Abstract:
A method of producing a probe assembly which uses thermal energy of a laser light for bonding a plurality of connection pads provided on a probe board and a probe disposed on each connection pad. In the neighborhood of at least one of the connection pads on the probe board, a dummy connection pad with no probe adhered is formed in order to uniform the thermal energy by irradiation of each bonding portion of each connection pad and the corresponding probe.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a probe assembly suitable for conducting a current test of electrical circuits such as integrated circuits formed on a semiconductor wafer and a method for producing it. 
       BACKGROUND 
       [0002]    Generally, a testing apparatus provided with a tester and a probe assembly with a plurality of probes for connecting the tester to each electrode pad of an integrated circuit which is a device under test is used for an electric test of multiple integrated circuits incorporated into a semiconductor wafer. 
         [0003]    In the production of a conventional probe assembly to be assembled into such a testing apparatus, a plurality of probes are adhered by solder to electrically conductive connection pads provided on a probe board. A laser light is used for welding the solder (see, for example, Patent Document 1). When a laser light is used as a heating source of the solder, the probes are arranged to correspond to the connection pads aligned on the probe board, and with solder applied to a bonding portion where the connection pad and the probe are to be bonded, the bonding portion is irradiated with a laser light as an instantaneous laser spot. 
         [0004]    The heat to be applied to the bonding portion by the laser light irradiation sometimes adversely affects the bonding quality of the bonding portion and other electronic parts provided on the probe board. In order to prevent such an ill effect and obtain a proper bonding, it is desirable to give minimum required energy to obtain a favorable bonding by melting the solder of the bonding portion. For this reason, a spot diameter of the laser light is set at the width diameter of the electrode pad or less. Also, on the probe board, a plurality of connection pads are aligned, so that, when a certain one connection pad is irradiated with the laser spot, a part of the heat energy is also absorbed by adjoining connection pads disposed adjacent to the probe board. Accordingly, the irradiation energy per shot is set optimally in consideration of a heat loss at each adjoining connection pad. 
         [0005]    However, even by the laser irradiation with the energy set as above, by irradiating both outward connection pads located outermost of a connection pad row, a high temperature rise is seen in comparison with the other connection pads aligned between both the outer connection pads. Furthermore, by irradiating the other connection pads isolated from the connection pad rows with the laser light, a further remarkable rise in temperature is seen. It is considered that this is because the other connection pads between both outer connection pads in the connection pad rows, other connection pads to be heat absorption sources adjoin at equal intervals in front and rear in the alignment direction, while to only one of both the outer connection pads the other connection pad is adjacent in the alignment direction, so that dispersion of heat hardly occurs between the other heat absorption sources. 
         [0006]    Therefore, in adhering the probes to the connection pads located outermost of such connection pad rows and isolated connection pads, it is desirable to reduce the laser output energy in comparison with a case of adhering to the other connection pads. Thus, in a method of producing a probe assembly which uses the conventional laser light, a need to control the laser light energy according to the arrangement of the connection pads, thereby complicating the structure of a laser irradiation apparatus and causing a rise in the production cost. 
         [0007]    As one of techniques to mount a semiconductor chip on a base plate, there is a flip-chip bonding (FCB) technique for bonding an electrode on a base plate and a bump of a semiconductor chip. Further, there is a prior art for bonding them by use of ultrasonic wave pressurized heat to enhance bonding of both by interposing a nonconductive resin between the chip and the mounting base plate (see, e.g., Patent Document 2). In the method according to Patent Document 2, a conductive dummy pattern to be covered by the nonconductive resin is formed on the chip mounting base plate. This dummy pattern aims to temperature distribution of the nonconductive resin covering the conductive dummy pattern uniform by its thermal capacity when an ultrasonic wave is applied. This prevents decrease in reliability of the connection between the base plate and the semiconductor chip due to non-uniform viscosity of the nonconductive resin. 
         [0008]    However, the conductive dummy pattern for providing a uniform viscosity to the nonconductive resin when using the ultrasonic wave pressurized heat is, as mentioned above, to aim at making the temperature distribution of the nonconductive resin covering the conductive dummy pattern uniform, and not to aim at uniforming heating of the individual bonding portion of the electrode of the base plate and the bump of the semiconductor chip by the ultrasonic wave pressurized heat. 
         [0009]    [Patent Document 1] Japanese Patent Appln. Public Disclosure No. 2002-158264 
         [0010]    [Patent Document 2] Japanese Patent Appln. Public Disclosure No. 2006-121115 
       BRIEF SUMMARY 
       [0011]    An object of the present invention is to provide a method of producing a probe assembly which dispenses with laser energy control according to the alignment of connection pads in a method comprising a step of heating the bonding portion of the connection pad and the probe with thermal energy of a laser light, and which enables to control non-uniform heating caused at the bonding portions of the connection pads in a row of the connection pads or of an isolated connection pad and a probe. 
         [0012]    The present invention relates to a method of producing a probe assembly which uses thermal energy of a laser light for bonding a plurality of connection pads provided on a probe board and a probe disposed on each connection pad, and is characterized in that a dummy connection pad with no probe adhered is formed, so as to uniform the thermal energy due to irradiation of the bonding portion of each connection pad and the corresponding probe with the laser light in the neighborhood of at least one of the connection pads on the probe board. 
         [0013]    According to the present invention, even it is in the outermost connection pad of a connection pad row or an isolated connection pad that a probe is provided, a dummy connection pad without any probe is provided in a position adjacent to the connection pad. Since this dummy connection pad acts as a heat capacity body, the thermal energy of the laser light applied to the outermost connection pad or the isolated connection pad is effectively dispersed between the connection pad and a neighboring dummy connection pad such as in case of irradiating another connection pad with the laser light. Consequently, without adjusting the energy of the laser light in accordance with the alignment of the connection pads, it is possible to prevent such a great temperature difference as the conventional one from being caused at the bonding portion between the connection pad and the probe to be bonded thereto according to the position of the connection pad in the alignment. 
         [0014]    Solder capable of melting by the thermal energy of the laser light can be applied to the bonding portion of the connection pad and the probe. 
         [0015]    The plurality of connection pads include a plurality of connection pads aligned at substantially equal intervals to form a connection pad row and connection pads disposed apart and isolated from the connection pad row, and at least one of the dummy connection pads may be formed in the neighborhood of the isolated connection pad. 
         [0016]    The isolated connection pad and the dummy connection pad disposed in the neighborhood thereof may be disposed on an extension of the connection pad row. 
         [0017]    When the isolated connection pad is disposed on an extension of the connection pad row, the dummy connection pad may be disposed on each side of the extension of the connection pad row. 
         [0018]    The plural connection pads are aligned at approximately equal intervals, and the dummy connection pad may be formed to adjoin at least one of both outermost connection pads in the alignment direction of the connection pad row. 
         [0019]    The dummy connection pad may be disposed more outward of the connection pad row than the outermost connection pad on the extension of the connection pad row. 
         [0020]    The dummy connection pad may be disposed on each side of the extension of the connection pad row. 
         [0021]    The probe assembly according to the present invention is one using thermal energy of a laser light for bonding a plurality of connection pads on a probe board and a probe disposed on each of the connection pad, and is characterized by forming a dummy connection pad where no probe is adhered, so as to uniform the thermal energy by irradiating each bonding portion of the connection pad and the probe corresponding to it in the neighborhood of at least one of the connection pads with the probe bonded. 
         [0022]    The connection pad and the probe can be bonded through solder which can melt by the thermal energy of the laser light. 
         [0023]    The dummy connection pad can be formed in the same planar shape as that of the connection pad where the probe on the probe board is to be bonded. 
         [0024]    The dummy connection pad can be formed on the same plane as the plane where the probe on the probe board to be bonded to the connection pad is provided. 
         [0025]    The dummy connection pad may be provided in the inside of the probe board. 
         [0026]    According to the present invention, as mentioned above, it is possible to effectively control generation of such a large dispersion in temperature rise as in the conventional case at each bonding portion of the connection pads and the probes. 
         [0027]    Also, by forming a dummy connection pad with the same thermal capacity as that of the connection pad, it is possible to provide substantially uniform thermal energy to each bonding portion of the connection pads and the probes without adjusting irradiation laser energy in accordance with the alignment of the connection pads. Consequently, a laser irradiation device having a comparatively simple constitution to bond appropriately the connection pads and the probes without adversely affecting the bonding quality of the bonding portions and other electronic parts provided on the probe board, so that a high-quality probe assembly less expensive than the conventional one can be provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a plan view showing part of the probe assembly according to the present invention. 
           [0029]      FIG. 2  is a side view of the probe assembly shown in  FIG. 1 . 
           [0030]      FIG. 3  is a sectional view obtained along the line III-III shown in  FIG. 1 . 
           [0031]      FIG. 4  is an explanatory view showing a laser irradiation process according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    As shown in  FIGS. 1 and 2 , the probe assembly  10  according to the present invention comprises a probe board  12 , and a plurality of probes  14  to be bonded on one face of the probe board. This probe assembly  10  is used for conduction test of plural semiconductor integrated circuits incorporated into, for example, a semiconductor wafer not shown. 
         [0033]    Although not shown, the other face of the probe board  12  is provided with a tester land to be connected to an electric circuit of the tester. Also, on the one face of the probe board  12  for the probes  14  to be bonded, connection pads  16  ( 16   a - 16   o ) to each of which the probe  14  is bonded, and a dummy connection pad  18  ( 18   a - 18   h ) without a probe  14  are provided. 
         [0034]    Although not shown, the connection pad  16  to which the probe  14  is bonded is connected to the corresponding tester land through a heretofore well-known wiring path provided on the probe board  12 . The probe board  12  can be formed from, for example, a laminated structure of a ceramic-like electrically insulated plate where a part of the wiring path is formed, as heretofore known, and a multi-layer wiring board where the remaining part of the wiring path is formed. 
         [0035]    One example of the probe  14  is shown in  FIG. 3  as a sectional view along the line III-III shown in  FIG. 1 . Each probe  14  has, as shown in  FIG. 3 , an attaching portion  14   a  as a bonding portion to the connection pad  16 , a rising portion  14   b  on the same plane as that of the attaching portion and rising therefrom, and an arm portion  14   c  extending from the top of the rising portion substantially horizontally in the lateral direction flush with the plane of both portions  14   a  and  14   b.  The arm portion  14   c  terminates at the front end face  14   e  through a curving part  14   d  toward the opposite side of the side where the attaching portion  14   a  is positioned. In the front end face  14   e  is formed a tip  14   f  projecting therefrom. 
         [0036]    It is desirable to make the part excluding the tip  14   f  of the probe  14  of a metal material comparatively rich in toughness such as, for example, nickel, its alloy or phosphor bronze, and to make the tip  14   f  of a metal material of high hardness in comparison with the part excluding the tip  14   f,  such as, for example, cobalt, rhodium or their alloys. Also, in the illustration, there is a long hole  20  through the arm portion  14   c  for promoting flexural deformation of the arm portion  14   c  in case pressing force acts on the tip  14   f  toward the probe board  12 , but the long hole  20  may be dispensed with. 
         [0037]    Each probe  14  is, as shown in  FIGS. 1 and 2 , bonded to the corresponding pad  16  so that its tip  14   f  may correspond to each electrode pad formed on the semiconductor wafer. In the example shown in  FIG. 1 , the electrode pads are aligned on an imaginary line L, and the connection pads  16  are aligned along an imaginary line K parallel to the imaginary line L so that the tips  14   f  of the probes may be aligned on the imaginary line L. 
         [0038]    The connection pads  16 , in the illustration, have the same elongated rectangular planar shape and are aligned in the same attitude with their width direction along the extending direction of the imaginary line K such that their longitudinal direction forms right angles to the imaginary line K. 
         [0039]    In the example shown in  FIG. 1 , in the left side part of the figure of the probe board  12 , the connection pads  16   a  to  16   e  are aligned at equal intervals, for example, of over 10 microns to several dozen microns, toward the right side part of the probe board  12  so as to correspond to the alignment spans of the electrode pads. Thereby, the connection pads  16   a  to  16   e  constitute a first connection pad row. 
         [0040]    Also, from the first connection pad row ( 16   a  to  16   e ) leftward along an imaginary line K are arranged successively an isolated connection pad  16   f,  a second connection pad row ( 16   g  to  16   l ) greatly apart from the isolated connection pad  16   f,  and a third connection pad row ( 16   m  to  16   o ) greatly apart from this connection pad row. 
         [0041]    The intervals between the respective connection pads  16   g  to  16   l  constituting the second connection pad row correspond to those between the corresponding electrode pads and are equal to the intervals between the respective connection pads  16   a  to  16   e  constituting the first connection pad row. The intervals between the respective connection pads  16   m  to  16   o  constituting the third connection pad row are likewise equal to those between the connection pads  16   a  to  16   e  of the first connection pad row. 
         [0042]    Dummy connection pads  18   a,    18   b  are aligned relative to the first connection pads ( 16   a - 16   e ), and dummy connection pads  18   c,    18   d  are disposed relative to the isolated pad  16   f.  Further, dummy connection pads  18   e,    18   f  are aligned relative to the second pad row ( 16   g - 16   l ), and dummy connection pads  18   g,    18   h  are aligned relative to the third connection pad row ( 16   m  to  16   o ). Each dummy connection pad  18  is of the same material and in the same configuration as those of the connection pad  16 , and is formed on the one plane of the probe board  12  where the connection pads  16  are provided. 
         [0043]    Both dummy connection pads  18   a,    18   b  relative to the first connection pad row ( 16   a  to  16   e ) are aligned on the imaginary line K so that the connection pad row ( 16   a  to  16   e ) constituting the first connection pad row may be located between both dummy connection pads. Therefore, one dummy connection pad  18   a  is disposed proximate to one connection pad  16   a  of both outermost connection pads  16   a,    16   e  to be disposed outward of the first connection pad row ( 16   a  to  16   e ). Also, the other dummy connection pad  18   b  is proximate to the other outermost connection pad  16   e  to be disposed outward of the first connection pad row ( 16   a  to  16   e ). Further, both dummy connection pads  18   a,    18   b  are disposed to align with the connection pads  16   a  to  16   e,  and the interval between each of the connection pads  16   a,    16   e  and each of the connection pads  16   a,    163  proximate to the dummy connection pad is approximately equal to the interval between the respective connection pads  16 . 
         [0044]    Likewise, relative to the isolated connection pad  16   f,  the dummy connection pads  18   c,    18   d  are aligned on the imaginary line K with the connection pad f therebetween so that the interval from the connection pad  16   f  may become equal to that of the respective connection pads  16 . 
         [0045]    Further, relative to the second connection pad row ( 16   g  to  16   l ), the dummy connection pad  18   e  is proximate to the one outermost connection pad  16   g  of the connection pad row on the imaginary line K to be disposed to align outward of the connection pad row. Also, the dummy connection pad  18   f  is proximate to the other outermost connection pad  16   l  of the connection pad row ( 16   g  to  16   l ) to be disposed outward of the connection pad row to align with the second connection pad row. The interval between each of the dummy connection pads  18   e,    18   f  and each of the connection pads  16   g,    16   l  proximate to the dummy connection pads is approximately equal to each of the connection pads  16 . 
         [0046]    Also, regarding the dummy connection pads  18   g,    18   h  relative to the third connection pad row ( 16   m  to  16   o ), as in the first and the second connection pad rows, both dummy connection pads  18   g,    18   h  are aligned on the imaginary line K with the third connection pad row ( 16   m  to  16   o ) therebetween such that the interval between the connection pads  16   m  and  16   o  approximately coincides with that of each of the connection pads  16 . 
         [0047]    Accordingly, in the illustration, the first to the third connection pad rows and the isolated connection pad  16   f  are aligned on a common extension of the imaginary line K. Also, except the intervals between the adjoining dummy connection pads ( 18   b  and  18   c,    18   d  and  18   e,  and  18   f  and  18   g ), the respective connection pads  16  and the respective dummy connection pads  18  are aligned so that the intervals between the respective adjoining connection pads  16  and  18  may become equal. 
         [0048]    As shown in  FIG. 4 , the probe  14  is disposed on each connection pad  16  with its attaching portion  14   a  abutting, each bonding portion of the probe  14  and the connection pad  16  is instantaneously irradiated with a laser irradiation light  24 , for example, from one side of the probe  14  in a state that the conventionally well-known solder  22  is applied. The solder  22  can be previously adhered to the attaching portion  14   a  as heretofore well known. 
         [0049]      FIGS. 1 and 2  show a state after the probes  14  are already bonded to the connection pads  16   a  to  16   f  but before the probes to be bonded are disposed on the connection pads  16   g  to  16   o.    
         [0050]    Referring to  FIG. 4  again, for bonding the isolated connection pad  16   f  and the probe disposed on the connection pad, the bonding portion of the probe  14  and the connection pad  16   f  is intensively and instantaneously irradiated as mentioned above with the laser irradiation light  24 . Thereby, the bonding portion of the probe  14  and connection pad  16   f  is raised to a temperature sufficient to melt the solder  22  instantaneously, but a part of the thermal energy to be applied to the bonding portion is dispersed into both dummy connection pads  18   c,    18   d  because the adjacent dummy connection pads  18   c,    18   d  act as thermal capacity bodies. 
         [0051]    Likewise, when the laser irradiation light  24  is applied for bonding, for example, the connection pad  16   a  of the first connection pad row ( 16   a  to  16   e ) and the probe  14  disposed on the connection pad, the thermal energy to be applied to the bonding portion is dispersed into the dummy connection pad  18   a  and the connection pad  16   b  acting as thermal capacity bodies adjacent to the connection pad  16   a.  Also, when the laser irradiation light  24  is applied for bonding the connection pad  16   b  and the probe  14  disposed on the connection pad, the thermal energy to be applied to the bonding portion is likewise dispersed into the connection pad  16   a  and the connection pad  16   c  acting as a thermal capacity bodies adjacent to the connection pad  16   b.    
         [0052]    Thus, by disposing the dummy connection pad  18  relative to each connection pad row ( 16   a - 16   e,    16   g - 16   l,  and  16   m - 16   o ) and the isolated pad  16   f,  it is possible to disperse the thermal energy of the laser irradiation light  24  for bonding the outermost connection pads  16   a,    16   e,    16   g,    16   l,    16   m,    16   o  of each row and the isolated connection pad  16   f  into the adjacent dummy connection pads  18 . Accordingly, non-uniform heating according to the connection pad rows caused by the laser irradiation light  24  to the bonding portion of the connection pad  16  and the probe  14  can be controlled. 
         [0053]    Also, as mentioned above, by using the dummy connection pad  18  of the same material and the same configuration as that of the connection pad  16 , the thermal capacity of the dummy connection pad  18  can be made equal to that of the connection pad  16 . Moreover, by aligning the dummy connection pads  18  at equal intervals in the connection pads  16 , it is possible to heat the bonding portion between each connection pad  16  and the probe  14  uniformly by the laser irradiation light  24  of the approximately uniform thermal energy without changing the energy of the laser irradiation light  24  according to the alignment positions of the connection pads  16 . Therefore, it is possible to bond properly the probe  14  to the connection pad  16  by the laser irradiation light  24  of substantially uniform energy, without adversely affecting the bonding quality of the bonding portion of the connection pad and the probe and other electronic parts provided on the probe board. 
         [0054]    An example of forming the dummy connection pad  18  on the plane of the probe board  12  where the connection pads  16  are provided is shown in the foregoing, but the dummy connection pad  18  may be embedded in the probe board  12  like the dummy connection pad  18   h  representatively shown by an imaginary line in  FIG. 2 . 
         [0055]    Further, in place of disposing on the extension (K) of the pad alignment, the dummy connection pad  18  may be formed on each side in the longitudinal direction of the outermost connection pad or the isolated connection pad so as to make pairs, with the outermost connection pad of each pad alignment or the isolated connection pad interposed. 
         [0056]    The present invention is not limited to the above embodiments but can be varied without departing from its purport. For instance, various shapes of contacts may be used as the probes  14 , or connection pads  16  and dummy connection pads  18  of various shapes may be adopted.