Abstract:
A board inspection probe for inspecting pattern lines on a circuit board for defects in a non-contact manner. The probe has an electrode for radiating an electrical signal or receiving an electrical signal radiated from a first pattern line. The probe also has a shield to prevent, from reaching the electrode, unwanted radiant waves emitted from pattern lines located in a region except a board region immediately below an electrode surface of the electrode. This shield is terminates near the electrode surface of the electrode, so that radiant waves from only pattern lines located on the board region immediately below the electrode are received.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an inspection probe used for inspecting a board in a non-contact manner, and an inspection method and apparatus using this probe. A target board is represented by a board printed with conductive patterns at a small pitch and includes e.g., a flexible board (a “flexible board” includes an LSI package which is not mounted with IC chip and is to be mounted therewith, and will be referred to simply as a “circuit board” hereinafter). More particularly, the present invention relates to a non-contact board inspection probe and an inspection method and apparatus, all of which are suitable for inspecting local patterns on a board for disconnections and the like.  
           [0002]    The board inspection probe and the inspection method and apparatus of the present invention are effective in inspecting a so-called bare circuit board on which no circuit elements such as IC packages are mounted yet although conductive patterns having a small pitch are printed thereon.  
           [0003]    In conventional board inspection, if a board on which conductive patterns having a small pitch are printed has a large pitch on the electrode side, as shown in FIG. 1, probes can be brought into contact with the electrode groups (two or more electrode groups) of the board to energize the board (power is supplied from one electrode group, and the inspection result is detected on the other electrode group).  
           [0004]    A recent highly-integrated circuit board, however, has small pitches in not only conductive patterns, but also electrodes. This makes it difficult to accurately bring probes into contact with the electrodes having a small pitch. An inspection for determining defectiveness/nondefectiveness (particularly, the presence/absence of a disconnection) of such a board having patterns (conductive paths) with a small pitch has often relied on visual observation or the like.  
           [0005]    In recent years, the conductive patterns of a board (inspection target board) have a higher density (smaller pitch) along with decreases in size and weight of electronic devices. The decrease in pitch tends to cause disconnections in conductive patterns. A strong demand has therefore arisen for board inspection meeting this tendency. Demands for improving workability and reliability and decreasing the cost have become important.  
           [0006]    In inspection for a board having patterns with a small pitch, in addition to a problem posed by the difficulty in accurate positioning of probes on electrodes, another problem is posed by an increase in the number of measuring points. More specifically, In such a board, when the wiring density of conductive patterns increases (i.e., when the pitch becomes small), the number of input and output points (the number of measuring points) increases. Even if contact probing is possible, it is technically difficult to maintain stable contact precision and contact properties. In addition, as the test conditions are becoming stricter than before, complicated, high-precision inspection jigs must be prepared, resulting in high cost.  
           [0007]    Under these circumstances, several prior-art techniques based on non-contact probing, i.e., the board inspection free from the problem posed by contact between probes and electrodes are known.  
           [0008]    For example, British Patent No. GB2143954A has proposed a technique for positioning a probe electrode at the end of a conductive path to form capacitive coupling between the electrode and the end of the conductive path. An AC signal is applied between the electrode and the one end of the conductive path, and a signal is detected at the other end of the conductive path through the above capacitive coupling. By this technique, a board can be inspected without bringing the probe into contact with the conductive pattern.  
           [0009]    Japanese Patent Laid-Open No. 6-34714 (U.S. Pat. No. 5,254,953) is deemed an improved proposal of the non-contact inspection method disclosed in GB2143954A described above.  
           [0010]    Japanese Patent Laid-Open No. 5-264672 (U.S. Pat. No. 5,274,336) discloses a capacitive coupling probe (probe chip) used in an in-circuit test for a high-density circuit board.  
           [0011]    In the above prior arts, the “non-contact” means coupling free from ohmic contact and is equivalently used as the “capacitive”. That is, a means for capacitive coupling is a capacitor.  
           [0012]    The present inventor found that when the above prior-art inspection method and apparatus, however, were applied to a circuit board such as a bare board prior to mounting circuit parts thereon, it was difficult to highly accurately detect the presence/absence of a defect (e.g., a disconnection). That is, even if the prior-art technique is used to inspect a board in which the presence of a disconnection has been confirmed, an inspection result representing the absence of a disconnection is obtained. The present inventor found the cause for this as follows.  
           [0013]    [0013]FIG. 2 is a block diagram of an inspection apparatus in U.S. Pat. No. 5,254,953. This prior-art technique is an apparatus serving as an in-circuit tester. This tester inspects to find whether a lead wire  111  of an IC package  110  is normally connected to a lead wire  140  on a circuit board by soldering  200 . That is, the tester inspects soldered portions, but does not inspects the pattern itself for any defects.  
           [0014]    Referring to FIG. 2, an AC signal is supplied from an oscillator  100  to the lead wire  140  between a probe electrode  120  and the lead wire  111  through a capacitor layer formed by air layer and the IC package  110 . A shield  130  is arranged to prevent the probe electrode  120  from picking up EMI (Electro-Magnetic Interference) from various devices (not shown) located above the probe electrode  120 .  
           [0015]    If soldering  200  is proper, the AC signal is detected by an electrode  310  and measured by an inspection apparatus  300 . Whether soldering is defective or nondefective is determined by the magnitude of the signal detected by the electrode  310 . Note that the capacitance of the capacitor layer formed by the air layer and the IC package  110  between the probe electrode  120  and the lead wire  111  is as small as several femtofarad (fF), and the amplitude of the signal detected by the electrode  310  is very small.  
           [0016]    The present inventor found that when this probe electrode  120  was applied to a bare board  500 , as shown in FIG. 3, the measurement of a signal by the electrode  310  upon intentionally forming a disconnection  510  in a lead wire  520  on the board  500  had almost no difference in the amplitude of the detection signal from the measurement of a signal by the electrode  310  through a lead wire  520  free from disconnections.  
           [0017]    According to the findings of the present inventor, no difference was found in detection signal between the cases in which the disconnection  510  was present and it was absent because the signal applied to the probe electrode  120  propagated in the electro-magnetic field formed in the air layer and was received by a lead wire portion  520   a , and the signal on the lead wire portion  520   a  was detected by the electrode  310 .  
           [0018]    Although the inspection apparatus in FIG. 3 has the shield  130  which is effective to protect the probe electrode  120  from the EMI signal coming from above, the inspection apparatus is defenseless against radiant waves from various radiant sources located below the electrode  120 .  
           [0019]    In inspecting a bare board, as shown in FIG. 3, the probe electrode must particularly come closer to the bare board. In the inspection apparatus disclosed in U.S. Pat. No. 5,254,953 to inspect an in-circuit board which need not bring a probe electrode closer to the board due to the presence of parts, the problem posed by the EMI signal from the board does not arise because the probe electrode is used far away from the board.  
         SUMMARY OF THE INVENTION  
         [0020]    It is an object of the present invention to provide a board detection probe and a board inspection method and apparatus, wherein a shield for preventing an EMI signal from acting on a pattern on a board or from being emitted from the pattern in the board inspection apparatus for inspecting the board by causing a probe to come close to the board, thereby realizing highly accurate inspection.  
           [0021]    In order to achieve the above object, a board inspection probe ( 600 ,  700 ) for inspecting a pattern line on a circuit board for a defect in a non-contact manner comprises:  
           [0022]    a main body;  
           [0023]    an electrode ( 620 ) formed at a position near a board side of the main body and having a conductive electrode surface ( 620   h ) for radiating an electrical signal toward a first pattern line ( 520 ) or receiving an electrical signal radiated from the first pattern line; and  
           [0024]    a shield ( 610 ) which is at least electrically grounded, wherein  
           [0025]    the shield ( 610 ) has  
           [0026]    a blank surface which does not shield a radiant wave to a second pattern line ( 520   a ) or a radiant wave from the second pattern line ( 520   a ) in a first region of the board which substantially corresponds to the electrode surface of the electrode, and  
           [0027]    a shield surface ( 610   a ,  610   b , or  650 ) having an end portion extending near an end portion of the electrode surface without being in electrical contact with the end portion of the electrode surface in order to mainly shield a radiant wave to a third pattern line ( 520   b ) or a radiant wave from the third pattern line ( 520   b ) in a second region except the first region on the board.  
           [0028]    It is another object of the present invention to provide an inspection method and apparatus using the probe having the above arrangement.  
           [0029]    It is still another object of the present invention to provide a probe in which the shield surface ( 610   a ,  610   b ) of the shield horizontally and vertically extends to partially cover a vertical surface of the electrode.  
           [0030]    It is still another object of the present invention to provide a probe in which the shield surface ( 610   a ,  610   b ) vertically and horizontally extends to entirely cover the vertical surface of the electrode.  
           [0031]    According to an aspect of the present invention, pattern lines having a pitch of several decade μm are formed on the board as a target board of a probe of the present invention.  
           [0032]    According to another aspect of the present invention, the board as a target board of the probe of the present invention is a bare board prior to mounting circuit parts thereon, and the electrode surface has an area substantially equal to that of the circuit parts in the horizontal direction.  
           [0033]    According to still another aspect of the present invention, the electrode surface of the probe has a size of several cm 2  to several mm 2 .  
           [0034]    According to still another aspect of the present invention, the shield surface is divided into a first region ( 610   v - 1 ) and a second region ( 610   v - 2 ) in a direction perpendicular to the electrode surface.  
           [0035]    It is still another object of the present invention to provide a probe structure suitable for a probe using a low-profile electrode, in which  
           [0036]    the shield comprises a two-dimensionally spread flat conductive member ( 650 ), and  
           [0037]    the member has an opening serving as the blank surface at substantially the center thereof, and  
           [0038]    a conductive region extending in a direction parallel to the electrode surface so as to surround the opening.  
           [0039]    It is still another object of the present invention to provide a board inspection method of applying an AC signal to the end portion of a pattern line serving as an inspection target or detecting an inspection signal at the end portion of the pattern line, and at the same time grounding the end portion of a pattern line except the target pattern line.  
           [0040]    According to an aspect of the inspection method of the present invention, the end portion of the target pattern line is sequentially switched.  
           [0041]    According to an aspect of the inspection apparatus of the present invention, the inspection apparatus further comprises means for moving a probe in an arbitrary direction.  
           [0042]    Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]    [0043]FIG. 1 is a view showing pattern lines terminating with large pitches at its two terminals;  
         [0044]    [0044]FIG. 2 is a diagram showing the arrangement of a board inspection apparatus system using a conventional probe;  
         [0045]    [0045]FIG. 3 is a view for explaining a state in which a probe used in the inspection system in FIG. 2 picks up unwanted radiant waves;  
         [0046]    [0046]FIG. 4 is a view showing the arrangement of a probe assembly according to the first embodiment of the present invention;  
         [0047]    [0047]FIG. 5 is a plan view showing the arrangement of a probe assembly suitable for inspecting a board on which pattern lines extend in four directions, the probe assembly being an example of the probe assembly of the first embodiment (FIG. 4);  
         [0048]    [0048]FIG. 6 is a perspective view showing the arrangement of a probe assembly in which a shield is divided into upper and lower regions, the probe assembly being as another example of the probe assembly of the first embodiment (FIG. 4);  
         [0049]    [0049]FIG. 7 is a view for explaining the arrangement of a probe assembly according to the second embodiment of the present invention;  
         [0050]    [0050]FIG. 8 is a perspective view showing an example of the probe assembly of the second embodiment (FIG. 7);  
         [0051]    [0051]FIG. 9 is a block diagram showing the arrangement of a board inspection apparatus (first embodiment) using a probe assembly of the present invention;  
         [0052]    [0052]FIG. 10 is block diagram showing the arrangement of a board inspection apparatus (second embodiment) using a probe assembly of the present invention; and  
         [0053]    [0053]FIG. 11 illustrates how teaching points are arranged in an inspection system according to a modified embodiment in which one probe assembly is moved to the points.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0054]    Two probes to which the present invention is applied, and one inspection apparatus using these probes will be described with reference to the accompanying drawings.  
         [0055]    &lt;Probe Assembly&gt; . . . First Embodiment  
         [0056]    [0056]FIG. 4 is a view for explaining the principle of the arrangement of a probe assembly  600  according to the first embodiment to which the present invention is applied.  
         [0057]    The probe assembly  600  includes an electrode  620  and a shield  610 . Reference numeral  500  denotes a board serving as an inspection target.  
         [0058]    Pattern lines  520  and  530  are formed on the board  500 . A disconnection  510  is present in the pattern line  520 . The pattern line  520  is separated into pattern line portions  520   a  and  520   b  due to the presence of this disconnection. FIG. 4 shows a state in which the probe assembly  600  according to the first embodiment is positioned above the pattern line portion  520   b  by a positioning device (not shown). An electrode  310  is connected to one end of the pattern line portion  520   a.    
         [0059]    When an AC inspection signal is applied to the electrode  310 , an electric field or electro-magnetic field is formed along the pattern line  520 . In other words, weak radiant waves are generated from all portions of the pattern line  520  and they are apt to reach the electrode  620 . Since the disconnection  510  is present on the board  500 , the pattern line portion  520   b  generates no radiant waves, but the pattern line portion  520   a  generates radiant waves. If the pattern line  530  is capacitively coupled to or in ohmic contact with the pattern line  520 , the pattern line  530  also generates radiant waves.  
         [0060]    Since the pattern line  520  serving as the inspection target has the disconnection  510 , the electrode  620  should not receive any radiant wave. The shield  610  prevents unwanted radiant waves (radiant waves from the pattern line portion  520   a  and the pattern line  530  in FIG. 4) from reaching the electrode  620 . The pattern line portion  520   b  generates no radiant waves, and the electrode  620  receives no radiant waves. Therefore, the amplitude of the detection signal is zero or has a very low level.  
         [0061]    If no disconnection  510  is present, the radiant waves from the pattern line portion  520   b  are received by the electrode  620  while the radiant waves from the pattern line portion  520   b  are shielded. When the electrode  620  is connected to an amplifier (not shown), an amplified signal can be monitored to determine the presence/absence of a disconnection.  
         [0062]    The shield  510  must covers the electrode  620  so that the electrode  620  may not receive any unwanted radiant waves. In FIG. 4, shields  610   a  and  610   b  cover vertical surfaces  620   a  and  620   b  of the flat electrode  620  so that these vertical surfaces  620   a  and  620   b  to detect radiant waves from the pattern line portion  520   a  and the pattern line  530 .  
         [0063]    Pattern lines (pitch: several decade μm) are formed at a very high density on a board to be inspected by this inspection probe assembly. The amplitude of a signal to be applied to the electrode  310  is small, and its frequency is also low (about 10 kHz). For this reason, to detect a signal having a large amplitude by the probe, the probe assembly  600  must come very close to the board surface.  
         [0064]    When the probe assembly  600  comes very close to the board, radiant waves from the pattern line portion  520   a  and the pattern line  530  will not round about to be received by a horizontal surface  620   h  of the electrode  620 .  
         [0065]    When the probe assembly  600  need not come very close to the board (e.g., when pattern lines have a large pitch, or the frequency or voltage of an inspection signal is high), the horizontal surface  620   h  of the electrode of the probe assembly  600  is separated from the substrate surface. Therefore, the horizontal surface  620   h  of the electrode  620  may receive the radiant waves from the pattern line portion  520   a  and the pattern line  530 . In this case, the shields  610   a  and  610   b  must be further extended downward.  
         [0066]    The shield  610  need not entirely cover the vertical surfaces of the electrode  620  because a vertical surface in a given direction may not have any pattern line portion in this direction. As the layout of pattern lines on a board serving as an inspection target is known, a vertical surface in an unnecessary direction need not be formed on the shield  610 . That is, the shield preferably has directivity, as needed.  
         [0067]    [0067]FIG. 5 is a plan view of an example of the probe assembly  600  for inspecting a board having pattern lines extending in four directions when viewed from the top. In this example, vertical surfaces  610   v  of a shield are formed to surround the horizontal surface  620   h  of the electrode  620 . FIG. 6 is a perspective view of the probe assembly  600  in FIG. 5.  
         [0068]    A central metal conductor  630  forms an electrode. The effective surface of this electrode is formed on the lower surface of the metal conductor  630 . Reference numeral  635  in FIG. 6 denotes an insulating layer for insulating the vertical surfaces  610   v  of the shield from the metal conductor  630  serving as an electrode. The shield having the vertical walls  610   v  is made of conductive metal. In the example shown in FIG. 6, the shield covers the vertical wall surfaces of the metal conductor  630  with inner surfaces. The shield is divided by a boundary  610  into an upper region made of a metal net and a lower region made of a copper plate. The upper region shields the electrode from radiant sources (e.g., power supply lines of the inspection apparatus and probing wiring lines) of various waves outside the board.  
         [0069]    The size of the electrode surface of the probe assembly is determined in accordance with the size of parts to be mounted on the bare boards serving as a measurement target, i.e., the degree of spread at the end portions of pattern lines on the board. For example, the sizes of parts generally range from several mm to several cm, and the sizes of electrode portions range from several mm to several cm, accordingly.  
         [0070]    &lt;Probe Assembly&gt; . . . Second Embodiment  
         [0071]    [0071]FIG. 7 shows the structure of a probe assembly  700  according to the second embodiment. An electrode  620  itself of the probe assembly of the second embodiment is identical to the electrode  620  of the probe assembly of the first embodiment. The probe assembly  700  is different from the probe assembly of the first embodiment in the shield structure.  
         [0072]    Since the electrode  620  receives radiant waves, the height of the electrode need not be large. The length of a vertical surface  620   v  in the direction of height can be small. The vertical surface  620   v  may receive unnecessary radiant waves although the vertical surface  620  is low (its length is small). For this reason, the probe assembly  700  of the second embodiment has a flat shield  650  extending in the horizontal direction.  
         [0073]    [0073]FIG. 8 is a perspective view of the shield  650 . An opening is formed at the center of the shield  650 . The electrode  630  is stored in the opening of the shield  650 . A gap  660  is formed between the electrode  620  and the shield  650  and is preferably filled with an insulating material. The material connects and fixes the electrode  620  to the shield  650 . The shield  650  moves together with the electrode  620  upon movement of the electrode  620 .  
         [0074]    &lt;Inspection Apparatus System&gt; . . . First Embodiment  
         [0075]    [0075]FIG. 9 is a block diagram showing the arrangement of a board inspection apparatus system to which a probe assembly of the present invention is applied. Each of the probe assemblies of the above two embodiments is applicable to the system shown in FIG. 9.  
         [0076]    This inspection system is suitable for an inspection of a board having a larger number of pattern lines such that the terminals (the electrode  310  in FIG. 4) of the pattern lines as an inspection target on one side have a relatively large pitch, and the terminals of the pattern lines on the side of mounted parts such as IC packages have a very small pitch.  
         [0077]    Referring to FIG. 9, reference numeral  600  denotes the probe assembly of the first or second embodiment. This probe assembly  600  is connected to a jig plate  900  which is capable of accommodating a plurality of probe assemblies. A personal computer  800  controls the jig plate  900  to move downward to fit the probe assemblies  600  closer to a board  700 , and to move upward to separate from the board  700  when a measurement test is terminated.  
         [0078]    A pattern line group constituted by a large-pitch pattern line portion  750  and a small-pitch pattern line portion  760  is formed on the board  700  as an inspection target. The board  700  is entirely grounded by a ground plate  680  disposed under the board  700 .  
         [0079]    The terminals of the large-pitch pattern line portion  750  are connected to the probes of a probe group  706 , respectively. The lead wires from the probe group  706  are connected to a switch box  705 .  
         [0080]    Referring to FIG. 9, reference numeral  701  denotes an oscillator for generating a DC inspection signal;  702 , a DC power supply for generating a DC signal; and  703 , a power supply relay for switching between the AC signal from the oscillator  701  and the DC signal from the power supply  702 . A switch  704  is a two-contact switch, one contact (contact b) of which is grounded.  
         [0081]    The switch box  705  has switch elements whose number is larger than or equal to that of the contact probes of the contact group  706 . Each switch element has two contacts. When each switch element is connected to the a side, the signal from the relay  703  is supplied to the corresponding contact probe of the probe group  706 . When each switch element is connected to the b side, the potential from the switch  704  is supplied to the corresponding contact probe of the probe group  706 .  
         [0082]    The signal detected by the probe assembly  600  is supplied to a waveform processor  710  and subjected to filtering in a filter (BPF)  711 . The output from the filter  711  is amplified by an amplifier  712 . The amplified signal is converted into a digital signal by an A/D converter  713 . The digital signal is fetched into the personal computer  800 .  
         [0083]    Note that the conductive pattern of the illustrated inspection target board  700  has 5-channel conductive paths for illustrative convenience. However, the number of channels is not limited to a specific one.  
         [0084]    Short-Circuiting Test  
         [0085]    A short-circuiting inspection for the conductive patterns of the pattern line portion  760  will be described first.  
         [0086]    The personal computer  800  controls the relay  703 , the switch  705 , and the switch box  705  as follows.  
         [0087]    That is, the switch  704  is connected to the a side, i.e., the output from the switch  704  is connected to the A/D converter.  
         [0088]    Of the plurality of switch elements of the switch box  705 , only the switch elements connected to the probes of the probe group  706  connected to the pattern lines serving as the inspection targets are connected to the terminal b sides, and the remaining switches in the switch box  705  are connected to the terminal a sides.  
         [0089]    At the same time, the personal computer  800  controls to connect the relay  703  to the terminal b side. A DC voltage is applied from the DC power supply  702  to the inspection target pattern lines.  
         [0090]    If short-circuiting has occurred in an arbitrary pattern line on the board  700 , the DC voltage applied to the inspection target pattern line (i.e., a pattern line connected to the uppermost probe in FIG. 9) is returned through the short-circuited pattern line and input to an A/D converter  714  through the contact a side of the switch  704 . If no short-circuiting is present, the potential detected on the terminal a side of the switch  704  must be low. The personal computer  800  monitors the output signal from the A/D converter  714  to determine whether short-circuiting has occurred in the inspection target pattern lines.  
         [0091]    Note that the target pattern lines in the short-circuiting test can be switched by switching the switches in the switch box  705 .  
         [0092]    Disconnection Test  
         [0093]    A disconnection inspection for a conductive pattern will be described below.  
         [0094]    To perform a disconnection test, the relay  703 , the switch  704 , and the switch box  705  will be controlled as follows. More specifically, the switch  704  is connected to the terminal b side and grounded. Of the plurality of switch elements in the switch box  705 , only the switch elements connected to the probes of the probe group  706  connected to the inspection target pattern lines are connected to the b sides, and the remaining switches in the switch box  705  are connected to the a sides. At the same time, the personal computer  800  controls to connect the relay  703  to the terminal a side. Therefore, an AC signal is applied from the oscillator  701  to the inspection target pattern lines.  
         [0095]    Pattern lines except the inspection target pattern lines are grounded to suppress generation of unnecessary radiant waves from the pattern lines except the inspection target pattern lines.  
         [0096]    The AC signal applied to the inspection target pattern lines is received as radiant waves by the electrode of the probe assembly  600 . The received radiant waves are filtered by the BPF  711  as an electrical signal. The electrical signal is amplified and converted into a digital signal.  
         [0097]    The personal computer  800  compares the input signal from the A/D converter  713  with a predetermined threshold value to determine whether a disconnection is present. More specifically, if a disconnection is present in one of the inspection target pattern lines, the voltage level of the signal from the A/D converter  713  is much lower than the reference level. Therefore, the presence/absence of a disconnection can be discriminated in accordance with this level difference.  
         [0098]    &lt;Inspection Apparatus&gt; . . . Second Embodiment  
         [0099]    The inspection apparatus of the first embodiment applies an AC inspection signal to the terminals of the large-pitch pattern line portion. An inspection system of the second embodiment applies an AC inspection signal from the electrode of a probe assembly  600  to a small-pitch pattern line portion.  
         [0100]    The constituent elements of the inspection apparatus of the first embodiment can be applied to the inspection apparatus of the second embodiment. The same reference numerals as in the first embodiment of FIG. 9 denote the same parts in FIG. 10.  
         [0101]    Short-Circuiting Test  
         [0102]    A short-circuiting inspection for conductive patterns of a pattern line portion  760  will be described first.  
         [0103]    Referring to FIG. 10, a personal computer  800  controls a relay  703 , a switch  704 , and a switch box  705  as follows.  
         [0104]    That is, the switch  704  is connected to the a side, i.e., the output from the switch  704  is connected to the A/D converter.  
         [0105]    Of the plurality of switch elements of the switch box  705 , only the switch elements connected to the probes of a probe group  706  connected to the pattern lines serving as the inspection targets are connected to the terminal b sides, and the remaining switches in the switch box  705  are connected to the terminal a sides. At the same time, the personal computer  800  controls to connect the relay  703  to the terminal b side. A DC voltage is applied from a DC power supply  702  to the inspection target pattern lines.  
         [0106]    If short-circuiting has occurred in an arbitrary pattern line on a board  700 , the DC voltage applied to the inspection target pattern line (i.e., a pattern line connected to the uppermost probe in FIG. 10) is returned through the short-circuited pattern line and input to an A/D converter  714  through the contact a side of the switch  704 . If no short-circuiting is present, the potential detected on the terminal a side of the switch  704  must be low. The personal computer  800  monitors the output signal from the A/D converter  714  to determine whether short-circuiting has occurred in the inspection target pattern lines.  
         [0107]    Note that the target pattern lines in the short-circuiting test can be switched by switching the switches in the switch box  705  as in the inspection apparatus of the first embodiment.  
         [0108]    Disconnection Test  
         [0109]    A disconnection inspection for a conductive pattern in the apparatus of the second embodiment will be described below.  
         [0110]    To perform a disconnection test, the relay  703 , the switch  704 , and the switch box  705  will be controlled as follows with referring to FIG. 10. More specifically, the switch  704  is connected to the terminal b side and grounded. Of the plurality of switch elements in the switch box  705 , only the switch elements connected to the probes of the probe group  706  connected to the inspection target pattern lines are connected to the b sides, and the remaining switches in the switch box  705  are connected to the a sides.  
         [0111]    Pattern lines except the inspection target pattern lines are grounded to suppress generation of unnecessary radiant waves from the pattern lines except the inspection target pattern lines.  
         [0112]    At the same time, the personal computer  800  controls to connect the relay  703  to the terminal a side, so that the relay  703  is connected to a BPF  711 .  
         [0113]    The personal computer  800  then drives an oscillator  701 . The AC signal from the oscillator  701  is applied to the inspection target pattern lines through the probe assembly  600 .  
         [0114]    The radiant waves received by the inspection target pattern lines appear on the probe group  706  and filtered by the BPF  711  as an electrical signal. The electrical signal is amplified and converted into a digital signal.  
         [0115]    The personal computer  800  compares the input signal from the A/D converter  713  with a predetermined threshold value to determine whether a disconnection is present. More specifically, if a disconnection is present in one of the inspection target pattern lines, the voltage level of the signal from the A/D converter  713  is much lower than the reference level. Therefore, the presence/absence of a disconnection can be discriminated in accordance with this level difference.  
         [0116]    &lt;Modifications&gt;  
         [0117]    Referring to FIG. 9, the jig plate  900  may be substituted by a positioning stage  900  capable of positioning the probe assembly  600  three-dimensionally (X, Y, and Z directions). The personal computer  800  controls the stage  900  to move the probe assembly  600  to an arbitrary position on a board  700 . As shown in FIG. 11, the target moving positions (indicated by open circles in FIG. 11) are in advance by teaching, and teaching point data for each board are stored in a memory (not shown) in the personal computer  800 .  
         [0118]    θ axis is preferably added to the X, Y, and Z directions in a positioning stage  900  in order to adjust directivity.  
         [0119]    &lt;Advantages of Embodiments&gt;  
         [0120]    As has been described above, since a probe according to the present invention can shield radiant waves which are emitted from all sources located below the probe electrode and interfere with inspection, board inspection using this probe can be performed with a high accuracy.  
         [0121]    As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.