Abstract:
When bump electrodes  26  of a semiconductor light emitting element  2  and electrode portions  21  of a mounting board  3  are joined to each other, power is supplied to the electrode portions  21  of the mounting board  3  to allow the semiconductor light emitting element  2  to emit light, the optical properties of the semiconductor light emitting element  2  having emitted light are detected, and the detected value of optical properties is processed to obtain the joining state of the bump electrodes  26  of the semiconductor light emitting element  2  and the electrode portions  21  of the mounting board  3 , so that the completion of joining is determined. Thus, the semiconductor light emitting element can be satisfactorily joined to the electrode portions on the mounting board via the metal electrodes formed on the semiconductor light emitting element.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an apparatus and method for mounting a semiconductor light emitting element on a mounting board. 
       BACKGROUND ART 
       [0002]    In recent years, semiconductor light emitting elements have been reduced in thickness and rigidity with increasing luminance and efficiency. Further, flip-chip mounting has been adopted as a technique for mounting bare chips of semiconductor light emitting elements on mounting boards. The flip-chip mounting is a technique for forming a metal electrode on the electrode portion of a semiconductor light emitting element to electrically join the metal electrode on the semiconductor light emitting element to a metal electrode on a mounting board. 
         [0003]    The process of flip-chip mounting is complicated, so that the joining surface cannot be directly observed. Thus, Patent Literature 1 proposes a technique for bringing a probe needle into direct contact with a semiconductor light emitting element before flip-chip mounting to evaluate the optical properties and electrical properties of the semiconductor light emitting element. 
         [0004]    Further, Patent Literature 2 proposes a technique for performing evaluations on a semiconductor element and a mounting board after flip-chip mounting using X-ray equipment or an infrared microscope. The inspection device is configured as shown in  FIG. 10 . 
         [0005]    In  FIG. 10 , X-rays irradiated from an X-ray generator  100  pass through a flip chip  103  and a circuit board  102 , and an X-ray sensor  104  converts the rays to light with the sensor surface to obtain images. The flip chip  103  is flip-chip joined onto the circuit board  102 . For the flip-chip joining portion, a heavy metal material such as lead and gold having high X-ray absorption is used. Thus, the flip-chip joining portion is darker than the surrounding in an X-ray image, so that the position of the joining portion can be easily specified. A position level with the underside of the flip chip  103  corresponding to the upper part of the joining portion is measured by a laser focus displacement meter  105 . The laser focus displacement meter  105  can measure the position from the side via a mirror  106  allowing the passage of X-rays without affecting the X-ray photography. 
         [0006]    Patent Literature 3 describes a die bonding method in which, in the assembly of an optical head, a light emitting element is electrified to correct a displacement of the light emitting element. 
         [0007]    Patent Literature 4 describes a technique for retaining a light emitting element by suction before mounting and electrifying the retained light emitting element to measure the luminance and select the light emitting element. 
         [0008]    Patent Literature 5 describes a technique for mounting a semiconductor element suctioned and retained by a bonding tool on a printed circuit board while detecting the pressing force with the bonding tool. 
       CITATION LIST 
     Patent Literatures 
       [0000]    
       
         Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2005-158932 
         Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 11-183406 
         Patent Literature 3: Japanese Patent Application Laid-Open Publication No. 6-45652 
         Patent Literature 4: Japanese Patent Application Laid-Open Publication No. 9-92699 
         Patent Literature 5: Japanese Patent Application Laid-Open Publication No. 7-161770 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0014]    However, in the technique of Patent Literature 1, only the properties of the semiconductor light emitting element before mounting can be secured. 
         [0015]    Further, in the technique of Patent Literature 2, only the final joining reliability of the semiconductor light emitting element after mounting can be secured. In other words, the technique of Patent Literature 2 is not designed for securing optical properties and requires the replacement of a semiconductor light emitting element having defective optical properties. Thus, large amounts of losses may be incurred. 
         [0016]    Further, since a typical mounting technique is implemented by open-loop control, joining energy may be applied to a semiconductor light emitting element although joining has been already completed. Moreover, the mounting step of the semiconductor light emitting element may be completed in the state of insufficient joining. As a result, cracks in the semiconductor light emitting element or defects due to damage on a light emitting layer in the semiconductor light emitting element may occur. 
         [0017]    An object of the present invention is to provide a technique for mounting a semiconductor light emitting element on a mounting board with higher reliability. 
       Solution to Problem 
       [0018]    A method for mounting a semiconductor light emitting element according to the present invention includes: supplying power to the electrode portion of a mounting board to allow a semiconductor light emitting element to emit light while the electrode portion of the semiconductor light emitting element and the electrode portion of the mounting board are joined to each other; and detecting the optical properties of the semiconductor light emitting element while the element emits light and controlling the joining of the electrode portion of the semiconductor light emitting element and the electrode portion of the mounting board based on the detected optical properties. 
         [0019]    Further, a method for mounting a semiconductor light emitting element according to the present invention includes: supplying power to the electrode portion of a mounting board to allow a semiconductor light emitting element to emit light while the electrode portion of the semiconductor light emitting element and the electrode portion of the mounting board are joined to each other; and detecting the optical properties of the semiconductor light emitting element while the element emits light and controlling the joining of the electrode portion of the semiconductor light emitting element and the electrode portion of the mounting board based on the detected optical properties, wherein the controlling of the joining comprises: controlling the joining with pressing; and then controlling the joining with ultrasonic waves. 
         [0020]    A method for mounting a semiconductor light emitting element according to the present invention includes: supplying power to the electrode portion of a mounting board to allow a semiconductor light emitting element to emit light while the electrode portion of the semiconductor light emitting element and the electrode portion of the mounting board are joined to each other; and detecting the optical properties of the semiconductor light emitting element while the element emits light, and completing the joining when detecting that the chromaticity of the optical properties falls within a prescribed chromaticity range and the luminance of the optical properties reaches at least prescribed luminance. 
         [0021]    An apparatus for mounting a semiconductor light emitting element according to the present invention includes: a pressing mechanism including a suction hole for suctioning a semiconductor light emitting element, for pressing the suctioned semiconductor light emitting element; a stage holding a mounting board; a power supply unit for supplying power to the electrode portion of the mounting board held by the stage; an optical property detector for detecting the optical properties of light from the suction hole; and a processing control unit for controlling the pressing of the pressing mechanism based on a value detected by the optical property detector. 
         [0022]    Further, an apparatus for mounting a semiconductor light emitting element according to the present invention includes: a pressing mechanism including a suction hole for suctioning a semiconductor light emitting element, for pressing the suctioned semiconductor light emitting element; an ultrasonic wave applying mechanism for applying ultrasonic waves to the semiconductor light emitting element; a stage holding a mounting board; a power supply unit for supplying power to the electrode portion of the mounting board held by the stage; an optical property detector for detecting the optical properties of light from the suction hole; and a processing control unit for controlling the pressing of the pressing mechanism or the ultrasonic waves applied by the ultrasonic wave applying mechanism based on a value detected by the optical property detector. 
         [0023]    Moreover, an apparatus for mounting a semiconductor light emitting element according to the present invention includes: a pressing mechanism including a suction hole for suctioning a semiconductor light emitting element and an optical waveguide disposed along the inner circumference of the suction hole, for pressing the suctioned semiconductor light emitting element; a stage holding a mounting board; a power supply unit for supplying power to the electrode portion of the mounting board held by the stage; a first optical property detector for detecting the optical properties of light from the suction hole; a second optical property detector for detecting the optical properties of light from the optical waveguide; and a processing control unit for controlling the pressing of the pressing mechanism based on values detected by the first optical property detector and the second optical property detector. 
       Advantageous Effects of Invention 
       [0024]    According to the present invention, the electrode of a semiconductor light emitting element and the electrode portion of a mounting board can be joined to each other stably and satisfactorily, so that the semiconductor light emitting element can be mounted on the mounting board with higher reliability. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0025]      FIG. 1  is a configuration diagram showing an apparatus for mounting a semiconductor light emitting element according to a first embodiment of the present invention. 
           [0026]      FIG. 2  is a cross-sectional view showing the main part of a head and the periphery thereof according to the first embodiment. 
           [0027]      FIG. 3(   a ) shows a first step according to the first embodiment.  FIG. 3(   b ) shows a second step according to the first embodiment.  FIG. 3(   c ) shows a third step according to the first embodiment.  FIG. 3(   d ) shows a fourth embodiment according to the first embodiment.  FIG. 3(   e ) shows a fifth embodiment according to the first embodiment. 
           [0028]      FIG. 4  is a flowchart of processing control according to the first embodiment. 
           [0029]      FIG. 5  is a relationship diagram of a detected optical property value and a mounting condition. 
           [0030]      FIG. 6  is a chart showing an example of controlling a pressing force according to the first embodiment. 
           [0031]      FIG. 7  is a configuration diagram showing the main part of an apparatus for mounting a semiconductor light emitting element according to a second embodiment of the present invention. 
           [0032]      FIG. 8  is a configuration diagram showing an apparatus for mounting a semiconductor light emitting element according to a third embodiment of the present invention. 
           [0033]      FIG. 9  is a detected signal waveform diagram of the main part of the apparatus for mounting a semiconductor light emitting element according to the third embodiment. 
           [0034]      FIG. 10  is a configuration diagram showing a mounting apparatus according to the related art. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Embodiments of the present invention will be described below in accordance with the accompanying drawings. 
       First Embodiment 
       [0036]      FIG. 1  is a configuration diagram showing an apparatus for mounting a semiconductor light emitting element according to a first embodiment of the present invention.  FIG. 2  is an enlarged cross-sectional view showing the main part of a head and the periphery thereof according to the first embodiment.  FIGS. 3(   a ) to  3 ( e ) show first to fifth steps according to the first embodiment.  FIG. 2  shows the cross sections of a pressing mechanism  9  and a moving mechanism  10  only in a head  4 .  FIG. 3(   a ) shows a mounting board  3 , a semiconductor light emitting element  2  and the peripheral parts thereof holding the mounting board and semiconductor light emitting element from above and below. The mounting board, the semiconductor light emitting element, and the peripheral parts are vertically illustrated at intervals. 
         [0037]    A mounting apparatus  1  of  FIG. 1  includes the head  4 , a stage  5 , a power feeder  6 , an optical property measuring part  7 , and a processing control unit  8 . The head  4  retains the semiconductor light emitting element  2  with bump electrodes  26  as an electrode portion, as shown in  FIG. 3(   b ). On the stage  5 , the mounting board  3  is placed on which the semiconductor light emitting element  2  is to be mounted. The power feeder  6  supplies power to the semiconductor light emitting element  2  while mounting. The optical property measuring part  7  measures the optical property value of the semiconductor light emitting element  2  while mounting. The processing control unit  8  controls operations of the mounting apparatus  1 . 
         [0038]    As shown in  FIG. 2 , the head  4  includes the pressing mechanism  9  and the moving mechanism  10 . The pressing mechanism  9  presses the retained semiconductor light emitting element  2  down. The moving mechanism  10  moves the pressing mechanism  9  to a predetermined mounting position of the mounting board  3 . The pressing mechanism  9  is cylindrically-shaped with a suction hole  11  formed therein. The diameter of the pressing mechanism  9  is 1.0 times to 1.5 times as large as the diagonal diameter of the semiconductor light emitting element  2 . The diameter of the suction hole  11  is not smaller than 0.05 mm and not more than 0.2 times as large as the diagonal diameter of the semiconductor light emitting element  2 . The diagonal diameter of the semiconductor light emitting element  2  is typically about 0.3 mm to 1.0 mm. 
         [0039]    A suction passage  13  communicating with a negative-pressure source  12  is connected to the suction hole  11 . The semiconductor light emitting element  2  is retained via the suction hole  11  and the suction passage  13  by the suctioning of the negative-pressure source  12 . 
         [0040]    As shown in  FIG. 2 , an optical property detector (first optical property detector)  14  is provided at the terminal end of the suction hole  11  opening at the distal end of the pressing mechanism  9 . The optical property detector  14  detects light having entered the suction hole  11 . Further, the optical property detector  14  sends intensity information according to the wavelength unit of the detected light to a processing part  15  of the processing control unit  8  via the optical property measuring part  7 . The inner circumferential surface (surface) of the suction hole  11  is coated with a coating material  16  with a low refractive index which reflects or propagates light with high efficiency. The coating material  16  guides light having entered the suction hole  11  to the optical property detector  14  at a low attenuation rate with high efficiency. The coating material  16  enables the optical property detector  14  to detect even weak light having entered the suction hole  11 . The coating material  16  is preferably SiO 2  and MgF 2  both having a refractive index of about 1.5. Further, the inner circumferential surface (surface) of the suction hole  11  may be mirror-finished. The inner circumferential surface of the suction hole  11  (surface of optical waveguide) having been mirror-finished can easily form a reflecting surface with slightly reduced reflectivity. 
         [0041]    The stage  5  includes a mounting board holder  17  and a moving mechanism  18 . The mounting board holder  17  holds the placed mounting board  3  by suction. The moving mechanism  18  moves the mounting board holder  17  in a horizontal plane. 
         [0042]    The power feeder  6  includes a DC power supply  19  for supplying electric power, a probe  22 , a voltage measuring device  20  for measuring a voltage, and a probe  23 . The probe  22  contacts an electrode portion  21  on the mounting board  3  to electrically connect the DC power supply  19  and the electrode portion  21 . The probe  23  contacts another electrode portion  21  on the mounting board  3  to electrically connect the voltage measuring device  20  and the electrode portion  21 . 
         [0043]    The optical property measuring part  7  performs processing on an output from the optical property detector  14  and sends the output to the processing part  15  of the processing control unit  8 . 
         [0044]    The processing control unit  8  has a circuit for performing calculations and drive circuits. The processing control unit  8  controls the head  4 , the stage  5 , the power feeder  6 , and the optical property measuring part  7 .  FIG. 1  shows only the processing part  15 , a press control part  24 , and a memory  25  as the constituents of the main part of the processing control unit  8 . The processing part  15  performs processing on a measured value from the optical property measuring part  7 . The press control part  24  controls the force of the pressing mechanism  9 . The memory  25  stores data and so on for determining a threshold value Φ th . 
         [0045]    The following will describe the specific configuration of the processing control unit  8  with reference to the flowchart of  FIG. 4 . 
         [0046]    In step S 1 , as shown in  FIG. 3(   b ), the semiconductor light emitting element  2  is suctioned and retained by the pressing mechanism  9  of the head  4 . Further, the mounting board  3  is suctioned and retained on the mounting board holder  17 . In other words, the semiconductor light emitting element and the mounting board are loaded. 
         [0047]    In step S 2 , as shown in  FIG. 3(   c ), the moving mechanisms  10  and  18  move the semiconductor light emitting element  2  and the mounting board  3  to a predetermined mounting position, and the semiconductor light emitting element  2  and the mounting board  3  are aligned. 
         [0048]    In step S 3 , as shown in  FIG. 2 , the probes  22  and  23  contact the electrode portions  21  on the mounting board  3 , and the DC power supply  19  and the voltage measuring device  20  measure an electrical property value of the mounting board  3 . The electrical property value indicates a physical quantity such as an impedance value and capacitance. 
         [0049]    In step S 4 , based on the measurement result in step S 3 , it is determined whether or not defects such as an electrode short are caused on the mounting board  3 . When defects are detected in step S 4  (in the case of “YES” in response to the question “defect?” in step S 4 ), the process advances to step S 11  which will be described later. 
         [0050]    When it is confirmed that there are no defects in step S 4  (in the case of “NO” in response to the question “defect?” in step S 4 ), the routine of step S 5  to step S 8  is repeated until the completion of joining is determined in step S 7 . 
         [0051]    In step S 5 , the press control part  24  controls the pressing mechanism  9  to press the semiconductor light emitting element  2  toward the mounting board  3 . 
         [0052]    In step S 6 , while the semiconductor light emitting element  2  continues to be pressed (during the pressing of step S 5 ), the power feeder  6  supplies electric power to the semiconductor light emitting element  2 , so that the semiconductor light emitting element  2  emits light. Further, in step S 6 , concurrently with the light emitting of the semiconductor light emitting element  2 , the optical property detector  14  measures the optical property value of the mounting board  3 . The optical property value indicates a physical quantity such as luminance and chromaticity. 
         [0053]    In step S 7 , based on the measurement result in step S 6 , the processing part  15  determines the completion of joining. 
         [0054]    Specifically, the processing part  15  compares the optical property value measured by the optical property measuring part  7  with the threshold value Φ th  stored in the memory  25 , and determines the completion of joining when the measurement result exceeds the threshold value Φ th. The threshold value Φ   th  will be specifically described in accordance with  FIG. 5 . 
         [0055]      FIG. 5  shows the transition of the optical property value when the bump electrodes  26  of the semiconductor light emitting element  2  continued to be pressed to the electrode portions  21  on the mounting board  3  at a constant pressure. The time when the bump electrodes  26  of the semiconductor light emitting element  2  come into contact with the electrode portions  21  on the mounting board  3  is indicated by T 1 . It is noted from  FIG. 5  that the optical property value of the light emitting portion of the semiconductor light emitting element  2  had increased for a while after T 1 , and thereafter had been kept virtually constant. The optical property value of the light emitting portion of the semiconductor light emitting element  2  had increased and thereafter had been kept virtually constant, no matter whether the joining was defective or not. 
         [0056]    Even when the joining was nondefective (in the case of  30  in  FIG. 5 ), after the bump electrodes  26  continued to be pressed at the constant pressure, redundant energy caused damage on the light emitting portion of the semiconductor light emitting element  2 , the short or open of the bump electrodes  26 , or cracks on the light emitting portion in some cases. At a point of  30   a  of  FIG. 5 , the light emitting portion cracked. When the joining was defective (in the cases of  31  and  32  in  FIG. 5 , even when the bump electrodes  26  of the semiconductor light emitting element  2  continued to be pressed to the electrode portions  21  of the mounting board  3  at the constant pressure, the optical property value of the mounted semiconductor light emitting element  2  did not reach the threshold value Φ th . 
         [0057]    Since the optical property value reached at least the constant value (Φ th  in  FIG. 5 ) in the case of nondefective mounting, the optical property value of the mounted semiconductor light emitting element  2  can be determined with reference to the threshold value Φ th , so that the joining state during mounting can be determined without destruction. 
         [0058]    In step S 7 , when it is determined that the joining is uncompleted (in the case of “NO” in response to the question “joining completed?” in step S 7 ), the process advances to step S 8 . In step S 8 , the processing part  15  determines whether or not defects occur on the joining, the process returns to step S 5  when it is determined that there are no defects (in the case of “NO” in response to the questions “defect?” in step S 8 ), and steps S 5  to S 7  are performed. 
         [0059]    When the completion of joining is determined in step S 7  (in the case of “YES” in response to the question “joining completed?” in step S 7 ), step S 9  is performed. 
         [0060]    In step S 9 , the processing part  15  sends a notification signal of completion of joining to the press control part  24 . The press control part  24  having received the signal stops the pressing mechanism  9  from pressing the semiconductor light emitting element  2 . 
         [0061]    Subsequently in step S 10 , as shown in  FIG. 3(   d ), in a state where the suction and retention of the mounting board  3  by the mounting board holder  17  are released, the head  4  is elevated and the mounting board  3  with the semiconductor light emitting element  2  is unloaded. The mounting board  3  is unloaded and the suction and retention of the semiconductor light emitting element  2  by the pressing mechanism  9  is released, so that the mounting of the semiconductor light emitting element  2  is completed as shown in  FIG. 3(   e ). 
         [0062]    In step S 8 , for example, in the case where the optical property value of the semiconductor light emitting element  2  does not exceed the threshold value Φ th  despite the pressing for a certain period of time (in the case of “YES” in response to the question “defect?” in step S 8 ), the process advances to step S 11 . At this point, in response to “YES” to the question “defect?” in step S 8 , it is determined that defects occur which include cracks or damage on the light emitting portion of the semiconductor light emitting element  2  and the short or open of the bump electrodes  26 . In step S 11 , a notification signal of defects is sent to the press control part  24 . The press control part  24  having received the notification signal in step S 11  stops the pressing mechanism  9  from pressing the semiconductor light emitting element  2  in step S 9 . 
         [0063]    As described above, in the mounting apparatus  1  of the first embodiment, during the pressing step of joining the semiconductor light emitting element  2  to the mounting board  3 , the optical property measuring part  7  measures the optical property value of the semiconductor light emitting element  2 . Then, based on the measured optical property value, it is determined whether or not the joining of the semiconductor light emitting element  2  and the mounting board  3  is completed. This prevents the joining operation from being completed despite an inadequate optical property value, so that stable joining strength and optical properties can be obtained. 
         [0064]    Further, the joining operation can be prevented from being excessively performed despite an adequate optical property value. Thus, the occurrence of cracks or damage on the light emitting portion of the semiconductor light emitting element  2  and defects on the bump electrodes  26  (short, open and so on) can be suppressed. 
         [0065]    In the first embodiment, the timing of completion of pressing is controlled according to the detected optical property value. The present invention is not limited to this point. In other words, in addition to the timing of completion of pressing, any parameter of the pressing may be controlled according to the detected optical property value in real time. An example of the parameter to be controlled is the pressing force in the pressing step. 
         [0066]      FIG. 6  shows an example of controlling the pressing force according to the detected optical property value.  FIG. 6  shows the example in which the pressing force is increased while the detected optical property value is low, and the pressing force is reduced with an increase in the detected optical property value. In this case, data showing the relationship between the optical property value and the pressing force as shown in  FIG. 6  is beforehand stored in the memory  25  as data for determination. Based on the data for determination, the processing part  15  may send a control signal to the press control part  24  according to the pressing force. As a matter of course, the example of controlling the pressing force in  FIG. 6  is one example among many, and appropriate control may be performed according to actual mounting conditions. 
         [0067]    In the present embodiment, the optical property detector  14  is provided in the pressing mechanism  9  to reduce the size of the apparatus. The present invention, however, is not limited to this configuration. For example, the optical property detector  14  may be provided on the exterior of the pressing mechanism  9  to guide light incident through the suction hole  11  to the optical property detector  14  by an optical fiber and so on. 
       Second Embodiment 
       [0068]      FIG. 7  is a configuration diagram showing the main part of an apparatus for mounting a semiconductor light emitting element according to a second embodiment of the present invention. In the first embodiment, the suction hole  11  is an air passage, the optical property detector  14  detects light propagated through the passage, and the processing control unit  8  controls the pressing force of joining via the optical property measuring part  7 . 
         [0069]    However, the propagation frequency characteristics of the suction hole  11  are affected by the reflection characteristics of the coating material  16 . Thus, in order that the processing control unit  8  controls the pressing force of joining by measuring luminance in a wide range of chromaticity, it is desirable that the propagation frequency characteristics of the detected light be further flattened. 
         [0070]    In the second embodiment, a plurality of optical fibers  33  are circularly arranged along the inner circumferential surface of a suction hole  11 . The optical fiber  33  is an optical waveguide having a core material which includes a distal end positioned on the suction hole  11  on the side of a semiconductor light emitting element  2  and another end positioned on the side of an optical property detector  14 . Further, in the second embodiment, in addition to the optical property detector  14 , another optical property detector  34  is provided. Light having propagated through the core materials of the optical fibers  33  is detected by the optical property detector  34 . In this case, the optical property detector  14  detects only light propagated through an air passage surrounded by the circularly-arranged optical fibers  33 . The outer peripheral surface of the optical fiber  33  may be coated by a coating material  16 . 
         [0071]    An output detected by the optical property detector  14  (hereinafter, will be referred to as the first detected output) and an output detected by the other optical property detector  34  (hereinafter, will be referred to as the second detected output) are inputted to a processing control unit  8  through an optical property measuring part  7 . Specifically, the optical property measuring part  7  is a spectrometer for measuring and outputting light intensity for each frequency. 
         [0072]    The first detected output and the second detected output inputted through the optical property measuring part  7  to the processing control unit  8  are weighted in a processing part  15  such that the weighted outputs have the same ratio per unit area even when the optical property detector  14  and the other optical property detector  34  are different in incidence area. After the outputs are thus weighted such that the weighted outputs have the same ratio per unit area, the first detected output and the second detected output are added and outputted to a press control part  24 . 
         [0073]    The weighting in the processing part  15  will be specifically described. The first detected output is denoted by A 1 , the incidence area of the optical property detector  14  is denoted by N 1 , the second detected output is denoted by A 2 , and the incidence area of the other optical property detector  34  is denoted by N 2 . In this case, the output from the processing part  15  is represented, for example, as follows: 
         [0000]      A1·N2+A2·N1
 
         [0000]    In the second embodiment, other numeral values and calculations are the same as those in the first embodiment, and an explanation thereof is omitted. 
         [0074]    In the second embodiment, with this configuration, the frequency properties of a detected signal inputted through the optical property measuring part  7  to the processing control unit  8  can be more flattened than in the first embodiment. Thus, it is possible to achieve a mounting condition in which variations in luminance and chromaticity are reduced. 
       Third Embodiment 
       [0075]      FIGS. 8 and 9  show an apparatus for mounting a semiconductor light emitting element according to a third embodiment of the present invention. 
         [0076]    In the following explanation, an example of a semiconductor light emitting element is backlight for illuminating a liquid crystal display panel from behind. Backlighting requires a large number of light emitting elements emitting white light to be vertically and horizontally mounted at predetermined intervals. Backlighting also requires few variations in brightness and luminescent color between the adjacent light emitting elements. 
         [0077]    The following will discuss why variations occur in brightness and luminescent color. 
         [0078]    Bump electrodes formed on the electrode portion of the light emitting element are pressed to electrode portions  21  of a mounting board  3  to be mounted on the mounting board  3 . Even when there are no variations in the brightness and luminescent color of the light emitting elements before pressing the bump electrodes to be mounted, variations in pressing force lead to variations in the deformed conditions of the bump electrodes  26 , resulting in variations in the contact area of the bump electrodes  26  with the electrode portions  21 . 
         [0079]    Specifically, when the contact area of the bump electrodes  26  with the electrode portions  21  is large, heat generated from the light emitting element by electric conduction is satisfactorily conducted to the electrode portions  21  via the bump electrodes  26 . On the other hand, when the contact area of the bump electrodes  26  with the electrode portions  21  is small, heat generated from the light emitting element by electric conduction is insufficiently conducted to the electrode portions  21  via the bump electrodes  26 . Thus, when the contact area is small, the temperature of the light emitting element increases and the brightness decreases with the passage of conduction time. 
         [0080]    Further, even when the contact area of the bump electrodes  26  with the electrode portions  21  is constant, the chromaticity of the luminescent color slightly fluctuates depending on the condition of the interfaces between the bump electrodes  26  and the electrode portions  21 . 
         [0081]    In response, in the third embodiment, the chromaticity is brought closer to the target chromaticity, in addition to bringing the luminance closer to the target luminance. Thus, in the third embodiment, below the mounting board  3  and between a mounting board holder  17  and a moving mechanism  18 , an ultrasonic wave applying mechanism  35  is interposed. Further, a processing control unit  8  performs control as shown in  FIG. 9(   a ). Other configurations are the same as in the second embodiment, and an explanation thereof is omitted. 
         [0082]    In  FIG. 9(   a ), the abscissa indicates time, the left ordinate indicates a load applied when a semiconductor light emitting element  2  is pressed toward the mounting board  3  by a pressing mechanism  9  controlled by a press control part  24 , and the right ordinate indicates the intensities of ultrasonic waves vibrating the semiconductor light emitting element  2  in a lateral direction parallel to the board surface of the mounting board  3 . In  FIG. 9(   b ), the abscissa indicates time, and the ordinate indicates the detected luminance of the semiconductor light emitting element  2  while being mounted. In  FIG. 9(   c ), the abscissa indicates time, and the ordinate indicates the detected chromaticity of the semiconductor light emitting element  2  while being mounted. In  FIGS. 9(   a ) to  9 ( c ), the time is denoted by t 0 , t 1 , and t 2  to clearly show the correspondence of timings. 
         [0083]    As shown in  FIG. 9(   a ), the processing control unit  8  of the third embodiment presses the semiconductor light emitting element  2  toward the mounting board  3  by the pressing mechanism  9  until the detected luminance reaches the target luminance value Ys of  FIG. 9(   b ). 
         [0084]    After detecting that the detected luminance reaches the target luminance value Ys of  FIG. 9(   b ), the processing control unit  8  maintains the load of the pressing mechanism  9  at this point as shown in  FIG. 9(   a ). Further, after detecting that the detected luminance reaches the target luminance value Ys of  FIG. 9(   b ), the processing control unit  8  causes the ultrasonic wave applying mechanism  35  to generate ultrasonic vibrations as shown in  FIG. 9(   a ), thereby applying lateral vibrations to the semiconductor light emitting element  2 . 
         [0085]    In joining under the lateral ultrasonic vibrations, there is no remarkable change in the contact area of the bump electrodes  26  with the electrodes  21  and little change in the heat dissipation properties of the semiconductor light emitting element  2 . Thus, as shown in  FIG. 9(   b ), the detected luminance exhibits extremely few fluctuations compared to the rate of change of load until the detected luminance reaches the target luminance value Ys. However, as shown in  FIG. 9(   c ), the detected chromaticity changes in one direction due to the ultrasonic lateral vibrations. The processing control unit  8  determines the completion of joining when the detected luminance reaches at least the target luminance value Ys and the detected chromaticity reaches the target chromaticity value Cs. Further, the processing control unit  8  instructs the ultrasonic wave applying mechanism  35  to turn off the ultrasonic output and the pressing mechanism  9  to take a load off. 
         [0086]    The configuration of the third embodiment makes it possible to bring the detected luminance to at least the target luminance and bring the detected chromaticity closer to the target chromaticity. Thus, the configuration is particularly effective for the manufacturing of backlight for illuminating a liquid crystal display panel from behind. 
       INDUSTRIAL APPLICABILITY 
       [0087]    The present invention is applicable to various apparatuses for manufacturing electronic equipment which require a semiconductor light emitting element to be mounted on a board.