Abstract:
An insulative block has a first face adapted to oppose a board on which an inspection circuit is arranged and a second face adapted to oppose a device to be inspected. The insulative block is formed with first through holes each of which communicates the first face and the second face. A conductive first plating layer is formed on the first face, the second face, and an inner face of at least one of the first through holes. Each of contact probes includes a conductive tubular body held in an associated one of the first through holes and a plunger which is retractably projected from one end of the tubular body and is adapted to come in contact with a terminal of the device.

Description:
BACKGROUND 
     The present invention relates to 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, is 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 narrow pulse width and short 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 semiconductor 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 is conducted by a special inspection unit, for example, as shown in  FIG. 8A  (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 this example, 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 this example, the contact probe is so constructed that a hollow space is formed between the inner conductor (the RF contact probe  63 ) and the outer conductor (the inner wall of the through hole in the metal block  61 ) of the coaxial structure so as to obtain a smaller diameter of the contact probe in order to cope with the narrow pitch. For this reason, insulating O-rings  69  are fitted to the contact probe  63  for RF signal, as shown in a partially enlarged view of  FIG. 8B , so that the contact probe  63  for RF signal can be held in the hollow space. 
     Meanwhile, the contact probe  65  for grounding is inserted into the metal block  61  with a ground socket  65   a  being interposed, thereby to avoid deformation and to obtain favorable contact with the metal block  61 . On the other hand, the contact probe  64  for power supply is inserted into the metal block  61  with an insulating tube  64   a  being interposed so as not to come into contact with the metal block  61 . In  FIG. 8A , denoted by numeral  67  is a coaxial cable, and  68  is a plate for retaining the metal pipes which form outer shells of the contact probes. Also in the case of an IC socket for inspecting the IC, the structure around the contact probe is almost the same, though it has a different outer shape. 
     As described above, it is possible to reduce a diameter of each through hole, in a case where a metal block is employed and a coaxial structure is formed by making a hollow space between the inner wall of the metal block as an outer conductor and a probe for RF signal as an inner conductor. This enables the whole unit can be made small, and it is possible to inspect even the device in which the electrode terminals are provided at a narrower pitch, while regulating the impedance. However, it is necessary to form through holes in the metal block  61  formed of metal such as brass or aluminum at a pitch of about 0.4 to 1 mm, requiring high manufacturing accuracy of about ±10 μm. Under the circumstances, there is a problem that it is difficult to substitute the metal block with a die-casting product, and even though it is substituted with the die-casting product, the through holes must be respectively produced by cutting works, which will lead to enormous increase of production cost. 
     Additionally, the probe for power supply must be isolated from the metal block. In a case where an interval between the contact probes is so set as to have a narrow pitch less than 0.5 mm, for example, a diameter of the probe for power supply must be inevitably smaller in order to cover the contact probe for power supply with an insulating tube. Therefore, there are such problems that cost for inserting the insulating tube will increase, and that contact resistance will increase in the probe for power supply. 
     SUMMARY 
     It is therefore one advantageous aspect of the invention to easily provide, at a low cost, an inspection unit for a high-frequency and high-speed device which can regulate high-frequency impedance while preventing intrusion of exterior noises as in a unit employing a metal block, and can use a probe for RF signal having a coaxial structure even in a case where contact probes (electrode terminals) are arranged at a narrow pitch. 
     It is also one advantageous aspect of the invention to provide an inspection unit for a high-frequency and high-speed device in which an inner wall of a through hole for a probe which needs not to be shielded, such as a probe for power supply, is not formed as a metal wall, whereby cost for covering a probe for power supply with an insulating tube can be reduced, and a diameter of the probe for power supply can be made as large as possible. 
     According to one aspect of the invention, there is provided an inspection unit, comprising: 
     an insulative block, having a first face adapted to oppose a board on which an inspection circuit is arranged and a second face adapted to oppose a device to be inspected, the insulative block being formed with first through holes each of which communicates the first face and the second face; 
     a conductive first plating layer, formed on the first face, the second face, and an inner face of at least one of the first through holes; and 
     a plurality of contact probes, each of which comprises a conductive tubular body held in an associated one of the first through holes and a plunger which is retractably projected from one end of the tubular body and is adapted to come in contact with a terminal of the device. 
     The contact probes may include a signal contact probe adapted to transmit an RF signal and held in one of the first through holes the inner face of which is provided with the first plating layer, in such a manner that a gap is formed between an outer periphery of the tubular body and the inner face. 
     The inspection unit may further comprise a retainer, opposing at least one of the first face and the second face of the insulative block and holding the signal contact probe coaxially with the one of the through holes. The retainer may comprise: an insulative member, formed with a second through hole communicating with one of the first through holes; and a conductive second plating layer, formed on at least a part of an outer face of the insulative member and an inner face of the second through hole. 
     The contact probes may include a power supply contact probe adapted to supply power. The first through holes may include at least one through hole an inner face of which is not provided with the first plating layer, and adapted to hold the power supply contact probe. 
     With the above configuration, because the plating layer is formed on the insulative block, it is possible to produce a large number of the insulative blocks by injection molding or the like, with an accurate size. Moreover, because the surface of the insulative block is covered with the plating layer, the interior of the insulative block can be shielded, and substantially the same function as the metal block can be performed. 
     Further, the inner wall of the through hole can serve as the outer conductor of the coaxial structure, while the contact probe for RF signal is made as the core conductor (the inner conductor) of the coaxial structure, and the gap between the core conductor and the outer conductor can be made hollow so as to cope with the downsizing requirement. 
     Accordingly, the inspection unit according to the invention can be manufactured very easily, as compared with the case where the through holes are individually formed in the metal block by drilling work. Therefore, it is possible to perform substantially the same function as the case where the conventional metal block is employed, while attaining remarkable cost reduction. 
     Still further, by employing such structure that the plating layer is not provided in the through hole for inserting the contact probe for power supply, even when the contact probe for power supply comes into contact with the inner wall of the through hole in the insulative block, the contact probe will get in touch with only the exposed face of the insulative block, because the plating layer is not formed thereon. Accordingly, short circuit will not be formed. Therefore, there is no necessity of making the contact probe for power supply smaller than required, but the contact probe for power supply can be made as large as possible in diameter, as far as it can be inserted into the through hole, and very high performance in terms of contact resistance can be also obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a section view of an IC socket according to one embodiment of the invention. 
         FIG. 1B  is an enlarged section view of contact probes, a grounding block and a retainer in the IC socket, showing a disassembled state. 
         FIG. 1C  is a section view of one of the contact probes. 
         FIG. 2  is a perspective, partial section view of through holes formed in the grounding block. 
         FIG. 3  is an enlarged section view of contact probes, a grounding block and retainers in an IC socket according to a modified example. 
         FIG. 4  is a graph comparing return loss characteristics of contact probes for RF signal in the IC socket of the invention with those in a conventional IC socket. 
         FIG. 5  is a graph comparing insertion loss characteristics of the contact probes for RF signal in the IC socket of the invention with those in the conventional IC socket. 
         FIG. 6  is a graph comparing device-side inductance characteristics of contact probes for grounding in the IC socket of the invention with those in the conventional IC socket. 
         FIG. 7  is a graph comparing board-side inductance characteristics of the contact probes for grounding in the IC socket of the invention with those in the conventional IC socket. 
         FIG. 8A  is a schematic section view of a conventional inspection unit. 
         FIG. 8B  is a partial section view of a contact probe in the conventional inspection unit. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the invention will be described below in detail with reference to the accompanying drawings. 
     As shown in  FIG. 1B , in an IC socket according to one embodiment of the invention, an insulative block  21  is provided with through holes  22  into which a probe 1SIG for RF signal, a probe 1GND for grounding, and a probe 1POW for power supply (herein, the probes for low-frequency and low-speed are treated in the same manner) can be inserted. By providing a plating layer  23  on an outer face of the insulative block  21  and on exposed faces of at least a part of the through holes  22 , a grounding block  2  is formed. The above mentioned probe 1SIG for RF signal, probe 1GND for grounding, and probe 1 POW for power supply are inserted into the through holes  22  in this grounding block  2 , and electrode terminals of a device to be inspected such as an IC (not shown) which is provided on one face of the grounding block  2  are connected to wiring terminals on a wiring board which is provided on the other face of the grounding block  2  and connected to an inspection device (not shown) by the respective probes  1 , whereby inspection is performed. 
     Specifically, the grounding block  2  is not formed of a metal block, but formed of the plating layer  23  which is provided on the outer face of the insulative block  21  such as a resin block and on inner faces of at least a part of the through holes  22 . Grounding the plating layer  23 , the grounding block  2  can serve as substantially same as the metal block provided in the inspection unit described in the background section of the specification. 
     In this embodiment, one end portion of the contact probe  1  (1SIG, 1GND and 1POW) is held within the through hole  22  by a recess having a stepped part  22   a  which is formed on a top face of the insulative block  21 , while the other end portion of the contact probe  1  is retained by a retainer  3  which is provided on a bottom face of the insulative block  21 . The plating layer  23  is formed all over the outer faces of the insulative block  21  and a plating layer  31   a  is formed all over the outer faces of an insulative plate  31 , the latter being used as the retainer  3 . 
     As shown in  FIG. 1A , a device guide  4  is mounted on the upper face of the grounding block  2  and positioning pins  6  are inserted into holes formed on the bottom face of the grounding block  2 . The IC socket is mounted on a wiring board (not shown) through the use of the positioning pins  6  to connect the respective contact probes  1  to an inspection circuit provided on the wiring board. Inserting an inspected device such as an IC into a recess formed on the device guide  4 , terminals of the inspected device are electrically connected to the inspection circuit through the contact probes  1 . 
     As shown in  FIG. 2 , the plating layer  23  is formed by applying plating to the whole outer face of the insulative block  21  and the exposed faces of all the through holes  22  except a through hole  26  for inserting the probe 1POW for power supply. In this figure, an area where the plating layer  23  is formed is hatched. The through holes  22  into which the probe for RF signal and a ground socket will be inserted are provided with the plating layer  23  on inner faces thereof as well as on the outer faces. Further, the plating layer  23  is not formed on a circumferential edge of the through hole  26 . 
     The plating layer  23  is formed of an Ni plating of about 2 to 3 μm which is formed by electroless nickel plating for example, and an Au plating of about 3 μm or less which is successively formed thereon by electroless plating. In this case, a plating resist may be applied to or a plating prevention pin may be inserted into the through hole which should not provide with the plating layer, so that the inner face of such a through hole may not get in touch with plating solution, whereby formation of the plating layer can be easily prevented. Alternatively, it is possible to partly remove the plating layer after the plating layer is formed on the whole surface. 
     As described above, the respective probes  1  can be held by the insulative block  21  provided with the plating layer  23  and the insulative plate  31  provided with the plating layer  31   b . However, as shown in  FIG. 3 , it is possible to provide the insulative plates  31  on both the top and bottom faces of the grounding block  2 . In this case, the plating layer  31   b  may be formed on the outer faces of the respective insulative plates  31 . On the other hand, in a case where the insulative plates  31  are very thin as compared with the insulative block  21 , RF performance will not be remarkably deteriorated even though the insulative plates  31  are not provided with the plating layer  23 , so far as the plating layer  23  is formed on the outer face of the insulative block  21  and the exposed faces of at least one or some of the through holes  22 . 
     In the above-mentioned embodiment, the inspection unit can be of the same structure as the conventional inspection unit employing the metal block, except that the grounding block  2  is formed by providing the plating layer  23  on the outer face of the insulative block  21 . Specifically, as shown in  FIGS. 1A and 1B , the contact probes  1  (1SIG, 1POW, 1GND) are inserted into the through holes  22  ( 25 ,  26 ,  27  in  FIG. 2 ) in the grounding block  2  which is provided with the plating layer  23 , and are retained by the retainer  3 . 
     This probe 1SIG for RF signal is formed in a coaxial structure making the contact probe  1  inserted into the through hole  25  for the RF signal probe as an inner conductor and the plating layer  23  formed on the exposed area of the through hole  22  as an outer conductor. The probe 1GND for grounding is provided with a ground socket  17  so as to be connected to the plating layer  23  which is formed in the through hole  27  for the grounding probe, and the ground socket  17  is fixed by insertion of the contact probe 1GND for grounding into the ground socket  17 . The probe 1POW for power supply (including probes for low-frequency and low-speed signals) is inserted into the through hole  26  for the power supply probe, where the plating layer is not provided on the inner wall thereof. 
     However, in a case where there is a sufficient space within the through hole  26 , the plating layer may be also formed on the inner wall thereof, and the probe 1POW for power supply may be inserted into the through hole  26  while interposing an insulating tube. In the above-mentioned embodiments, the contact probes of a type that a pin at a distal end thereof is movable by a spring or the like are employed. However, an ordinary contact pin which is not provided with a movable pin may be employed. 
     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. 
     The contact probes  1  may have substantially the same structure irrespective of their uses, namely for signal, for power supply and for grounding. However, the contact probe 1SIG for RF signal is so formed as to satisfy a prescribed relationship between its outer diameter and an inner diameter of the plating layer  23  inside the through hole  25 , in order to establish the coaxial structure in which the inner wall of the through hole  25  in the grounding block  2  as the outer conductor. In a case where the probes are arranged in a matrix manner at a pitch of 0.4 mm, the outer diameter of the probes is set to be about 0.15 mm, and the inner diameter of the plating layer  23  is set to be about 0.35 mm. It would be desirable that the contact probe 1POW for power supply and the contact probe 1GND for grounding are as thick as possible, and may be formed having such a size to be inserted into the through holes  26 ,  27  having substantially the same size as the through holes  25  which are formed for the RF signal probes according to the pitch (In a case where the ground socket is used, the size will be smaller correspondingly). 
     The contact probe 1POW for power supply will not cause short circuit, because it is inserted into the through hole  26  which is not provided with the plating layer  23 . However, the contact probe 1POW for power supply must be covered with the insulating tube which is not shown, in a case where it is inserted into the through hole provided with the plating layer. As to the contact probe 1GND for grounding, the ground socket  17  formed of phosphor bronze is inserted into the through hole  27 , as shown in  FIG. 1B , for the purpose of improving contact condition with the plating layer  23  in the through hole  27 , and the contact probe 1GND for grounding will be inserted into the ground socket  17 . 
     The insulative block  21  is formed of resin such as polyether imide (PEI), polyimide (PI), polyether ether ketone (PEEK), polyamide imide (PAI), by cutting work, molding work or the like, so that the above described through holes  22  for the contact probes  1  may be arranged in a matrix manner. Then, the above described plating layer  23  is provided in the through holes  25 ,  27  except the through hole  26  for the probe 1POW for power supply. 
     Thickness and dimension of this insulative block  21  may vary depending on its uses, for example, in a case where the inspection unit is used as the IC socket which simply interconnects the IC and the wiring board provided with the wirings, or in a case where the inspection unit is used as an inspecting tool to be connected to a board to which a coaxial cable or the like is connected. But usually, the insulative block  21  is formed having a thickness of about 3 to 8 mm, and an area of 30 to 50 mm square. 
     The retainer  3  includes the insulative plate  31  formed with the plating layer  31   b  on its surface, and an insulating spacer  32  which is provided on an area for the contact probe 1SIG for RF signal. Specifically, this insulative plate  31  has a through hole  31   a  through which the plunger  11  of the contact probe  1  is projected, and in which a stepped part is formed. The insulating spacer  32  is fitted with the stepped part of the through hole  31   a , and provided with a through hole  32   a  through which the plunger  11  of the contact probe  1  is projected, and in which a stepped part is formed. More specifically, the stepped part formed in the insulating spacer  32  is so formed as to fit with an outer shape of the metal pipe  13  of the contact probe  1 , so that the contact probe  1  may not escape from the metal block  2 , while the plunger  11  is retractably projected. 
     The insulative plate  31  is formed of PEI, PI, PEEK or the like in the same manner as the insulative block  21  in a form of an insulating board having a thickness of about 1 to 2 mm. The insulating spacer  32  is formed of polyether imide (PEI) for example, having a thickness of about 0.5 mm. It is to be noted that the through holes  31   a  for the probes for grounding and power supply need not to provide with the insulating spacer. Denoted by numeral  31   c  is a through hole for the positioning pin  8 . 
     In the embodiment shown in  FIG. 1B , the retainer is not provided at the upper end side of the contact probe  1 , and the stepped part  22   a  is formed in the through hole  22 . An insulating spacer  32  having the same structure as described above is fitted with the stepped part, thereby to constitute the retainer. However, as shown in  FIG. 3 , it is also possible to provide the retainer  3  having the same configuration at the upper end side of the contact probe  1  as well. 
     In this embodiment, as shown in  FIG. 1B , an O-ring  7  formed of silicone rubber or the like is inserted at the lower end side of the probe 1SIG for RF signal. Each of the contact probes  1  are individually inserted into the associated through hole  22  from the upper end side thereof. Then, the lower ends of the respective contact probes  1  are collectively inserted into the through holes  31   a  of the retainer  3 . The O-ring  7  is provided in order to maintain the vertical attitude of the contact probe  1  when the lower end side of the contact probe  1  is covered with the retainer  3 , thereby avoiding the interference between the lower end of the contact probe  1  and the through hole  31   a  of the retainer  3 . 
       FIGS. 4 through 7  show comparisons between the conventional inspection unit employing the metal block and the inspection unit of the invention in which a grounding block is formed by providing a Ni plating of 2-3 μm in thickness and an Au flash-plating on an insulative block, and retainers provided with no plating are mounted on top and bottom faces of the grounding block, in connection with return loss of the contact probe for RF signal, insertion loss of the contact probe for RF signal, inductance of the contact probe for grounding at a side of the device, and wiring board-side inductance of the contact probe for grounding. The comparisons are made under the same condition. In the figures, P designates the inspection unit of the invention and Q designates the conventional inspection unit. As apparent from the results, it has been found that there is no significant difference in high-frequency performance between them, and they can be treated in the same manner. 
     As described above, according to the invention, by forming the plating layer such as Ni, Au or the like on the surface of the insulative block formed of resin or the like thereby to constitute the grounding block, it is possible to conduct inspection of the performances which is substantially equal to the inspection by the structure employing the conventional metal block. It is also possible to produce the grounding block having the through holes very easily by insertion molding or the like, without conducting drilling work performed with respect to the conventional metal block. It is also possible to easily obtain the grounding block by applying the plating layer to the desired places, and hence, remarkable cost reduction can be attained. 
     Although only some exemplary embodiments of the invention have been described in detail above, those skilled in the art will readily appreciated that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the invention. 
     The disclosure of Japanese Patent Application No. 2005-374268 filed Dec. 27, 2006 including specification, drawings and claims is incorporated herein by reference in its entirety.