Abstract:
A probe apparatus is provided with a number of space transformer segments that are fixated such that probe offset due to warping is kept to a minimum. In a first embodiment, the space transformer segments are permanently fixated. In a second embodiment the space transformer segments are included together with correspondingly shaped sheath segments in probe modules that may be individually removed from the probe apparatus for a selective maintenance. As a result a large number of chips may be tested simultaneously without reducing the operational cycle interval of the probe apparatus.

Description:
FIELD OF INVENTION  
         [0001]    The present invention relates to space transformer configurations of chip testing probe apparatus. Particularly, the present invention relates to a probe apparatus having a segmented space transformer.  
         BACKGROUND OF INVENTION  
         [0002]    The demand for reduced test cycle times during the chip fabrication results in development of probe apparatus that are capable of testing an increasing number of chips simultaneously. Chips are conventionally fabricated and tested on wavers. For a given chip size, the waver diameter defines the maximum number of chips that can be simultaneously fabricated on a single waver. On the other hand, the maximum number of simultaneously tested chips is mainly restricted by the configuration of the probe apparatus.  
           [0003]    Conventional probe apparatus have a number of probes configured and uniformly assembled in order to evenly contact a number of chip terminals. The maximum number of probes feasibly combined in such probe apparatus depends on a number of factors, which are, for example, a probe failure likelihood opposed by a required probe apparatus life span or, in another example, position tolerances of all the probes&#39; tips within the probe assembly.  
           [0004]    Probe failure likelihood may be statistically defined as an average failure rate per probe and test cycle. Multiplying the number of assembled probes with the average failure rate results in an average probe apparatus cycle interval during which the probe apparatus may be operated uninterrupted. The repair of individual probes within a conventional probe assembly is highly unpractical due to the fragile nature of probes and the tight probe assembly. In cases where individual probe tips become offset relative to the probe tip plane, grinding and/or sanding operations have to be performed on all probes in order to bring them again into common alignment. Thus increasing the number of probes increases also the maintenance and repair effort between the cycle intervals.  
           [0005]    Position tolerances of all the probe tips within the probe assembly are crucial for establishing and maintaining identical contacting conditions between the individual probe tips and the terminals of the tested chips. In-plane position tolerances affect the position of the probe tips relative to the corresponding terminals. Off-plane position tolerances affect the contacting force with which the probes are pressed against the terminals. In-plane and off-plane position tolerances are defined by a fabrication precision and a thermal expansion behavior of the probe apparatus. Since chips are tested at various elevated temperatures, probe apparatus are exposed to varying thermal conditions during their operation. With increasing size of the probe apparatus temperature discrepancies within the probe apparatus become more difficult to control. In addition, individual components of the probe apparatus have dissimilar expansion characteristics, which results in warping and consequently in an increased off-plane position range of the probe tips.  
           [0006]    Space transformers that are made from two or more layers of different materials are especially sensitive to warping. Warping of space transformers increases more than proportional with the size of space transformer and is thus a main limitation of probe apparatus sizes for given probe tip position tolerances.  
           [0007]    For simultaneously testing extended numbers of chips, there exists therefore a need for a probe apparatus in a configuration that bypasses the limitations imposed by probe failure likelihood and space transformer warping. The present invention addresses this need.  
           [0008]    The U.S. Pat. No. 5,534,784, for example, discloses a probe apparatus having more than one space transformers on top of each other. The invention does not disclose laterally arranged space transformer segments.  
         SUMMARY  
         [0009]    A probe apparatus is introduced that combines a number of laterally arranged probe blocks in a modular assembly within a frame structure.  
           [0010]    In the preferred embodiment, the probe blocks include space transformer segments that are configured, laterally arrayed and fixated within the frame structure such that the off-plane position range of the probe tips remains only affected by the warping of the individual space transformer segments. In addition, the frame structure may have thermal distribution characteristic defined such that temperature discrepancies of the individual space transformer segments remain within a predetermined range for a given operation environment.  
           [0011]    In a second embodiment of the present invention the probe modules include space transformer segments, corresponding probes and a guiding structure for glidingly fixating the corresponding probes. The frame structure may provide features for fixating and removing the probe modules in order to replace individual probe modules within the probe apparatus in cases of probe failure or other factors like, for example, partial change of the chip layout of the waiver series to be tested. As a result, the number of probes within the probe apparatus may be selected independently from the average probe failure likelihood and the probe apparatus may be more easily configured and adjusted to varying chip production cycles.  
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]    [0012]FIG. 1 shows an isometric view of a single space transformer segment above a tested waiver.  
         [0013]    [0013]FIG. 2 shows a top view of an exemplary and simplified probe apparatus having four space transformer segments with one space transformer segment not being shown. The exemplary probe apparatus is shown above a tested waiver.  
         [0014]    [0014]FIG. 3 shows the exemplary probe apparatus of FIG. 2 in isometric view.  
         [0015]    [0015]FIG. 4 shows an enlarged detail of the probe apparatus of FIG. 2. The enlarged detail is indicated in FIG. 2.  
         [0016]    [0016]FIG. 5 shows the isometric view of FIG. 3 of the probe apparatus of FIG. 2 completely broken along the probe breaking line.  
         [0017]    [0017]FIG. 6 shows the isometric view of FIG. 3 of the segment fixating frame. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention. FIG. 1 shows the space transformer segment  11  with the peripheral terminals  12  above a tested waiver  14  with the chips  15 . The transformer segment  11  is shown in a simplified fashion and in an exemplary position relative to the waiver  14 . The exemplary position corresponds to a testing position of a probe apparatus PA (see FIGS. 2, 3,  5 ) featuring a number of space transformer segments  11 ,  11 B,  11 C,  11 D as it is partially shown in the FIGS.  2 - 5 . The testing position is the position of the probe apparatus PA during which up to all chips  15  of the waiver  14  may be simultaneously accessed by the probes  13 ,  13 B,  13 C,  13 D as shown in the FIGS.  2 - 5 . For the purpose of clarity, only a view probes  13 ,  13 B,  13 C,  13 D are shown in the FIGS.  2 - 5 . It is clear to one skilled in the art that the probes  13 ,  13 B,  13 C,  13 D may be in any number as is commonly practiced for testing circuit chips.  
         [0019]    The probe apparatus PA shown in the FIGS.  2 - 5  is presented in simplified form solely for the purpose to illustrate the main inventive features that would enable one skilled in the art to make and use the invention. For example, in FIGS.  2 - 5 , four space transformer segments  11 ,  11 B,  11 C,  11 D are shown in circular arrangement with corresponding rectangular contour indicated in FIG. 1 by the segment length SL, the segment width SW and the segment height SH. It is noted, that the scope of the invention is not limited to the number of segments or geometric orientation of the individual segments relative to each other. Moreover, the segments may be arranged in any number and geometric configuration suitable to accomplish the inventive goals as set forth in the following detailed description. For example, the segments may be arranged in the number of three, each of them having a triangular contour or a tart shape.  
         [0020]    The main task of a space transformer is to provide peripheral terminals  12 ,  12 B,  12 C,  12 D in a larger scale than the terminals or vias contacted by the probe ends such that cables can be attached to them. In the present invention where a number of space transformer segments  11 ,  11 B,  11 C,  11 D are laterally arranged the up scaling of the peripheral terminals  12 ,  12 B,  12 C,  12 D is in radial direction away from the testing area center TAC (see FIG. 4). The up scaling within the space transformer segments  11 ,  11 B,  11 C,  11 D may be accomplished within a scaling range SCR, which is defined by the number of segments circularly arranged around the testing area center TAC. For the example illustrated in the FIGS.  2 - 5  the scaling range may be up to  90 . The scaling range SCR is averaged by the scaling vectors SVA, SVB, SVC, SVD (see FIGS. 1, 2,  4 ).  
         [0021]    Space transformer segments  11 ,  11 B,  11 C,  11 D may have to withstand the contacting forces of the individual beams that are brought into contact with the test terminals. This applies particularly for buckling beam probes as is well known to those skilled in the art. The space transformer segments  11 ,  11 B,  11 C,  11 D provide also a number of conductive layers alternating with insulating layers. This is to provide the conductive traces that connect the peripheral terminals  12 ,  12 B,  12 C,  12 D with the probe terminals or probe vias that are arrayed on the bottom side space transformer segments  11 ,  11 B,  11 C,  11 D. As a result, the space transformer segments  11 ,  11 B,  11 C,  11 D have to have a certain segment height SH as is well known for conventional space transformers.  
         [0022]    Circuit chips are commonly tested at elevated temperatures, which induces a thermal load onto the space transformer segments  11 ,  11 B,  11 C,  11 D. Since the thermal load induced on the space transformer segments  11 ,  11 B,  11 C,  11 D is difficult to be fully balanced, warping of the space transformer segments  11 ,  11 B,  11 C,  11 D is unavoidable. Warping of the space transformer segment  11  is exemplarily shown in FIG. 1 with the warping radius WR and the warping height WH.  
         [0023]    In a case where all chips  15  of a waiver  14  are tested simultaneously, the space transformer segments  11 ,  11 B,  11 C,  11 D significantly extend laterally beyond a warping relevant area WRA where probe beams are contacting the space transformer segments  11 ,  11 B,  11 C,  11 D. In this case, the warping relevant area WRA corresponds approximately with the waiver diameter WD. For the purpose of simplicity, the warping relevant area WRA as well as a negative warping area NWA and a positive warping area PWA are illustrated on the top surface of the space transformer segment  11 . It is clear that the warping relevant area WRA, the negative warping area NWA and the positive Warping area PWA are of relevance on the bottom surface of the space transformer segments  11 ,  11 B,  11 C,  11 D.  
         [0024]    The positive warping area PWA may be an area on the bottom side of the space transformer segments  11 ,  11 B,  11 C,  11 D, at which a warping movement of the space transformer segments  11 ,  11 B,  11 C,  11 D results in an distance increase in perpendicular direction away from the waiver  14 . The negative warping area NWA may be an area on the bottom side of the space transformer segments  11 ,  11 B,  11 C,  11 D, at which a warping movement of the space transformer segments  11 ,  11 B,  11 C,  11 D results in an distance decrease in perpendicular direction towards the waiver  14 . The space transformer segments  11 ,  11 B,  11 C,  11 D are preferably fixated within the probe apparatus PA such that the positive and negative warping areas NWA and PWA have approximately the same area. As a result, the maximum length offset due to warping within the warping relevant area WRA is kept to a minimum. A peripheral region of the space transformer segments  11 ,  11 B,  11 C,  11 D that carry solely peripheral terminals  12  on their top surface may experience increased vertical displacement which is of no influence to the off-plane tolerance within which the probe tips may be contacted for a given operational thermal bandwidth of the probe apparatus PA.  
         [0025]    [0025]FIG. 2 shows a top view of the simplified probe apparatus PA with the four space transformer segments  11 ,  11 B,  11 C,  11 D (space transformer segment  11 C is not shown) being fixedly held within the segment fixating areas  22  provided by the segment fixating frame  21 . The segment fixating frame  21  may be configured to provide sufficient space for a lateral thermal expansion of the space transformer segments  11 ,  11 B,  11 C,  11 D in direction of their scaling vectors SVA, SVB, SVC, SVD.  
         [0026]    The probe apparatus PA is broken along a number of breaking lines in order to better illustrate the vertical arrangement of the individual components. The segment fixating frame  21  is broken along the frame breaking line  21 BR (see also FIG. 4), the space transformer segments  11 ,  11 B,  11 C,  11 D are broken along the segment breaking line  11 BR (see also FIG. 4) and the sheath  23  of the probe apparatus PA is broken along the sheath breaking line  23 BR (see also FIG. 4). As a result, the probes  13 ,  13 B,  13 C,  13 D are visible in their operational position and orientation as well as the chips  15  on the waiver  14 .  
         [0027]    [0027]FIG. 3 shows the probe apparatus PA in isometric view in order to clearly illustrate the vertical arrangement of the individual elements and the breaking lines.  
         [0028]    In a first embodiment of the present invention, the space transformer segments  11 ,  11 B,  11 c,  11 D are rigidly connected with the probe apparatus PA.  
         [0029]    [0029]FIG. 4 shows an enlarged detail view of the central detail of the probe apparatus PA as is indicated in FIG. 2 with the circle DET 4 .  
         [0030]    The space transformer segments  11 ,  11 B,  11 C,  11 D may have their probes  13 ,  13 B,  13 C,  13 D commonly aligned such that all probe tips of a single space transformer segment point into a common direction relative to their probe ends. Particularly in the case where buckling beam probes are utilized the probes  13 ,  13 B,  13 C,  13 D have a probe tip/end offset TEO which is the lateral offset between their tips and their ends. The probes  13 ,  13 B,  13 C,  13 D may thus be oriented with their tips on their tip position circle TPC for a given probe end position on their space transformer segments  11 ,  11 B,  11 C,  11 D.  
         [0031]    Test terminals (not shown) on the chips  15  may be in a distance to each other, which has to be matched by the probe tip distance PTD. On the other hand, the space transformer segments  11 ,  11 B,  11 C,  11 D may have to be assembled within the probe apparatus PA with a segment assembly gap SSP. In addition, the probe ends may only be contacting their terminals or vias up to the segment margin SM. Consequently, for a given required probe tip distance PTD along the segment assembly gap SSP, the sum of the segment assembly gap SSP and the segment margin SM may have to be equaled the sum of probe tip distance PTD plus the probe tip/end offset TEO under consideration of the scaling range SCR. This relation is formulated in mathematic terms as follows:  
           SM+SSP/ 2 =PTD/ 2 +TEO *sin  SCR/ 2  
         [0032]    [0032]FIG. 5 shows a section view of the probe apparatus PA cut along a section line resulting in the cut sections  21 BR 2 . FIG. 5 shows a second embodiment of the present invention where the space transformer segment  11  is included with the module sheath  51  and the probes  13  in a probe module that may be disassembled as a whole. The segment fixating areas  22  comprise for that removable fixtures like, for example, alignment bolts together with screws. As a result, the probes  13  may be maintained independently from the probes  13 B,  13 C,  13 D. The segment fixating areas  22  may further comprise vertical adjustment features like, for example adjustment screws for independently positioning the probe module in vertical and/or lateral direction such that sanding operations may be performed. A shortening of the probes  13  resulting from the sanding may be compensated by resetting the adjustment features.  
         [0033]    [0033]FIG. 6 shows the segment fixating frame  21  which may have thermal distribution features  24  and/or thermally decoupled carrying features  25 . The distribution features  24  may be of a shape and material to balance the thermal load throughout the a relevant region of the segment fixating frame  21  which may correspond to the warping relevant area WRA. The carrying features  25  may be configured and positioned to be insulated from the thermal load in order to prevent thermally related deformation of them.  
         [0034]    The segment fixating frame  21  may also include a sheath holding feature  26 .  
         [0035]    Accordingly the scope of the invention described in the specification above is set forth be the following claims and their legal equivalent: