JP4675667B2 - Electronic component mounting method - Google Patents

Description

  The present invention relates to an electronic component mounting method for obtaining an electronic circuit board by mounting electronic parts such as an IC chip, a chip capacitor, and a piezoelectric element on a wiring board.

  2. Description of the Related Art Conventionally, an electronic component having a lead terminal that spreads in a gull wing shape around a package is known as a bonding electrode for bonding to an electrode of a wiring board. For example, QFP (Quad Flat Pack) is used. In this type of electronic component, in order to increase the number of lead terminals (number of I / Os) while maintaining the strength of the lead terminals spreading around the package to some extent, the package size must be increased.

  Therefore, in recent years, electronic devices of the lower surface electrode type in which a plurality of bonding electrodes are arranged in an array on the lower surface of the package are becoming mainstream. For example, LGA (Land Grid Array), BGA (Ball Grid Array), CSP (Chip Size Package), and the like. In these electronic components, the number of I / Os can be increased without increasing the size of the package by disposing flat bonding electrodes in an array on the lower surface of the package.

  Such a bottom electrode type electronic component is generally mounted on a wiring board using a solder paste. Specifically, first, a solder paste is printed on each of the plurality of substrate electrodes in the wiring pattern of the wiring substrate by a printing method using a printing mask. Next, the electronic component is placed on a solder paste printed on the wiring board. Then, in the reflow process, the wiring board is put into a reflow furnace together with the electronic components and heated to melt the solder particles as the conductive bonding material in the solder paste. Thereafter, the molten solder is solidified by cooling, thereby joining the substrate electrode of the wiring board and the joining electrode of the electronic component.

  In such an electronic component mounting method, if the coefficient of thermal expansion differs between the material of the electronic component and the material of the wiring board, the relative position of the electrodes in the reflow process accompanied by heating shifts, causing a misalignment of the bonding position. There is a risk that. In recent years, where finer pitch bonding tends to be required as electronic devices become smaller, a slight difference in coefficient of thermal expansion is expected to appear as a large misalignment in the bonding position. The

  On the other hand, there is conventionally known an electronic component mounting method for performing soldering by irradiating a substrate made of a laser light transmissive material with laser light from the back side thereof (for example, one described in Patent Document 1). ). In this electronic component mounting method, laser light that has passed through a laser light-transmitting substrate is applied to a substrate electrode formed on the front surface of the substrate, thereby causing the substrate electrode to generate heat. As a result, the solder interposed between the substrate electrode and the joining electrode in the lower surface electrode type electronic component is melted to join the two electrodes.

  According to such an electronic component mounting method, rather than heating the electronic component and the wiring board as a whole, the electrode and the surrounding area are locally heated, so that the bonding position shift due to the difference in the coefficient of thermal expansion between each other. Can be suppressed.

JP 9-260820 A

  However, in this electronic component mounting method, there is a risk of causing a bonding failure between the electronic component and the wiring board or scorching the wiring board for the following reason. In other words, even if a substrate made of a laser beam transmitting material is used as the substrate material for the wiring board, it may be burnt or denatured depending on the energy intensity of the laser beam. For this reason, it is necessary to use a laser beam that is weak enough to prevent the substrate material from being burned or denatured and that has an energy intensity that is strong enough to melt a conductive bonding material such as solder. Depending on the combination of the substrate material and the conductive bonding material, the difference between the energy intensity of the former and the energy intensity of the latter becomes considerably small, and it is necessary to strictly adjust the energy intensity of the laser beam. For example, in the case of a combination of a resin material such as polyethylene terephthalate (hereinafter referred to as PET) and lead-free solder, the resin material can be burnt or the solder can be sufficiently melted due to a slight difference in energy intensity. There is not.

  The present invention has been made in view of the above background, and the object of the present invention is to suppress the bonding position deviation between the substrate electrode and the bonding electrode and also suppress the burning of the substrate material and bonding failure. An electronic component mounting method is provided.

In order to achieve the above object, the invention of claim 1 is directed to a wiring board having a substrate made of a laser light transmissive material and a plurality of substrate electrodes which are electrodes formed on the front surface of the substrate. In addition, a mounting step of mounting an electronic component having a plurality of bonding electrodes for bonding to any of the plurality of substrate electrodes so that the corresponding electrodes overlap with each other via a conductive bonding material, By irradiating a laser beam from the back surface side of the wiring substrate and applying the laser beam transmitted through the substrate from the back surface side to the front surface side, the back surface of the substrate electrode, In an electronic component mounting method of mounting an electronic component on the wiring board by performing a bonding step of melting the conductive bonding material interposed between the bonding electrode corresponding to the above and bonding both electrodes, A combination of a wiring board and the above electronic components , When as above described置工, used as the same direction of the projected image of the substrate electrode projected image of the substrate thickness direction of the plurality of the bonding electrode correspond each relation having a portion protruding to the substrate surface direction, Rutotomoni irradiated with laser light and a light-collecting a spot shape having a respective portion protruding from the plane to each of the substrate electrode at the upper Symbol bonding process, a portion which protrudes from the plane in the laser beam The conductive bonding material interposed between the bonding electrode and the substrate electrode after being obliquely reflected toward the center of the optical axis on the surface of the peripheral edge against the peripheral edge of the bonding electrode It is characterized by being applied to the side surface.
According to a second aspect of the present invention, there is provided a plurality of substrates on a wiring substrate having a substrate made of a material that transmits laser light and a plurality of substrate electrodes that are electrodes formed on the front surface of the substrate. A mounting step of mounting an electronic component having a plurality of bonding electrodes for bonding to any of the electrodes so that the corresponding electrodes overlap with each other via a conductive bonding material; and a back surface side of the wiring board The substrate electrode and the bonding electrode corresponding thereto are applied by irradiating the laser beam from the back surface of the substrate electrode with the laser beam transmitted through the substrate from the back surface side toward the front surface side. In the electronic component mounting method of mounting an electronic component on the wiring board by melting a conductive bonding material interposed between the two and joining both electrodes, the wiring board and the electronic component As a combination with In the bonding step, each of the plurality of bonding electrodes has a relationship in which projected images in the substrate thickness direction of the bonding electrodes have portions protruding from the corresponding projected images of the substrate electrodes in the substrate surface direction. A spot-shaped laser beam having a portion protruding from the plane is applied to the substrate, a portion protruding from the plane in the laser beam is applied to the bonding electrode, and a plurality of the bonding components are used as the electronic component. Each of the electrodes has a concave curved surface on the surface facing the wiring board .
Also, the invention of claim 3, in the electronic component mounting method according to claim 1 or 2, in the bonding step, passing the laser beam to the aperture mask opening for the laser passage is formed in the laser beam light shielding member Thus, the laser light having a spot diameter larger than the plane and smaller than the plane of the bonding electrode corresponding to the substrate electrode is applied to each substrate electrode.
According to a fourth aspect of the present invention, in the electronic component mounting method of the third aspect , the aperture mask having a plurality of openings is used.
According to a fifth aspect of the present invention, in the electronic component mounting method according to the fourth aspect , a plurality of aperture masks having different opening patterns are prepared as the aperture mask, and the joining step is performed while switching the aperture mask to be used. It is characterized by implementing.

In these inventions, the electronic component and the wiring board are not heated as a whole, but locally heated by laser light, so that the joining position shift between the electronic component and the wiring board can be suppressed.
Further, the substrate electrode is heated by applying a laser beam irradiated toward the substrate electrode to the substrate electrode. Further, the portion protruding from the substrate electrode in the cross-sectional direction is advanced toward the electronic component without touching the substrate electrode, and from the projection image in the substrate thickness direction of the substrate electrode in the entire region of the bonding electrode. Heat the bonding electrode against the protruding portion. Thereby, the conductive bonding material such as solder interposed between the substrate electrode and the bonding electrode is heated not only from the substrate electrode side but also from the bonding electrode side. Then, unlike a conventional mounting method in which the conductive bonding material is heated only from the substrate electrode side, it is possible to use a laser beam having a lower energy intensity as a laser beam for melting the conductive bonding material. Become. As a result, the conductive bonding material interposed between the substrate electrode and the bonding electrode can be reliably melted while suppressing the burning of the substrate material, and bonding failure between the two electrodes can be suppressed.

  In particular, in the invention of claim 2, not only is the peripheral edge of the laser light applied to the peripheral edge of the bonding electrode to heat the bonding electrode, but also the laser light is irradiated at the peripheral edge of the bonding electrode having a concave curved surface. Is reflected toward the center of the optical axis and applied to the side surface of the conductive bonding material interposed between the center portion of the bonding electrode and the substrate electrode. Thereby, the conductive bonding material can be more efficiently melted by direct irradiation with laser light.

In particular, in the invention of claim 1 , not only is the peripheral edge of the laser light applied to the bonding electrode to heat the bonding electrode, but also the peripheral edge of the condensing laser light is used as the peripheral edge of the bonding electrode. Then, the light is reflected obliquely toward the center of the optical axis and applied to the side surface of the conductive bonding material interposed between the center portion of the bonding electrode and the substrate electrode. Thereby, the conductive bonding material can be more efficiently melted by direct irradiation with laser light.

In particular, in the invention of claim 3, 4 or 5 , by passing laser light through an aperture mask and making the spot diameter smaller than the plane of the bonding electrode, the laser light is directed to the lower surface of the electronic component. , Apply only to the bonding electrode forming portion. As a result, it is possible to avoid a situation in which the laser light is applied to the non-electrode forming portion on the lower surface of the electronic component and is damaged.

In particular, in the invention of claim 4 or 5 , the laser beam is divided into a plurality by an aperture mask, and each is applied to different substrate electrodes or bonding electrodes, whereby a plurality of substrate electrodes can be obtained by one laser irradiation. And a bonding electrode can be bonded simultaneously. As a result, the mounting time can be shortened.

In particular, in the invention of claim 5 , the arrangement pitch of the plurality of laser beams divided by the aperture mask is switched by switching the aperture mask. Accordingly, even when the arrangement pitch of the substrate electrodes and the bonding electrodes is not constant, by appropriately switching the arrangement pitch, it is possible to efficiently perform bonding at a plurality of locations by simultaneous irradiation with laser light.

Before describing an embodiment of electronic component mounting to which the present invention is applied, an electronic component mounting method according to a reference embodiment that is helpful in understanding the present invention will be described. This reference form is an electronic component mounting method (hereinafter simply referred to as a mounting method) in which a plurality of electronic components such as a CSP and a chip capacitor are mounted on an FPC (Flexible Printed Circuits) which is a wiring board.

  FIG. 1 is an enlarged cross-sectional view showing a mother substrate used in this mounting method. In the figure, a mother substrate 1 as a wiring substrate has a circuit pattern made of copper as a conductive material formed on the front surface of a substrate 2 made of a material having laser light transparency. The circuit pattern includes a wiring portion and a plurality of electrode pads 3 provided on the wiring portion. These electrode pads 3 serve as joints with electronic components. Examples of the material of the substrate 2 include soda lime glass, synthetic quartz, borosilicate glass, and ceramic that can transmit YAG laser light having a wavelength of 1064 [nm]. Further, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), amorphous polyolefin, ceramic, 4,4 ′ diaminodiphenyl ether / pyromellitic anhydride polycondensate may be used. The 4,4 ′ diaminodiphenyl ether / pyromellitic anhydride polycondensate is a resin obtained by mixing dimethylacetamide with polyimide, and is sold, for example, by Toray DuPont under the trade name “Kapton”. Among the materials of the substrate 2 listed above, PEN is particularly suitable because it is a material having a relatively low coefficient of thermal expansion.

  In this mounting method, a bonding layer is interposed between a plurality of bonding electrodes provided on the lower surface of the electronic component placed on the front surface of the mother substrate 1 and the electrode pads 3 of the mother substrate 1. Then, the bonding layer is melted by the heat of the electrode pad 3 heated by the YAG laser light irradiation, and the bonding electrode and the electrode pad 3 are bonded.

  As a method for interposing the bonding layer between the bonding electrode and the electrode pad 3, a method in which the surface of the electrode pad 3 covered with a bonding layer made of a metal material such as gold or tin is used as the mother substrate 1. It can be illustrated. Alternatively, the electronic component may be a method in which each of a plurality of bonding electrodes provided on the lower surface thereof is coated with a bonding layer made of a metal material. Alternatively, a method of printing a solder paste lump on each surface of each electrode pad 3 of the mother substrate 1 using a printing mask may be used. Hereinafter, the present mounting method will be described by taking as an example the case of employing a method of printing a solder paste lump.

  In the solder paste lump printing process, an adhesion process in which a printing mask as a stencil is adhered to the front surface of the mother board 1, a filling process in which each hole of the adhered printing mask is filled with a solder paste, and a printing mask are provided. And a peeling step of peeling from the mother substrate. Specifically, first, as shown in FIGS. 2 and 3, the printing mask 4 is brought into close contact with the front surface of the mother substrate 1 on which the circuit pattern is formed. The print mask 4 is formed with a print pattern including a plurality of through holes 4 a corresponding to the electrode pads 3 of the mother substrate 1. In the adhesion process, the printing mask 4 is adhered to the mother substrate 1 while performing alignment so that each through hole 4a of the printing mask 4 is positioned directly above each electrode pad 3. When such an adhesion process is completed, next, as shown in FIG. 4, the solder paste 6 is printed on the printing side surface of the printing mask 4 that is in close contact with the mother substrate 1 by using a squeegee 5. A solder paste is filled in each through-hole 4a of the mask 4. Then, as shown in FIG. 5, the printing mask 4 is peeled off from the mother substrate 1, and the solder paste 6 in each through hole 4 a is transferred onto the electrode pad 3 of the mother substrate 1.

  After performing the printing process in this way, next, a mounting process for mounting the electronic component on the front surface of the mother substrate 1 and a bonding process for bonding the electrode pad 3 and the electronic component by laser irradiation are performed. To do. Although all the electronic components are placed on the mother substrate 1 in a single placement process, the joining process may be performed on each electronic component. However, the electronic components are joined while being placed little by little. May be. In this case, the placing process and the joining process are repeated alternately. Hereinafter, this mounting method will be described by taking as an example a method of alternately repeating the placing step and the joining step.

  FIG. 6 is a schematic configuration diagram showing a mounting apparatus used in this mounting method. This mounting apparatus includes a laser irradiation unit having a laser oscillator 100 and the like, an XY table 110, a mounter unit having a component suction nozzle 120 and the like. In performing the mounting process and the bonding process, first, the mother substrate 1 that has finished the printing process is fixed on the XY table 110 of the mounting apparatus. The XY table 110 is configured to be movable in the X direction, which is the left-right direction in the figure, and the Y direction, which is the depth direction in the figure, by a known technique. A chamber chamber 111 is formed inside the XY table 110. A suction means (not shown) made of a blower or the like is connected to the chamber chamber 111, whereby the air in the chamber chamber 111 is sucked, whereby the inside of the chamber chamber 111 is decompressed. The top plate 112 and the bottom plate 113 of the XY table 110 are glass plates that exhibit laser beam transparency, and the top plate 112 has numerous suction holes (not shown) formed therein. The mother substrate 1 as a work placed on the top plate 112 is fixed on the XY table 110 by being sucked into the suction holes as the pressure in the chamber chamber 111 is reduced.

  FIG. 7 is an enlarged configuration diagram illustrating a mounter unit of the mounting apparatus. The mounter unit includes a component suction nozzle 120, an optical monitoring device 121, a monitor 122, and the like. The component suction nozzle 120 is fixed to a robot arm (not shown), and the electronic component 200A can be sucked by the negative pressure generated at the tip of the nozzle. In the placement process, the component suction nozzle 120 is brought to the electronic component 200A placed in a jig (not shown) by the operation of the robot arm, and is sucked by the component suction nozzle 120. Next, the component suction nozzle 120 is moved onto the mother board 1 sucked and fixed on the XY table by operating the robot arm. Then, an optical monitoring device 121 fixed to a movable support base (not shown) is interposed between the mother board 1 and the component suction nozzle 120. The optical monitoring device 121 simultaneously captures an image of the lower surface of the electronic component 200 </ b> A adsorbed by the component adsorbing nozzle 120 that exists immediately above it and an image of the front surface of the mother board 1 that exists immediately below it. Thus, both images can be superimposed and projected on the monitor 122. The operator moves an XY table (not shown) in the XY direction while watching the image displayed on the monitor 122. Then, the plurality of bonding electrodes 200a formed on the lower surface of the electronic component 200A and the solder paste printed on each of the plurality of electrode pads 3 of the mother substrate 1 are aligned so as to be perfectly overlapped with each other. . Next, after retracting the optical monitoring device 121 from under the component suction nozzle 120, the component suction nozzle 120 is vertically lowered toward the mother substrate 1 by operating the robot arm. Then, as shown in FIG. 8, the electronic component 200 </ b> A is placed on the solder paste 6, and the solder paste 6 and the electronic component 200 </ b> A are stacked on the front surface of the mother board 1. After placing the electronic component 200, the suction of the electronic component 200A by the component suction nozzle 120 is stopped, and then the component suction nozzle 120 is pulled up vertically. In addition, it is also possible to automate the work performed by the operator by performing computer analysis on the video displayed on the monitor 122 using image analysis software or the like.

  Some electronic components 200 have a plurality of flat bonding electrodes arranged in an array on the lower surface of a package, such as LGA, BGA, and CSP. In some cases, flat electrodes are provided only near both longitudinal ends of the lower surface of the package, such as chip capacitors and chip resistors. Among these electronic components 200, the latter one tends to cause chip standing due to a tombstone phenomenon. Only one end portion in the longitudinal direction is soldered, and the other end portion is separated from the solder, and the package is fixed in a standing state.

  In this mounting method, among all the electronic components 200 mounted on the mother substrate 1, first, LGA, BGA, and CSP that are difficult to cause chip standing are collectively placed on the mother substrate 1. And a 1st joining process is implemented, leaving the chip capacitor and chip resistance which are easy to raise | generate a chip | tip remain without mounting. When this first bonding process is completed, next, chip capacitors and chip resistors that are likely to cause chip standing are mounted. At this time, one of them is mounted and then bonded. Repeat the process. That is, in the first placement process and the joining process, electronic components that are unlikely to stand up are placed and joined together. In the second and subsequent placement processes and the joining process, the electronic component 1 is used. The process is repeated for each one.

Next, a characteristic configuration of the mounting method will be described.
FIG. 9 is a cross-sectional view showing the mother substrate 1 and a plurality of electronic components 200 placed on the front surface thereof in the first placement step. The two electronic components 200A and 200B shown in the figure are of different types, and the size and arrangement pitch of the bonding electrodes 200a and 200b formed on the lower surface are different. In order to correspond to such a difference, the size and arrangement pitch of the electrode pads 3 are different in the regions Ra and Rb corresponding to the respective electronic components 200A and 200B on the mother substrate 1. More specifically, the bonding electrode 200a of the electronic component 200A shown on the left side in the drawing has a smaller planar area and arrangement pitch than the bonding electrode 200b of the electronic component 200B shown on the right side of the drawing. In order to cope with this, the electrode pad 3 in the region Ra also has a smaller plane area and arrangement pitch than the electrode pad 3 in the region Rb.

  The point to be noted here is that the bonding electrode and the electrode pad 3 have different plane areas and arrangement pitches depending on the type of the electronic component. The bonding electrode has a larger plane area than the electrode pad 3. For example, among the plurality of electrode pads 3 formed on the front surface of the mother substrate 1, the electrode pad 3 formed in the region Ra corresponds to the bonding electrode 200a of the electronic component 200A on the left side in the drawing. is there. The bonding electrode 200a of the electronic component 200A on the left side in the drawing has a larger planar area than these electrode pads 3 (electrode pads formed in the region Ra). Although the planar area is smaller than that of the electrode pad 3 formed in the region Rb, these electrode pads 3 do not correspond to the electronic component 200A on the left side in the drawing, but correspond to the electronic component 200B on the right side in the drawing. . In the electronic component 200B on the right side in the figure, the bonding electrode 200b also has a larger plane area than the electrode pad 3 in the region Rb corresponding thereto. Thus, in the combination of bonding electrodes and electrode pads corresponding to each other, the former always has a larger plane area. In such a relationship, in the combinations corresponding to each other, as shown in FIG. 10, the projected image of the bonding electrode in the substrate thickness direction protrudes beyond the projected image of the electrode pad 3.

  FIG. 11 is an enlarged cross-sectional view showing a state of the mother substrate 1 and the electronic component 200A (the left electronic component in FIG. 9) in the first bonding step. In this mounting method, each electrode pad 3 which is a substrate electrode of the mother substrate 1 is irradiated with YAG laser light having a spot diameter larger than the plane area. In the first bonding step, the YAG laser light L irradiated from the back side of the substrate toward the region Ra of the mother substrate 1 first passes through the laser light transmissive substrate 2 in the mother substrate 1. As the substrate 2, a material in which a lubricant is not kneaded with the material PEN is used. Therefore, damage to the substrate 2 caused by reacting the lubricant in the PEN with the YAG laser light L can be avoided.

  As shown in the figure, the central portion of the YAG laser light L that has passed through the substrate 2 hits the back surface of the electrode pad 3 made of copper in the region Ra. As a result, the temperature of the electrode pad 3 is increased and the lump of solder paste 6 formed on the surface of the electrode pad 3 is heated. On the other hand, the peripheral edge portion of the YAG laser light L that has passed through the substrate 2 proceeds toward the electronic component 200 </ b> A without hitting the electrode pad 3. Then, it hits the peripheral edge of the bonding electrode 200a having a larger planar area than the electrode pad 3. As a result, the temperature of the bonding electrode 200a is raised and the lump of solder paste 6 in contact with the surface thereof is heated. Thus, in this mounting method, the lump of the solder paste 6 interposed between the electrode pad 3 serving as the substrate electrode and the bonding electrode 200a is not only from the electrode pad 3 side, but also from the bonding electrode 200a side. Also heat from. The heated solder paste lump 6 is caused to evaporate the flux component inside thereof and to melt innumerable solder grains inside. In this mounting method, unlike the conventional mounting method in which the solder is heated only from the electrode pad 3 side, the YAG laser light for melting the solder as the conductive bonding material has a lower energy intensity. Things can be used. As a result, it is possible to reliably melt the solder interposed between the electrode pad 3 and the bonding electrode 200a while suppressing the burning of the substrate 2 and to suppress the bonding failure between the two electrodes.

  FIG. 12 is an enlarged cross-sectional view showing a state of the mother substrate 1 and the electronic component 200B (the electronic component on the right side in FIG. 9) in the first bonding step. In the figure, each electrode pad 3 in the region Rb has a larger planar area than the electrode pad 3 in the region Ra previously shown in FIG. Is irradiated with a YAG laser beam L having a large spot diameter. Accordingly, the peripheral edge portion of the YAG laser beam L can be applied to the peripheral edge portion of the bonding electrode 200b without being applied to the electrode pad 3 and heated.

  When all of the electronic components that are unlikely to stand up on the mother substrate 1 have been joined in the first joining step, the electronic parts that are likely to stand up are placed and joined. At this time, after performing the placement process and the joining process for one electronic component, the operation of performing the placement process and the joining process of the next electronic component is repeated. Hereinafter, such a repeated process is referred to as a placement joining repeated process.

  In this placement and bonding repeating step, first, as shown in FIG. 13, an electronic component 200 </ b> C that is easy to stand up is placed on the mother substrate 1 by the component suction nozzle 120. As shown in the figure, even in the placement bonding repeating step, all the bonding electrodes 200c formed on the lower surface of the electronic component 200C have a larger planar area than the corresponding electrode pads 3 on the mother substrate 1, respectively. Thus, the electrode pattern of the mother substrate 1 is configured.

  When the first mounting step in the mounting and joining repeating step is finished, the YAG laser light L is applied to the back surface of the substrate while pressing the electronic component 200C toward the mother substrate 1 by the component suction nozzle 120 as shown in FIG. Irradiate from the side. At this time, among the plurality of electrode pads 3 formed on the mother substrate 1, the YAG laser light L having a spot diameter larger than the plane area is applied to the electrode pad 3 to be laser irradiated. . Therefore, the lump of solder paste 6 interposed between the bonding electrode 200c and the electrode pad 3 is heated not only from the electrode pad 3 side but also from the bonding electrode 200c side. When the joining of all the joining electrodes 200c in the electronic component 200C is completed, the component suction nozzle 120 is pulled up as shown in FIG. Needless to say, the mother substrate 1 is not moved from the start of the first mounting process until the lifting of the component suction nozzle 120 is completed.

  When the first placement process and the joining process in the placement joining repetition process are completed, the placing process and the joining process are performed for the next electronic component. By repeating this, all electronic components are finally mounted on the mother board 1.

  In such a placement and bonding repeating process, the electronic component 200C is pressed against the mother substrate 1 from the melting to the solidification of the solder grains, thereby avoiding chip standing due to the Tombstone phenomenon (Manhattan phenomenon). .

Next, a mounting method according to each embodiment will be described. Mounting method according to the embodiments, the mounting method according to a reference embodiment is obtained by adding a more characteristic configuration.
[First Embodiment ]
Figure 16 is an enlarged sectional view showing an electronic component 200D used in the mounting method according to the first embodiment. In this mounting method, as all the electronic components mounted on the mother board (1), those whose bottom surface (opposite surface to the mother board) is a concave curved surface are used as in the illustrated bonding electrode 200d.

  FIG. 17 is an enlarged cross-sectional view showing a state of the mother substrate 1 and the electronic component 200D in the first bonding step of the mounting method. As shown in the drawing, the peripheral portion of the YAG laser beam L transmitted through the substrate 2 having laser beam transparency from the back surface to the front surface is an electrode formed on the front surface of the mother substrate 1. When hitting the pad 3, the process proceeds to the electronic component 200D as it is. Then, it hits the peripheral edge of the concave curved surface of the bonding electrode 200d made of gold provided on the lower surface of the electronic component 200D. A part of the YAG laser light L that has been struck is reflected on the surface of the bonding electrode 200d without being absorbed by the bonding electrode 200d made of gold. At this time, since the bonding electrode 200d has a concave curved surface, the reflected YAG laser light L travels toward the center of the optical axis (the center of the bonding electrode). Then, the solder paste 6 is directly heated against the side surface of the lump of the solder paste 6 interposed between the center portion of the bonding electrode 200d and the electrode pad 3. By this direct heating, the solder grains in the solder paste 6 can be more efficiently melted.

[Second Embodiment ]
Figure 18 is an enlarged sectional view showing a state of the mother substrate 1 and the electronic component 200E in the first bonding step of mounting method according to the second embodiment. As shown in the figure, the YAG laser beam L irradiated from the back side to the mother substrate 1 travels almost in parallel with the optical axis, while the peripheral portion is inclined toward the optical axis. It is a condensing laser beam. After passing through the substrate 2, the peripheral edge of the YAG laser light L having the light collecting property does not hit the electrode pad 3 but hits the peripheral edge of the bonding electrode 200 e of the electronic component 200 </ b> E. A portion of the YAG laser beam L that has been struck is not absorbed by the bonding electrode 200e made of gold but reflected by the surface of the bonding electrode 200e. At this time, due to the light condensing property, the electrode surface is reflected in an oblique direction toward the optical axis. Then, the solder paste 6 is directly heated by hitting the side surface of the lump of the solder paste 6 interposed between the center portion of the bonding electrode 200e and the electrode pad 3. By this direct heating, the solder grains in the solder paste 6 can be more efficiently melted.

[Third Embodiment ]
Figure 19 is a block diagram showing the mounting apparatus used for mounting method according to the third embodiment. The laser irradiation unit of the mounting apparatus includes a laser oscillator 100 that transmits YAG laser light L, a first condenser lens 101, an optical fiber 102, a second condenser lens 103, a mask disk rotator 104, an imaging lens 105, and the like. ing. The YAG laser light L emitted from the laser oscillator 100 becomes a Gaussian beam having a mountain-shaped energy intensity distribution as shown in FIG. Then, an image is formed on one end face of the optical fiber 102 by the first condenser lens 103 and enters the optical fiber 102. There are various types of optical fibers that are laser light conducting members, such as step index (SI) type, graded index (GI) type, and single mode (SM) type. Is. In the SI type optical fiber 102, as shown in FIG. 21, a part of the laser light advances from the laser incident side to the emission side while being multiple-reflected by the inner wall of the fiber. When multiple reflection is performed in this manner, the laser beam becomes a top hat beam having a trapezoidal energy intensity distribution as shown in FIG. That is, the SI optical fiber 102 functions as an intensity distribution uniformizing optical system that uniformizes the intensity distribution in the cross-sectional direction of the laser light.

  In FIG. 19 described above, the YAG laser light L whose energy intensity distribution is made uniform in the optical fiber 102 is attached to the mask disk 104a of the mask disk rotator 104 by the second condenser lens 103 (not shown). An image is formed on the lower surface of the aperture mask.

  FIG. 23 is a plan view showing the mask disk 104a. A plurality of aperture masks 104d having different opening patterns are mounted on the disc-shaped mask disc 104a so as to be arranged in the circumferential direction. The center of the mask disk 104a is fixed to the motor shaft 104b. The mask disk rotator 104 shown in FIG. 19 operates in the optical path of the YAG laser light L among the plurality of aperture masks mounted on the mask disk rotator 104 by operating the motor 104c that rotates the motor shaft 104d. You can switch what you position. The YAG laser light L imaged on the lower surface of the aperture mask is divided into a plurality of parts by passing through a plurality of openings of the aperture mask. The plurality of divided lights obtained by the division are sequentially transmitted through the imaging lens 105, the glass bottom plate 113 and the top plate 112 of the XY table 110, and reach the lower surface of the mother substrate 1. Then, after passing through the base layer of the mother substrate 1, the central portion corresponds to the electrode pad 3. The electrode pad 3 is heated by irradiation with YAG laser light and melts the solder grains of the solder paste printed on the upper surface thereof. Further, the peripheral edge portion of the YAG laser beam L hits the peripheral edge portion of the bonding electrode of the electronic component and heats the bonding electrode. This also melts the solder grains. The molten solder particles are solidified with natural cooling, whereby the electrode pads of the mother board and the electronic components are joined.

  In such a joining step, the energy distribution in the cross-sectional direction of the YAG laser light L is made uniform by the optical fiber 102, so that the energy difference between the center portion and the outer edge portion of the YAG laser light L is made extremely small. When the central portion of the YAG laser beam L after the homogenization is set to an energy intensity that is weak enough not to cause scorching or modification to the PET that is the base layer material of the mother substrate 1 and strong enough to melt the solder grains, The outer edge portion is set to substantially the same setting. Further, the energy intensity sufficient to melt the solder grains can be exerted also on the outer edge portion. Therefore, it is possible to sufficiently melt the solder grains and suppress the bonding failure between the electrode pad (3) of the mother substrate 1 and the electronic component.

  In the first bonding step, the YAG laser light L is intermittently irradiated while the mother substrate 1 is continuously moved in the direction orthogonal to the optical axis of the YAG laser light L by the XY table 110, thereby a plurality of solders. The paste is melted sequentially. Specifically, for example, in FIG. 19 shown above, first, an aperture mask having 4 × 8 = 32 aperture patterns formed by rotation of the mask disk 104a is selected. Then, as shown in FIG. 24, the mother substrate 1 is moved in the X direction by moving the XY table. Next, of the 64 electrode pads 3 corresponding to the 8 × 8 = 64 bonding electrodes 200a formed on the lower surface of the electronic component 200A, 4 × 8 = 32 electrode pads 3 move to the laser irradiation position. The YAG laser beam is emitted at the timing. Then, the YAG laser light L divided into 32 by the aperture mask passes through the substrate 2 of the mother substrate 1 and strikes the lower surfaces of these 32 electrode pads 3 as shown in FIG. As a result, as shown in FIG. 26, 32 out of 64 solder pastes 6 corresponding to the 64 joining electrodes 200a of the electronic component (only 4 are shown, but 8 are arranged in the depth direction, respectively). Melting). The YAG laser light L that has passed through the aperture ask has a spot area that is larger than that of the electrode pad 3 and smaller than that of the bonding electrode 200a. Therefore, the peripheral portion of each YAG laser beam L reliably hits the bonding electrode 200a and does not hit the non-electrode forming portion of the electronic component 200A. Thus, the electronic component is obtained by applying the YAG laser light L to the non-electrode forming portion of the electronic component 200A while reliably heating the solder paste 6 interposed between the electrode pad 3 and the bonding electrode 200a from both electrode sides. Damage of 200A can be avoided.

  If the YAG laser light L is simultaneously irradiated to the 32 bonding electrodes 200a, then the 64 bonding electrodes 200a of the XY table electronic component 200A are moved while the mother substrate 1 is moved in the X direction. Of the corresponding 64 electrode pads 3, 32 are not yet irradiated with the YAG laser light L, and the timing of moving to the laser irradiation position is measured. Then, the YAG laser beam L is emitted at that timing. Then, the YAG laser beam L divided into 32 by the aperture mask hits the lower surfaces of the remaining 32 electrode pads 3 as shown in FIG. Thereby, the remaining 32 solder pastes 6 are melted. As described above, the first electronic component 200A and the mother substrate 1 are joined.

  There are still a plurality of electronic components that are not joined on the mother substrate 1. Therefore, the movement of the mother substrate 1 is continued as it is, and the timing at which the next electronic component moves to the laser irradiation position is estimated. And if it moves, YAG laser beam L will be emitted and it will join.

  The plurality of electronic components mounted on the mother substrate 1 are not all of the same type. There are many different types. If the types of electronic components are different, the electrode pattern on the lower surface of the package and the corresponding arrangement pattern of the electrode pads 3 of the mother substrate 1 are different. Then, a situation occurs in which the aperture pattern of the aperture mask is not suitable for the arrangement pattern of the electrode pads 3 to be bonded. Therefore, in this mounting method, when the opening pattern is no longer suitable for the arrangement pattern of the electrode pads 3 to be joined, the aperture mask is made suitable for the arrangement pattern by the rotation of the mask disk 104a shown in FIG. Switch to something.

  In the first joining step as described above, the outer edge portion of the YAG laser beam L is cut by passing the YAG laser beam L after the intensity distribution is made uniform by the optical fiber 102 through the aperture mask. Then, instead of the trapezoidal energy distribution shown in FIG. 22, YAG laser light L having a rectangular energy distribution, that is, no energy intensity difference between the central portion and the outer edge portion can be obtained.

  Further, the YAG laser light L is divided into a plurality of portions by an aperture mask, and each is applied to the electrode pads 3 existing at different positions, whereby a plurality of solders can be melted simultaneously by one laser irradiation. As a result, the time required for the joining process can be reduced.

  Further, by switching the aperture mask by the rotation of the mask disk 104a, it is possible to sequentially join a plurality of electronic components 200 having different electrode patterns without interrupting the operation.

  In addition, the YAG laser light L is emitted at an appropriate timing while the mother substrate 1 is continuously moved, and a plurality of solders are sequentially melted, so that three processes of moving, stopping, and laser irradiation of the mother substrate 1 are performed. The time can be shortened compared with the case of repeating.

  So far, the example of melting the solder particles in the solder paste 6 by one laser irradiation has been described. However, the same electrode pad is irradiated with the laser multiple times to melt the conductive bonding material such as solder. May be.

The expanded sectional view which shows the mother board | substrate used for the mounting method which concerns on a reference form. The expanded sectional view which shows the printing mask used for the mounting method with the mother board | substrate. The expanded sectional view which shows the contact | adherence process of the printing method used for the mounting method. The expanded sectional view which shows the filling process of the printing method. The expanded sectional view which shows the peeling process of the printing method. The schematic block diagram which shows the mounting apparatus used for the mounting method. The expanded block diagram which shows the mounter part of the mounting apparatus. The expanded sectional view which shows the component adsorption nozzle of the mounter part with the mother board | substrate. Sectional drawing which shows a mother board | substrate and the some electronic component mounted in the front surface of this in the 1st mounting process in the mounting method. The top view which shows a mother board | substrate and an electronic component from a board | substrate back surface side. The expanded sectional view which shows the state of the mother board | substrate and electronic component in the 1st joining process of the mounting method. The expanded sectional view which shows the state of the mother board | substrate and other electronic component in the 1st joining process. The expanded sectional view which shows the mother board | substrate and electronic component in the mounting process of the 1st time implemented by the mounting joining repetition process of the mounting method. The expanded sectional view which shows the mother board | substrate and electronic component in the joining process of the 1st time implemented by the same mounting joining repetition process. The expanded sectional view which shows the same motherboard and electronic component which the 1st joining process was completed. Enlarged sectional view showing an electronic component used in the mounting method according to the first embodiment. The expanded sectional view which shows the state of the mother board | substrate and electronic component in the 1st joining process of the mounting method. Enlarged cross-sectional view illustrating a state of a mother board and the electronic component in a first bonding step of mounting method according to the second embodiment. Diagram showing the mounting apparatus used for mounting method according to the third embodiment. The graph which shows energy intensity distribution of a Gaussian beam. The schematic diagram which shows the behavior of the laser beam in SI type optical fiber. The graph which shows energy intensity distribution of a top hat beam. The top view which shows the mask disk of the same mounting apparatus. Sectional drawing for demonstrating the initial stage of the 1st joining process in the mounting method. Sectional drawing for demonstrating the 1st laser irradiation in the 1st joining process. Sectional drawing which shows the state immediately after completion | finish of the laser irradiation. Sectional drawing for demonstrating the 2nd laser irradiation in the 1st joining process.

Explanation of symbols

1 Mother board (wiring board)
2 Substrate 3 Electrode pad (Substrate electrode)
6 Solder paste (contains conductive bonding material)
104d Aperture mask 200A, B, C, D, E Electronic component 200a, b, c, d, e Bonding electrode L YAG laser beam

Claims (5)

On a wiring board having a substrate made of a material that is transparent to laser light and a plurality of substrate electrodes that are electrodes formed on the front surface thereof, for bonding to any of the plurality of substrate electrodes A mounting step of mounting electronic components having a plurality of bonding electrodes such that the corresponding electrodes overlap with each other via a conductive bonding material;
By irradiating a laser beam from the back surface side of the wiring substrate and applying the laser beam transmitted through the substrate from the back surface side to the front surface side, the back surface of the substrate electrode, In an electronic component mounting method for mounting an electronic component on the wiring board by performing a bonding step of melting the conductive bonding material interposed between the bonding electrode corresponding to the above and bonding both electrodes,
As a combination of the wiring board and the electronic component, in the placing step, the projected images in the substrate thickness direction of the plurality of bonding electrodes respectively correspond to the corresponding projected images of the substrate electrodes in the substrate surface direction. used as the relationship with the part protruding to, Rutotomoni rely on SL laser light and a light-collecting a spot shape having a portion protruding from the plane respectively for each substrate electrode at the bonding step, the The portion of the laser beam that protrudes from the plane is applied to the peripheral edge of the bonding electrode and reflected obliquely toward the center of the optical axis on the peripheral surface, and then the bonding electrode and the substrate electrode An electronic component mounting method, wherein the electronic component mounting method is applied to a side surface of the conductive bonding material interposed therebetween . On a wiring board having a substrate made of a material that is transparent to laser light and a plurality of substrate electrodes that are electrodes formed on the front surface thereof, for bonding to any of the plurality of substrate electrodes A mounting step of mounting electronic components having a plurality of bonding electrodes such that the corresponding electrodes overlap with each other via a conductive bonding material;
By irradiating a laser beam from the back surface side of the wiring substrate and applying the laser beam transmitted through the substrate from the back surface side to the front surface side, the back surface of the substrate electrode, A bonding step of melting the conductive bonding material interposed between the bonding electrodes corresponding to and bonding both electrodes
In an electronic component mounting method for mounting an electronic component on the wiring board,
As a combination of the wiring board and the electronic component, in the placing step, the projected images in the substrate thickness direction of the plurality of bonding electrodes respectively correspond to the corresponding projected images of the substrate electrodes in the substrate surface direction. Using a part having a protruding part, a spot-shaped laser beam having a part protruding from the plane is applied to each substrate electrode in the bonding step, and a part protruding from the plane in the laser beam is applied. A method of mounting an electronic component, wherein the electronic component is applied to the bonding electrode and the surface facing the wiring board in each of the plurality of bonding electrodes is a concave curved surface. In the electronic component mounting method according to claim 1 or 2 ,
By passing the laser beam through an aperture mask in which a laser beam opening is formed in the laser beam shielding member in the bonding process, each substrate electrode is larger than the plane and corresponds to the substrate electrode. An electronic component mounting method, wherein the laser beam having a spot diameter smaller than the plane of the bonding electrode is applied. In the electronic component mounting method according to claim 3 ,
What is claimed is: 1. An electronic component mounting method, comprising: using the aperture mask having a plurality of openings. In the electronic component mounting method according to claim 4 ,
An electronic component mounting method comprising preparing a plurality of aperture masks having different opening patterns as the aperture mask and performing the joining step while switching the aperture mask to be used.

Images