Abstract:
A manufacturing method of circuit modules comprising steps of melting a solder on a land by an energy of irradiating laser beam, and pressing an external electrode of an electronic component to a melted solder before the melted solder hardens. This method is capable of connecting the electrode of the component to the land of the substrate using the solder sufficiently heated and melted. A manufacturing apparatus of circuit modules comprises an adsorbing nozzle which adsorbs an electronic component and mounts it on a substrate, an optical system which projects laser beams to a solder preliminarily applied to an electrode of a substrates, and a control device which controls a component mounting and a laser beam irradiation so that the electrode of the electronic component is pressed to the solder melted by an energy of a irradiating laser beam before the melted solder hardens. This apparatus is capable of connecting the component with the above laser beam while controlling the component mounting and the laser beam irradiation.

Description:
This application is a division of application Ser No. 09/054,395, filed Apr. 3, 1998, now U.S. Pat. No. 6,333,483. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a manufacturing method of circuit modules which electrically connects an electronic component to a substrate by utilizing laser beam, and relates to a manufacturing apparatus of circuit modules which is suited for carrying out the above method. 
     2. Description of the Prior Art 
     Japanese Patent Application Laid-Open No. 4-314390 discloses a method for mounting an electronic component on a substrate by utilizing a laser beam. Speaking concretely, this patent application discloses a method which loads an electronic component on a substrate so that an external electrode of the component is brought into contact with a cream solder preliminarily applied to a surface of a land and electrically connects the external electrode to the land by way of the solder by irradiating with a laser beam for the cream solder and melting it. 
     Since this method irradiates the cream solder with the laser beam after the electronic component is loaded on the substrate so that the external electrode of the electronic component is brought into contact with the cream solder preliminarily applied to the surface of the land, it is incapable of directly irradiating the cream solder applied to areas which are sandwiched and shaded by the external electrode and the land. 
     In other words, this method has a defect that it allows the cream solder to remain unmelted on the areas which are sandwiched and shaded by the external electrode and the land, thereby causing improper connections due to insufficient connecting areas and strengths. 
     This defect can be corrected to a certain degree by setting an energy (a product of a power multiplied by an irradiation time) of the irradiating laser beam at a high level. When the power of the laser beam is strengthened, however, the electronic component is subjected to bad thermal damage, thereby posing problems of degradation in qualities and variations of characteristics. When the irradiation time of the laser beam is prolonged, on the other hand, each component requires a longer connecting time, thereby making it impossible to accelerate manufacturing of circuit modules. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide a manufacturing method of circuit modules which solves the problem of improper connection and permits favorably connecting electronic components with a laser beam, and a manufacturing apparatus of circuit modules which is capable of securely carrying out this method. 
     To attain this object, the manufacturing method according to the present invention comprising steps of melting a connecting material preliminarily disposed on electrodes of a substrate by an energy of an irradiating laser beam, and loading an electronic component on the substrate so as to press electrodes of this component to the melted connecting material before the melted connecting material hardens. 
     This method is capable of solving the problem of the residual unmelted connecting material by sufficiently heating and melting the connecting material on the electrodes of the substrate with the irradiating laser beam, thereby making it possible to connecting the electrodes of the component to the electrodes of the substrate with connecting materials which are sufficiently heated and melted. 
     On the other hand, the manufacturing apparatus according to the present invention comprises a component loading device having an adsorbing nozzle which absorbs an electronic component and loads it on a substrate, a laser beam irradiation device which irradiates a laser beam to a connecting material preliminarily disposed on an electrode of the substrate, and a control device which controls the component loading and the laser beam irradiation so that the electrodes of the electronic component are pressed to the melted connecting materials after the connecting materials are melted by an energy of the irradiating laser beam and before the melted connecting materials harden. 
     This apparatus is capable of securely carrying out the manufacturing method described above with the component mounting device, the laser beam irradiation device and the control device which controls the former two devices. 
     The object described above, other objects, features and advantages of the present invention will be apparent from the following description and the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS.  1 ( a ) through  1 ( f ) are views illustrating component mounting processes in a first embodiment of the manufacturing method according to the present invention; 
     FIG. 2 is a constitutional diagram illustrating an optical system and a control system used for a component mounting in the first embodiment; 
     FIG. 3 is a timing chart of the component mounting in the first embodiment; 
     FIGS.  4 ( a ) through  4 ( c ) are diagrams illustrating shapes of irradiating laser beams on lands in the first embodiment; 
     FIGS.  5 ( a ) and  5 ( b ) are diagrams illustrating conditions of irradiation with laser beams relative to lands in the first embodiment; 
     FIG. 6 is a timing chart illustrating a control method for varying a power of an irradiating laser beam; 
     FIGS.  7 ( a ) and  7 ( b ) are diagrams illustrating a modified method to irradiate a land with a laser beam; 
     FIGS.  8 ( a ) and  8 ( b ) are diagrams illustrating another modified method to irradiate a land with a laser beam; 
     FIGS.  9 ( a ) through  9 ( e ) are diagrams illustrating modified optical systems; 
     FIGS.  10 ( a ) and  10 ( b ) are diagrams illustrating a modified adsorbing nozzle; 
     FIGS.  11 ( a ) and  11 ( b ) are diagrams illustrating other modified adsorbing nozzles; 
     FIG. 12 is a diagram illustrating a method to heat and melt solder using second laser beams in combination; 
     FIGS.  13 ( a ) through  13 ( d ) are diagrams illustrating constitutions for mechanically controlling of irradiating timing with a laser beam and operations of the constitutions; 
     FIG. 14 is a constitutional diagram illustrating a mounting machine in a second embodiment of the present invention, and an optical system and a control system which are used in the mounting machine. 
     FIG. 15 is a top view of a rotating head in the second embodiment; 
     FIGS.  16 ( a ) and  16 ( b ) are diagrams illustrating a method to control a position of an adsorbed electronic component in the second embodiment; and 
     FIGS.  17 ( a ) and  17 ( b ) are diagrams illustrating a modified adsorbing nozzle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 through 5 illustrate a first embodiment of the present invention. FIGS.  1 ( a ) through  1 ( f ) showing component mounting processes, FIG. 2 showing a constitutional diagram of an optical system and a control system to be used for a component mounting, FIG. 3 showing a timing chart of the component mounting, FIG. 4 showing shapes of irradiating laser beams on lands, and FIG. 5 showing conditions of irradiation with laser beams relative to lands. 
     In FIGS.  1 ( a ) through  1 ( f ), a reference numeral  1  represents an electronic component, a reference numeral  2  designates an adsorbing nozzle which is movable up and down, a reference numeral  3  denotes a substrate, a reference numeral  4  represents lands (electrodes of the substrate) and a reference numeral  5  denotes a solder. 
     The electronic component  1  is a component which has a flat prism-shape and a pair of external electrodes  1   a  at both ends in a longitudinal direction, for example, a chip component such as a chip resistor, a chip capacitor or a chip inductor. 
     The solder  5  is cream solder which consists of basic material made of Sn—Pb series alloy kneaded with a flux and has a melting temperature around 150 to 400 degrees, and is preliminarily coated over entire top surfaces of the lands  4 . Needless to say, a solder  5  which contains basic material, for example, of an Sn series alloy, an Ag series alloy, an IN series alloy or an Au series alloy can be used dependently on kinds and wavelengths of the laser beam LB as well as heat resistance and electrode materials of the electronic component  1  and the substrate  3 . Further, the solder  5  is not limited to the cream solder, and may be precoated by solder plating or another method or have a bump form. 
     In FIG. 2, a reference numeral  11  represents a computer which performs a sequence control of operations of the adsorbing nozzle  2  and laser oscillation, a reference numeral  12  designates a laser power source, a reference numeral  13  denotes a laser oscillator, a reference numeral  14  represents a beam splitter, a reference numeral  15  designates an optical fiber which transmits a laser beam, a reference numeral  16  denotes an objective optical element consisting of a condenser lens, etc., and a reference symbol LB represents a laser beam. 
     The laser oscillator  13  is a laser which has a wavelength in the infrared region, for example a YAG laser, a CO 2  laser or a CO laser having CW oscillation or pulse oscillation and has a power on the order of 100 W. Needless to say, another infrared laser or a visible ray laser such as YAG:SHG may be used. Though a kind and a wavelength of the laser are adequately selected dependently on heat resistances and electrode materials of the electronic component  1  and the substrate  3  as well as kinds and properties of the solder  5 , it is preferable to use the YAG laser which allows a little loss to be caused due to reflection on solder surfaces. The laser oscillator  13  has a built-in shutter (not shown) which controls laser oscillation. 
     The beam splitter  14  is equipped with a half mirror  14   a  and three mirrors  14   b.  This beam splitter  14  splits a laser beam LB emitted from the laser oscillator  13  into two beams having energies matched with each other. Needless to say, a number and a configuration of the mirrors are not limited to those illustrated in the drawing so far as the laser beam LB emitted from the laser oscillator  13  can be split with no difference between their optical paths and projected simultaneously, and the beam splitter may use, for example, the half mirror  14   a  and a single mirror  14   b.    
     The optical fibers  15  transmit the split laser beams LB to the two objective optical elements  16  respectively. The optical fibers  15  are selected from among quartz series fibers, KRS series fibers and other known optical fibers dependently on kinds and wavelengths of the laser to be used. 
     The objective optical elements  16  project the laser beams LB to the two lands  4  corresponding to the electronic component  1 . In the example shown in the drawing, the two objective optical elements  16  are disposed symmetrically on both sides in a longitudinal direction of the electronic component  1  which is perpendicularly lowered at an acute angle relative to a mounting surface of the substrate  3 . 
     Now, processes of component mounting in the first embodiment will be described with reference to FIG.  1  and FIGS. 3 through 5. 
     First, the electronic component  1  supplied to a component supply location (not shown) in an attitude turned sideways is taken out while adsorbing a middle portion of its top surface with the adsorbing nozzle  2 , and the adsorbing nozzle  2  adsorbing the electronic component  1  is shifted over to the substrate  3  and kept at a standby location at which the external electrodes  1   a  of the electronic component  1  are positioned to corresponding the lands  4 . 
     Then, the electronic component  1  is lowered from the standby location by the adsorbing nozzle  2  perpendicularly (at a right angle relative to the mounting surface of the substrate  3 ) at a constant speed and the laser beams LB are projected simultaneously to the solder  5  on the lands  4  as shown in FIG.  1 ( a ) when a predetermined time t 1  has elapsed after starting the lowering. Each of the irradiating laser beams LB has a power of about 1 to 50 W though it is different dependently on heat resistances and electrode materials of the electronic component  1  and the substrate  3  as well as kinds of the solder  5 . 
     As seen from FIG.  1 ( a ), each of the irradiating laser beams LB is inclined at an acute angle θ (approximately 75 degrees in the drawing) relative to the mounting surface of the substrate  3  so that the laser beams LB are irradiated to the solder  5  from both the sides in the longitudinal direction of the electronic component  1 . 
     Though the laser beam LB may have an irradiating shape IS for the land  4  which is circular or elliptic as shown in FIG.  4 ( a ), it is desirable to configure the irradiating shape IS as close as possible to a shape of a planar surface of the land  4  so that the solder  5  is heated and melted without ununiformity as a whole even when the planar shape of the land  4  is rectangular. It is possible to heat the solder  5  uniformly as a whole and prevent the solder from being melted ununiformly by using a mask or the like so as to match the irradiating shape IS of the laser beam LB nearly with a planar shape of the land  4 , for example, when the planar shape of the land  4  is rectangular (see FIG.  4 ( b )) or configuring the irradiating shape IS of the laser beam LB so as to have a circular shape which is nearly matched with a circular planar shape when the land  4  has a circular planar shape (see FIG.  4 ( c )). 
     Further, an image formation heating mode which is configured on a premise to use a mask M as shown in FIG.  5 ( a ) and a focal point heating mode which is configured on a premise not to use a mask as shown in FIG.  5 ( b ) can be utilized as occasion demands for irradiation of the land  4  with the laser beam LB. The image formation heating mode permits obtaining an optional irradiating shape by selecting a mask which has an adequate shape. The focal point heating mode assures no energy loss since the laser beam LB is not shielded by a mask. 
     Upon lapse of a predetermined time t 2  after starting the irradiation with the laser beam LB, the external electrodes  1   a  of the electronic component  1  enter optical paths of the laser beams LB as shown in FIG.  1 ( b ), whereby portions of the irradiating laser beams LB irradiate the external electrodes  1   a  respectively of the electronic component  1 . For the time t 2  mentioned above, each solder  5  is irradiated as a whole with the laser beam LB, thereby being sufficiently heated and melted by an energy of the laser beam LB. 
     Upon lapse of a predetermined time t 3  after the external electrodes  1   a  of the electronic component  1  enter the optical paths of the laser beams LB, bottom surfaces of the external electrodes  1   a  of the electronic component  1  are brought into contact with the melted solders  5  as shown in FIG.  1 ( c ). For the time t 3  mentioned above, the external electrodes  1   a  of the electronic component  1  are heated to a temperature higher than normal temperature by the energy of the laser beams LB. 
     Until a predetermined time t 4  elapses after the external electrodes  1   a  of the electronic component  1  are brought into contact with the melted solders  5 , each of the external electrodes  1   a  is pressed to the melted solder  5 , and the melted solder  5  turns and adheres to other surfaces of each of the external electrodes  1   a  as shown in FIG.  1 ( d ). By the way, the external electrodes  1   a  of the electronic component  1  are pressed to the melted solders  5  under a maximum pressure of 300 to 2000 g. 
     Though irradiation with the laser beam LB is stopped upon lapse of the above-mentioned time t 4 , the pressing of the electronic component  1  is continued till lapse of a predetermined time t 5  after the stop of the irradiation with the laser beam LB. For this time t 5 , the melted solder  5  sets, whereby the external electrodes  1   a  of the loaded electronic component  1  are electrically connected to the lands  4  of the substrate  3  by way of the solders  5 . 
     Upon lapse of the above-mentioned time t 5 , the adsorbing nozzle  2  is freed from a negative pressure and rise, and a mounting of one electronic component  1  completes. 
     By the way, each of the above-mentioned predetermined times t 1 , t 2 , t 3  and t 5  is approximately 10 msec, and the time t 4  is approximately 5 msec. That is, a time required to mount one electronic component  1  is approximately 45 msec as measured from the start of lowering of the electronic component  1  from the standby location, so that the component mounting can be performed in an extremely short time. 
     Further, a time for which the external electrodes  1   a  of the electronic component  1  are irradiated with the laser beams LB (=t 3 +t 4 ) is approximately 15 msec or a ratio of this time relative to t 2  can be defined by an inclination angle θ and a loading speed of the electronic component  1 . In other words, the time for which the external electrodes  1   a  are irradiated with the laser beams LB can be shortened by reducing the angle θ or accelerating a loading speed. 
     The first embodiment, which is configured to press the external electrodes  1   a  of the electronic component  1  after melting the solders  5  with the energy of the irradiating laser beams LB by irradiating the solders  5  on the lands  4  and before the melted solders  5  hardens, is capable of sufficiently heating and melting the solders  5  on the lands  4  with the irradiating laser beams LB, and connecting the external electrodes  1   a  of the electronic component  1  to the lands  4  of the substrate  3  using the solder  5  sufficiently heated and melted. Accordingly, the first embodiment is capable of connecting components extremely favorably with the laser beams LB by solving the problems of improper connection due to residual unmelted solder without setting an energy of the irradiating laser beams LB at a high level. 
     Further, the first embodiment, which is configured to allow the external electrodes  1   a  of the electronic component  1  to enter the optical paths of the laser beams LB so as to be irradiated with the laser beams LB from mid course of the lowering process, heats the external electrodes  1   a  to a temperature higher than normal temperature before soldering, thereby bringing the external electrodes  1   a  into closer contact with the melted solder  5  and carrying out soldering with a higher quality. 
     Furthermore, the first embodiment, which continues the irradiation of the solders  5  with the laser beams LB until the time t 4  elapses after the external electrodes  1   a  of the electronic component  1  are pressed to the melted solder  5 , is capable of maintaining the solder  5  in an adequately melted condition by supplementing heat which is deprived due to the contact with the external electrodes  1   a  and turning the melted solder  5  to the surfaces of the external electrodes  1   a.    
     Still further, the first embodiment, which can complete mounting of one electronic component  1  in approximately 45 msec after the electronic component  1  starts lowering from the standby location, is capable of shortening a time required for mounting per component and accelerating components mounting, and provides an advantage to follow a high speed type electronic components feeding apparatus which is capable of supplying components at a feeding rate of 0.1 sec per component. 
     Moreover, the first embodiment, which is capable of heating and melting only the solders  5  on the lands  4  on which the electronic component  1  is to be mounted, makes it possible to mount components at a narrow pitch and with a high precision by solving a problem posed by the reflow soldering that the solders  5  on adjacent lands  4  are simultaneously heated and melted and caused mutual shorting. 
     Though the first embodiment described above exemplifies the laser beams LB which have a constant power and are subjected to an on-off control for irradiation, it is possible to control the irradiating laser beams LB so as to vary a power thereof. FIG. 6 exemplifies a variable control wherein a power of the irradiating laser beams LB is gradually strengthened to a maximum level after starting irradiation with the laser beams LB until the time t 2  elapses, the power of the irradiating laser beams LB is kept lower than the maximum level after the external electrodes  1   a  of the electronic component  1  enter the optical paths of the irradiating laser beams LB until time t 3  elapses, the power of the irradiating laser beams LB is gradually lowered after the external electrodes  1   a  of the electronic component  1  are brought into contact with the melted solder  5  until the time t 4  elapses and the irradiation with the laser beams LB is stopped upon lapse of the time t 4 . By controlling the power of the irradiating laser beams as described above, it is possible to prevent solder balls or the like from being produced due to abrupt heating of the solder  5  and suppress thermal damage on the electronic component  1  due to irradiation of the external electrodes  1   a  with the irradiating laser beams LB. 
     By the way, it is possible to adopt, as a method for varying the power of the irradiating laser beams LB, not only a method which controls the power source  12  of the laser oscillator  13  but also any one of a method to interpose an intensity adjusting filter such as an ND filter in mid course of the optical path, a method which varies a passing amount of the laser beam LB by interposing an optical element having an intensity control hole such as a slit in mid course of the optical path and a method which varies an energy density of the irradiating laser beam LB using a lens, a beam expander or the like as occasion demands. 
     FIGS. 7 and 8 show methods for irradiation with laser beams which are respectively different from that adopted for the first embodiment. 
     The irradiation method shown in FIGS.  7 ( a ) and  7 ( b ) is configured to irradiate each solder  5  obliquely with laser beams LB from one side in a width direction of the electronic component  1 . Each of the laser beams LB (a laser beam on a deeper side not shown) is inclined at an acute angle θ relative to the mounting surface of the substrate  3  (approximately 75 degrees in the drawings) and projected to each solder  5  obliquely from the one side in the direction of the width of the electronic component  1 . When the laser beams LB are projected as described above, it is possible, similarly to the first embodiment, to melt the solders  5  on lands  4  with the energy of the irradiating laser beams LB, then press external electrodes  1   a  of the electronic component  1  to the melted solders  5  before it sets and warm up the external electrodes  1   a  of the electronic component  1  with the laser beams LB from mid course of the lowering process. 
     The irradiation method shown in FIGS.  8 ( a ) and  8 ( b ) is configured to project each laser beam LB perpendicularly to solders  5  on each land  4  (perpendicularly to a mounting surface of a substrate  3 ). While projecting each laser beam LB (a laser beam on a deeper side not shown) perpendicularly to each solder  5 , a moving path for lowering an electronic component  1  with an adsorbing nozzle  2  is inclined at an acute angle θ relative to the substrate  3  (approximately 50 degrees in the drawings) so that external electrodes  1   a  of the electronic component  1  to be mounted on the substrate  3  are irradiated with portions of the irradiating laser beams LB in the course of the lowering process. When the laser beams LB are projected as described above, it is also possible, similarly to the first embodiment, to melt the solders  5  on the lands  4  with the energy of the irradiating laser beams LB, then press the external electrodes  1   a  of the electronic component  1  to the melted solders  5  before it sets and warm up the external electrodes  1   a  of the electronic component  1  with the laser beams LB from mid course of the lowering process. 
     FIGS.  9 ( a ) through  9 ( b ) show optical systems having configurations which are different from that of the optical system of the first embodiment. 
     The optical system shown in FIG.  9 ( a ) is configured to project laser beams LB to solder on the lands  4  obliquely from one side in a direction of width of an electronic component  1  and applicable to the irradiation method with laser beams shown in FIGS.  7 . Laser beams LB emitted from a laser oscillator (not shown) are projected simultaneously to two lands  4  corresponding to the electronic component  1  by way of optical fibers  15  and objective optical elements  16 . 
     The optical system shown in FIG.  9 ( b ) is configured to project laser beams LB to solder on the lands  4  from both sides in a direction of length or from one side in a direction of width of an electronic component  1 , and applicable to the method shown in FIGS. 1 and 7. Laser beams LB emitted from a laser oscillator (not shown) are projected to reflecting mirrors  17  by way of optical fibers  15  and objective optical elements  16 , and beams reflected by the reflecting mirrors  17  are projected to two lands  4  corresponding to the electronic component  1 . 
     The optical systems shown in FIGS.  9 ( c ) and  9 ( d ) are fundamentally the same as that shown in FIG.  9 ( b ), except for locations and directions of objective optical elements  16  and configuration of reflecting mirrors  17  which are different from those in the optical system shown in FIG.  9 ( b ). In the optical systems shown in FIGS.  9 ( c ) and  9 ( d ), locations of laser beams LB can be adjusted by changing angles of the reflecting mirrors  17 . 
     The optical system shown in FIG.  9 ( e ) is configured to project a laser beam LB perpendicularly to solder on a land  4  and is applicable to the irradiation method with the laser beam shown in FIGS.  8 . Laser beams LB emitted from a laser oscillator (not shown) are projected simultaneously to two lands  4  corresponding to an electronic component  1  by way of optical fibers  15  and objective optical elements  16 . 
     FIGS. 10 show an adsorbing nozzle which has a structure different from that adopted for the first embodiment. 
     An adsorbing nozzle  21  shown in FIGS.  10 ( a ) and  10 ( b ) has a collar portion  21   a  at a tip thereof which covers a top surface of the electronic component  1 . This adsorbing nozzle  21  is capable of suppressing thermal damage on the electronic component  1  since the collar portion  21  functions to prevent laser beams LB from irradiating external electrodes  1   a  of the electronic component  1 , mainly a top surface thereof, which is in mid course of a lowering process. 
     FIGS.  11 ( a ) and  11 ( b ) show adsorbing nozzles which have structures different from that adopted for the first embodiment. 
     The adsorbing nozzle  22  shown in FIG.  11 ( a ) has not only a collar portion  22   a  which covers a top surface of the electronic component  1  but also a cavity  22   b  which is matched with a shape of the top surface of an electronic component  1  inside a collar portion  22   a.  This adsorbing nozzle  22  is capable of preventing the electronic component  1  from being thermally damaged by shielding mainly the top surface of external electrodes  1   a  of the electronic component  1  from laser beams LB in mid course of a lowering process. Further, the cavity  22   b  can be utilized to position the electronic component  1  relative to the adsorbing nozzle  22 . 
     The adsorbing nozzle  23  shown in FIG.  11 ( b ) is equipped at its tip with a filter  23   a  which covers a top surface of the electronic component  1 . The filter  23   a  is composed, for example, of a reflection type ND filter which is formed by depositing chromium on a glass substrate and is capable of suppressing thermal damage of the electronic component  1  by attenuating an intensity of laser beams LB which are to fall mainly on the top surface of external electrodes  1   a  of the electronic component  1 . 
     FIG. 12 illustrates a method which heats and melts the solders  5  by using second laser beams in combination. This method is useful in a case where a substrate  31  which allows transmission of laser beams is used, and is configured to project the laser beams LB 2  to the lands  4  from a bottom side (rear side) of the substrate  31  through the substrate  31  when laser beams LB 1  are projected to the solders  5  on the lands  4  from a top side of the substrate  31 . Since this method makes it possible to supplement heat required for heating and melting the solders  5  with the laser beams LB 2  projected from the bottom side, it is capable of similarly connecting components even by using laser beams at a lower energy level as the laser beams LB 1  from the top side, thereby suppressing thermal damage on the electronic component  1  due to the laser beams LB 1  from the top side. 
     In addition, the method illustrated in FIG. 12 is useful also in a case where a substrate which does not transmit a laser beam is used since it is capable of supplementing the heat for heating and melting the solders  5  by heating portions located mainly under the lands  4  of the substrate with the laser beams LB 2  which are projected to the lands  4  from the bottom side (rear side) of the substrate when the laser beams LB 1  are projected to the solders  5  on the lands  4  from the top side of the substrate. 
     FIGS.  13 ( a ) through  13 ( d ) show a configuration and operations of a system which mechanically controls a timing of irradiation with laser beams. In these drawings, a reference numeral  41  represents a moving arm which supports an adsorbing nozzle  2  so as to be movable up and down under an urging force of a coil spring  42 , a reference numeral  43  designates a switch which is disposed an outside surface of the moving arm  41  and used for turning on laser beams, a reference numeral  44  denotes a light shielding plate which is attached to the moving arm  41 , a reference numeral  44   a  represents a beam passing hole formed in the light shielding plate  44 , and a reference numeral  45  designates a switch which is disposed inside the moving arm  41  and used for turning off the laser beams. An optical fiber  15 , an objective optical element  16  and a reflecting mirror  17  are the same as those shown in FIG.  9 ( d ). 
     When the moving arm  41  lowers for a predetermined distance from a standby position thereof, the switch  43  turns on to allow a laser beam LB to emit through the objective optical element  16  as shown in FIG.  13 ( a ). Since the light shielding plate  44  is interposed between the objective optical element  16  and the mirror  17  at this time, the laser beam LB emerging from the objective optical element  16  is intercepted by the light shielding plate  44 . 
     When the moving arm  41  further lowers, the beam passing hole  44   a  of the light shielding plate  44  becomes coincident with an optical path of the laser beam LB as shown in FIG.  13 ( c ), the laser beam LB emerging from the objective optical element  16  passes through the beam passing hole  44   a  and irradiates the reflecting mirror  17 , whereby a beam reflected by the reflecting mirror  17  is projected to solder on the land  4 . 
     The irradiation with the laser beam is carried out continuously while the electronic component  1  lowers for a distance corresponding to a vertical length of the beam passing hole  44   a.  After an external electrode of the lowering electronic component  1  is pressed to the solder (melted solder) on the land  4 , the adsorbing nozzle  2  penetrates into the moving arm  41  against the urging force of the coil spring  42  as the moving arm  41  lowers. Upon lapse of a predetermined time after the external electrode of the electronic component  1  is pressed to the solder (melted solder) on the land  4 , the light shielding plate  44  enters between the objective optical element  16  and the mirror  17  as shown in FIG.  13 ( d ), whereby the laser beam emerging from the objective optical element  16  is intercepted by the light shielding plate  44 . Simultaneously, the switch  45  which turns off the laser beam is activated by the adsorbing nozzle  2  penetrating into the moving arm  41 , thereby stopping the emission of the laser beam through the objective optical element  16 . 
     By adopting such a configuration, it is possible to mount components as in the first embodiment by mechanically controlling the timing of the irradiation with the laser beam LB without performing a sequence control such as that adopted in the first embodiment. Needless to say, the light shielding plate  44  is not always necessary when the actuating positions of the switches  43  and  45  which turn on and off the laser beam can be defined strictly. 
     FIGS. 14 through 16 illustrate a second embodiment of the present invention. FIG. 14 being a constitutional diagram showing a mounting machine, and an optical system and a control system which are used with the mounting machine, FIG. 15 being a top view of a rotating head, and FIGS. 16 being diagrams showing procedures for correcting a position of an adsorbed electronic component. 
     In FIG. 14, a reference numeral  51  represents a mounting machine, a reference numeral  52  designates a computer which performs a sequence control of the mounting machine and laser oscillation, a reference numeral  53  denotes a laser power source, a reference numeral  54  represents a laser oscillator and a reference numeral  55  designates a beam slitter. The laser power source  53 , the laser oscillator  54  and the beam splitter  55  are the same as those used in the first embodiment and will not be described in componenticular. 
     The mounting machine  51  is equipped with a rotating head  51   a,  twelve rods  51   b  which are disposed on a bottom surface of the rotating head  51   a  at intervals of 30 degrees, adsorbing nozzles  51   c  disposed on bottom surfaces of the rods  51   b  respectively, an XYθ table  51   d  which supports the substrate  3 , a pair of objective optical elements  51   e,  an XY table  51   f  which supports the objective optical elements  51   e  and optical fibers  51   g  which transmit laser beams LB from a beam splitter  55  to the objective optical elements  51   e.    
     The rotating head  51   a  is intermittently rotated counterclockwise as seen from above at intervals of 30 degrees by a driving source (not shown). The rods  51   b  are rotatable around its axial center, and movable up and down, and rotatated or moved up and down by a driving source (not shown). 
     The mounting machine  51  adsorbs the electronic components  1  at a location A of the rotating head  51   a  shown in FIG. 15, inspects heights of the adsorbed components  1  at a location B, inspects and detects widths, lengths and directions of the adsorbed components  1  at a location C, and corrects angles of the adsorbed components  1  at a location D. After correcting a mounting location and a laser beams irradiating locations with at a location E, the mounting machine mounts the adsorbed components  1  on the substrate  3 , discharges defective components at a location F, and cleans nozzles at a location G. 
     Now, description will be made of processes to mount components in the second embodiment. 
     When a rod  51   b  is stopped at the location A by the intermittent rotation of the rotating head  51   a,  the mounting machine  51  first lowers the rod  51   b  from a raised position thereof, takes out the electronic component  1  which is supplied under the location A in an attitude rotated sideways while adsorbing it in the center of the top surface with an adsorbing nozzle  51   c,  and resets the rod  51   b  from a lowered position to the raised position. 
     When the rod  51   b  adsorbing the electronic component  1  is stopped at the location B by the intermittent rotation of the rotating head  51   a,  the mounting machine  51  then photographs an image of a side surface of the electronic component  1  adsorbed by the adsorbing nozzle  51   c  with a CCD camera (not shown) and judges whether or not a height is good on the basis of image data. 
     When the rod  51   b  adsorbing the electronic component  1  is stopped at the location C by the intermittent rotation of the rotating head  51   a,  the mounting machine  51  photographs an image of a bottom surface of the electronic component  1  adsorbed by the adsorbing nozzle  51   c  with a CCD camera (not shown), judges whether or not a width, a length and a direction are good on the basis of image data, and detects deviation amounts in the XYθ directions when the direction is improper. 
     The deviation amounts in the XYθ directions are detected as described below. First, a deviation amount α of the electronic component  1  in the θ direction from a standard line passing through a center P 1  of the adsorbing nozzle  51   c  is detected from the image of the bottom surface of the electronic component  1  obtained with the CCD camera as shown in FIG.  16 ( a ). Then, locations of a center P 1  of the adsorbing nozzle  51   c  and a center P 2  of the electronic component  1  on an XY coordinates system are detected in a condition where the adsorbing nozzle  51   c  is rotated by the angle corresponding to the deviation amount α in the θ direction as shown in FIG.  16 ( b ), thereby detecting deviation amounts in the X direction and the Y direction from relative locations. 
     When the adsorbed component  1  has an deviation amount α in the θ direction in a condition where the rod  51   b  adsorbing the electronic component  1  is stopped at the location D by the intermittent rotation of the rotating head  51   a,  the rod  51   b  is rotated by the angle corresponding to the deviation amount α to correct the deviation. 
     When the adsorbed electronic component  1  has such deviation amounts as those described above in the X direction and the Y direction in a condition where the rod  51   b  is stopped at the location E by the intermittent rotation of the rotating head  51   a,  a mounting location is corrected by displacing the table  51   d  in the XY directions to correct the deviation and locations to be irradiated with the laser beams are corrected by displacing the table  51 f in the XY directions. Then, the mounting machine  51  lowers the rod  51   b  (adsorbing nozzle  51   c ) from the raised position and connects a component through processes which are the same as those illustrated in FIGS.  1 ( a ) through  1 ( f ). 
     When the electronic component  1  is judged as a defective component as results of the dimensional inspections at the locations B and C, component mounting is not carried out at the location E and the electronic component  1  is moved to the location F as it is kept in the adsorbed condition. When the rod  51   b  is stopped at the location F by the intermittent rotation of the rotating head  51   a,  the defective electronic component  1  is released from the adsorption by the adsorbing nozzle  51   c,  allowed to drop by its own weight and recovered into a container or the like. 
     When the rod  51   b  is stopped at the location G by the intermittent rotation of the rotating head  51   a,  air is blasted to the adsorbing nozzle  51   c  to carry out cleaning of a nozzle. 
     As apparent from the foregoing description, the second embodiment is capable of successively carrying out component mounting in the course of the intermittent rotation of the rotating head  51   a  with laser beams which are similar to those used in the first embodiment. 
     Further, the second embodiment is capable of mounting the electronic component  1  at a precise location on the substrate  3  since it is configured to detect deviation amounts in the XYθ directions of the electronic component  1  adsorbed by the adsorbing nozzle  51   c,  and correct the component mounting location and the locations to be irradiated with the laser beams on the basis of the deviation amounts at a stage preceding to the component mounting. 
     Furthermore, the second embodiment is capable of preventing the defective electronic component  1  from being mounted on the substrate  3  by accident since it is configured to detects dimensions of the electronic component  1  adsorbed by the adsorbing nozzle  51   c,  not to carry out the component mounting when the dimensions are judged as improper and recover the electronic component  1  when it is improper in dimensions thereof. 
     The second embodiment is described as an example wherein the objective optical elements  51   e  themselves are moved to correct the locations to be irradiated with the laser beams. When the optical system shown in FIGS.  9 ( b ) through  9 ( d ) which uses the mirrors is used, however, it is possible to similarly correct locations to be irradiated with laser beams by changing angles of the mirrors. Needless to say, it is possible to perform a similar correction by using other optical path changing elements such as prisms. 
     The second embodiment exemplifies adsorbing nozzles which has flat tip surfaces as the adsorbing nozzles  51   c.  When a guide cavity  51   c   1  which has a tapered surface is formed in the adsorbing nozzle  51   c  as shown in FIG.  17 ( a ), however, it is possible to correct a deviation in the θ direction by correcting adsorbed position of the electronic component  1  relative to the adsorbing nozzle  51   c  by utilizing the guide cavity  51   c   1  as shown in FIG.  17 ( b ). 
     In addition, though the electronic component having flat prism-shaped and a pair of the external electrodes at both the ends in the longitudinal direction is exemplified as an electronic component in the first and second embodiments described above, it is needless to say that the mounting method is applicable also to any kind of electronic component such as an electronic component which has a form other than the flat prism-shaped, an electronic component which has external electrodes at locations other than both ends in a longitudinal direction or an electronic component which has lead terminals. 
     Further, though the solder is used as a connecting material in the first and second embodiments described above, component mounting can be carried out using metallic materials other than the solder or electrically conductive resin materials which can be melted by laser beams.