 , whereby no change of the DUT board  60  is necessary since it will be the same electrical behavior if testing one or two DUTs  20  in parallel. If a damage on one of the DUT boards  40  occurs, the other DUT boards (s) is/are still in use, thus leading to a high reliability and short time break. 
     In a high volume phase for testing high quantities of the DUT  20 , the small DUT board(s) (of the start and/or volume phase) can be copied and used e.g. in the high pin count test head  40 . Again, no change of the DUT board  60  and/or the test head  40  (except of a possible upgrade—if required) is necessary, and a damage in one DUT board can easily be covered by the other DUT boards. In particular for the high volume phase, applying a plurality of individual (small) DUT boards  60  can represent a significant cost advantage over large and costly combined DUT boards. 
     In a lower volume phase of the DUT  20 , e.g. at the end phase of a product cycle, the high pin count test head  40  might be used for testing a different type-of DUT, so that only e.g. the medium pin count of the test head  40  will be applied for testing the DUT  20  of the lower volume phase. 
     The solution according to the invention provides the advantage that the user can control his investments in the test system  10  depending on the test volume of the devices to be tested. And even after a certain investment has been made, e.g. for the high volume phase, the user can still use this investment and transfer more and more of the testing resources without requiring unduly and costly hardware modifications for testing different DUTs.