Patent Publication Number: US-2022229106-A1

Title: Compliant ground block and testing system having compliant ground block

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 17/494,086 filed on Oct. 5, 2021, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to the field of testing microcircuits (e.g., chips such as semiconductor devices, integrated circuits, etc.). More specifically, the disclosure relates to compliant ground blocks that provide electrical and/or thermal grounding to a device under test (DUT) by making contact to a load board of a testing system, and relates to testing systems having compliant ground blocks. 
     BACKGROUND 
     The manufacturing processes for microcircuits cannot guarantee that every microcircuit is fully functional. Dimensions of individual microcircuits are microscopic and process steps very complex, so small or subtle failures in a manufacturing process can often result in defective devices. Mounting a defective microcircuit on a circuit board is relatively costly. Installation usually involves soldering the microcircuit onto the circuit board. Once mounted on a circuit board, removing a microcircuit is problematic because the very act of melting the solder for a second time may ruin the circuit board. Thus, if the microcircuit is defective, the circuit board itself is probably ruined as well, meaning that the entire value added to the circuit board at that point is lost. For all these reasons, a microcircuit is usually tested before installation on a circuit board. Each microcircuit must be tested in a way that identifies all defective devices, but yet does not improperly identify good devices as defective. Either kind of error, if frequent, adds substantial overall cost to the circuit board manufacturing process. 
     Microcircuit test equipment itself is quite complex. First of all, the test equipment must make accurate and low resistance temporary and non-destructive electrical contact with each of the closely spaced microcircuit contacts. Because of the small size of microcircuit contacts and the spacing between them, even small errors in making the contact will result in incorrect connections. A further problem in microcircuit test equipment arises in automated testing. Testing equipment may test one hundred devices a minute, or even more. The sheer number of tests cause wear on the tester contacts making electrical connections to the microcircuit terminals during testing. This wear dislodges conductive debris from both the tester contacts and the device under test (DUT) terminals that contaminates the testing equipment and the DUTs themselves. The debris eventually results in poor electrical connections during testing and false indications that the DUT is defective. The debris adhering to the microcircuits may result in faulty assembly unless the debris is removed from the microcircuits. Removing debris adds cost and introduces another source of defects in the microcircuits themselves. 
     Other considerations exist as well. Inexpensive tester contacts that perform well are advantageous. Minimizing the time required to replace them is also desirable, since test equipment is expensive. If the test equipment is off line for extended periods of normal maintenance, the cost of testing an individual microcircuit increases. Test equipment in current use has an array of test contacts that mimic the pattern of the microcircuit terminal array. The array of test contacts is supported in a structure that precisely maintains the alignment of the contacts relative to each other. An alignment board or plate or template aligns the microcircuit itself with the test contacts. The test contacts and the alignment board are mounted on a load board having conductive pads that make electrical connection to the test contacts. The load board pads are connected to circuit paths that carry the signals and power between the test equipment electronics and the test contacts. 
     One particular type of microcircuit often tested before installation has a relatively large, centrally located ground (CG) terminal on a flat, bottom surface of the microcircuit package. The microcircuit signal and power (S&amp;P) terminals surround the CG terminal in a predetermined array. Microcircuit packages having this configuration of terminals may be called CG packages. Establishing a solid ground connection to this pad is critically important to get reliable test results. ICs are not entirely uniform in their production, so making reliable contact with this ground pad is difficult. 
     BRIEF SUMMARY 
     Embodiments disclosed herein provide a solution that addresses each of the above-mentioned problems. Embodiments disclosed herein provide a compliant ground block that is composed of simple elements, uses an elastomeric component (e.g., made of a non-conductive material), is configurable to a wide-variety of shapes and sizes, can be cleaned by existing methods without changes, is robust in a production environment, and is low-cost. In one embodiment, the compliant ground block can be composed of a stack of blades (e.g., thin contact blades made of an electrical and/or thermal conductive material). Each blade of the blades is the same as each other. Each blade is inverted with respect to its adjacent blade in a longitudinal direction of the blade or the compliant ground block. Each contact blade has an elongated aperture near the center (e.g., below a centerline of the blade in the longitudinal direction), with the elongated aperture axis perpendicular to the axis of compliance of the ground block. In one embodiment, the contact portion of the blade has raised teeth or protrusions that make good contact with the DUT and load board ground pads. 
     Also disclosed is a compliant ground block for a testing system for testing integrated circuit devices. The compliant ground block includes a plurality of electrically conductive blades in a side by side generally parallel relationship. The blades are configured to be longitudinally slidable with respect to each other. The block also includes an elastomer configured to retain the plurality of blades. Each blade of the plurality of blades includes a first end and a second end opposite to the first end in a longitudinal direction. The plurality of blades is arranged so that the first end of each blade of the plurality of blades is opposite to the first end of an adjacent blade in the longitudinal direction, so that the first end of one blade is adjacent to the second end of the adjacent blade. The elastomer is at least tubular (e.g., hollow or solid cylindrical) in part and non-conductive. 
     Also disclosed is a testing system for testing integrated circuit devices. The testing system includes a DUT and a compliant ground block. The compliant ground block includes a plurality of blades and an elastomer configured to retain the plurality of blades. Each blade of the plurality of blades includes a first end and a second end opposite to the first end in a longitudinal direction. The plurality of blades is arranged so that the first end of each blade of the plurality of blades is opposite to the first end of an adjacent blade in the longitudinal direction. The elastomer includes a non-conductive outer surface. The plurality of blades includes a conductive outer surface. A size of the compliant ground block is at least partially aligned with a ground pad of the DUT. 
     Also disclosed is a method of assembling and positioning a compliant ground block in a testing system for testing integrated circuit devices. The method includes arranging a plurality of electrically conductive blades of the compliant ground block so that a first end of each blade of the plurality of blades is opposite to a first end of an adjacent blade in a longitudinal direction. The first end of one blade is adjacent a second end of an adjacent blade. The second end is opposite to the first end in the longitudinal direction. The method also includes retaining the blades with an elastomer of the compliant ground block. The blades is in a side by side generally parallel relationship. The blades are configured to be longitudinally slidable with respect to each other. The elastomer is at least tubular (e.g., hollow or solid cylindrical) in part and non-conductive. The method further includes installing the compliant ground block in a housing. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       References are made to the accompanying drawings that form a part of this disclosure and which illustrate embodiments in which the systems and methods described in this specification can be practiced. 
         FIG. 1A  is a perspective view of a part of a test system for receiving a DUT for testing, according to one embodiment. 
         FIG. 1B  is a perspective bottom view of a DUT, according to one embodiment. 
         FIG. 2A  is a side-view drawing of a portion of the test system for receiving a DUT for electrical testing, according to one embodiment. 
         FIG. 2B  is a side-view drawing of the test system of  FIG. 2A , with the DUT electrically engaged, according to one embodiment. 
         FIG. 3  is an exploded view of building blocks of a test contactor of a test assembly for the testing of a DUT, according to one embodiment. 
         FIG. 4  is a perspective view of a test assembly, according to one embodiment. 
         FIG. 5A  is an enlarged top view of a portion of the test assembly of  FIG. 4 , according to one embodiment. 
         FIG. 5B  is an enlarged bottom view of a portion of the test assembly of  FIG. 4 , according to one embodiment. 
         FIG. 6A  is a perspective top view of a compliant ground block installed in a housing of a test contactor, according to one embodiment. 
         FIG. 6B  is a perspective bottom view of a compliant ground block installed in a housing of a test contactor, according to one embodiment. 
         FIG. 7A  is an exploded view of a compliant ground block to be installed in a housing of a test contactor, according to one embodiment. 
         FIG. 7B  is a perspective view of a compliant ground block, according to one embodiment. 
         FIG. 8A  is a perspective cross-sectional view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 8B  is an exploded cross-sectional view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 8C  is an exploded cross-sectional view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 8D  is a perspective cross-sectional view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 9A  is a side view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 9B  is a side view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 10A  is a side view of a blade, according to one embodiment. 
         FIG. 10B  is a perspective view of a blade, according to one embodiment. 
         FIG. 11A  is a side cross-sectional view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 11B  is a side cross-sectional view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 12A  is a schematic view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 12B  is a schematic view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 13A  is a perspective cross-sectional view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 13B  is a perspective cross-sectional view of a compliant ground block, according to one embodiment. 
         FIG. 14A  is a perspective bottom view of a compliant ground block installed in a housing of a test contactor, according to one embodiment. 
         FIG. 14B  is a perspective cross-sectional view of a compliant ground block installed in a housing of a test contactor, according to one embodiment. 
         FIG. 14C  is another perspective cross-sectional view of a compliant ground block installed in a housing of a test contactor, according to one embodiment. 
         FIG. 14D  is a perspective cross-sectional view of a compliant ground block, according to one embodiment. 
         FIG. 14E  is an exploded bottom view of a compliant ground block to be installed in a housing of a test contactor, according to one embodiment. 
         FIG. 14F  is a side view of a blade, according to one embodiment. 
         FIG. 15A  is a perspective bottom view of a compliant ground block installed in a housing of a test contactor, according to one embodiment. 
         FIG. 15B  is an exploded bottom view of a compliant ground block to be installed in a housing of a test contactor, according to one embodiment. 
         FIG. 15C  is a side view of a blade, according to one embodiment. 
         FIG. 16A  is a perspective view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 16B  is a perspective view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 16C  is a side view of a blade, according to one embodiment. 
         FIG. 17A  is a side view of a compliant ground block in an uncompressed state, according to one embodiment. 
         FIG. 17B  is a side view of a compliant ground block in a compressed state, according to one embodiment. 
         FIG. 18A  is a perspective view of a blade, according to one embodiment. 
         FIG. 18B  is a perspective view of a compliant ground block, according to one embodiment. 
         FIG. 18C  is a perspective view of a blade, according to another embodiment. 
         FIG. 19A  is a cross-sectional view of blades, according to one embodiment. 
         FIG. 19B  is a cross-sectional view of blades, according to another embodiment. 
         FIG. 19C  is a cross-sectional view of blades, according to yet another embodiment. 
         FIG. 19D  is a cross-sectional view of blades, according to yet another embodiment. 
         FIG. 20  is a cross-sectional view of a compliant ground block, according to one embodiment. 
         FIGS. 21A-21E  are side views of a blade, according to some embodiments. 
         FIG. 21F  is a perspective view of a blade, according to one embodiment. 
         FIG. 21G  is a top view of a compliant ground block, according to one embodiment. 
         FIG. 21H  is a perspective view of a compliant ground block, according to one embodiment. 
         FIG. 22A  is a side view of a compliant ground block, according to one embodiment. 
         FIG. 22B  is a perspective view of a blade pair of the compliant ground block of  FIG. 22A , according to one embodiment. 
         FIG. 22C  is a perspective view of the compliant ground block of  FIG. 22A , according to one embodiment. 
         FIG. 22D  is a cross-sectional view of the compliant ground block of  FIG. 22A , according to one embodiment. 
         FIG. 22E  is an exploded view of the compliant ground block of  FIG. 22A  and a housing for the compliant ground block, according to one embodiment. 
         FIG. 23A  is a side view of a compliant ground block, according to another embodiment. 
         FIG. 23B  is a perspective view of a blade pair of the compliant ground block of  FIG. 23A , according to another embodiment. 
         FIG. 23C  is a perspective view of the compliant ground block of  FIG. 23A , according to another embodiment. 
         FIG. 23D  is a cross-sectional view of the compliant ground block of  FIG. 23A , according to another embodiment. 
         FIG. 23E  is an exploded view of the compliant ground block of  FIG. 23A  and a housing for the compliant ground block, according to another embodiment. 
         FIG. 24A  is a side view of a compliant ground block, according to yet another embodiment. 
         FIG. 24B  is a perspective view of a blade pair of the compliant ground block of  FIG. 24A , according to yet another embodiment. 
         FIG. 24C  is a perspective view of the compliant ground block of  FIG. 24A , according to yet another embodiment. 
         FIG. 24D  is a cross-sectional view of the compliant ground block of  FIG. 24A , according to yet another embodiment. 
         FIG. 24E  is an exploded view of the compliant ground block of  FIG. 24A  and a housing for the compliant ground block, according to yet another embodiment. 
         FIG. 25A  is a side view of a compliant ground block, according to yet another embodiment. 
         FIG. 25B  is a perspective view of a blade pair of the compliant ground block of  FIG. 25A , according to yet another embodiment. 
         FIG. 25C  is a perspective view of the compliant ground block of  FIG. 25A , according to yet another embodiment. 
         FIG. 25D  is a cross-sectional view of the compliant ground block of  FIG. 25A , according to yet another embodiment. 
         FIG. 25E  is an exploded view of the compliant ground block of  FIG. 25A  and a housing for the compliant ground block, according to yet another embodiment. 
         FIG. 26A  is a side view of a compliant ground block, according to yet another embodiment. 
         FIG. 26B  is a perspective view of a blade pair of the compliant ground block of  FIG. 26A , according to yet another embodiment. 
         FIG. 26C  is a perspective view of the compliant ground block of  FIG. 26A , according to yet another embodiment. 
         FIG. 26D  is a cross-sectional view of the compliant ground block of FIG.  26 A, according to yet another embodiment. 
         FIG. 26E  is an exploded view of the compliant ground block of  FIG. 26A  and a housing for the compliant ground block, according to yet another embodiment. 
         FIG. 27A  is a side view of a compliant ground block, according to yet another embodiment. 
         FIG. 27B  is a perspective view of a blade pair of the compliant ground block of  FIG. 27A , according to yet another embodiment. 
         FIG. 27C  is a perspective view of the compliant ground block of  FIG. 27A , according to yet another embodiment. 
         FIG. 27D  is a cross-sectional view of the compliant ground block of  FIG. 27A , according to yet another embodiment. 
         FIG. 27E  is an exploded view of the compliant ground block of  FIG. 27A  and a housing for the compliant ground block, according to yet another embodiment. 
     
    
    
     Like reference numbers represent like parts throughout. 
     DETAILED DESCRIPTION 
     A test contactor (i.e., a part of a test assembly including alignment plate, socket or membrane, etc.) can often provide electrical and thermal grounding to a DUT by making metal-to-metal contact to the printed circuit board (e.g., the load board) in an oversized ground contact area. It is very important that the force exerted by the ground contact in no way damages the DUT integrated circuit package or cracks the die housed within the package. A grounding system that has compliance has advantages to a non-compliant ground block because it can accommodate test handler, handler kit, and package tolerances. It will be appreciated that the term “compliance” may refer to a property of a material of undergoing elastic deformation or change in volume when subjected to an applied force. Compliance can be equal to the reciprocal of stiffness. 
     Typically, a few of the same compliant electrical contacts used for the S&amp;P leads are used. Quite often, the limited space available in the ground area limits the number of signal contacts to be placed, thus reducing the electrical and thermal effectiveness of the ground. For example, a limited set of contact pins can be used in the ground area. Another approach is to install a solid block of metal (e.g., a solid copper insert) in the ground area, however that often does not work because of the complete or partial lack of compliance in the test system. In other words, the ground pad on the chip may make poor, inadequate or no contact with the ground conductor on the housing due to deviations from expected tolerances in chip package manufacture, temperature variations, misalignment by the insertion handler, etc. Another approach is to combine a metal block with compliant contact elements. This solves some of the problems in contactor grounding performance, however it adds a tremendous amount of cost to the contactor assembly. Another approach is to replace the metal ground block with a Z-axis conductive elastomer. The Z-axis conductive elastomer either has embedded wires or metallic particles suspended in the elastomer which provides the electrical and thermal ground contacts. The drawbacks of this approach is that these type of elastomers have very little usable compliance and easily get contaminated with debris. In some of these types of designs, a flexible metal layer may be added to improve the life. Another approach is the incorporation of a wedge-shaped metal blocks that are biased by a non-conductive elastomer. 
     Embodiments disclosed herein provide a compliant ground block for test contactors and other devices that includes, for example, a stack of plates (or blades) or other adjacent conductive elements), which in some embodiments contain an aperture that accepts an elastomer that is used as a compliant member. The aperture, in some embodiments, in the plate stack is shaped such that the compressive forces on the elastomer allow it to bulge/expand into an open cavity instead of shearing the elastomer and so that the compressive forces do not increase with deflection and make the plates immovable. 
     Embodiments disclosed herein provide a solution that addresses each of the above-mentioned problems. Embodiments disclosed herein provide a compliant ground block that is composed of simple elements, uses an elastomeric component (e.g., made of a non-conductive material), is configurable to a wide-variety of shapes and sizes, can be cleaned by existing methods without changes, is robust in a production environment, and is low-cost. In one embodiment, the compliant ground block can be composed of a stack of blades (e.g., thin contact blades made of an electrical and/or thermal conductive material or plating). In some embodiments, each blade of the blades is identical to lower manufacturing costs. In other embodiments, each blade of the blades may not be identical. Every other blade may have an inverted orientation with respect to its adjacent blade in a height/vertical/longitudinal direction of the blade or the compliant ground block. Each contact blade may have an elongated aperture near the center (e.g., below a centerline of the blade in the height direction), with the elongated aperture axis perpendicular to the axis of compliance of the ground block. In one embodiment, the contact portion of the blade may have raised teeth or protrusions that make good contact with the DUT and load board ground pads. 
       FIG. 1A  is a perspective view of a part of a test system  100  for receiving a DUT  110  for testing, according to one embodiment. 
     The test system  100  includes a test assembly  120  for a DUT (e.g., a microcircuit, etc.)  110 . The test assembly  120  includes a load board  170  that supports an alignment plate  160  having an opening or aperture  130  that precisely defines the X and Y (see the coordinate indicators X and Y, where the coordinate X is perpendicular to the coordinate Y, and the coordinate Z is perpendicular to the plane of X and Y) positioning of the DUT  110  in test assembly  120 . If the DUT  110  has orientation features, it is common practice to include cooperating features in aperture  130 . Load board  170  carries on its surface, connection pads connected to a cable  180  by Signal and Power (S&amp;P) conductors. Cable  180  connects to the electronics that perform that electrical testing of the DUT  110 . Cable  180  may be very short or even internal to the test assembly  120  if the test electronics are integrated with the test assembly  120 , or longer if the test electronics are on a separate chassis. 
     A test contact array  140  having a number of individual test contact elements precisely mirrors the terminals (see  112  in  FIG. 1B ) carried on the surface of the DUT  110 . When the DUT  110  is inserted in the aperture  130 , terminals of the DUT  110  precisely align with test contact array  140 . The test assembly  120  is designed for compatibility with a test contact array  140  incorporating the device. Test contact array  140  is carried on a contact membrane or sheet or socket  150 . Socket  150  initially includes an insulating plastic core layer with a layer of conductive copper on each surface of the core layer. The core layer and the copper layers may each be on the order of 25 microns thick. Individual test contacts in array  140  are preferably formed on and in socket  150  using well-known photolithographic and laser machining processes. Socket  50  has alignment features such as holes or edge patterns located in the area between alignment plate  160  and load board  170  that provide for precise alignment of socket  150  with corresponding projecting features on alignment plate  160 . All of the test contacts  140  are in precise alignment with the socket  150  alignment features. In this way, the test contacts of array  140  are placed in precise alignment with aperture  130 . 
       FIG. 1B  is a perspective bottom view of a DUT  110 , according to one embodiment. The DUT (e.g., a microcircuit, etc.)  110  includes a top main surface (not shown), and a bottom main surface  114  opposite to the top main surface in the Z (see the coordinate indicators X, Y, and Z in  FIG. 1A ) direction. In one embodiment, the DUT  110  can have flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN). Flat no-leads, also known as micro lead-frame (MLF) and SON (small-outline no leads), is a surface-mount technology, one of several package technologies that connect the DUT  110  to the surfaces of e.g., socket  150  or other printed circuit boards (PCBs) without through-holes. In one embodiment, flat no-lead can be a near chip scale plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands (e.g., terminals  112 ) on the package bottom provide electrical connections to the socket  150  or the PCB. Flat no-lead packages can include an exposed thermally conductive pad (e.g., the ground pad  116  in the middle of the surface  114 ) to improve heat transfer out of the DUT  110  (e.g., into the PCB). The QFN package can be similar to the quad-flat package (QFP) and a ball grid array (BGA). 
       FIG. 2A  is a side-view drawing of a portion of the test system  100  for receiving the DUT  110  for electrical testing, according to one embodiment.  FIG. 2B  is a side-view drawing of the test system  100  of  FIG. 2A , with the DUT  110  electrically engaged, according to one embodiment. 
     As shown in  FIG. 2A , the DUT  110  is placed onto the test assembly  120 , electrical testing is performed, and the DUT  110  is then removed from the test assembly  120 . Any electrical connections are made by pressing components into electrical contact with other components; there is no soldering or de-soldering at any point in the testing of the DUT  110 . The entire electrical test procedure may only last about a fraction of a second, so that rapid, accurate placement of the DUT  100  becomes important for ensuring that the test system  100  is used efficiently. The high throughput of the test assembly  120  usually requires robotic handling of the DUT  110 . In most cases, an automated mechanical system places the DUT  110  onto the test assembly  120  prior to testing, and removes the DUT  110  once testing has been completed. The handling and placement mechanism may use mechanical and optical sensors to monitor the position of the DUT  110 , and a combination of translation and rotation actuators to align and place the DUT  110  on or in the test assembly  120 . Alternatively, the DUT  110  may be placed by hand, or placed by a combination of hand-fed and automated equipment. 
     The DUT  110  typically includes signal and power terminals  112  (see also terminals  112  of  FIG. 1B ) that connect to the socket  150  or other PCBs. The terminals may be on one side of the DUT  100 , or may be on both sides of the DUT  110 . For use in the test assembly  120 , all the terminals  112  should be accessible from one side of the DUT  110 , although it will be understood that there may be one or more elements on the opposite side of the DUT  110 , or that there may be other elements and/or terminals on the opposite side that may not be tested by accessing terminals  112 . Each terminal  112  is formed as a small, pad on button side of the DUT  110  or possibly a lead protruding from the body of the DUT  110 . Prior to testing, the pad or lead  112  is attached to an electrical lead that connects internally to other leads, to other electrical components, and/or to one or more chips in the DUT. The volume and size of the pads or leads may be controlled quite precisely, and there is typically not much difficulty caused by pad-to-pad or lead-to-lead size variations or placement variations. During testing, the terminals  112  remain solid, and there is no melting or re-flowing of any solder. 
     The terminals  112  may be laid out in any suitable pattern on the surface of the DUT  110 . In some cases, the terminals  112  may be in a generally square grid, which is the origin of an expression that describes the DUT  110 , QFN, DFN, MLF or QFP for leaded parts. There may also be deviations away from a rectangular grid, including irregular spacing and geometries. It will be understood that the specific locations of the terminals may vary as needed, with corresponding locations of pads on the load board  170  and contacts on the socket  150  or housing being chosen to match those of the terminals  112 . In general, the spacing between adjacent terminals  2  is in the range of 0.25 to 1.5 mm, with the spacing being commonly referred to as a “pitch”. When viewed from the side, as in  FIG. 2A , the DUT  110  displays a line of terminals  112 , which may optionally include gaps and irregular spacing. These terminals  112  are made to be generally planar, or as planar as possible with typical manufacturing processes. In many cases, if there are chips or other elements on the DUT  110 , the protrusion of the chips is usually less than the protrusion of the terminals  112  away from the DUT  110 . 
     The test assembly  120  of  FIG. 2A  includes a load board  170 . The load board  170  includes a load board substrate  174  and circuitry that is used to test electrically the DUT  110 . Such circuitry may include driving electronics that can produce one or more AC voltages having one or more particular frequencies, and detection electronics that can sense the response of the DUT  110  to such driving voltages. The sensing may include detection of a current and/or voltage at one or more frequencies. In general, it is highly desirable that the features on the load board  170 , when mounted, are aligned with corresponding features on the DUT  110 . Typically, both the DUT  110  and the load board  170  are mechanically aligned to one or more locating features on the test assembly  120 . The load board  170  may include one or more mechanical locating features, such as fiducials or precisely-located holes and/or edges, which ensure that the load board  170  may be precisely seated on the test assembly  120 . These locating features typically ensure a lateral alignment (X, Y, see  FIG. 1A ) of the load board  170 , and/or a longitudinal alignment (Z, see  FIG. 1A ) as well. 
     In general, the load board  170  may be a relatively complex and expensive component. The housing/test assembly  120  performs many functions including protecting the contact pads  172  of the load board  170  from wear and damage. Such an additional element may be an interposer membrane (or socket)  150 . The socket  150  also mechanically aligns with the load board  170  with suitable locating features (not shown), and resides in the test assembly  120  above the load board  170 , facing the DUT  110 . The socket  150  includes a series of electrically conductive contacts  152 , which extend longitudinally outward on either side of the socket  150 . Each contact  152  may include a resilient element, such as a spring or an elastomer material, and is capable of conducting an electrical current to/from the load board  170  from/to the DUT  110  with sufficiently low resistance or impedance. Each contact  152  may be a single conductive unit, or may alternatively be formed as a combination of conductive elements. In general, each contact  152  connects one contact pad  172  on the load board  170  to one terminal  112  on the DUT  110 , although there may be testing schemes in which multiple contact pads  172  connect to a single terminal  112 , or multiple terminals  112  connect to a single contact pad  172 . For simplicity, we assume in the text and drawings that a single contact  152  connects a single pad  172  to a single terminal  112 , although it will be understood that any of the tester elements disclosed herein may be used to connect multiple contact pads  172  connect to a single terminal  112 , or multiple terminals  112  to a single contact pad  172 . 
     Typically, the socket  150  electrically connects the load board pads  172  and the bottom contact surface of the DUT  110 . Although the socket  150  may be removed and replaced relatively easily, compared with removal and replacement of the load board  170 , we consider the socket  150  to be part of the test assembly  120  for this document. During operation, the test assembly  120  includes the load board  170 , the socket  150 , and the mechanical construction that mounts them and holds them in place (not shown). Each DUT  110  is placed against the test assembly  120 , is tested electrically, and is removed from the test assembly  120 . A single socket  150  may test many DUTs  110  before it wears out, and may typically last for several thousand tests or more before requiring replacement. In general, it is desirable that replacement of the socket  150  be relatively fast and simple, so that the test assembly  120  experiences only a small amount of down time for socket replacement. In some cases, the speed of replacement for the socket  150  may even be more important than the actual cost of each socket  150 , with an increase in tester up-time resulting in a suitable cost savings during operation. 
       FIG. 2A  shows the relationship between the test assembly  120  and the DUTs  110 . When each DUT  110  is tested, it is placed into a suitable robotic handler with sufficiently accurate placement characteristics, so that a particular terminal  112  on the DUT  110  may be accurately and reliably placed (in X, Y and Z, see  FIG. 1A ) with respect to corresponding contacts  152  on the socket  150  and corresponding contact pads  172  on the load board  170 . The robotic handler (not shown) forces each DUT  110  into contact with the test assembly  120 . The magnitude of the force depends on the exact configuration of the test, including the number of terminals  112  being tested, the force to be used for each terminal, typical manufacturing and alignment tolerances, and so forth. In general, the force is applied by the mechanical handler of the tester (not shown), acting on the DUT  110 . In general, the force is generally longitudinal, and is generally parallel to a surface normal of the load board  170 . 
       FIG. 2B  shows the test assembly  120  and DUT  110  in contact, with sufficient force being applied to the DUT  110  to engage the contacts  152  and form an electrical connection  154  between each terminal  112  and its corresponding contact pad  172  on the load board  170 . As stated above, there may alternatively be testing schemes in which multiple terminals  112  connect to a single contact pad  172 , or multiple contact pads  172  connect to a single terminal  112 , but for simplicity in the drawings we assume that a single terminal  112  connects uniquely to a single contact pad  172 . 
       FIG. 3  is an exploded view of the building blocks of a test contactor  122  of a test assembly  120  for the testing of a DUT, according to one embodiment. It will be appreciated that the connection assembly such as fasteners and/or parts that mount and manipulate the various building blocks of the testing assembly are not shown. 
     The test contactor  122  includes an optional stiffener  190 , a socket (also known as membrane)  150 , an alignment plate  160 , and an optional clamping plate  195 . The stiffener  190  can provide structural support to a load board (not shown also as known as daughter board, PCB, etc., see  FIGS. 1A-2B ) to minimize deflection to ensure socket  150  contacting with the load board. The load board is used to route signals from the DUT (via the socket  150 ) to a tester (not shown) or vice versa. The tester is used to test the DUT (e.g., by sending commands/inputs to the DUT and/or by receiving data/outputs from the DUT). The load board is mounted to a test head in the tester. In the test assembly  120 , the load board is disposed between the stiffener  190  and the socket  150 . 
     The socket  150  is used to provide a pathway for inputs/outputs of the DUT to the tester (via the load board). The device alignment plate  160  is to align the DUT to the socket  150 . The alignment plate  160  is aligned and is attached to the stiffener  190  by e.g., fasteners that go through holes of the socket  150  and the load board. The alignment plate  160  has a recess/opening (e.g., in the middle of the alignment plate  150 ) with alignment features and a holder (e.g., Z direction up-stop) to hold the DUT and align the DUT to the socket  150  (so that the S&amp;P pins/pads/leads/balls/lines of the DUT are aligned with the S&amp;P pins/pads/leads/balls/lines of the socket  150 ). 
     The clamping plate  195  can be optional. The clamping plate  195  can hold the DUT firmly against the load board (via the alignment plate  160  and the socket  150 ) during testing. In one embodiment, vacuum (instead of the clamping plate  195 ) can be used as a hold down mechanism for the DUT. In another embodiment, the alignment of the DUT (by the alignment plate  160 ) can be made as flush as possible, and the DUT can be held at the corners rather than using a clamping plate. 
       FIG. 4  is a perspective view of a test assembly  120 , according to one embodiment. The test assembly  120  includes a socket  150  and an alignment plate  160 . The circled portion A of the test assembly  120  includes a housing (of the test contactor). 
       FIG. 5A  is an enlarged top view of a portion (the circled portion “A”) of the test assembly  120  of  FIG. 4 , according to one embodiment.  FIG. 5B  is an enlarged bottom view of a portion (the circled portion “A”) of the test assembly  120  of  FIG. 4 , according to one embodiment. 
     The test contactor includes a housing  220 . A plurality of S&amp;P terminals  210  is disposed on the housing  220 . The housing has an opening in e.g., a central portion of the housing, to accommodate a block  230 . In one embodiment, the block  230  is a compliant ground block. It will be appreciated that in one embodiment, the size of the opening that accommodating the block  230  matches the size of the ground pad  116  of the DUT  110  (see  FIG. 1B ). The S&amp;P terminals  210  align with the S&amp;P terminals  112  of the DUT  110  (see  FIG. 1B ). 
       FIG. 6A  is a perspective top view of a compliant ground block  230  installed in a housing  220  of a test contactor, according to one embodiment.  FIG. 6B  is a perspective bottom view of the compliant ground block  230  installed in the housing  220  of the test contactor, according to one embodiment. It will be appreciated that the housing  220  is simplified (e.g., not showing other components of the housing as shown in  FIGS. 5A and 5B ). 
     The housing  220  includes an opening  222 . As shown in  FIG. 6A , on the top surface of the housing  220 , the opening  222  may include four circumferential curve cutouts  224  at the four corners of the opening  222 . The cutouts  224  can help with preventing wear and tear caused by e.g., the sharp edges of the compliant ground block  230 . The compliant ground block  230  includes a plurality (e.g., two, at or about 20, or more for contact redundancy and for a big heat sink) of blades (or plates)  232  stacked together laterally in a thickness direction (e.g., Y direction, see  FIG. 1A ) of the blade  232 . In one embodiment, each of the blades  232  is the same as each other. A thickness of each blade is at or about 0.050 mm. A size/area of the top surface (e.g., having a rectangular or a square shape) of the compliant ground block  230  is at or about 1.1 mm 2 . As shown in  FIG. 6B , on the top surface of the housing  220 , the opening  222  may include two circumferential curve cutouts  226  at sides of the opening opposite to each other in the thickness direction of the blades  232 . The compliant ground block  230  includes an elastomer  234 . In one embodiment, the elastomer  234  has a cylindrical shape. The elastomer  234  is wedged into the housing, thus retaining the blade stack assembly (i.e., the blades  232 ). In one embodiment, the diameter of the elastomer  234  is at or about 0.4 mm. 
     It will be appreciated that the cutouts  226  is designed to facilitate the installation of the compliant ground block  230  from e.g., the bottom side of the housing  220 . It will be appreciated that on the bottom surface of the housing  220 , the opening  222  can also include two circumferential cutouts  226  at sides of the opening opposite to each other in the thickness direction of the blades  232 . In such embodiment, the cutouts  226  can be designed to facilitate the installation of the compliant ground block  230  from e.g., the top side of the housing  220  as well. In one embodiment, each blade  232  can be plated with e.g., gold, etc. In another embodiment, each blade  232  may not be plated if the metal of the blade is metallurgically suitable. 
       FIG. 7A  is an exploded view of a compliant ground block  230  to be installed in a housing  220  (showing a bottom surface of the housing) of a test contactor, according to one embodiment.  FIG. 7B  is a perspective view of a compliant ground block  230 , according to one embodiment. 
     The blades  232  form an aperture  236  at or near the middle of the blades  232 , which extends in the thickness direction of the blade  232 . The elastomer  234  is inserted through the aperture  236  and is wedged into the housing  220 , thus retaining the blades  232  in the housing  220 . As shown in  FIG. 7A , in one embodiment, the cutouts  224  and/or  226  may extend from the bottom surface of the housing  220  but not reach the top surface of the housing  220 . In another embodiment, the cutouts  226  may extend from the bottom surface of the housing  220  to the top surface of the housing  220 . 
       FIG. 8A  is a perspective cross-sectional view of a compliant ground block  230  in an uncompressed state, according to one embodiment.  FIG. 8B  is an exploded view of the compliant ground block  230  in the uncompressed state, according to one embodiment.  FIG. 8C  is an exploded view of the compliant ground block  230  in a compressed state, according to one embodiment.  FIG. 8D  is a perspective cross-sectional view of a compliant ground block  230  in the compressed state, according to one embodiment. 
       FIG. 9A  is a side view of a compliant ground block  230  in an uncompressed state, according to one embodiment.  FIG. 9B  is a side view of a compliant ground block  230  in a compressed state, according to one embodiment. 
     As shown in  FIGS. 8A and 9A , the aperture  236  is elongated in a width/transverse direction (X direction) of the blade  232  to allow for compression of the elastomer  234 . The elastomer  234  contacts the top and bottom ends of the aperture  236  in a height direction (Z direction). Cavities  238  and  240  are formed between the left and right ends of the aperture  236  in the width direction. Two blades  232  (a top  232  and a bottom  232 ) are shown in  FIGS. 9A and 9B . Each of the blades is inverted in the height direction relative to an adjacent (adjacent in the thickness direction Y) blade. For example, each blade  232  has a first end  244  and a second end  246  opposite to the first end  244  in the height direction. The first end  24  of the bottom blade  232  is opposite to the first end  244  of the top blade  232  in the height direction. The second end  246  of the bottom blade  232  is opposite to the second end (not shown, behind the bottom blade  232  in the thickness direction) of the top blade  232 . The aperture  236  is disposed at or near middle of the stacked blades  232 . It will be appreciated that for each individual blade  232 , the aperture  236  is disposed below a central line in the height direction and is closer to the second end  246  than to the first end  244 . Each blade  232  may include a plurality of protrusions  242  at the first end  244 . In one embodiment, a distance between adjacent protrusions  242  can be the same. In one embodiment, each blade can be made of any conductive material such as copper, copper alloys, nickel alloys, steels, precious metals, etc. It will be appreciated that flexibility is not a requirement with respect to the blade. Elastomer can be made of any elastic rubber-like material such as silicone, etc. In one embodiment, the elastomer may be non-conductive. 
     As shown in  FIGS. 8D and 9B , the compliant ground block  230  is in a compressed state. The top surface of the compliant ground block  230  may contact the ground pad  116  (see  FIG. 1B ) of the DUT  110 . The bottom surface of the compliant ground block  230  may contact the ground portion of the load board  170  (see  FIG. 1 ). Forces exerted from both the ground pad  116  and the ground portion of the load board  170  can compress the compliant ground block  230  by compressing the elastomer  234 . The round (in the cross-sectional side view in  FIG. 9A ) elastomer may compress perpendicularly to the compression axis (in the height direction Z) and the flow of the elastomer may move into the elongated (in the width direction X) open areas (cavities  238 ,  240 ) of the aperture  236 . One advantage of such design is that the blades  232  have some freedom to gimbal over the elastomer  234  and can accommodate angular variations in the compliant ground block  230  compression into the open areas (cavities  238 ,  240 ). See e.g.,  FIG. 20 . 
       FIG. 10A  is a side view of a blade  232 , according to one embodiment.  FIG. 10B  is a perspective view of a blade  232 , according to one embodiment. 
     As shown in  FIG. 10A , a central line C 1  is between the first end  244  and the second  246 , and has a same distance from the first end  244  and the second  246  in the height direction. A center line C 2  of the aperture  236  in the height direction is disposed below C 1  (i.e., C 2  is closer to the second end  246  than to the first end  244 ). In one embodiment, each blade  232  of the stack (the compliant ground block  230 ) can be an identical component. In another embodiment, each blade  232  of the stack (the compliant ground block  230 ) may not be identical. The first end  244  of the blade  232  includes a series of small protrusions (teeth) that are contact points to the DUT pad (e.g., ground pad) or the PCB (e.g., the load board or the socket) pad (e.g., ground pad). The second end  246  of the blade  232  may be flat. The aperture  236  is an elongated (in the width direction) hole that is roughly the same diameter as the elastomer  234 , but has a clearance cavity ( 238 ,  240 ) on either side in the width direction. The stack (the compliant ground block  230 ) is assembled by alternating the teeth up and down until a predetermined number of blades  232  make up the stack. The aperture  236  is centrally located laterally (in the width direction), but below center vertically (in the height direction)—thus resulting in the staggered up/down assembly (of the compliant ground block  230 ) and allowing for the stack compression. 
       FIG. 11A  is a side cross-sectional view of a compliant ground block  230  in an uncompressed state, according to one embodiment.  FIG. 11B  is a side cross-sectional view of a compliant ground block  230  in a compressed state, according to one embodiment. 
     Compared with the uncompressed state, the first end  244  of a blade  232  is closer to the second end  246  of an adjacent (adjacent in the thickness direction Y) blade  232  in the height direction Z. 
       FIG. 12A  is a schematic view of a compliant ground block  230  in an uncompressed state, according to one embodiment.  FIG. 12B  is a schematic view of a compliant ground block  230  in a compressed state, according to one embodiment. 
     The compliant ground block  230  shows two blades (plates)  232  and the elastomer  234 . The upper and lower blades slide up and down against each other when force is applied to compress the elastomer  234 . When being compressed, the elastomer  234  installed in the aperture  236  compresses and shears. Each blade  232  slides against the mating (adjacent) blade. Some of the elastomeric resilience is taken up by a shear-type deformation of the elastomer  234 . 
       FIG. 13A  is a perspective cross-sectional view of a compliant ground block  230  in a compressed state, according to one embodiment.  FIG. 13B  is a perspective cross-sectional view of a compliant ground block  230 , according to one embodiment. 
     As shown in  FIG. 13A , when being compressed, the elastomer  234  also slightly bulges into the cavities  250  vacated by the opposing (adjacent) blade (see the bulges  248 ) in the height direction opposite to the direction of the force applied. As shown in  FIG. 13B , a portion “A” of the compressed compliant ground block  230  is enlarged. The blades  232  show that the corners (see the radius  252 , sized about a few microns) of the blades  232  in the thickness direction are not sharp. The non-sharp corners (the radius  252 ) of the blades  232  can help reducing the shearing action of the blade  232  movement, and the distributed load of the elastomer  234  causes the elastomer  234  to squeeze into the aperture cavities ( 238 ,  240 ). 
     In a larger blade stack (e.g., the compliant ground block  230 ), the amount of shear can be greatly reduced because the load (e.g., the force applied) is distributed over the entire length of the elastomer  234 . Since the edges (in the thickness direction, see also  252 ) of the aperture  236  also have a slight radius, thus reducing the shearing action of the blade movement. The distributed load of the elastomer  234  causes the elastomer  234  to squeeze into the aperture cavities ( 238 ,  240 ). The sheer redundancy of the blades  232  can guarantee reliable electrical connection of the stack. Multiple blades  232  distribute load over elastomer  234  length, cause elastomer  234  to bulge out into open aperture cavity  250  rather than shear. Blade  232  edges (in the thickness direction) have small radius  252  that can minimize elastomer  234  cutting. 
       FIG. 14A  is a perspective bottom view of a compliant ground block  230   a  installed in a housing  220   a  of a test contactor, according to one embodiment.  FIG. 14B  is a perspective cross-sectional view of a compliant ground block  230   a  installed in a housing  220   a  of a test contactor, according to one embodiment.  FIG. 14C  is another perspective cross-sectional view of a compliant ground block  230   a  installed in a housing  220   a  of a test contactor, according to one embodiment.  FIG. 14D  is a perspective cross-sectional view of a compliant ground block  230   a , according to one embodiment.  FIG. 14E  is an exploded bottom view of a compliant ground block  230   a  to be installed in a housing  220   a  of a test contactor, according to one embodiment.  FIG. 14F  is a side view of a blade  232   a , according to one embodiment. 
     It will be appreciated that regarding  FIG. 14A , the perspective top view of the compliant ground block  230   a  installed in the housing  220   a  is the same as  FIG. 6A , where the elastomer is not visible. It will also be appreciated that unless explicitly described herein, the components, material, size, attributes, and/or properties, etc. of the compliant ground block  230   a  and/or the housing  220   a  are the same or similar to those of the compliant ground block  230  and/or the housing  220  described in other embodiments. 
     As shown in  FIGS. 14A-14C and 14E , the opening  222   a  at the bottom surface of the housing  220   a  has a size that substantially matches (or for press-fit, slightly smaller than) a size of the compliant ground block  230   a  so that the compliant ground block  230   a  can be installed or inserted from the bottom of the housing  220   a . The opening  222   b  at the top surface of the housing  220   a  has a size that is smaller than the size of the compliant ground block  230   a  to support/maintain/stop the compliant ground block  230   a . The opening  222   a  at the bottom surface of the housing  220   a  extends in the height (Z) direction but does not reach the top surface of the housing  220   a . The corners of the opening  222   a  are curved to help with preventing wear and tear caused by e.g., the sharp edges of the compliant ground block  230   a.    
       FIG. 14B  is a perspective cross-sectional view of a compliant ground block  230   a  installed in a housing  220   a , cut in the middle of the housing  220   a  along the thickness (Y) direction.  FIG. 14C  is a perspective cross-sectional view of the compliant ground block  230   a  installed in the housing  220   a , cut in the middle of the housing  220   a  along the width (X) direction. 
     The blade  232   a  has recesses (or apertures)  236   a  and  236   b  at sides of the blade  232   a  in the width (X) direction. The centerline C 1  of the blade is above the centerline C 2  of the recesses  236   a  and  236   b . There is no opening in the middle of the blade  232   a . Each blade  232   a  is inverted with respect to its adjacent blade  232   a  in the height direction. In one embodiment, the recesses  236   a  and  236   b  can have a half-circle shape. The elastomer  234   a  can have an O-ring or other ring shape and can be stretched around blades  232   a  for retention. The elastomer  234   a  can snap over the concave semicircular apertures  236   a  and  236   b  on both sides of the blade  232   a.    
       FIG. 15A  is a perspective bottom view of a compliant ground block  230   b  installed in a housing  220   b  of a test contactor, according to one embodiment.  FIG. 15B  is an exploded bottom view of a compliant ground block  230   b  to be installed in a housing  220   b  of a test contactor, according to one embodiment.  FIG. 15C  is a side view of a blade  232   a , according to one embodiment. 
     It will be appreciated that regarding  FIG. 15A , the perspective top view of the compliant ground block  230   b  installed in the housing  220   b  is the same as  FIG. 6A , where the elastomer is not visible. It will also be appreciated that unless explicitly described herein, the components, material, size, attributes, and/or properties, etc. of the compliant ground block  230   b  and/or the housing  220   b  are the same or similar to those of the compliant ground block  230  and/or the housing  220  described in other embodiments. In one embodiment,  FIG. 15C  is the same as  FIG. 14F . 
     Compared with  FIGS. 14A-14E , in  FIGS. 15A and 15B , two individual elastomer strips  234   b  are used instead of an O-ring elastomer  234   a . Each of the elastomers  234   b  may have a cylindrical shape disposed on each side of the blades  232   a  in the width (X) direction. Each of the elastomers  234   b  extends in the thickness (Y) direction. A length of each elastomer  234   b  may be slightly greater than a thickness of the stacked blades  232   a . The stacked blades  232   a  and each blade  232   a  in in  FIGS. 15A and 15B  may be the same as the stacked blades  232   a  and each blade  232   a  respectively in  FIGS. 14A-14E . 
     In  FIGS. 15A and 15B , the opening  222   c  at the bottom surface of the housing  220   b  has an H-shape retention cut-outs, instead of the O-ring shape of  222   a . The opening  222   c  has a size that substantially matches (or for press-fit, slightly smaller than) a size of the compliant ground block  230   b  so that the compliant ground block  230   b  can be installed or inserted from the bottom of the housing  220   b . The opening  222   b  at the top surface of the housing  220   b  has a size that is smaller than the size of the compliant ground block  230   b  to support/maintain/stop the compliant ground block  230   b . The opening  222   b  at the bottom surface of the housing  220   b  extends in the height (Z) direction but does not reach the top surface of the housing  220   b . The corners of the opening  222   b  are curved to help with preventing wear and tear caused by e.g., the sharp edges of the compliant ground block  230   b.    
       FIG. 16A  is a perspective view of a compliant ground block  230   c  in an uncompressed state, according to one embodiment.  FIG. 16B  is a perspective view of the compliant ground block  230   c  in a compressed state, according to one embodiment.  FIG. 16C  is a side view of a blade  232   b , according to one embodiment. 
     It will be appreciated that some DUT ground pad and/or PCB (load board or socket) ground pad surfaces may be very delicate. The compliant ground block  230   c  can help to eliminate the teeth or protrusions in each blade and can provide a gentler touch. The contact edge (e.g., the first end  244   a ) of the blade  232   b  does not include the teeth or protrusions as in the blade  232  or  232   a . The compliant ground block  230   c  is designed for customer devices and/or PCB ground pads with very fragile surfaces. It will be appreciated that the flat blade  232   b  can be combined with a tooth-blade  232  or  232   a.    
     As shown in  FIG. 16C , the blade  232   b  is the same as the blade  232  of  FIG. 10A , except that the first end  244   a  of the blade  232   b  is flat (without the protrusions  242 ). Same as the blade  232  of  FIG. 10A , two or four ends/corners of the blade  232   b  are slightly trimmed to remove the sharp corners. 
       FIG. 17A  is a side view of a compliant ground block  230   d  in an uncompressed state, according to one embodiment.  FIG. 17B  is a side view of the compliant ground block  230   d  in a compressed state, according to one embodiment. 
     It will be appreciated that  FIGS. 17A and 17B  are the same as  FIGS. 9A and 9B , except that each blade  232   c  has two or more apertures  236   c . Each aperture  236   c  accommodate an elastomer  234   c . It will also be appreciated that large DUT or PCB ground pads can be accommodated by a compliant ground block  230   d  that uses two or more elastomers. Such embodiment can provide additional stability. The blade  232   c  can be divided equally in the width (X) direction based on the number of the apertures  236   c . Each aperture  236   c  is centrally located laterally (in the width direction) in each division of the blade  232   c , but below center vertically (in the height direction). For example, as shown in  FIGS. 17A and 17B , each blade  232   c  has two apertures  236   c . The blade  232   c  can be divided into two parts along the width direction. Each aperture  236   c  is centrally located laterally (in the width direction) in each part of the blade  232   c , but below center vertically (in the height direction) of that part. 
       FIG. 18A  is a perspective view of a blade  232   d , according to one embodiment.  FIG. 18B  is a perspective view of a compliant ground block  230   e , according to one embodiment.  FIG. 18C  is a perspective view of a blade  232   e , according to another embodiment. 
     It will be appreciated that the blades  232   d  and/or  232   e  are the same as other blades such as  232  and  232   a - 232   c , except that the blades  232   d  and/or  232   e  include bumps  260 . The blade  232   d  include one or more bumps  260 . It will be appreciated that bump(s) may be part of the same material as the blade and are fabricated in the same process as the blade. The thickness of the bump(s) may be generally at or less than 10% of the thickness of the blade. As shown in  FIG. 18A , the blade  232   d  includes four bumps  260  near four corners of the blade  232   d  on a main side surface of the blade. Each bump  260  has a circular or any other suitable shape and extends (or is raised) in the thickness direction. 
     The blade  232   e  has one or more slight flexible cantilever member  270 . A U-shape opening  280  separates the cantilever member  270  from other part of the blade  232   e . The bump is disposed on or near the tip of the cantilever member  270 . As shown in  FIG. 18C , the blade  232   e  include two or more cantilever members  270 , each cantilever member  270  is disposed between an end of the aperture and an edge of the blade  232   e.    
     The bump(s)  260  can ensure electrical reliability (e.g., electrical connection reliability) from blade to blade, and focus the contact points to specific spots to guarantee reliable connection and provide some compliance in the blades stack-up. 
     It will be appreciated that the bumps can help to maintain good electrical contact among blades flat blades an slide up and down when compressed or uncompressed, and the biasing of the blades to each other is critical. If there are some debris between the two blades, the debris can decrease the electrical conductivity between the two blades. The bumps can help to improve the electrical connection between the blades on the PCB (load board or socket) side or on the DUT side. The bumps can put high stress points through the blades. When the bumps are on the tip of the cantilever, a flexible feature can be achieved. 
       FIG. 19A  is a cross-sectional view of blades  232   f , according to one embodiment.  FIG. 19B  is a cross-sectional view of blades  232   g , according to another embodiment.  FIG. 19C  is a cross-sectional view of blades  232   h , according to yet another embodiment.  FIG. 19D  is a cross-sectional view of blades  232   i , according to yet another embodiment. 
     Curved or nested blades can help to improve the electrical connection between blades. The blades can be flexible members, allowing for thickness compliance. The blades can be fabricated with a curve (e.g., in a few micron scale) in the height Z direction. When the curved blades are stacked, higher force concentrations can improve the electrical contact pressure and lower contact resistance. The blades (i.e., the shapes of a blade and the adjacent blade) can be nested in various concave and/or convex configurations, such as concave-convex nesting  232   f , concave-concave nesting  232   g , and convex-convex nesting  232   h . The curves (convex, concave, etc.) can cause higher contact points and higher contact pressure from blade to blade. The blades can be tilted or angled blades  232   i . Slightly angling the blades  232   i  can naturally bias (e.g., creating a normal force between the blades) each blade against the mating/adjacent plate over the compression cycle. The angle of the blade can vary from at or about 2 degrees to at or about 5 degrees from vertical. 
       FIG. 20  is a cross-sectional view of a compliant ground block  230 , according to one embodiment.  FIG. 20  shows a DUT  110  on top of a compliant ground block  230 , where the DUT  110  is not presented perfectly flat. Such embodiment allows for a gimbaling motion—allowing for ground pads that are not flat.  FIG. 20  illustrates that not only is the blade stack (i.e., the compliant ground block  230 ) compliant in the Z direction, but the compliant ground block  230  allows for compliance if a DUT  110  is presented into the ground block at a slight angle, allowing for imperfections in the part handling. 
       FIGS. 21A-21E  are side views of a blade  232 , according to some embodiments. It will be appreciated that the blade  232  of  FIGS. 21A-21E  can be the same as or similar to the blade  232  of  FIGS. 10A and 10B  (including the centerlines C 1  and C 2  as shown in  FIG. 10A ), except for the differences explicitly described hereinafter. 
     In an embodiment, the blade  232  can include a radius  241 A at one side of the blade  232 . The blade  232  can also include a radius  241 B at the other side of the blade  232  opposite to the one side of the blade  232  in the width/transverse direction (X direction). The radius ( 241 A and/or  241 B) can extend from the top end  244  of the blade  232  to the bottom end  246  of the blade  232 . It will be appreciated that the radius ( 241 A and/or  241 B) can provide improved assembly ease and allow blades  232  to tip and/or rock without catching on the housing  220 . 
     In an embodiment, the blade  232  can include chamfer  243  at one or more of the four corners of the blade  232 . The chamfer  243  can extend from the side ( 241 A or  241 B) of the blade  232  to the end ( 244  or  246 ) of the blade  232 . It will be appreciated that the corner chamfer(s)  243  can provide improved assembly ease. In an embodiment, compared with the protrusion(s)  242  of  FIGS. 10A and 10B , the protrusion(s) or tip(s)  242  in  FIGS. 24A and 24C-24E  can be larger and can provide increased life and better wear conditions. It will be appreciated that in an embodiment (see  FIG. 21B ), the blade  232  can have a flat top end  244  without any protrusion  242  for low inductance and/or high gain applications. 
     In some embodiments, compared with the aperture  236  in  FIGS. 10A and 10B , the apertures  236 D- 236 F in  FIGS. 21A-21E  can have an increased size and can make room for a larger elastomer and provide more compliance. In some embodiments, the blade  232  can have an elliptical aperture  236 D, a rectangular aperture  236 E for increased compliance compared with the elliptical aperture, and/or an “X” shaped aperture  236 F for increased compliance and increased contact forces compared with the elliptical aperture. 
     In an embodiment, the blade  232  can include one or more relief channels  245 . The relief channel  245  can be disposed at a position (e.g., between the protrusions  242 ) between the aperture (e.g.,  236 D- 236 F) and a side ( 241 A or  241 B) in the X direction. The relief channel  245  can extend from the top end  244  of the blade  232  to the bottom end  246  of the blade  232  in the height direction (Z direction). The relief channel  245  can be recessed from the main surface of the blade  232  in the thickness direction (Y direction) of the blade  232 . The relief channel  245  can include a breakoff tab  245 A at an end of the relief channel  245  near the bottom end  246 . Curved (e.g., in the Z direction) recesses can be disposed at one or more of the two sides of the breakoff tab  245 A in the X direction. It will be appreciated that the relief channel(s)  245  can reduce wear from the breakoff tab(s)  245 A that may diminish life, and can add clearance that prevents wear and corrosion so that the blades  232  can meet the life specifications at a desired temperature. 
     In an embodiment, the blade  232  can include a notch (or opening)  237  extending from the bottom end  246  of the blade to the aperture ( 236 D- 236 F). It will be appreciated that the notch  237  can have a trapezoid shape with a base at the bottom being longer than the base at the top of the notch  237 . One or more or the bases of the notch  237  may have a length less than the length of the aperture ( 236 D- 236 F) in the X direction. Notch  237  may be any discontinuity in the aperture which allows for insertion of the elastomer. The notch or gap  237  preferably provides a one way opening which allows and elastomer to be received therein but inhibits it removal, primarily to having a larger peripheral gap and relative to the (smaller) inner gap. This can be accomplished with a tapering of the gap from external to internal. The notch is preferably in the bottom wall, but may be an intrusion in to any wall. It will also be appreciated that the notch  237  can aid in elastomer assembly in production or for field serviceability. 
     In some applications, surface(s) of the terminals/ground-pad of the DUT may be plated/coated with (or may be made of) e.g., gold, nickel-palladium-gold, matte tin, or the like. In the compliant ground block, the blade (that is configured to contact the DUT) may be plated/coated with (or may be made of) gold, palladium, or the like. For matte tin DUT terminals/ground-pad, the debris (matte tin, generated from the terminals/ground-pad) may stick onto the tips/protrusions of the DUT contacting blade when e.g., the DUT contacting blade is plated with (or made of) gold, which may increase the resistance and/or reduce the performance of the compliant ground block. In an embodiment, for matte tin DUT terminals/ground-pad, the DUT contacting blade being plated with (or made of) palladium can make the debris less sticky and can decrease the resistance and/or increase the performance of the compliant ground block. That is, using a palladium (plating or material) on at least the blade(s) contacting the DUT can reduce the amount of matte tin debris that sticks to the compliant ground block and improve the performance of the compliant ground block. The blade(s) that is configured to contact the load board can be plated with (or made of) palladium as well for the same reason or with/of gold for cost consideration. 
     Embodiments disclosed herein can also provide scrubbing action (or scrubbing motion, scrubbing effect, scrubbing affect, or the like) so that the DUT contacting blade(s) can slide on the surface(s) of the terminals/ground-pad of the DUT, provide self-cleaning of the debris (e.g., matte tin debris or the like), and/or knock off the debris. 
       FIG. 22A  is a side view of a compliant ground block  301 .  FIG. 22B  is a perspective view of a blade pair ( 310 ,  330 ) of the compliant ground block  301  of  FIG. 22A .  FIG. 22C  is a perspective view of the compliant ground block  301  of  FIG. 22A .  FIG. 22D  is a cross-sectional view of the compliant ground block  301  of  FIG. 22A .  FIG. 22E  is an exploded view of the compliant ground block  301  of  FIG. 22A  and a housing  401  for the compliant ground block  301 . 
     As shown in  FIGS. 22A-22E , the compliant ground block  301  includes a plurality of electrically conductive blade pairs. The material, arrangement, and/or disposition of the blade pairs are the same as the blades or blade pairs described herein, except for the differences explicitly disclosed below. The plurality of blade pairs are disposed in a side by side (in Y direction or thickness direction) generally parallel relationship. Blades in the plurality of blade pairs are configured to be longitudinally/vertically (Z direction, from the DUT to the load board) slidable with respect to each other. 
     Each blade pair includes a first blade  310 , a second blade  330 , and a single elastomer  350  configured to retain the plurality of blade pairs. The material, arrangement (including e.g., interaction with cavities  238  and  240  of  FIG. 9A ), and/or disposition of the elastomer  350  are the same as the elastomer(s) described herein, except for the differences explicitly disclosed below. The first blade  310  is configured to contact the DUT (e.g., the ground pad/terminal), and the second blade  330  is configured to contact the load board (e.g., the ground pad/terminal). 
     The blade  310  includes a plurality of protrusions or tips  316  at an end or upper edge of the blade  310  that is configured to contact the DUT. The blade  310  may also include gaps such as flat surface(s)  318  between the adjacent protrusions  316 . In an embodiment, all the flat surfaces  318  extend along a same line. Protrusions  316  are preferably spaced apart along at least the upper edge of the blade where it will engage a DUT contact pad. 
     The blade  310  further includes sides  312  and  314 . In an embodiment, when the compliant ground block  301  is assembled and in a free state (no force from either the DUT or from the load board is applied to the compliant ground block  301 , see  FIG. 22A ), the sides  312  and  314  extend in the Z direction, and the surfaces  318  extend at an angle with respect to the X direction (horizontal direction, transverse direction), so that the tip(s) at or towards the side  312  is disposed higher (closer to the DUT) than the tip(s)  316  at or towards the side  314 . The blade  310  also includes a hinge (or hinge point)  320  protruding from the side  314 . In an embodiment, the hinge  320  can be retained/fixed on the neighboring blade  330  or received within a recess in the housing so that the blade can deflect circumferentially in response to engagement with the DUT pad. In another embodiment, or the hinge  320  can be retained/fixed with in the housing  401  (e.g., into a recess of the housing) for the compliant ground block  301 . 
     The blade  310  may include a curved edge  322  that is configured to be tangent to a portion of a periphery of the elastomer  350 . The blade  310  may also include a straight edge portion  324  extending and transitioning from an end of the curved edge  322  roughly tangent to the elastomer outer surface. 
     The blade  330  includes an aperture  334  for the elastomer  350  to pass through in the Y direction. The aperture  334  is a through aperture (in Y direction) and is contained entirely in the blade  330 . The blade  330  also includes sides  344  and  346 , a top end  332 , and radius  340  and  342  at the top corners of the blade  330 . In an embodiment, the end  332  is has a flat surface extending in the X direction. At the bottom end, the blade  330  includes a plurality of protrusions or tips  336  similar to tips  316 . The blade  330  also includes surface(s)  338  (e.g., flat surfaces, curved surfaces, or the like) between the adjacent protrusions  336 . 
     During operation, the DUT may come down, making contact with and/or pressing the higher tip(s)  316  at or near the side  312 . The blade  310  is configured to swing or rotate about the hinge  320  (so that all tips  316  are at a same level in the X direction) when e.g., pressed down by the DUT, causing a scrubbing action where the tips translate somewhat across the face of the DUT pad. When the DUT is removed or released, the elastomer  350  can provide tension and rebound the blade  310 , causing a scrubbing action. Edge  326  extends from the hinge point  320  to the curved edge  322 . It is shown here as a straight edge but may follow other paths and may engage a stop (not shown) to limit downward movement of blade  310 . 
     It will be appreciated that when the blade  310  is fully pressed by the DUT (or when the compliant ground block  301  is in the free state), the end  332  of the blade  330  is at or below the tip(s)  316  of the blade  310  so that only blade  310  is contacting the DUT, and a bottom of the blade  310  is at or above the tips  336  of the blade  330  so that only the blade  330  is contacting the load board. 
     The housing  401  includes an enclosure  440 , a slot  450  for the elastomer  350 , a slot  410  for the blade pairs ( 310 ,  330 ), and an opening  420  so that the compliant ground block  301  can contact the load board when it is accommodated in the housing  401 . The opening of the housing  401  (so that the compliant ground block  301  can contact the DUT when it is accommodated in the housing  401 ) is not shown. 
       FIGS. 23A-23E  are identical to  FIGS. 22A-22E , respectively, except for the difference(s) described below between the first blade  310 A of the compliant ground block  302  in  FIGS. 23A-23E  and the first blade  310  in  FIGS. 22A-22E . The blade  310 A is identical to the blade  310 , except that the surface/trough  319  of the blade  310 A is a curved surface and the surface/trough  318  of the blade  310  is a flat surface. In an embodiment, all the curved surfaces  319  extend along a same curved line. This curvature is preferably an arc interrupted by tips/peaks  316 . It will be appreciated that the curved surface(s)  319  can provide a better DUT contact than non-curved surface(s). Trough  318  may be used to receive debris which may fall off the DUT pad during scraping action. 
       FIG. 24A  is a side view of a compliant ground block  501 .  FIG. 24B  is a perspective view of a blade pair ( 510 ,  530 ) of the compliant ground block  501  of  FIG. 24A .  FIG. 24C  is a perspective view of the compliant ground block  501  of  FIG. 24A .  FIG. 24D  is a cross-sectional view of the compliant ground block  501  of  FIG. 24A .  FIG. 24E  is an exploded view of the compliant ground block  501  of  FIG. 24A  and a housing  601  for the compliant ground block  501 . This embodiment differs from the previous primarily in that the hinge is another biasing elastomer. 
     As shown in  FIGS. 24A-24E , the compliant ground block  501  includes a plurality of electrically conductive blade pairs. The material, arrangement, and/or disposition of the blade pairs are the same as the blades or blade pairs described herein, except for the differences explicitly disclosed below. The plurality of blade pairs are disposed in a side by side (in Y direction or thickness direction) generally parallel relationship. Blades in the plurality of blade pairs are configured to be longitudinally/vertically (Z direction, from the DUT to the load board) slidable with respect to each other. 
     Each blade pair includes a first blade  510 , a second blade  530 , and two elastomers ( 550 A,  550 B) configured to retain the plurality of blade pairs. The material, arrangement, and/or disposition of the elastomers  550 A,  550 B are the same as the elastomer(s) described herein, except for the differences explicitly disclosed below. The first blade  510  is configured to contact the DUT (e.g., the ground pad/terminal), and the second blade  530  is configured to contact the load board (e.g., the ground pad/terminal). 
     The blade  310  includes a plurality of protrusions or tips  516  at an end of the blade  510  that is configured to contact the DUT. The blade  510  also includes flat surface(s)  518  between the adjacent protrusions  516 . In an embodiment, all the flat surfaces  518  extend along a same line. In the alternative, the blat surfaces  518  may be arcuate in the same way as they are in  FIG. 23B . 
     The blade  510  further includes sides  512  and  514 . In an embodiment, when the compliant ground block  501  is assembled and in a free state (no force from either the DUT or from the load board is applied to the compliant ground block  501 , see  FIG. 24A ), the sides  512  and  514  extend in the Z direction, and the surfaces  518  extend at an angle with respect to the X direction (horizontal direction, transverse direction), so that the tip(s) at or towards the side  512  is disposed higher (closer to the DUT) than the tip(s)  516  at or towards the side  514 . 
     The blade  510  includes a curved edge or recess  524  on side  514  that is configured to be tangent to a portion of a periphery of the elastomer  550 A, and a curved edge or recess  522  on side  512  that is configured to be tangent to a portion of a periphery of the elastomer  550 B. In a free state or being pressed by the DUT, the recess  522  is disposed below the recess  524  in the X direction. 
     The blade  530  includes sides  543  and  545 , a top end  532 , and radius  540  and  542  at the top corners of the blade  530 . In an embodiment, the end  532  is has a flat surface extending in the X direction. At the bottom end, the blade  530  includes a plurality of protrusions or tips  536 . The blade  530  also includes surface(s)  538  (e.g., flat surfaces, curved surfaces, or the like) between the adjacent protrusions  536 . 
     The blade  530  also includes an elongated recess with a curved edge or recess  544  on side  545  that is configured to be tangent to a portion of a periphery of the elastomer  550 B, and a curved edge or recess  546  on side  543  that is configured to be tangent to a portion of a periphery of the elastomer  550 A. In a free state or being pressed by the DUT, the recess  544  is disposed below the recess  546  in the X direction. The elastomer  550 A is configured to be biased into the recesses  524  and  546 , and the elastomer  550 B is configured to be biased into the recesses  522  and  544 . 
     It will be appreciated that in blade  530 , if the side  545  extends in its original direction, the elastomer  550 B may be entirely enclosed by the side  545  and the recess  544 . For recesses  522 ,  524 , and  546 , if the corresponding side extends in its original direction, the corresponding elastomer is partially (not entirely) enclosed by the corresponding side and the corresponding recess. 
     In an embodiment, the elastomers ( 550 A,  550 B) can have the same durometers. In another embodiment, the elastomers ( 550 A,  550 B) can have different durometers to make the blade  510  swing/rotate more (e.g.,  550 A has a softer durometer than  550 B). It will be appreciated that having an elastomer on the short or hinging side  514  of the blade  510  can provide the blade  510  more freedom to move. If the elastomer at the rebounding side  512  has a softer durometer, the blade can move further. In fact, the durometers of all elastomers can vary stepwise or segment-wise along its longitudinal extent, or continuously varied, according to user needs. 
     During operation, the DUT may come down, making contact with and/or pressing the higher tip(s)  516  at or near the side  512 , and the whole blade  510  may come down as a result from the top side first, creating a scrubbing action as the tip(s)  516  slides along and the lower tip(s)  516  makes contact with the DUT one after the other. As the blade  510  rotates, the tips  516  may scrub along the ground pad of the DUT causing the scrubbing effect (for both rotation and lateral movement). That is, the blade  510  is configured to swing or rotate (e.g., due to its shape) about an axis (not shown) (so that all tips  516  are at a same level in the X direction) when e.g., pressed down by the DUT, causing a scrubbing action. When the DUT is removed or released, the elastomers  550 A and  550 B can provide tension and rebound the blade  510 , causing a scrubbing action. 
     It will be appreciated that when the blade  510  is fully pressed by the DUT (or when the compliant ground block  501  is in the free state), the end  532  of the blade  530  is at or below the tip(s)  516  of the blade  510  so that only blade  510  is contacting the DUT, and a bottom  526  of the blade  510  is at or above the tips  536  of the blade  530  so that only the blade  530  is contacting the load board. Blade  510  also differs from blade  310 A in there is an accurate extension that partially surrounds elastomer  550 B. Elastomer  550 B is surrounded roughly halfway around by this extension. 
     The housing  601  includes an enclosure  640 , a slot  650 A for the elastomer  550 A, a slot  650 B for the elastomer  550 B, a slot  610  for the blade pairs ( 610 ,  630 ), and an opening  620  so that the compliant ground block  501  can contact the load board when it is accommodated in the housing  601 . The opening of the housing  601  (so that the compliant ground block  501  can contact the DUT when it is accommodated in the housing  601 ) is not shown. 
       FIGS. 25A-25E  are identical to  FIGS. 24A-24E , respectively, except for the difference(s) described below between the first blade  510 A of the compliant ground block  502  in  FIGS. 25A-25E  and the first blade  510  in  FIGS. 24A-24E . The blade  510 A is identical to the blade  510 , except that the surface  519  of the blade  510 A is a curved surface and the surface  518  of the blade  510  is a flat surface. In an embodiment, all the curved surfaces  519  extend along a same curved line. It will be appreciated that the curved surface(s)  519  can provide a better DUT contact than non-curved surface(s). 
       FIG. 26A  is a side view of a compliant ground block  700 .  FIG. 26B  is a perspective view of a blade pair ( 710 ,  730 ) of the compliant ground block  700  of  FIG. 26A .  FIG. 26C  is a perspective view of the compliant ground block  700  of  FIG. 26A .  FIG. 26D  is a cross-sectional view of the compliant ground block  700  of  FIG. 26A .  FIG. 26E  is an exploded view of the compliant ground block  700  of  FIG. 26A  and a housing  701  for the compliant ground block  700 . 
     As shown in  FIGS. 26A-26E , the compliant ground block  700  includes a plurality of electrically conductive blade pairs. The material, arrangement, and/or disposition of the blade pairs are the same as the blades or blade pairs described herein, except for the differences explicitly disclosed below. The plurality of blade pairs are disposed in a side by side (in Y direction or thickness direction) generally parallel relationship. Blades in the plurality of blade pairs are configured to be longitudinally/vertically (Z direction, from the DUT to the load board) slidable with respect to each other. 
     Each blade pair includes a first blade  710 , a second blade  730 , and a single elastomer  750  configured to retain the plurality of blade pairs. The material, arrangement, and/or disposition of the elastomer  750  are the same as the elastomer(s) described herein, except for the differences explicitly disclosed below. The first blade  710  is configured to contact the DUT (e.g., the ground pad/terminal), and the second blade  730  is configured to contact the load board (e.g., the ground pad/terminal). 
     The blade  710  includes a plurality of protrusions or tips  716  at an end of the blade  710  that is configured to contact the DUT. The blade  710  also includes flat surface(s)  718  between the adjacent protrusions  716 . In an embodiment, all the flat surfaces  718  extend along a same line. In another embodiment, instead of flat surface(s)  718 , there can be curved surface(s) between the adjacent protrusions  716 . All the curved surfaces can extend along a same curved line. It will be appreciated that the curved surface(s) can provide a better DUT contact than non-curved surface(s). 
     The blade  710  further includes sides  712  and  714 . In an embodiment, when the compliant ground block  700  is assembled and in a free state (no force from either the DUT or from the load board is applied to the compliant ground block  700 , see  FIG. 26A ), the sides  712  and  714  extend in the Z direction, the surfaces  718  extend in the X direction (horizontal direction, transverse direction), and all tips  716  are at a same level in the X direction. 
     The blade  710  includes a curved edge  724  that is configured to be tangent to a portion of a periphery of the elastomer  750 . The blade  710  also includes a straight edge  725  extending from an end of the curved edge  724 . The blade  710  further includes a sliding edge  722  extending from the side  712  to the bottom end  726  of the blade  710 . 
     The blade  730  includes a recess  748  (on side  746 ) that is configured to be tangent to a portion of a periphery of the elastomer  750 . The elastomer  750  is configured to be biased into the recess  748  and the curved edge  724 . The blade  730  also includes sides  744  and  746 , a top end  732 , and radius  740  and  742  at the top corners of the blade  730 . In an embodiment, the end  732  is has a flat surface extending in the X direction. At the bottom end, the blade  730  includes a plurality of protrusions or tips  736 . The blade  730  also includes surface(s)  738  (e.g., flat surfaces, curved surfaces, or the like) between the adjacent protrusions  736 . 
     In an embodiment, the blade  730  includes a ramp preferably having an outwardly protruding ledge  734  partitioning the second blade into a first portion  733  and a second portion  735  along the ramp  734 . A thickness of the first portion  733  is greater than a thickness of the second portion  735  extends from a point at or near the radius  740  to a point at or near a middle of the bottom end of blade  730 . The ramp  734  is configured to support the sliding edge  722 . A thickness of the first portion  733  is greater than a thickness of the second portion  735  so that the sliding edge  722  can slide along the ramp  734  when the blade  710  is pressed by the DUT. In an embodiment, the thickness of the first portion  733  is the thickness of the second portion  735  plus a thickness of the blade  710 . 
     In another embodiment, the housing  701  includes a support structure (not shown) to support the sliding edge  722  so that the sliding edge  722  can slide along the support structure. 
     During operation, the DUT may come down, making contact with and/or pressing and/or pushing down on the tip(s)  716  of blade  710 . The blade  710  is configured to slide along/down the ramp  734  (or along/down the support structure of the housing  701 ) and push against the elastomer  750  (one side of the elastomer  750  holding in the housing  701  and another side holding in the neighboring blade  730 ) to retain tension when e.g., pressed down by the DUT, causing a scrubbing action. When the DUT is removed or released, the elastomer  750  can provide tension and rebound the blade  710  so that the blade  710  slides/returns back/up to its original position in a free state, causing a scrubbing action. 
     It will be appreciated that when the blade  710  is fully pressed by the DUT (or when the compliant ground block  700  is in the free state), the end  732  of the blade  730  is at or below the tip(s)  716  of the blade  710  so that only blade  710  is contacting the DUT, and a bottom  726  of the blade  710  is at or above the tips  736  of the blade  730  so that only the blade  730  is contacting the load board. 
     The housing  701  includes an enclosure  704 , a slot  705  for the elastomer  750 , a slot  703  for the blade pairs ( 710 ,  730 ), and an opening  702  so that the compliant ground block  700  can contact the load board when it is accommodated in the housing  701 . The opening of the housing  701  (so that the compliant ground block  700  can contact the DUT when it is accommodated in the housing  701 ) is not shown. 
       FIG. 27A  is a side view of a compliant ground block  800 .  FIG. 27B  is a perspective view of a blade pair ( 810 A and  810 B,  830 ) of the compliant ground block  800  of  FIG. 27A .  FIG. 27C  is a perspective view of the compliant ground block  800  of  FIG. 27A .  FIG. 27D  is a cross-sectional view of the compliant ground block  800  of  FIG. 27A .  FIG. 27E  is an exploded view of the compliant ground block  800  of  FIG. 27A  and a housing  801  for the compliant ground block  800 . 
     As shown in  FIGS. 27A-27E , the compliant ground block  800  includes a plurality of electrically conductive blade pairs. The material, arrangement, and/or disposition of the blade pairs are the same as the blades or blade pairs described herein, except for the differences explicitly disclosed below. The plurality of blade pairs are disposed in a side by side (in Y direction or thickness direction) generally parallel relationship. Blades in the plurality of blade pairs are configured to be longitudinally/vertically (Z direction, from the DUT to the load board) slidable with respect to each other. 
     Each blade pair includes a first blade assembly ( 810 A,  810 B), a second blade  830 , and two elastomers ( 850 A,  850 B) and an optional elastomer  850 C configured to retain the plurality of blade pairs. The material, arrangement (including e.g., interaction with cavities  238  and  240  of  FIG. 9A ), and/or disposition of the elastomers ( 850 A,  850 B,  850 C) are the same as the elastomer(s) described herein, except for the differences explicitly disclosed below. The blade assembly ( 810 A,  810 B) is configured to contact the DUT (e.g., the ground pad/terminal), and the second blade  830  is configured to contact the load board (e.g., the ground pad/terminal). 
     In an embodiment, the blade assembly includes a first portion  810 A and a second portion  810 B that mirror each other in the Z direction. 
     The portion  810 A includes two or more protrusions or tips  816  at an end of the portion  810 A that is configured to contact the DUT. The portion  810 A also includes flat surface(s)  818  between the adjacent protrusions  816 . In an embodiment, all the flat surfaces  818  extend along a same line. In another embodiment, instead of flat surface(s)  818 , there can be curved surface(s) between the adjacent protrusions  816 . All the curved surfaces can extend along a same curved line. It will be appreciated that the curved surface(s) can provide a better DUT contact than non-curved surface(s). 
     The portion  810 A further includes sides  812  and  814 . In an embodiment, when the compliant ground block  800  is assembled and in a free state (no force from either the DUT or from the load board is applied to the compliant ground block  800 , see  FIG. 27A ), the side  814  extends in the Z direction, and the surface(s)  818  extends at an angle with respect to the X direction (horizontal direction, transverse direction), so that the tip(s)  816  at or towards the side  814  is disposed higher (closer to the DUT) than the tip(s)  816  at or towards the side  812 . 
     The portion  810 A includes an edge  820  extending from an end of side  814  toward a bottom  822  of the portion  810 A. The edge  820  and the side  812  intersect at or around the bottom  822 . 
     The portion  810 B includes two or more protrusions or tips  816  at an end of the portion  810 B that is configured to contact the DUT. The portion  810 B also includes flat surface(s)  818  between the adjacent protrusions  816 . In an embodiment, all the flat surfaces  818  extend along a same line. In another embodiment, instead of flat surface(s)  818 , there can be curved surface(s) between the adjacent protrusions  816 . All the curved surfaces can extend along a same curved line. It will be appreciated that the curved surface(s) can provide a better DUT contact than non-curved surface(s). 
     The portion  810 B further includes sides  812  and  814 . In an embodiment, when the compliant ground block  800  is assembled and in a free state (no force from either the DUT or from the load board is applied to the compliant ground block  800 , see  FIG. 27A ), the side  814  extends in the Z direction, and the surface(s)  818  extends at an angle with respect to the X direction (horizontal direction, transverse direction), so that the tip(s)  816  at or towards the side  814  is disposed higher (closer to the DUT) than the tip(s)  816  at or towards the side  812 . 
     The portion  810 B includes an edge  820  extending from an end of side  814  toward a bottom  822  of the portion  810 A. The edge  820  and the side  812  intersect at or around the bottom  822 . 
     The portion  810 A mirrors the portion  810 B in the Z direction. The portion  810 A and the portion  810 B define or form a “V” shape recess. Hinge or pivot points (not show) is at or around the bottom(s)  822  so that the portion  810 A and the portion  810 B can rotate about the hinges. 
     The blade  830  includes sides  844  and  846 , a top end  832 , and radius  840  and  842  at the top corners of the blade  830 . In an embodiment, the end  832  is has a flat surface extending in the X direction. At the bottom end, the blade  830  includes a plurality of protrusions or tips  836 . The blade  830  also includes surface(s)  838  (e.g., flat surfaces, curved surfaces, or the like) between the adjacent protrusions  836 . 
     The blade  830  includes a recess  845  (on side  844 ) that is configured to be tangent to a portion of a periphery of the elastomer  850 A. The elastomer  850 A is configured to be biased into the recess  845  and the edge  820  of the portion  810 A. The blade  830  also includes a recess  847  (on side  846 ) that is configured to be tangent to a portion of a periphery of the elastomer  850 B. The recess  845  is disposed at a same level as the recess  847  in a horizontal direction. The elastomer  850 B is configured to be biased into the recess  847  and the edge  820  of the portion  810 B. 
     The blade  830  can include an optional aperture  834  for the optional elastomer  850 C to pass through in the Y direction. The aperture  834  is a through aperture (in Y direction) and is contained entirely in the blade  830 . The elastomer  850 C is disposed in the V-shape recess formed by side  812 . In an embodiment, the elastomer  850 C is smaller (e.g., has a smaller diameter) than the elastomers  850 A and  850 B. It will be appreciated that a small elastomer in the middle (of the blade  830  or of the blade assembly  810 A and  810 B) (for retention features) can keep tension and keep the parts in place. 
     During operation, the DUT may come down, making contact with and/or pressing the higher tip(s)  316  at or near the side  814  (of the portion  810 A and the portion  810 B). The blade assembly ( 810 A,  810 B) is configured to rotate about the hinge (so that all tips  816  are at a same level in the X direction) when e.g., pressed down by the DUT, causing a scrubbing action. When the DUT is removed or released, the elastomers ( 850 A,  850 B) can provide tension and rebound the blade assembly ( 810 A,  810 B), causing a scrubbing action. 
     That is, when the DUT presses down, forcing the two portions ( 810 A,  810 B) to further open and create a scrubbing effect on the DUT. The two portions ( 810 A,  810 B) may press against the elastomers ( 850 A,  850 B) and create tension. When the DUT is removed or released, the elastomers ( 850 A,  850 B) may return the two portions ( 810 A,  810 B) back to their position in a free state. The elastomers ( 850 A,  850 B) are disposed at or on the sides ( 844 ,  846 ), the blade  830  is facing down, and the two portions ( 810 A,  810 B) (e.g., two smaller triangular blades) are sitting in between the elastomers ( 850 A,  850 B). When the DUT presses down, it may force the two portions ( 810 A,  810 B) to rock/rotate around/against the hinge (i.e., the pivot point) and create scrubbing motion. 
     It will be appreciated that when the two portions ( 810 A,  810 B) are fully pressed by the DUT (or when the compliant ground block  800  is in the free state), the end  832  of the blade  830  is at or below the tip(s)  816  of the blade assembly ( 810 A,  810 B) so that only the blade assembly ( 810 A,  810 B) is contacting the DUT, and a bottom  822  of the blade assembly ( 810 A,  810 B) is at or above the tips  836  of the blade  830  so that only the blade  830  is contacting the load board. 
     The housing  801  includes an enclosure  804 , a slot  805 A for the elastomer  850 A, a slot  805 B for the elastomer  850 B, an optional slot  805 C for the optional elastomer  850 C, a slot  803  for the blade pairs ( 810 A and  810 B,  830 ), and an opening  802  so that the compliant ground block  800  can contact the load board when it is accommodated in the housing  801 . The opening of the housing  801  (so that the compliant ground block  800  can contact the DUT when it is accommodated in the housing  801 ) is not shown. 
     The description of the invention and its applications as set forth herein is illustrative and is not intended to limit the scope of the invention. Variations and modifications of the embodiments disclosed herein are possible and practical alternatives to and equivalents of the various elements of the embodiments would be understood to those of ordinary skill in the art upon study of this patent document. These and other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention. 
     Aspects 
     It is noted that any one of aspects below can be combined with each other. 
     Aspect 1. A compliant ground block for a testing system for testing integrated circuit devices, comprising: 
     a plurality of electrically conductive blade pairs in a side by side generally parallel relationship, blades in the plurality of blade pairs configured to be longitudinally slidable with respect to each other; and 
     an elastomer configured to retain the plurality of blade pairs, 
     wherein each blade pair of the plurality of blade pairs includes a first blade and a second blade, 
     the first blade includes a hinge and a curved edge tangent to a portion of a periphery of the elastomer, the first blade is configured to rotate about the hinge when pressed, 
     the second blade includes an aperture for the elastomer to pass through. 
     Aspect 2. The compliant ground block according to aspect 1, wherein the first blade includes a plurality of protrusions at an end of the first blade. 
     Aspect 3. The compliant ground block according to aspect 2, wherein the first blade includes curved surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 4. The compliant ground block according to aspect 2, wherein the first blade includes flat surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 5. The compliant ground block according to any one of aspects 1-4, wherein the aperture is a through aperture and is contained entirely in the second blade. 
     Aspect 6. A compliant ground block for a testing system for testing integrated circuit devices, comprising: 
     a plurality of electrically conductive blade pairs in a side by side generally parallel relationship, blades in the plurality of blade pairs configured to be longitudinally slidable with respect to each other; and 
     a first elastomer and a second elastomer configured to retain the plurality of blade pairs, 
     wherein each blade pair of the plurality of blade pairs includes a first blade and a second blade, 
     the first blade includes a first recess on a first side of the first blade and a second recess on a second side of the first blade, the second recess of the first blade is disposed below the first recess of the first blade in a horizontal direction, 
     the second blade includes a first recess on a first side of the second blade and a second recess on a second side of the second blade, the second recess of the second blade is disposed below the first recess of the second blade in a horizontal direction. 
     Aspect 7. The compliant ground block according to aspect 6, wherein the first blade includes a plurality of protrusions at an end of the first blade. 
     Aspect 8. The compliant ground block according to aspect 7, wherein the first blade includes curved surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 9. The compliant ground block according to aspect 7, wherein the first blade includes flat surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 10. The compliant ground block according to any one of aspects 6-9, wherein the first elastomer is configured to be biased into the first recess of the first blade and the first recess of the second blade, and the second elastomer is configured to be biased into the second recess of the first blade and the second recess of the second blade. 
     Aspect 11. A compliant ground block for a testing system for testing integrated circuit devices, comprising: 
     a plurality of electrically conductive blade pairs in a side by side generally parallel relationship, blades in the plurality of blade pairs configured to be longitudinally slidable with respect to each other; and 
     an elastomer configured to retain the plurality of blade pairs, 
     wherein each blade pair of the plurality of blade pairs includes a first blade and a second blade, 
     the first blade includes a recess on a first side of the first blade and a sliding edge extending from a second side of the first blade to a bottom end of the first blade, 
     the second blade includes a recess at a first side of the second blade, 
     the elastomer is configured to be biased into the recess of the first blade and the recess of the second blade. 
     Aspect 12. The compliant ground block according to aspect 11, wherein the first blade includes a plurality of protrusions at an end of the first blade. 
     Aspect 13. The compliant ground block according to aspect 12, wherein the first blade includes curved surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 14. The compliant ground block according to aspect 12, wherein the first blade includes flat surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 15. The compliant ground block according to any one of aspects 11-14, wherein the second blade includes a ramp partitioning the second blade into a first portion and a second portion along the ramp, the ramp is configured to support the sliding contact, a thickness of the first portion is greater than a thickness of the second portion. 
     Aspect 16. A compliant ground block for a testing system for testing integrated circuit devices, comprising: 
     a plurality of electrically conductive blade pairs in a side by side generally parallel relationship, blades in the plurality of blade pairs configured to be longitudinally slidable with respect to each other; and 
     a first elastomer and a second elastomer configured to retain the plurality of blade pairs, 
     wherein each blade pair of the plurality of blade pairs includes a first blade assembly and a second blade, 
     the first blade assembly includes a first portion and a second portion, the first portion of the first blade assembly and the second portion of the first blade assembly define a “V” shape recess, 
     the second blade includes a first recess on a first side of the second blade and a second recess on a second side of the second blade, the first recess of the second blade is disposed at a same level as the second recess of the second blade in a horizontal direction. 
     Aspect 17. The compliant ground block according to aspect 16, wherein the first blade assembly includes a plurality of protrusions at an end of the first blade assembly. 
     Aspect 18. The compliant ground block according to aspect 17, wherein the first blade assembly includes curved surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 19. The compliant ground block according to aspect 17, wherein the first blade assembly includes flat surfaces between adjacent protrusions of the plurality of protrusions. 
     Aspect 20. The compliant ground block according to any one of aspects 16-19, wherein the first elastomer is configured to be biased into the first recess of the second blade, and the second elastomer is configured to be biased into the second recess of the second blade. 
     Aspect 21. The compliant ground block according to any one of aspects 16-20, further comprising a third elastomer, 
     the second blade includes an aperture for the third elastomer to pass through, the aperture is a through aperture and is contained entirely in the second blade. 
     The terminology used in this specification is intended to describe particular embodiments and is not intended to be limiting. The terms “a,” “an,” and “the” include the plural forms as well, unless clearly indicated otherwise. The terms “comprises” and/or “comprising,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components. 
     With regard to the preceding description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size, and arrangement of parts without departing from the scope of the present disclosure. This specification and the embodiments described are exemplary only, with the true scope and spirit of the disclosure being indicated by the claims that follow.