Abstract:
A conductive member having a first face adapted to be mounted on a board on which an inspection circuit is arranged, and a second face adapted to be opposed to a device to be inspected is prepared. The conductive member is formed with a first through hole having a first diameter and communicating the first face with the second face. A contact probe including a tubular body having a second diameter which is smaller than the first diameter, and a plunger retractably projected from one end portion of the tubular body is prepared and disposed in the first through hole. A conductive plate having a second through hole is prepared. Molten resin is injected into the second through hole such that at least a part of inner face of the second through hole is covered with solidified resin, thereby forming a third through hole. The conductive plate is disposed so as to oppose to the second face of the conductive member and to communicate the third through hole with the first through hole. The solidified resin is brought into contact with at least the one end portion of the tubular body so as to coaxially retain the contact probe in the first through hole while only the plunger is projected from the conductive plate.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a method of manufacturing an inspection unit for a high frequency/high-speed device for ensuring reliable connection between the inspection unit and the device to be inspected, on occasion of inspecting its electrical performance, before a module of a high frequency/high-speed circuit such as an amplifier circuit, a mixer circuit, a filter circuit, a memory, a CPU, etc. or an IC to be incorporated in a mobile phone, for example, has been assembled to a circuit board. In this specification, the term “high frequency” refers to an analogue signal having a high frequency (1 GHz or more), while the term “high-speed” refers to a digital signal having very short pulse width and pulse interval, and both of which are hereinafter collectively referred to as RF (radio frequency). 
   On occasion of inspecting electrical performance of the RF device such as a semi-conductor wafer, an IC, or a module, insufficient contacts between the terminals may particularly cause fluctuation of impedance or other measurement factors, which may sometimes vary to change measured values. Under the circumstances, such inspection has been conducted by a special inspection unit, for example, as shown in  FIG. 6  (disclosed in Japanese Patent Publication No. 2001-99889A). In such an inspection, an RF circuit, which is the device to be inspected, is constructed in a form of a module  50  including an amplifier circuit and a mixer circuit, and is housed in a metal casing for avoiding interference with the exterior. The module  50  includes input and output terminals  51 ,  54  for RF signals, a power supply electrode terminal  52 , and a grounding terminal  53 , which are provided on a back face of the metal casing. Then, the inspection is conducted by electrically connecting the terminals to respective terminals of a wiring board  66  on which certain wirings for the inspection are arranged. 
   In the example as shown in  FIG. 6 , there are employed contact probes each having a spring and a plunger contained in a metal pipe, one end of the plunger being adapted to be projected to the exterior by the spring and contracted when pushed. The respective electrode terminals are connected by contact probes  63  for RF signals, a contact probe  64  for power supply, and a contact probe  65  for grounding which are contained in a metal block  61  for preventing them from being affected by noises. Each of the contact probes  63  for RF signals is formed in a coaxial structure, using the contact probe as a core conductor and using an inner wall of a through hole in the metal block  61  as an outer conductor, especially for preventing intrusion of noises. In  FIG. 6 , denoted with numeral  67  is a coaxial cable, and  68  is a plate for pressing the metal pipes surrounding the contact probes. Such a structure around the contact probes is almost the same in a case where an IC socket for inspecting ICs, though such socket has a different outer shape. 
   Although  FIG. 6  shows only two contact probes  63  for RF signals (for input and output), and one each contact probes  64 ,  65  each for power supply and for grounding, a large number of these contact probes are actually provided in the metal block  61 . In the maximum case, the electrode terminals of about 600 pieces per 1 cm 2  are provided in a matrix manner with a narrow pitch of about 0.4 mm. 
   In such the narrow-pitch device, an outer diameter of the contact probe for RF signals including a dielectric layer must be reduced in size. Meanwhile, it is also necessary to adjust the impedance of the coaxial structure formed by the contact probe and the inner wall of the through hole to a predetermined characteristic impedance (50Ω, for example) satisfying the following Equation (1). 
                 Zo   =       60       ɛ   r         ⁢     log   e     ⁢     D   d               (   1   )               
where, d is the outer diameter of the core conductor (the contact probe), D is the inner diameter of the outer conductor (the through hole), and ε r  is a dielectric constant of the dielectric substance between them.
 
   In order to satisfy the Equation (1), it is possible to reduce the inner diameter D of the outer conductor by providing a tube made from dielectric substance with small dielectric constant between each contact probe and each through hole. However, even though a tube of polytetrafuluoroethylene having dielectric constant of 2.1, which is the dielectric substance having the smallest dielectric constant available at present, is employed, and the contact probe having the smallest diameter available (having the outer diameter of 0.15 mm) is employed, the inner diameter of the outer conductor (the inner diameter of the through hole formed in the metal block) requires about 0.5 mm to obtain 50Ω as the characteristic impedance of the coaxial structure This cannot attain the pitch of 0.4 mm. 
   For the purpose of solving the problem as described above, in a related-art structure, a hollow space is formed between the contact probe and the through hole to obtain the specific dielectric constant of approximately 1, thereby narrowing the pitch. As a retainer for retaining the contact probe at a center of the through hole, in the related-art structure, there are provided metal plates  72  on both faces of a metal block  71  and inserting insulating spacers  73  respectively into dented parts  72   a  which are formed in the metal plates  72 , as shown in  FIG. 5A , thereby to fix the contact probe  10 . According to this structure, it is possible to make the diameter of the contact probe to be about 0.15 mm, and the inner diameter of the insertion hole  71   a  to be about 0.35 mm, which can be applied to the pitch of 0.4 mm. 
   However, this insulating spacer  73  is very small in size, having a thickness t of about 0.6 mm, an outer diameter A of about 0.33 mm, and an inner diameter B of a dented part of about 0.17 mm, as shown in  FIG. 5B , and has poor workability. It requires a large number of working steps to accurately produce such a small product having a diameter less than 0.8 mm, either by machine work or by molding work. Moreover, it is difficult to insert the insulating spacer  73 , which has been separately prepared, into the dented part  72   a  of the metal plate  72  and fix it therein. In addition, there is a problem of cost-up, because the production of the insulating spacer  73  is very difficult in view of mechanical strength of the insulating spacer  73 . Further, in tendency of narrowing the pitch, it is impossible to prepare the insulating spacer  73  which has a smaller wall thickness than ever. Not only in a case where the contact probe for RF signals in which the coaxial structure is employed, but also in a case where the contact probe for power supply, it is necessary to employ the contact probe having as large diameter as possible for the purpose of decreasing a resistance loss, and the wall thickness of the insulating spacer  73  must be reduced to the limit, so as to comply with the tendency of narrowing the pitch. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide an inspection unit which can perform highly reliable inspection without being affected by noises, employing contact probes of a coaxial structure which can be easily manufactured but are not so expensive, even in a case where an inspection is conducted with respect to a device for RF signals in which electrode terminals are arranged with a very narrow pitch as small as 0.4 mm. 
   In order to achieve the above object, according to the invention, there is provided a method of manufacturing an inspection unit, comprising: 
   preparing a conductive member having a first face adapted to be mounted on a board on which an inspection circuit is arranged, and a second face adapted to be opposed to a device to be inspected, the conductive member being formed with a first through hole having a first diameter and communicating the first face with the second face; 
   preparing a contact probe comprising a tubular body having a second diameter which is smaller than the first diameter, and a plunger retractably projected from one end portion of the tubular body; 
   disposing the contact probe in the first through hole; 
   preparing a conductive plate having a second through hole; 
   injecting molten resin into the second through hole such that at least a part of inner face of the second through hole is covered with solidified resin, thereby forming a third through hole; and 
   disposing the conductive plate so as to oppose to the second face of the conductive member and to communicate the third through hole with the first through hole, wherein the solidified resin is brought into contact with at least the one end portion of the tubular body so as to coaxially retain the contact probe in the first through hole while only the plunger is projected from the conductive plate. 
   With this configuration, an insulating spacer formed by the solidified resin can be made as thin as possible up to the limit that electrical insulation can be obtained. Accordingly, the pitch between the contact probes can be made small. In addition, the same structure can be applied for a contact probe having a small diameter (e.g., a coaxial contact probe for signals) and for a contact probe having a diameter as large as possible (e.g., a contact probe for power supply). 
   The manufacturing method may further comprises forming a recessed portion on an inner face of the second through hole before the molten resin is injected. 
   The manufacturing method may further comprises forming a groove on at least one of faces of the conductive plate which are connected by the second through hole before the molten resin is injected, the groove being communicated with the second through hole. 
   With the above configurations, since the recessed portion and the groove are filled with the molten resin, the solidified resin can be securely fixed to the conductive plate. 
   The manufacturing method may further comprises forming a resin layer on a face of the conductive plate which is to be opposed to the device to be inspected. 
   In this case, the resin layer serves as an insulator with respect to the device to be inspected. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
       FIG. 1A  is a section view of an inspection unit according to a first embodiment of the invention, showing an assembled state thereof; 
       FIG. 1B  is an enlarged section view of the inspection unit of  FIG. 1A , showing a disassembled state thereof; 
       FIG. 1C  is a section view of a contact probe in the inspection unit of  FIG. 1A ; 
       FIGS. 2A to 2E  are views for explaining how to manufacture the inspection unit of  FIG. 1A ; 
       FIG. 3  is a section view of a modified example of the inspection unit of  FIG. 1A , showing a disassembled state thereof: 
       FIG. 4  is an enlarged section view of an insulating spacer in an inspection unit according to a second embodiment of the invention; 
       FIG. 5A  is a section view of a related-art inspection unit, showing an assembled state thereof; 
       FIG. 5B  is a section view of an insulating spacer in the inspection unit of  FIG. 5A ; and 
       FIG. 6  is a schematic section view of a conventional inspection unit. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Embodiments of the invention will be described below in detail with respect to the accompanying drawings. 
   As shown in  FIG. 1 , an IC socket according to a first embodiment of the invention comprises a metal block  2  formed with through holes  21 . Within one of the through holes  21 , a contact probe  1 SIG for RF signals is disposed while leaving a gap, so as to be a core conductor of a coaxial structure, and further, contact probes  1 POW,  1 GND for power supply and for grounding are respectively provided in other through holes  21  of the metal block  2 . A retainer  3  for fixing the contact probes  1 SIG,  1 POW,  1 GND so as not to escape from the metal block  2 , while only plungers  11  of the contact probes  1 SIG,  1 POW,  1 GND are projected, is provided on one face of the metal block  2 . 
   In this embodiment, the contact probes  1  ( 1 SIG,  1 POW,  1 GND) are fixed to the metal plate  2  by the retainer  3 , and a device guide plate  4  is mounted thereon. In this IC socket, the contact probes  1 SIG,  1 POW,  1 GND are connected to an inspection board which is not shown, by positioning a plurality of positioning pins  6  provided on the metal block  2  in alignment with predetermined positions of the inspection board, and the IC or the like is inserted into a recess of the device guide plate  4  at the top, whereby electrode terminals of the IC or the like are connected to the contact probes  1  to execute the inspection. 
   As shown in  FIG. 1C , the contact probe  1  has such a structure that a spring  14  and one ends of the plungers  11 ,  12  are contained in a metal pipe  13 , and the plungers  11 ,  12  are held so as not to escape from the metal pipe  13  by neck portions  13   a  formed in the metal pipe  13 , and to be urged outwardly by the spring  14 . When the tip ends of the plungers  11 ,  12  are pressed, the spring  14  will be contracted so that the tip ends may be pushed into the metal pipe  13 , and while no force is applied, the tip ends of the plungers  11 ,  12  are projected by about 1 mm, for example. Although the plungers  11 ,  12  are provided at both ends of the contact probe, depending on the structure of an inspection unit, it may be sufficient that the plunger  11  is provided on at least one side of the contact probe which comes into contact with the device to be inspected. 
   The metal pipe  13  has a length of about a few millimeters and may be formed of nickel silver (copper, nickel, zinc alloy) for example. As the plungers  11 ,  12 , a wire member having a diameter of about 0.1 mm and formed of SK material or beryllium copper may be used. The spring  14  may be formed of a piano wire or the like. 
   Although the contact probes  1  have substantially the same structure irrespective of their uses, namely, for signals, for power supply and for grounding, the contact probe  1 SIG must be formed in a coaxial structure in combination with an inner wall of the through hole  21  of the metal block  2  which serves as the outer conductor, as described below. For this purpose, an outer diameter d of the contact probe  1 SIG and an inner diameter D of the through hole  21  are determined so as to satisfy the above mentioned Equation (1). For example, in the case of the inspection unit in which the contact probes are arranged in a matrix manner with a pitch of 0.4 mm, the outer diameter d is set to be 0.15 mm, and the inner diameter D of the through hole  21  is set to be about 0.35 mm. 
   On the other hand, the contact probes  1 POW,  1 GND have preferably as large diameters as possible, and formed in such sizes to be inserted into the through holes  21  having substantially the same size as the through holes  21  which are formed for the RF signals, according to their pitch. In addition, the contact probe  1 POW is covered with an insulative tube  16  having such a thickness that the contact probe  1 POW may not make a short circuit with the metal block  2 . Although not shown, the contact probe  1 GND is also covered with a ground tube made of phosphor bronze, for the purpose of improving contact performance with the inner wall of the through hole  21 . 
   The metal block  2  is intended to hold the contact probe  1 SIG, the contact probe  1 POW, and so on, which are brought into contact with the electrode terminals of the IC or module which is the device to be inspected, while shielding external noises. By forming the metal block  2  by metallic material such as aluminum or brass for example, it is possible to form the coaxial structure including the inner wall of the through hole  21  as the outer conductor and the contact probe  1 SIG as the core conductor. Also for the contact probe  1 POW, by employing the retainer  3  provided with the insulating spacer  32  which has the small thickness as described above, it is possible to make the contact probe  1 POW larger, while keeping the narrow pitch of the contact probes and while shielding the external noises. 
   Thickness and dimension of the metal block  2  may vary depending on the type of inspection unit into which the metal block is incorporated, for example, an IC socket which simply interconnects the IC and the inspection board provided with wirings, or an inspecting tool connected to the inspection board to which a coaxial cable or the like is connected. However, in general cases, the metal block  2  is formed having a thickness of about 3 to 8 mm, and an area of 30 to 50 mm square. 
   This retainer  3  includes a metal plate  31  and an insulating spacer  32 . The metal plate  31  is formed with through holes  31   a  through which the plungers of the contact probes  1  are adapted to pass, and dented parts  31   b  into which shoulder parts of the contact probes  1  (end portions of the metal pipes  13 ) can be inserted. Insulating spacers  32  are respectively provided inside the dented parts  31   b . The insulating spacer  32  is also formed with a through hole  32   a  which is concentric with the above described through hole  31   a  and through which the plunger  11  is adapted to pass, and a dented part  32   b  into which the shoulder part of the contact probe can be inserted, thereby to attain electrical insulation between the contact probe  1  and the metal plate  31 . 
   In this embodiment, the retainer  3  is prepared by forming the through hole  31   a  through which the plunger  11  of the contact probe  1  can pass, in the metal plate  31  in alignment with the position of the contact probe  1 , then, forming the dented part  31   b  in the metal plate  31  at a side facing the metal block  2  concentrically with the through hole  31   a , and by filling the dented part  31   b  with insulative resin, so that the dented part  32   b  which is concentric with the though hole  31   a  and into which the shoulder part of the contact probe  1  can be inserted is formed by the solidified resin. 
   A process for forming the retainer  3  will be further described in detail, referring to  FIGS. 2A to 2E . 
   As a first step, as shown in  FIG. 2A , in the metal plate  31  formed of aluminum or brass, for example, and having a thickness R of about 1-5 mm to be attached to one face of the metal block  2 , the through holes  31   a , each having a diameter C of about 0.25 mm which is larger than a diameter of the plunger  11  so that the plunger  11  of the contact probe  1  can pass through, are formed in alignment with positions of the contact probes  1 SIG,  1 POW and so on to be provided in the metal block  2 . Then, the dented part  31   b  having an inner diameter D of about 0.35 mm is formed concentrically with the through hole  31   a , at a depth S of about 1.3 mm from the face of the metal plate  31  opposed to the metal block  2  (only the though hole  31   a  and the dented part  31   b  corresponding to one of the contact probes are shown in this figure). 
   It is preferable that on occasion of forming the dented part  31   b , as shown in  FIG. 2D , grooves  31   c  may be formed at one or more positions on an inner face of the dented part  31   b  along an axial direction of the dented part  31   b . This is because rotation of the insulating resin  32   d  can be prevented, when the through hole  32   a  and the dented part  32   b  are formed in the insulating resin  32   d  by a drill or the like, as described below. 
   Alternatively or additionally, it is possible to form lattice-shaped grooves  31   f , which can be filled with resin, on a surface of the metal plate  31  so as to communicate with the through holes  31   a  or the dented parts  31   b  as shown in  FIG. 2E . When the lattice-shaped grooves  31   f  are formed, additional grooves may be formed inside the metal plate  31 , so as to extend from inner walls of each grooves  31   f  in a direction parallel to the surface of the metal plate  31 . The additional grooves are filled with resin, thereby forming resin portions inside the metal plate  31  such that each of the additional grooves has a width wider than that of the groove  31   f . Such resin portions effectively prevent the insulating resin  32   d  from not only being rotated but also being moved in a direction perpendicular to the surface of the metal plate  31 . The grooves  31   f  may not be lattice-shaped, but may be parallel grooves extending in one direction of the lattice. In any event, provision of these grooves  31   c  and/or  31   f  somehow contribute in preventing the insulating spacer  32  from being escaped from the metal plate  31 . 
   Then, the insulating resin  32   d  is filled and solidified in the through hole  31   a  and the dented part  31   b  of the metal plate  31 , as shown in  FIG. 2B . As the insulating resin  32   d , material which has a small and uniform dielectric constant for dealing with the high-speed or high frequency signals and can be subjected to minute works may be selected. For example, epoxy resin, glass fiber (E-glass) impregnated resin, polyetherimide (PEI), etc. are employed. 
   Although the through hole  31   a  of the metal plate  31  is filled with the resin up to the surface of the metal plate  31  as shown in  FIG. 2B , the entirety of the dented part  31   b  need not be filled with the resin. Particularly, a part of the dented part  31   b  at a side opposed to the metal block  2  need not be filled with the resin. On the other hand, the through hole  31   a  also need not be filled with the resin along its entire length. That is, it would be sufficient that the insulating spacer  32  is formed only in an area for fixing the shoulder part of the contact probe  1 . 
   Thereafter, as shown in  FIG. 2C , the through hole  32   a  and the dented part  32   b  are formed in the insulating resin  32   d . The through hole  32   a  having a diameter (E) of about 0.12 to 0.17 mm is firstly formed by a drill by centering it at the center of the through hole  31   a  of the metal plate  31 , from the surface  31   d  of the metal plate  31  at the side opposed to the metal block, and then, the dented part  32   b  having an inner diameter F of about 0.17 to 0.33 mm and a depth T of 1.1 mm is continuously formed. Consequently, the insulating spacer  32  which is very thin having a wall thickness of about 0.05 mm is formed in tight contact inside the through hole  31   a  and the dented part  31   b  of the metal plate  31 . On this occasion, the resin will be also filled in the grooves  31   c  and/or the grooves  31   f  if they are formed in the dented part  31   b  of the metal plate  31 , as described above, and therefore, the insulating resin will not be removed from the metal plate  31  nor rotate, even in case where the through hole  32   a  and the dented part  32   b  are formed by drilling. 
   The retainer  3  including the insulating spacer  32  formed in the dented part  31   b  of the metal plate  31  is attached to one face of the metal block  2 , and after the contact probe  1  has been set in the through hole  21  of the metal block  2 , the other retainer  3  which has been prepared in the same manner is attached to the other face of the metal block  2 , as shown in  FIG. 1 . In this manner, both ends of the contact probe  1  can be secured by the retainer  3  which has been produced in the above described process, and the contact probe  1  can be held inside the through hole  21  of the metal block  2  with excellent concentricity. Specifically, the shoulder parts of the contact probe  1  are secured by the dented parts  32   b  of the insulating spacers  32  so that the contact probe  1  may not jump out from the metal block  2  while the plungers  11  are freely projected. For information, numeral  31   e  represents a through hole for a positioning pin  8 . 
   The metal plate  31  is accurately positioned with respect to the metal block  2  by the positioning pins  8  which are fitted into a positioning hole  22  provided in the metal block  2 . It is also possible to insulate the metal block  2  from the metal plate  31  in terms of direct current, by interposing an insulating sheet between them. 
   The retainer  3  for the contact probe  1  need not be provided on both the faces of the metal block  2 , but such a structure, as shown in  FIG. 3 , that a dented part  23  is directly formed at the other side of the metal block  2 , and an insulating spacer  24  is inserted the dented part  23  may be employed. It is also possible to fix the contact probe  1  directly to the wiring board or the like by soldering or so, without employing the plunger of this type. Further, only one end of the contact probe  1  can be fixed by an insulating board which has been directly formed with a through hole and a dented part. In the embodiment as shown in  FIG. 3 , an insulating sheet  7  having a thickness of about 75 μm and formed of PEI or the like is inserted between the metal block  2  and the metal plate  31 , so that the contact probe  1  may not be inclined when the metal plate  31  is fitted, thus enabling the metal plate  31  to be easily fitted. Even though the insulating sheet  7  is interposed, electrical connection in a form of high frequency is maintained, and the inspection will not at all be hindered. Other elements can be constructed in the same manner as in the conventional inspection unit, as described below. 
   Next, a second embodiment of the invention will be described with reference to  FIG. 4 . Similar components to those in the first embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted. 
   In this embodiment, a mold having projecting parts for forming the dented part  32   b  and the through hole  32   a  of the insulating spacer  32  is prepared. The metal plate  31  which has been beforehand formed with the dented part  31   b  and the through hole  31   a  is positioned in the mold in such a manner that the projecting parts may be aligned with the dented part  31   b  and the through hole  32   a , and then, the resin is filled into the mold and solidified, whereby the insulating spacer  32  can be integrally molded on inner faces of the dented part  31   b  and the through hole  31   a  of the metal plate  31 . According to this process, secondary work by the drill is not required, and more excellent accuracy than the work by the drill can be obtained. 
   In this embodiment a resin film  5  having a thickness of 0.1 to 0.2 mm is formed integrally all over the metal plate  31 . This resin film  5  serves as an insulating sheet for performing electrical insulation from the device to be inspected or the circuit board which are provided in contact with this face. Conventionally, the insulating sheet such as a PI (polyimide) sheet has been separately attached for performing the insulation, which has been detrimental in respect of cost and dimensional accuracy. However, by employing this process, the insulating film can be formed at the same time with the insulating spacer  32 . The resin film  5  can be formed in the same manner, not only in a case where forming the insulating spacer by resin molding, but also in a case where drilling after the resin has been filled, as described above. 
   Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.