Abstract:
A retention arrangement that includes one or more templates for securing and aligning probes for testing a device under test.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 11/580,204, entitled “Probe Cards Employing Probes Having Retaining Portions for Potting in a Potting Region”, to January Kister, filed on Oct. 11, 2006 now U.S. Pat. No. 7,786,740, and the specification and claims thereof are incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable. 
     COPYRIGHTED MATERIAL 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention (Technical Field) 
     This invention relates generally to apparatus and method for retaining probes in an electrical testing arrangement such as a probe card, and more specifically to securing and aligning such probes in a retention arrangement to ensure superior mechanical and electrical performance. 
     2. Description of Related Art 
     Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes. 
     The testing of semiconductor wafers and other types of integrated circuits (ICs), collectively known as devices under test (DUTs), needs to keep pace with technological advances. Each IC has to be individually tested, typically before dicing, in order to ensure that it functions properly. The demand for testing products is driven by considerations of new chip designs and higher volumes. 
     In particular, chips are getting smaller and they have more tightly spaced contact pads. The pads are no longer located about the circuit perimeter, but in some designs may be found within the area occupied by the circuit itself. As a result, the spacing or pitch of probe arrays required to establish electrical contact with the pads or bumps is decreasing. In addition, the requirements on planarity are increasing. 
     Some of the problems associated with small pitch of contact pads and their arrangement in a dense two-dimensional array are addressed in the prior art. For example, U.S. Pat. No. 6,881,974 to Wood et al. teaches to arrange probes in a probe card that has a substrate with a plurality of blind holes on a front face. The holes are filled with a metal to establish electrical contact for testing purposes and have closed bottoms spaced from a back of the substrate. Another approach is taught in U.S. Pat. No. 6,586,955 and U.S. Published Application No. 2002/0000815 both to Fjelstad et al. where probe cards include a layer of dielectric material provided with a plurality of cavities on a substrate. The dielectric material separates the fusible conductive material that is used to form the probe contacts. Both approaches provide ways to arrange probes that can address pads in a dense array. 
     In an approach that employs a housing for holding the individual probes, U.S. Pat. No. 6,566,898 to Theissen et al. teach an improved vertical pin probing device that has upper and lower spacers made of Invar. The spacers have a thin sheet of silicon nitride ceramic material held in a window in the spacer by an adhesive. The sheets of silicon nitride have laser-drilled matching patterns of holes supporting the probe pins and insulating them from the housing. The probes held in the holes can be arranged to address pads in a dense array. 
     Unfortunately, merely providing a geometry or method of holding probes that can address a dense array of pads is not sufficient. It is also important to ensure that the probes have suitable mechanical resilience and compliance properties. One way of addressing these mechanical issues is discussed, for example, in U.S. Published Application No. 2002/0117330 to Eldridge et al. This reference teaches structures that have improved resilience or compliance because the wire used for contact is overcoated with at least one layer of a material chosen for its structural resiliency or compliance characteristics. The probes have springy shapes and are attached to a substrate in, e.g., a probe card. 
     Although the prior art solutions individually address some of the problems, there is no apparatus or method that combines the requisite characteristics in a single probe card or testing apparatus. Specifically, what is needed is an electrical testing apparatus that can address densely packed pads or bumps with probes that are held securely while offering requisite mechanical properties such as resilience, compliance and reliable scrub motion to remove oxide from the pads or bumps. 
     In view of the above prior art limitations, it is an object of the invention to provide for a method and apparatus for electrical testing of devices under test (DUTs) that have densely spaced contact pads or bumps. The object is to ensure that the probes used in such apparatus are appropriately held and designed to ensure advantageous mechanical properties, including resilience, compliance and scrub motion. 
     It is another object of the invention to ensure that the apparatus is easy to assemble and disassemble despite the small pitch of the probes. 
     These and other objects and advantages of the invention will become apparent from the ensuing description. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the present invention comprises a probe retention arrangement for holding one or more probes. The probe retention arrangement of this embodiment of the present invention preferably comprises at least one guide plate, wherein the guide plate comprises at least one opening for disposing one or more probes, at least one spacer, and at least one anti-wicking template disposed above at least one guide plate. The anti-wicking template preferably comprises a pliable material, and more preferably comprises a polyimide material. The arrangement of this embodiment can optionally comprise a potting agent, preferably an epoxy. The guide plate preferably comprises a compliant material and more preferably comprises a polyimide material. The probe retention arrangement preferably comprises two guide plates and two anti-wicking templates. The probe retention arrangement of this embodiment of the present invention preferably does not comprise a holder at a probe tip level. 
     Another embodiment of the present invention comprises a method of assembling a probe retention assembly. The method of this embodiment preferably comprises providing at least one guide plate having holes, disposing above the at least one guide plate, a first anti-wicking template having holes, aligning the holes of the at least one guide plate and the anti-wicking template, pressing one or more probes into the holes of the at least one guide plate and the anti-wicking template, and aligning the probes in the probe retention assembly. A second guide plate is optionally provided and a spacer is preferably placed between the first guide plate and the second guide plate. A potting agent is preferably disposed between the first guide plate and second guide plate. A second anti-wicking template is preferably disposed above the second guide plate. The aligning step of this method can be performed either automatically or manually. The probes of this embodiment of the present invention are preferably fixed in a vertical position in the probe retention assembly. 
     Yet another embodiment of the present invention comprises a retention arrangement for holding one or more probes. This embodiment of the present invention preferably comprises a top plate having openings for one or more probes, a bottom plate having openings for one or more probes, and a removable tip holder disposed on the retention arrangement, the removable tip holder comprising openings for holding the one or more probes near one or more probe tips. The retention arrangement of this embodiment of the present invention can optionally include a frame positioning the bottom plate relative to the tip holder. The top plate and bottom plate preferably comprise a space therebetween. The retention arrangement of this embodiment can also include a potting region between the top plate and bottom plate for potting a potting agent. At least intermediate plate can optionally be provided in the potting region. The intermediate plate comprises openings for the one or more probes. 
     One embodiment of the present invention comprises a retention arrangement for holding one or more probes. This embodiment preferably comprises a top plate having openings for one or more probes, a bottom plate having openings for one or more probes, and a tip holder disposed on the retention arrangement, the tip holder comprising openings for holding one or more probes near the tips of one or more probes, and a frame positioning the bottom plate relative to the tip holder. This embodiment can also include a potting region between the top plate and the bottom plate for potting a potting agent in the retention arrangement. Optionally, an intermediate plate is provided and is located in the potting region and has probe guide openings for the probes. The tip holder can be removable. A lateral barrier can be provided for enclosing a potting agent. 
     Another embodiment of the present invention comprises a retention arrangement for holding one or more probes. This embodiment preferably comprises a top plate having opening for one or more probes, a bottom plate having opening for one or more probes, a potting region between the top plate and the bottom plate for potting a potting agent in the retention arrangement, and at least one intermediate plate located in the potting region and having one or more probe guide openings for one or more probes. This embodiment of the present invention can optionally include a tip holder disposed on the retention arrangement, the tip holder comprising openings for holding the probes near the contacting tips. A frame is optionally provided for positioning the bottom plate relative to the tip holder. A lateral barrier is preferably provided for enclosing the potting agent in the potting region. 
     The objects and advantages of the invention are secured by a method and an apparatus for electrical testing of a device under test (DUT). The apparatus has a number of probes each of which has a connect end for applying a test signal, a retaining portion, at least one arm portion and a contact tip for making an electrical contact with the DUT. Further, the apparatus has a retention arrangement for holding each of the probes. Specifically, the retention arrangement has a tip holder for holding each of the probes by its contacting tip and a plate with openings for holding each of the probes below the retaining portion. The retaining portion of each of the probes is potted in a potting region defined above the plate with the aid of a potting agent. The potting agent can be any suitable potting material such as an epoxy selected for appropriate viscosity and curing properties. In some embodiments the apparatus further comprises a lateral enclosure or, more generally a lateral barrier for enclosing the potting region to help contain the epoxy prior to curing. 
     In a preferred embodiment the openings in the plate are laser-machined openings. The laser machining process allows one to achieve very precise dimensional tolerances and opening profiles. 
     In some applications the apparatus is used in conjunction with a space transformer. The space transformer has closely spaced or high pitch contacts for contacting each of the probes at the connect end. The connection can be permanent or, preferably temporary. Suitable temporary connections can be achieved by soldering. The use of the space transformer is particularly advantageous when the apparatus is employed in a probe card. 
     The apparatus admits the use of many types of probes. Preferably, however, the probes are non-linear. For example, each probe has at least two arm portions joined by a knee. In one specific embodiment, the probes have at least two arm portions with a base arm portion extending away from a center axis of the probe and a reverse arm portion extending toward the center axis. The knee joins the base arm portion with the reverse arm portion. The contacting tip is located on the reverse arm portion distal from the knee and the contacting tip has a non-zero offset relative to the center axis. Alternatively, the probes can have at least one non-linear arm portion that extends from the center axis such that the contacting tip again exhibits a non-zero offset relative to the center axis. In any of the embodiments of the apparatus, the probes can be of the type endowed with a protrusion on the contacting tip for ensuring high quality electrical contact. 
     The invention further extends to a method for electrical testing of a DUT with a number of probes each having a connect end for applying a test signal, at least one arm portion and a contacting tip for making an electrical contact with the DUT. Each of the probes is provided with a retaining portion and a retention arrangement is provided for holding each of the probes by its contacting tip and also below its retaining portion. According to the method a potting region is created for potting the retaining portion of each probe in a potting agent. The potting agent is admitted into the potting region once the probes are properly held to pot the retaining portions of the probes. 
     Preferably, the retention arrangement has a plate with holes for holding each of the probes below its retaining portion and the holes are made by laser machining. Additionally, the retention arrangement has a tip holder for holding each of the probes by its contacting tip. The tip holder can be removed after potting or left in place for testing. 
     According to the method, a space transformer can be provided for contacting the probes at their connect ends and applying the test signals thereto. 
     A detailed description of the preferred embodiments of the invention is presented below in reference to the appended drawing figures. 
     Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings: 
         FIG. 1  is a diagram illustrating an apparatus of the invention employed with a space transformer; 
         FIG. 2  is an isometric view of two probes that can be used in accordance with the invention; 
         FIG. 3  is an isometric view of another probe that can be used in accordance with the invention; 
         FIG. 4  is a three-dimensional view of other probes with non-linear portions; 
         FIG. 5  is a three dimensional view of still other probes with non-linear portions; 
         FIG. 6  is a three-dimensional view illustrating an array of probes held in a retention arrangement; 
         FIG. 7  is a three-dimensional view illustrating the operation of a scrubbing protrusion on a contacting tip of a probe from the array of  FIG. 6 ; 
         FIG. 8  is a three-dimensional view illustrating the array of probes and retention arrangement of  FIG. 6  attached to a space transformer in accordance with the invention; 
         FIG. 9A  is a plan cross sectional view illustrating a method of attaching probes held in a retention arrangement of  FIG. 9  to a space transformer; 
         FIG. 9B  is a plan cross sectional view illustrating the operation of probes in the retention arrangement of  FIG. 9A  when the holder is not removed; 
         FIG. 10  is a prior art retention arrangement; and 
         FIG. 11  is a retention arrangement comprising two templates for fixing probes in a vertical position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be best understood by first reviewing an apparatus  10  of the invention as shown in the diagram of  FIG. 1 . Apparatus  10  can be employed in a probe card or other electrical testing equipment for testing a device under test (DUT)  12 . Frequently, DUT  12  is an integrated circuit on a wafer that requires testing prior to dicing. Alternatively, DUT  12  is an electronic device or circuit that is already mounted. The functionality of DUT  12  is verified by applying test signals to a number of its bumps or pads  14 . 
     Apparatus  10  has a number of probes  16  arranged in an array and designed for establishing electrical contact with pads or bumps  14 . Typically, the number of probes  16  is large and their spacing or pitch is very small, e.g., on the order of several microns. For clarity, only three probes  16 A,  16 B,  16 C are illustrated. The construction of all probes  16  is analogous and will be explained by referring explicitly to probe  16 A. 
     Probe  16 A has connect end  18 A for applying the test signal, retaining portion  20 A and two arm portions  22 A,  24 A. Arm portion  24 A terminates in contacting tip  26 A for making electrical contact with corresponding bump  14 A of DUT  12 . 
     Apparatus  10  has retention arrangement or assembly  28  for holding each of probes  16  below its retaining portion  20  and just above arm portions  22 ,  24 . More precisely, retention arrangement  28  has plate  30  with openings  32 . Preferably, plate  30  is a ceramic plate. Openings  32  are provided for receiving and guiding retaining portions  20  of probes  16 . To ensure accurate placement of probes  16  in retention arrangement  28  openings  32  are precision machined. Preferably, openings  32  are laser-machined openings. 
     Further, retention arrangement or assembly  28  has holder  34  for holding probes  16  by their contacting tips  26 . Holder  34  can be made of various materials, but in the present case it is made of polyimide. A series of holes  36  in holder  34  is designed to retain contacting tips  26 . Holes  36  preferably have a suitable structure or cross-section to ensure that, once inserted, contacting tips  26  stay in holes  36  unless intentionally removed. Frame  38  keeps holder  34  in the appropriate position with respect to plate  30  to ensure that probes  16  are all well-aligned and their contacting tips  26  maintain a high level of planarity. 
     Retaining portions  20  of probes  16  are potted with potting agent  43  in potting region  40  defined above plate  30 . Lateral enclosure  42 , here in the form of a lateral barrier mounted on top of and about the perimeter of plate  30  defines potting region  40 . A person skilled in the art will recognize that lateral enclosure  42  is especially useful for containing any low-viscosity potting agent  43  prior to curing or when a significant thickness of potting agent  43  needs to be employed. A suitable potting agent  43  is an epoxy that exhibits proper wetting with respect to plate  30  and retaining portions  20  of probes  16  and hardens upon contact with atmospheric oxygen. Potting agent  43  may be poured into potting region  40  from above once probes  16  are properly aligned both horizontally and vertically. As potting agent  42  cures and hardens, probes  16  are retained in their proper positions. 
     Apparatus  10  also has space transformer  44  with probe contacts  46  on its bottom surface  48  for contacting probes  16  at their connect ends  18 . Specifically, space transformer  44  is employed for establishing electrical connections between test signal leads  50  from testing device  52 , e.g., a testing circuit on a printed circuit board, and probes  16 . In contrast to signal leads  50 , probe contacts  46  on bottom surface  48  are densely spaced and can be directly connected to probes  16 . For example, in the case of probe  16 A, its connect end  18 A is assigned to establish electrical connection with contact  46 A. In practice this is preferably done by providing a soldering ball on contact  46 A and soldering connect end  18 A thereto. Other alternatives, such as a side friction connector between connect end  18 A and contact  46 A can also be used to establish electrical connection. 
     Space transformer  44  allows the user to convert relatively sparsely spaced leads  50  to an array of much more densely spaced or high pitch probe contacts  46  for accessing very densely spaced probes  16 . Probes  16 , in turn, require tight spacing in order to access very densely packed and small pads or bumps  14  of DUT  12 . Various types of space transformers and routing strategies are known to those skilled in the art. Any of those can be applied in apparatus  10 . In addition, testing device  52  can generate test signals directly, receive external instructions for generating test signals or simply receive some or all of the test signals and assign them to signal leads  50 . 
     During operation, probes  16  of apparatus  10  are placed in physical contact with bumps  14  to establish electrical contact. Electrical contact is not only due to physical contact, but also due to a scrubbing motion executed by contacting tips  26  of probes  16  while engaging with bumps  14 . The scrubbing motion removes surface oxidation from bumps  14  and thus ensures a low-resistance electrical contact so that the test signals are efficiently delivered to bumps  14 . 
     Apparatus  10  can employ probes of various types and geometries, including probes with two or more arm portions.  FIG. 2  is an isometric view of two exemplary probes  60 A,  60 B that can be used in apparatus  10 . Each one of probes  60  has retention portion  62 A,  62 B and two arm portions  64 A,  66 A and  64 B,  66 B, respectively. More precisely, arm portions  64 A,  64 B are base arm portions extending away from center axes AA, AB of probes  60 A,  60 B, and arm portions  66 A,  66 B are reverse arm portions extending back toward center axes AA, AB. Base and reverse arm portions  64 A,  64 B and  66 A,  66 B inflect at corresponding joints or knees  68 A,  68 B. This geometry lends probes  60 A,  60 B a measure of mechanical flexibility that allows contacting tips  70 A,  70 B of probes  60 A,  60 B to perform effective scrubbing movements when brought in contact with pads or bumps  14  of DUT  12 . 
     Probes  60  have round cross-sections and are spaced at a pitch Δ. In a preferred embodiment, contacting tips  70 A,  70 B are located on reverse arm portions  66 A,  66 B distal from knees  68 A,  68 B with a non-zero offset δ relative to center axes AA, AB, respectively. Non-zero offset δ further improves the scrubbing behavior of probes  60 . 
     Apparatus  10  can use other probes that have non-circular cross-sections.  FIG. 3  illustrates in an isometric view of probe  80  that has a generally rectangular and varying cross-section. Probe  80  has retention portion  82 , base arm portion  84 , reverse arm portion  86 , knee  88  and contacting tip  90 . Once again, contacting tip  90  has a non-zero offset δ relative to a center axis AA of probe  80  to achieve improved scrubbing motion. 
     In still other embodiments, apparatus  10  uses probes that have one or more non-linear arm portions.  FIG. 4  illustrates an array of probes  100  each having a retention portion for being potted in retention arrangement  28  and contact end  104 . Each probe  100  has non-linear arm portion  106  with knee  108 . Arm portion  106  terminates in contacting tip  110 . Note that contact end  104  of each probe  100  is designed for making side friction connections rather than a soldered connection. In other words, contact end  104  is designed to be placed into a metallized hole of a ceramic plate located above retention arrangement  28  and contact is established by sliding the ceramic plate sideways to ensure mechanical contact with contact end  104 . In this case space transformer  44  establishes electrical connections with contact end  104  via a soldered connection to the ceramic plate. Alternatively, space transformer  44  may itself be provided with metallized holes for receiving contact end  104  of each probe  100 . Also note that in this embodiment there is no offset between contacting tip  110  and the center axis of probe  100 . 
       FIG. 5  shows an array of probes  120  each having retention portion  122  terminated in contact end  124 . Stop  126  is provided at the lower end of retention portion  122  to help align probes  120  in a retention arrangement and aid in maintaining their planarity. The presence of stop  126  also aids in keeping the potting agent in the potting region during assembly. 
     Each probe  120  has non-linear arm portion  128  with joint or knee  130 . Non-linear arm portion  128  has a varying degree of curvature along its length and terminates in a contacting tip  132 . Tip  132  is offset from the center axis of probe  120  in order to provide for improved scrubbing behavior. 
       FIG. 6  is a three dimensional view illustrating an array of probes  140  each having non-linear arm portion  142  and contacting tip  144 . Probes  140  are mounted in a retention arrangement  146  and extend out from plate  148  through openings  150 . The holder for holding probes  140  at contacting tips  144  has been removed in this embodiment. Arrangement  146  is fully assembled and probes  140  are potted in the potting agent in the potting region (not visible) of arrangement  146 . 
       FIG. 7  illustrates contacting tip  144  of a particular probe  140  in more detail. The bottom surface of tip  144 , which is the surface that comes in contact with pad or bump  154 , is provided with scrubbing protrusion  152 . Protrusion  152  is a raised, rectangular portion of the bottom surface of tip  144 . Although other geometries are possible, this type of protrusion  152  is preferred. During operation, as a contact force is applied, tip  144  comes in contact with bump  154  and executes a lateral scrubbing motion, as indicated by arrow S. The scrubbing motion helps to remove oxide from bump  154  and establish a good electrical contact. 
     Terminating the tips with scrubbing protrusions in any apparatus of the invention is preferred, since it improves the scrubbing behavior of the probes. It should also be noted, that due to the improved hold of the probes achieved by potting them in the potting enclosure, as well as any axial offset of their tips, all of these measures cooperate to produce a very effective scrubbing movement. 
       FIG. 8  is a three-dimensional view of the array of probes  140  in retention arrangement  146  attached to space transformer  156 . In this embodiment connections to space transformer  156  contacts are soldered connections  158 . Once completed, connections  158  can be capped with an epoxy or adhesive for protection. 
       FIG. 9A  is a plan cross sectional view illustrating set of probes  160  in retention arrangement  162  that employs plate  164  and holder  166 . Plate  164  has openings  168  for holding probes  160  below their retaining portions  170 . Holder  166  has openings  172  for keeping contacting tips  174  of probes  160 . Potting region  176  is defined above plate  164 . Potting region  176  does not include any lateral barriers for containing a potting agent  178 . In this embodiment, agent  178  is a sufficiently viscous epoxy to not require containment prior to curing. In addition, epoxy  178  may be applied and cured in layers to build up to the required thickness without the need for lateral containment. 
     In the view shown by  FIG. 9  probes  160  are already potted in potting agent  178  and are being attached to space transformer  182 . To establish the electrical connection, connect ends  184  or probes  160  are brought in contact with and soldered to pads  186  of transformer  182  by re-flowing solder balls  188 . Preferably, underfill  180  (see  FIG. 9B ), typically of an epoxy or other stable dielectric is provided in order to strengthen the mechanical connection between transformer  182  and retention arrangement  162 . 
       FIG. 9B  is a plan cross sectional view illustrating the use of probes  160  mounted in retention arrangement  162  with holder  166  left in place over contacting tips  174  rather than removed. Due to the presence of holder  166  the motions and scrubs, as indicated by arrow S, of probes  160  are mechanically coupled. Thus, as contacting tips  174  engage with contact pads or bumps  200  of DUT  202  they will tend to execute more concerted scrub motion. Of course, a person skilled in the art will recognize that the decision to remove or keep holder  166  can be made on a case by case basis and depending on planarity, scrub length and contact force requirements when dealing with any particular DUT  202 . 
       FIG. 10  illustrates prior art retention arrangement or assembly  204  comprising guide plates  206  and  208  having holes (not shown), spacer  210 , and holder  212  for holding tips  214  of probes  216 . Guide plates  206  and  208  are preferably made of a ceramic material, but can be made of any supportive material. Potting agent  218  preferably holds probes in place. Since ceramic or other material may be brittle and cannot take a probe press fit, the holes in guide plates  206  and  208  are oversized over the cross-sectional diameter or width of probes  216 . The oversized holes are typically at least approximately 5 μm oversized over probes  216  cross sections. The oversized holes in the prior art do not fix probes  216  in the vertical location causing probe tip alignment errors. Using a template around the probe tips causes probe deformation during template removal, and a sagging template causes alignment errors. 
       FIG. 11  illustrates an embodiment of the present invention comprising retention arrangement or assembly  220 . Retention arrangement or assembly  220  preferably comprises guide plates  222  and  224  having holes (not shown), spacer  226 , and anti-wicking templates  228  and  230 . Anti-wicking templates  228  and  230 , preferably comprise smaller or undersized holes, more preferably holes between approximately 1 and 5 μm in diameter, and most preferably holes approximately 4 to 5 μm in diameter. Anti-wicking templates  228  and  230  allow for a light press fit between probes  232  and the holes in guide plates  222  and  224 . Probes  232  are then preferably fixed in position, preferably a vertical position, thereby minimizing probe tip alignment errors. Templates  228  and  230  preferably comprise a compliant material and more preferably comprise a polyimide material. Templates  228  and  230  also prevent potting agent  234  from wicking up and/or down the probe shaft. Potting agent  234  is preferably used to assist in holding probes  232  in place. Retention arrangement or assembly  220  can secure probes without a holder located near the probe tips. Retention arrangement or assembly  220  preferably does not comprise a holder around the probe tips. Since no holder is required around the probe tips, the arrangement of probes in retention arrangement  220  can be automated by “pick and place”. The automation can be by robotic or other means. Also since no tip holder is required, it is much easier for manual arrangement of probes in retention arrangement  220 . 
     Any of the above-described embodiments can be implemented in a full-fledged testing system or probe card. The retention arrangement of the invention provides excellent mechanical characteristics to the probes it holds. In particular, even in very dense arrays that address densely packed probe pads or bumps the probes are held securely while offering requisite mechanical properties such as resilience, compliance and reliable scrub motion to remove oxide from the contact pads or bumps. 
     Many other embodiments of the apparatus and method are possible. Therefore, the scope of the invention should be judged by the appended claims and their legal equivalents. 
     Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.