Abstract:
A buckling beam probe assembly and a process to make the assembly using insulated metal to hold the vertical beam probe wires. The buckling beam probe assembly electrically connects a test apparatus with contact pads on the surface of a device to be tested. The assembly comprises a plurality of buckling beam wires each having a head, a body, and a tail and being pressed vertically onto the contact pads and buckling laterally to adapt to height differences of the contact pads caused by irregularities on the surface of the device to be tested. A top plate has a first plurality of apertures receiving the heads of the plurality of buckling beam wires. A bottom plate has a second plurality of apertures receiving the tails of the plurality of buckling beam wires. A plurality of intermediate metal sections are positioned between the top plate and the bottom plate. Each of the intermediate metal sections have a plurality of openings, the openings being coated with an insulation layer and receiving the bodies of the plurality of buckling beam wires.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to the field of semiconductor wafer testing probe systems and, more specifically, to a buckling beam probe system and to a process for manufacturing the system using insulated metal to hold the probe wires.  
         BACKGROUND OF THE INVENTION  
         [0002]    Small metal wires on the order of tens of microns (a few thousandths of an inch) in diameter are typically used to contact electrical test pads on individual die or to contact electrical test pads on portions of an entire semiconductor wafer. The configuration of the individual contact wires or probes depends on the layout of the test pads to be contacted. The test pads can be in a linear configuration, in an array, or in combinations. In most cases, the size of the test pads is on the order of 75 to 125 microns (three to five thousandths of an inch) in diameter and the center-to-center spacing from pad to pad can be as little as 85 microns (about three and one-half thousandths of an inch) for linear arrays and as little as 150 microns (six thousandths of an inch) for area arrays. The high density of electrical test pads on silicon die and wafers creates a challenge when attempting to contact the electrical test pads. Many different processes have been developed to meet that challenge.  
           [0003]    One traditional process, directed to linear arrays, uses cantilever probes to contact the electrical test pads. These probes are small wires made from metal, having a high yield stress, such as beryllium copper or tungsten. The wires are formed in a long beam with a bend on one end that contacts the test pad. The other end of the wire is held by a card, usually made of polymer, that provides electrical interface to the test electronics and mechanical alignment and stability for the probe array. Typical industry examples are epoxy-ring and blade probe cards.  
           [0004]    Area arrays present more of a challenge than linear arrays because the probe array must extend in a perpendicular direction away from the device under test (DUT) as opposed to a radial fan out direction for linear arrays. The density of an area array does not allow radial fan out of the probes. (“Fan out” means that the probes have a greater pitch at their tips than at their bases.) Accordingly, vertical conducting wires are used to contact area arrays. The vertical probes must be held in place to maintain mechanical alignment and to ensure that the probe tips contact the test pads for the DUT.  
           [0005]    Typically, polymer or ceramic materials are chosen to hold all of the vertical probe wires. Cobra™ probes (available from International Business Machines Corporation of Armonk, N.Y.) and the buckling beam probes disclosed in U.S. Pat. No. 4,027,935 are both examples of vertical metal wire arrays held in place by polymer or ceramic materials. The probe wires can also be permanently bonded to a surface that is part of an electrical space transformer. The configuration of the bond pads on the space transformer is a mirror image of the configuration of the pads on the DUT. The probe wires are permanently bonded on the space transformer to form an array that will contact the array of pads on the DUT. In this case, the individual probe wires are held in place by a space transformer which functions as a three-dimensional fan out for the area array probes—thus bringing the high density of the probe array to a larger dimensional area array that is compatible with larger contact systems to interface with the test electronics. An industrial example of a bonded array probe is the system made by Formfactor, Inc. of Livermore, Calif. and disclosed in International Patent Application No. PCT/US97/08604.  
           [0006]    The requirements for any probe system are electrical performance, mechanical and thermal stability, and manufacturability. Conventional Cobra™ and buckling beam probes have good manufacturability because they can be repaired. These probes have poor electrical performance, however, because electrical coupling exists between the individual probe wires.  
           [0007]    In contrast, bonded probes have good electrical performance because the probe wires can be shorter than Cobra™ or buckling beam wires. But bonded probes have poor manufacturability: if one probe is damaged, it cannot be repaired. The entire system must be reworked because the probe system is integral with the space transformer.  
           [0008]    The mechanical and thermal stability of either bonded probes or vertical wire probes can be adequate if the area of the probe array is not as large as an entire 200 mm (eight inch) wafer or greater. In this case, the thermal coefficient of expansion (TCE) becomes a major factor because many electrical tests are conducted at elevated temperatures. The space transformer holding the bonded probes or the materials holding the vertical wire probes must be matched to the TCE of the DUT which, in the case of silicon, is very low compared to most materials. Only certain ceramics and metals have a TCE matching silicon.  
           [0009]    The requirements of probe systems for high-density chip and wafer testing must also be evaluated considering the future of device testing. The chip fabrication industry is moving in the direction of full wafer testing. This trend will require probe and space transformer systems that are suitable for large areas up to about 300 mm (twelve inches) in diameter. Although International Business Machines Corporation has developed and patented space transformers that satisfy this requirement, the present probe systems will not meet this requirement.  
           [0010]    The buckling beam probe has been in use for over twenty years. It has high density and is both reliable and repairable. The probe has poor high-frequency characteristics, however, and is not suitable for large-area, elevated-temperature applications. One reason for these disadvantages is the polymer used to hold and guide the array of vertical probe wires. The dielectric properties of the polymer allow electrical coupling between the probe wires. The high inductance and AC coupling between adjacent probe wires render conventional probes suitable only for DC testing. This undesirable coupling is especially difficult because buckling beam wires are generally long to allow for buckling of the wires and permit compliance when contacting the DUT. The longer the probe wire, the worse the electrical coupling. In addition, the polymers used to hold the probe beams in place have a high TCE and are not thermally stable.  
           [0011]    In view of the shortcomings of the prior art, it is an object of the present invention to provide a buckling beam probe system using insulated metal to hold the vertical beam probe wires. In this design, the desirable features of the buckling beam are preserved while correcting the deficiencies. The TCE of the metal can exactly match silicon (about 3 to 5×10 −6  per °C.). Because the material is metal, the beam probes cannot electrically couple. Another object of the present invention is to provide a buckling beam probe system in which the probe wires are not integral with the space transformer, thereby separating the probe system from the space transformer and facilitating repairs.  
           [0012]    It is still another object of the present invention to provide a process for manufacturing a buckling beam probe system. The process makes each beam wire a transmission line with controlled impedance. Controlled impedance allows the beams to be as long as necessary for compliance with no degradation in high-frequency (above 300 mHz) electrical performance. It is a further object of the present invention to provide a buckling beam probe that allows high density (less than a 0.2 mm or an 8 mil pitch), high electrical performance, low inductance, and high reliability; is repairable and mechanically, dimensionally, and thermally stable; and provides testing compatible and consistent with the present and future needs of the chip testing industry. Such needs include testing of larger area arrays up to 300 mm (twelve inches).  
         SUMMARY OF THE INVENTION  
         [0013]    To achieve these and other objects, and in view of its purposes, the present invention provides a buckling beam probe assembly for electrically connecting a test apparatus with contact pads on the surface of a device to be tested. The assembly comprises a plurality of buckling beam wires each having a head, a body, and a tail and being pressed vertically onto the contact pads and buckling laterally to adapt to height differences of the contact pads caused by irregularities on the surface of the device to be tested. A top plate has a first plurality of apertures receiving the heads of the plurality of buckling beam wires. A bottom plate has a second plurality of apertures receiving the tails of the plurality of buckling beam wires. A plurality of intermediate metal sections are positioned between the top plate and the bottom plate. Each of the intermediate metal sections have a plurality of openings, the openings being coated with an insulation layer and receiving the bodies of the plurality of buckling beam wires.  
           [0014]    The process for making the buckling beam probe assembly according to the present invention includes the steps of:  
           [0015]    (a) providing a top plate having a first plurality of apertures and a bottom plate having a second plurality of apertures;  
           [0016]    (b) forming a plurality of intermediate metal sections each having a plurality of openings coated with an insulation layer;  
           [0017]    (c) stacking the bottom plate and the top plate with the plurality of intermediate metal sections between the bottom plate and the top plate;  
           [0018]    (d) loading a plurality of buckling beam wires into the apertures of the top and bottom plates and into the openings in each of the plurality of intermediate metal sections;  
           [0019]    (e) shifting at least one of the plurality of intermediate metal sections with respect to the others of the plurality of intermediate metal sections; and  
           [0020]    (f) applying fasteners holding in position the stack of bottom plate, shifted plurality of intermediate metal sections, and top plate.  
           [0021]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0022]    The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:  
         [0023]    [0023]FIG. 1 is a cross section of a buckling beam probe assembly according to a first exemplary embodiment of the present invention;  
         [0024]    [0024]FIG. 2 illustrates the buckling beam wire used in combination with the buckling beam probe assembly shown in FIG. 1;  
         [0025]    [0025]FIG. 3 is a partial sectional view of a buckling beam probe assembly according to the first exemplary embodiment of FIG. 1 with the buckling beam wires in a straight position;  
         [0026]    [0026]FIG. 4 is a partial sectional view of a buckling beam probe assembly according to the first exemplary embodiment of FIG. 1 with the buckling beam wires in the buckled state;  
         [0027]    [0027]FIG. 5 is a partial sectional view of a buckling beam probe assembly according to a second exemplary embodiment of the present invention;  
         [0028]    [0028]FIG. 6 is a top view of a section of the buckling beam probe assembly shown in FIG. 5;  
         [0029]    [0029]FIGS. 7A, 7B,  7 C,  7 D,  7 E,  7 F, and  7 G are top or bottom views of some of the different shapes of openings suitable for the buckling beam probe assembly of the present invention;  
         [0030]    [0030]FIG. 8 is a top or bottom view of any of the plates or sections of the buckling beam probe assembly of the present invention illustrating the alignment holes;  
         [0031]    [0031]FIG. 9 is a sectional view of a fixture with the metal layers used to form the plates and sections of the buckling beam probe assembly of the present invention in position; and  
         [0032]    [0032]FIG. 10 is a cross-sectional view of an insulated buckling beam wire positioned within an opening in one of the sections of the buckling beam probe assembly of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    Referring now to the drawing, wherein like reference numerals refer to like steps and elements throughout, FIG. 1 is a sectional view of a buckling beam probe assembly  10  according to a first exemplary embodiment of the present invention. FIG. 1 shows buckling beam wire  100  positioned inside assembly  10  in the unbuckled or straight configuration. FIG. 2 illustrates buckling beam wire  100  positioned outside assembly  10 , also in the unbuckled or straight configuration. Buckling beam wire  100  has a head  110 , typically a swaged head; a tail  114 ; and a long beam or body  112 .  
         [0034]    [0034]FIG. 1 also shows buckling beam probe assembly  10  having a top plate  20 ; sections  30 ,  40 ,  50 ,  60 , and  70 ; and a bottom plate  80 . Top plate  20  has apertures  22  and  24 . Bottom plate  80  has apertures  85 . Larger aperture  22  receives head  110  and smaller aperture  24  receives body  112  of buckling beam wire  100  when buckling beam wire  100  is inserted into buckling beam probe assembly  10 . Similarly, aperture  85  receives tail  114  of buckling beam wire  100  when buckling beam wire  100  is inserted into buckling beam probe assembly  10 .  
         [0035]    Sections  30 ,  40 ,  50 ,  60 , and  70  are identical in shape, size, and thickness. Each of sections  30 ,  40 ,  50 ,  60 , and  70  has the same number of layers  15  producing the thickness of each section. Also, each of sections  30 ,  40 ,  50 ,  60 , and  70  has the same shape and size of openings  35 ,  45 ,  55 ,  65 , and  75 , respectively. Each of sections  30 ,  40 ,  50 ,  60 , and  70  is made using thin layers  15  and is provided with openings  35 - 75  to accommodate buckling beam wire  100 . The number of sections  30 ,  40 ,  50 ,  60 , and  70  can be varied according to design specifications to accommodate a longer or a shorter buckling beam wire  100 . Thus, the five sections  30 ,  40 ,  50 ,  60 , and  70  are but one example; fewer or more sections are within the scope of the present invention.  
         [0036]    When buckling beam probe assembly  10  is not under any testing conditions, the buckling beam wire  100  is straight, as shown in FIGS. 1 and 2. During wafer testing, buckling beam probe assembly  10  provides electrical connection between the test pads  92  on the DUT  94  and the pads  96  on the space transformer  98 . The buckling beam wires  100  are not integral with the space transformer  98 , rather they are loosely connected, thereby separating the probe system from the space transformer and facilitating repairs.  
         [0037]    The pads  96  on the space transformer  98  are a mirror image of the configuration of the test pads  92  on the DUT  94 . Thus, each individual buckling beam wire  100  conducts from each test pad  92  on the DUT  94  to the corresponding pad  96  on the space transformer  98 . As shown in FIG. 1, the buckling beam wire  100  is slightly longer than the total, combined length of top plate  20 ; sections  30 ,  40 ,  50 ,  60 , and  70 ; and bottom plate  80  of buckling beam probe assembly  10 . This extra length causes the buckling beam wire  100  to extend slightly above top plate  20  and below bottom plate  80 . Buckling beam wire  100  is typically made of beryllium copper, tungsten, or alloys containing platinum or palladium.  
         [0038]    In operation, bottom plate  80  is placed against the DUT  94  and top plate  20  is placed against the space transformer  98 . The DUT  94 , the space transformer  98 , and buckling beam probe assembly  10  are properly aligned and cause each buckling beam wire  100  in the array to contact the correct pads  92 ,  96  on the DUT  94  and space transformer  98 . The extra length of the buckling beam wires  100  causes each wire to come under vertical load between the DUT  94  and space transformer  98 . Typically, the load is between 10 to 25 grams per buckling beam wire  100 . This load causes each buckling beam wire  100  to buckle (as buckled, the buckling beam wires are designated by the reference number  100 ′) as shown in FIG. 4. The buckling of buckling beam wires  100  provides a spring-loading action between the pads  92  on the DUT  94  and the pads  96  on the space transformer  98 . This action allows for compensation of small planarity differences between the DUT  94  and space transformer  98 .  
         [0039]    [0039]FIGS. 3 and 4 show a portion of a buckling beam probe assembly  10  illustrating only sections  30 ,  40 ,  50 , and  60  of FIG. 1. FIG. 3 illustrates three buckling beam wires  100  in their straight position in buckling beam probe assembly  10  when the assembly is not under testing conditions. FIG. 4 illustrates buckling beam wires  100 ′ in a buckled state in buckling beam probe assembly  10  when the probe is under testing conditions. The buckled state of buckling beam wires  100 ′ shown in FIG. 4 is for illustration purposes only and in no way limits the way in which buckling beam wires  100  buckle. Rather, the nature and direction of buckling of buckling beam wires  100  will vary as a function of a number of factors, including the shape and size of openings  35 ,  45 ,  55 ,  65 , and  75 .  
         [0040]    [0040]FIG. 5 is a partial sectional view of the buckling beam probe assembly  10  according to a second exemplary embodiment of the present invention. FIG. 5 shows sections  30  and  40  similar to any two sections of buckling beam probe assembly  10  of FIG. 1. The only differences between the embodiment of FIG. 5 and the embodiment of FIG. 1 are that the identical openings (e.g.,  35  and  45 ) each have an added insulation layer  12  and the buckling beam wires  10 ,  10 ′ each have an added insulation coating  102 . Such insulation prevents short circuits.  
         [0041]    Although both openings and buckling beam wires are illustrated with insulation in FIG. 5, insulation on both features of buckling beam probe assembly  10  is usually unnecessary. In practical application, therefore, insulation layer  12  will be provided on openings  35 ,  45 ,  55 ,  65 , and  75  or, alternatively, insulation coating  102  will be provided on buckling beam wires  10 ,  10 ′. Insulation layer  12  may also be provided on apertures  22  and  24  of top plate  20  and on apertures  85  of bottom plate  80 .  
         [0042]    [0042]FIG. 6 is a top view of section  30  of FIG. 5. FIG. 6 illustrates the shape of openings  35  and  45 , insulation layer  12 , insulation coating  102 , and buckling beam wires  100  and  100 ′. The bottom view of section  40  of FIG. 5 would be similar to the view shown in FIG. 6. FIG. 6 also shows the position of openings  35  and  45  relative to each other. As shown in FIG. 6, openings  35 ,  45  have oval shapes giving space for buckling beam wires  100  to buckle into buckling beam wires  100 ′ as shown in FIGS. 5 and 4.  
         [0043]    Openings  35 ,  45 ,  55 ,  65 , and  75  of FIG. 1 can have any geometric shape, however, including circular, square, rectangular, or any other shape according to design specifications and parameters. As examples, using section  30  and its openings  35  for purposes of illustration, FIGS. 7A (circular),  7 B (square),  7 C (large circular),  7 D (diamond),  7 E (oval),  7 F (rectangular), and  7 G (trapezoidal) show a top or bottom view illustrating a variety of different shapes possible for the openings  35 ,  45 ,  55 ,  65 , and  75  in sections  30 ,  40 ,  50 ,  60 , and  70 , respectively, shown in FIG. 1. Openings  35 ,  45 ,  55 ,  65 , and  75  can also be of any size needed to satisfy particular design specifications. Advantageously, some of the metal layers  15  in a particular component can have oval-shaped openings, to allow buckling beam wire  100  to buckle under load, while the openings of other metal layers of that same component can have different shapes to adjust the air gap around the buckling beam wire  100  for impedance control.  
         [0044]    [0044]FIG. 8 shows a top or a bottom view of one of sections  30 ,  40 ,  50 ,  60 , or  70 ; or of top plate  20 ; or of bottom plate  80  of the buckling beam probe assembly  10  shown in FIG. 1. Section  30  is used for purposes of illustration. FIG. 8 illustrates alignment holes  120  and  130  in addition to the openings  35  which accept buckling beam wires  100 . As shown in FIG. 8, alignment holes  120  and  130  are circular but they can have any suitable shape and size. Sections  40 ,  50 ,  60 , and  70  and top plate  20  and bottom plate  80  each have similar alignment holes  120  and  130 .  
         [0045]    Assembly of the buckling beam probe assembly  10  involves loading all the sections  30 ,  40 ,  50 ,  60 , and  70  and top plate  20  and bottom plate  80  in the stack shown in FIG. 1. Top plate  20 , bottom plate  80 , and all sections  30 ,  40 ,  50 ,  60 , and  70  have two sets of alignment holes  120  and  130 . To assemble sections  30 - 70  and plates  20 ,  80  of buckling beam probe assembly  10 , dowel pins can be inserted into alignment holes  120  before loading the buckling beam wires  100 . Alignment holes  120  are arranged in each component of the stack to cause apertures  22  and  24 ; openings  35 ,  45 ,  55 ,  65 , and  75 ; and apertures  85  to be in alignment. This arrangement facilitates loading the buckling beam wires  100 .  
         [0046]    After all buckling beam wires  100  are inserted into the buckling beam probe assembly  10 , the dowel pins are removed and the sections  30 ,  40 ,  50 ,  60 , and  70  are then shifted relative to each other. As shown in FIGS. 1, 4, and  5 , the section shifts are necessary to allow the buckling beam wires  100  to buckle under load in a preferred direction. For example, shift between sections  30  and  40  is represented by arrow “A” as illustrated in FIG. 5. After the sections are shifted, dowel pins are inserted into the second set of alignment holes  130  to maintain the sections  30 ,  40 ,  50 ,  60 , and  70  in their proper position. The entire buckling beam probe assembly  10  is then held together by fasteners such as screws through the length of the assembly.  
         [0047]    In a typical buckling beam probe assembly, each section  30 ,  40 ,  50 ,  60 , and  70  is made of an organic material such as polytetrafluoroethylene (available under the trademark Teflon from E.I. DuPont deNemours &amp; Co., Inc. of Wilmington, Del., FR4, polyimide, and the like. The openings  35 ,  45 ,  55 ,  65 , and  75  for buckling beam wires  100 , the alignment holes  120  and  130  for the dowel pins, and any additional orifices (if required) for the fasteners are drilled or machined into each section. The same is true for the apertures  22 ,  24 , and  85  of top plate  20  and bottom plate  80 . Because the top plate  20  and the bottom plate  80  determine the alignment of buckling beam wires  100  to the DUT  94  and space transformer  98 , they must be drilled to a tight tolerance: usually less than about ±10 microns (±0.5 thousandths of an inch). Openings  35 ,  45 ,  55 ,  65 , and  75  in sections  30 ,  40 ,  50 ,  60 , and  70  need not have as tight a tolerance; these openings should have a tolerance of at least ±25 microns (±1.0 thousandths of an inch) or less. Although the thickness of individual sections  30 ,  40 ,  50 ,  60 , and  70  can be varied according to the application, 2.5 to 5 mm (0.100 to 0.200 inches) is typical.  
         [0048]    The materials used for, and the processes used to manufacture, the components of conventional buckling beam probe assemblies impair certain characteristics of such assemblies. In addition, conventional materials and processes often limit design options. Sections  30 - 70  may be too thick, for example, to be drilled or machined.  
         [0049]    To improve the electrical performance, TCE match, and probe positional accuracy for large area applications, according to the present invention the buckling beam top plate  20 , bottom plate  80 , and sections  30 - 70  are each made of layers  15  of metal. Preferably, layers  15  are a steel alloy containing about 36% nickel, commercially available under the trademark Invar from Creusot-Loire, because the TCE of the Invar alloy matches silicon and can be photo etched. Metals such as molybdenum, stainless steel, iron, and nickel, or iron-nickel alloys, can also be used depending on the desired TCE. Other metals can also be incorporated in the alloys such as chromium and copper.  
         [0050]    Top plate  20  and bottom plate  80  can be made thinner than sections  30 - 70  and could be drilled or machined in some fashion—but this is not the preferred process. Rather, each of these components are manufactured, according to the present invention, using a process that incorporates thin metal layers  15  which are approximately 50 to 500 microns (0.002 to 0.020 inches) thick. Such metal layers  15  can be photo etched with high precision to very tight tolerances in the range of ±2.5 microns (±0.0001 inches). Therefore, for example, if it is desired to make a section 2.5 mm (0.100 inches) thick, twenty-five metal layers  15  which are 100 microns (0.004 inches) thick would be used. Such etching allows precision location of the apertures, holes, and openings and higher density than can be achieved by drilling or machining a polymer component. In addition, each component can have its apertures, holes, and openings etched differently from those of the components above or below it.  
         [0051]    Any other thickness from 50 microns up to 2.5 mm (0.002 up to 0.100 inches) or thicker could be used. The process used to form the openings, holes, and apertures depends to some extent, however, on the thickness of the metal layers  15 . For chemical etching, the standard procedure is to have a one-to-one ratio for layer thickness to opening or aperture diameter. It is difficult to etch a 100 micron (0.004 inch) diameter hole, for example, in a metal layer 200 microns (0.008 inches) thick. This example corresponds to a thickness-to-diameter ratio of two and, although possible, is not desirable. Other processes like electro discharge machining (EDM) could also be used to form the openings, holes, and apertures in thicker or thinner metal layers. Chemical etching is the preferred process, however, economically and for the best dimensional control. Each layer  15  has the identical etched array of openings  35  in section  30 , openings  45  in section  40 , openings  55  in section  50 , openings  65  in section  60 , and openings  75  in section  70  for buckling beam wires  100 ; alignment holes  120 ,  130 ; and fastener orifices (if any).  
         [0052]    After etching the required openings, holes, and apertures in each layer  15 , each layer  15  is then coated with a thin layer of a conductor such as gold. Layers  15  are stacked, for example, in a fixture  150  as shown in FIG. 9. Layers  15  could also be held in alignment during lamination and fusing in a cavity die. Other mechanisms such as dowel pins or spring-loaded dowel pins could also be used. The design of the cavity die or the shape and location of the dowel pins can vary as desired.  
         [0053]    Uniform pressure is applied to layers  15  in fixture  150 , thus forcing each layer  15  into intimate contact. At a uniform pressure in the range between 1,000 to 50,000 psi (preferably 15,000 psi) and a temperature range of 200 to 300° C., a gold-gold diffusion bond takes place between each layer  15  thus fusing the layers  15  into one integral component (i.e., section  30 ,  40 ,  50 ,  60 ,  70 ; top plate  20 ; or bottom plate  80 ). The resultant component has the required thickness and has all of the openings, holes, and apertures in precise locations similar to the conventional, organic counterpart formed using drilling or machining operations.  
         [0054]    Various metals other than gold can also be used to coat and bond layers  15 . Such metals include lead-tin solder of various compositions, silver, and copper—all either plated or evaporated. The thickness of the bonding metal can be from 500 Angstroms up to a few microns. Polymers could also be used such as polyimides, silicones, urethanes, and the like. Conductive polymers could also be used.  
         [0055]    Another process for bonding layers  15  is to bolt layers  15  together and allow parylene (see below) to bond the buckling beam probe assembly  10  together. Openings, holes, and apertures would be etched in each layer  15  and filled with adhesive before or during lamination. The adhesive would cure and hold the layers  15  together similar to a bolt through the individual layers  15 .  
         [0056]    The final step in fabricating a functional section or plate for the buckling beam probe assembly  10  is coating the laminated and fused metal section or plate with an insulating polymer film. This step can be accomplished, for example, by using parylene. Parylene is the generic name for members of a unique polymer series.  
         [0057]    The basic member of the series, called Parylene N, is poly-para-xytylene, a completely linear, highly crystalline material. Parylene C, the second commercially available member of the series, is produced from the same monomer modified only by the substitution of a chlorine atom for one of the aromatic hydrogens. Parylene D, the third member of the series, is produced from the same monomer modified by the substitution of a chlorine atom for two of the aromatic hydrogens. Parylene D is similar in properties to Parylene C with the added ability to withstand higher use temperatures.  
         [0058]    Parylene N is a primary dielectric, exhibiting a very low dissipation factor, high dielectric strength, and a dielectric constant invariant with frequency. This form has the highest penetrating power of all the parylenes. Parylene C has a useful combination of electrical and physical properties plus a very low permeability to moisture and corrosive gases. Along with its ability to provide a true pinhole-free conformal insulation, Parylene C is the material of choice for coating critical electronic assemblies. Due to the uniqueness of the vapor phase deposition, the parylene polymers can be formed as structurally continuous films from as thin as a fraction of a micrometer to as thick as several mils.  
         [0059]    The parylene polymers are deposited from the vapor phase by a process which in some respects resembles vacuum metallizing. Unlike vacuum metallization, however, which is conducted at pressures of 10 torr or below, the parylenes are formed at around 0.1 torr. Under these conditions, the mean free path of the gas molecules in the deposition chamber is on the order of 0.1 cm. Therefore, unlike vacuum metallizing, the deposition is not line of sight, and all sides of an object to be encapsulated are uniformly impinged by the gaseous monomer. This advantage is responsible for the truly conformal nature of the coating.  
         [0060]    Thus, parylene can be vapor deposited and can penetrate into the small openings and apertures of the components of the buckling beam probe assembly  10  and deposit a uniform coating. Parylene is similar to the Teflon polymer. It has good wear characteristics and a low coefficient of friction.  
         [0061]    Parylene is preferably used as the insulation layer  12  illustrated in FIGS. 5 and 6. Other materials that are vapor deposited, such as ceramics or other polymers, could be used. Dipping might be possible using a very low viscosity fluid. Metal oxidation could also be used to insulate the surface of the metal. The step of coating layers  15  before lamination with another metal that is later oxidized could be done. Metal layers  15  could also be coated with an insulating polymer and then laminated. The polymer functions to insulate apertures  22 ,  24 , and  85  and openings  35 ,  45 ,  55 ,  65 , and  75  and to laminate layers  15  together.  
         [0062]    Insulation coating  102  applied to buckling beam wire  100  is also an insulating polymer such as polyimide. FIG. 10 shows buckling beam wire  100  having an insulation coating  102  in opening  35  of section  30 . The electrical environment of each buckling beam wire  100  can be tailored. The insulated buckling beam wire  100  in insulated apertures  22 ,  24 ,  85  and openings  35 ,  45 ,  55 ,  65 , and  75  thus forms a transmission line.  
         [0063]    Typical dimensions for an exemplary buckling beam probe assembly  10  manufactured in accordance with the present invention are provided for illustration purposes. Larger apertures  22  in top plate  20  may have a diameter of about 0.2 mm (0.0078 inches) and a depth of about 0.25 mm (0.010 inches). Smaller apertures  24  in top plate  20  and apertures  85  in bottom plate  85  may all have a diameter of about 0.08 mm (0.0032 inches). Assuming oval openings  35 ,  45 ,  55 ,  65 , and  75  in sections  30 ,  40 ,  50 ,  60 , and  70 , respectively, such openings may have a long axis of about 0.18 mm (0.007 inches) and a short axis of about 0.1 mm (0.004 inches). The parylene insulation layer  12  in the openings  35 ,  45 ,  55 ,  65 , and  75  may be about 0.01 mm (0.0005 inches) thick.  
         [0064]    Each section  30 ,  40 ,  50 ,  60 , and  70  may be about 3 mm (0.116 inches) tall. Top plate  20  and bottom plate  80  may each be about 0.51 mm (0.020 inches) tall. Thus, the complete height of exemplary buckling beam probe assembly  10  may be about 15.75 mm (0.620 inches). Buckling beam wire  100  may be about 15.9 mm (0.627 inches) tall with a diameter of about 35 to 100 microns (0.0014 to 0.004 inches) and, more specifically, of about 0.064 mm (0.0025 inches). Thus, buckling beam wire  100  may extend 0.18 mm (0.007 inches) beyond the height of exemplary buckling beam probe assembly  10 . The polyimide insulation coating  102  on buckling beam wire  100  may be about 2 to 5 microns and, more specifically, about 0.005 mm (0.0002 inches) thick.  
         [0065]    The dimensions provided above yield a characteristic impedance of 30 ohms which will allow a 2 gHz bandwidth for the buckling beam probe assembly  10 . The impedance of the metal buckling beam probe assembly  10  can be adjusted by modifying the size and shape of openings  35 ,  45 ,  55 ,  65 , and  75 . This relationship is an inherent advantage of the present invention because the openings  35 - 75  are photo etched allowing any geometry.  
         [0066]    The top plate  20 , bottom plate  80 , and sections  30 ,  40 ,  50 ,  60 , and  70  are all manufactured using thin, photo etched metal layers  15  that are gold coated and laminated at elevated temperature to form components of the metal buckling beam probe assembly  10 . After lamination, each component is coated with parylene. The components are stacked and the buckling beam wires  100  are loaded in the conventional manner. The sections  30 ,  40 ,  50 ,  60 , and  70  are shifted and, after the fasteners are positioned, buckling beam probe assembly  10  is ready for use. The mechanical operation of buckling beam probe assembly  10 , manufactured according to the present invention, is identical to the conventional, organic counterparts in all respects. The manufacturing process allows superior electrical performance and expansion to larger area arrays up to 300 mm (twelve inches) because the metal of the buckling beam probe assembly  10  has a low TCE and the openings, holes, and apertures are etched with high positional accuracy over a large area.  
         [0067]    Thus, a buckling beam probe assembly  10  is described that incorporates insulated metal components to hold and guide the individual buckling beam wires  100 . Dimensionally, the metal components are similar to the conventional polymer or plastic components previously used for those functions. The use of metal components creates a coaxial conducting path for each buckling beam wire  100 , allowing impedance control by design. The insulated metal components also prevent electrical coupling between adjacent buckling beam wires  100 . The combination of the coaxial design with the elimination of inductive and capacitive coupling provides high alternating current bandwith.  
         [0068]    Although illustrated and described above with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and departing from the true spirit and scope of the invention.