Patent Publication Number: US-2015070924-A1

Title: Printed circuit board and vehicular lamp

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2013-187578 filed on Sep. 10, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a printed circuit board on which a surface mount device is mounted, and a vehicular lamp including the printed circuit board. 
     2. Description of Related Art 
     There is known a vehicular lamp including a plurality of LEDs and a plurality of reflectors that respectively reflect light from the LEDs (see, for example, Japanese Patent Application Publication No. 2011-81975 (JP 2011-81975 A)). 
     In a vehicular lamp including an LED and a parabolic reflector, when the LED and the reflector have positional relationship as designed, a distribution pattern is formed at a desired position ahead of the vehicle. 
     The LED is usually mounted on a printed circuit board by soldering the electrodes of the LED on lands formed on the printed circuit board. However, the LED may be moved with respect to the lands while the solder is molten, so there is a possibility that the LED is not mounted at the position as designed. In this case, the positional relationship between the LED and the reflector breaks as designed is not realized, so there is a possibility that the distribution pattern deviates from the desired position. 
     SUMMARY OF THE INVENTION 
     The invention provides a printed circuit board and a vehicular lamp that are able to improve the accuracy of mounting an electronic device onto the printed circuit board. 
     A first aspect of the invention provides a printed circuit board on which a surface mount device is mounted. The printed circuit board includes a plurality of lands respectively soldered to a plurality of electrodes of the surface mount device. The plurality of lands includes at least a pair of adjacent lands each of which has a side surface not covered with a solder resist, and the side surfaces not covered with the solder resists are opposite to each other. 
     A shape of at least one of the adjacent lands may be the same as a shape of the electrode that is soldered onto the at least one of the adjacent lands. A size of at least one of the adjacent lands may be smaller than or equal to a size of the electrode that is soldered onto the at least one of the adjacent lands. 
     A thickness of each land may be larger than or equal to twice as large as a thickness of the solder resist provided on the printed circuit board and smaller than or equal to six times as large as the thickness of the solder resist. 
     A second aspect of the invention provides a vehicular lamp. The vehicular lamp includes: the printed circuit board according to the first aspect; a light-emitting element mounted on the printed circuit board; and an optical member that is fixed to the printed circuit board and radiates light emitted from the light-emitting element forward. 
     A plurality of the light-emitting elements may be mounted on the printed circuit board, and the optical member may include a plurality of reflectors each of which reflects light emitted from a corresponding one of the light-emitting elements. 
     With the above configuration, it is possible to improve the accuracy of mounting an electronic device onto the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a schematic horizontal cross-sectional view of a vehicular lamp according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional view of the vehicular lamp, taken along the line II-II in  FIG. 1 ; 
         FIG. 3  is a view that shows a high-beam distribution pattern that is formed by a high-beam lamp unit; 
         FIG. 4  is a view that shows a low-beam distribution pattern that is formed by a low-beam lamp unit; 
         FIG. 5  is a view that shows a device mounting surface of a high-beam circuit board; 
         FIG. 6  is a view for illustrating an assembled structure of the high-beam circuit board and a high-beam reflector unit; 
         FIG. 7  is a view that shows the device mounting surface of a printed circuit board and the back surface of an LED; 
         FIG. 8  is a view that shows the cross-sectional structure of the printed circuit board and the LED; 
         FIG. 9  is a view that shows a state where the LED is soldered to lands of the printed circuit board; and 
         FIG. 10A  and  FIG. 10B  are views for illustrating movement of the LED due to solder tension. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a vehicular lamp according to an embodiment of the invention will be described in detail with reference to the accompanying drawings. In the specification, when the terms indicating directions, such as “upper”, “lower”, “front”, “rear”, “right”, “left”, “inner” and “outer”, are used, those mean the directions in position at the time when the vehicular lamp is mounted on a vehicle. 
       FIG. 1  is a schematic horizontal cross-sectional view of the vehicular lamp  10  according to the embodiment of the invention.  FIG. 2  is a cross-sectional view of the vehicular lamp  10 , taken along the line II-II in  FIG. 1 . The vehicular lamp  10  shown in  FIG. 1  is a headlamp arranged one by one at each of the right and left sides of the front of the vehicle. The structure of the vehicular lamp  10  is substantially equivalent between the right and left sides, so the structure of the vehicular lamp arranged at the left side of the vehicle will be described. 
     As shown in  FIG. 1  and  FIG. 2 , the vehicular lamp  10  includes a lamp body  12  and a transparent outer cover  13 . The outer cover  13  covers the front opening of the lamp body  12 . The lamp body  12  and the outer cover  13  define a lamp chamber  14 . As shown in  FIG. 1 , the outer cover  13  is formed in a shape along a slant nose shape of the vehicle. The outer cover  13  is slanted rearwardly in a direction from the vehicle inner side toward the vehicle outer side. The lamp body  12  is formed in a stepped shape being slanted rearwardly in the direction from the vehicle inner side toward the vehicle outer side according to the shape of the slanted outer cover  13 . Thus, the lamp chamber  14  defined by the lamp body  12  and the outer cover  13  is a space slanted rearwardly in the direction from the vehicle inner side toward the vehicle outer side. 
     A high-beam circuit board  15   a , a low-beam circuit board  15   b , a high-beam reflector unit  16  and a low-beam reflector unit  17  are accommodated in the lamp chamber  14 . 
     The high-beam circuit board  15   a  and the low-beam circuit board  15   b  each are a printed circuit board. The printed circuit board is formed such that a circuit pattern made of copper foil is formed on the surface of a board called substrate. The high-beam circuit board  15   a  and the low-beam circuit board  15   b  are arranged side by side at the upper side inside the lamp chamber  14 . The high-beam circuit board  15   a  is arranged on the vehicle inner side, and the low-beam circuit board  15   b  is arranged on the vehicle outer side. As shown in  FIG. 1 , the high-beam circuit board  15   a  and the low-beam circuit board  15   b  each are formed in a shape slanted rearwardly in the direction from the vehicle inner side toward the vehicle outer side according to the shape of the slanted outer cover  13 . 
     Three LEDs (first LED  18   a  to third LED  18   c ) are mounted on the high-beam circuit board  15   a  such that light-emitting faces of the LEDs are directed downward. These three LEDs are surface mount LEDs. Each of the LEDs has an anode and a cathode on its back surface. The first LED  18   a  to the third LED  18   c  each emit light upon reception of current that is supplied from the high-beam circuit board  15   a . The first LED  18   a  to the third LED  18   c  are LEDs that are used to radiate a high beam, and are provided along the vehicle width direction of the high-beam circuit board  15   a . Among these three LEDs, the first LED  18   a  is provided at the vehicle innermost side, the second LED  18   b  is provided on the outer side of the first LED  18   a , and the third LED  18   c  is provided on the outer side of the second LED  18   b.    
     Similarly, three LEDs (fourth LED  18   d  to sixth LED  18   f ) are mounted on the low-beam circuit board  15   b  such that light-emitting faces of the LEDs are directed downward. These three LEDs are surface mount LEDs. Each of the LEDs has an anode and a cathode on its back surface. The fourth LED  18   d  to the sixth LED  18   f  each emit light upon reception of current that is supplied from the low-beam circuit board  15   b . The fourth LED  18   d  to the sixth LED  18   f  are LEDs that are used to radiate a low beam, and are provided along the vehicle width direction of the low-beam circuit board  15   b . Among these three LEDs, the fourth LED  18   d  is provided at the vehicle innermost side, the fifth LED  18   e  is provided on the outer side of the fourth LED  18   d , and the sixth LED  18   f  is provided on the outer side of the fifth LED  18   e.    
     The high-beam reflector unit  16  and the low-beam reflector unit  17  are arranged side by side on the lower side of the high-beam circuit board  15   a  and the low-beam circuit board  15   b  in the lamp chamber  14 . The high-beam reflector unit  16  is arranged on the vehicle inner side, and the low-beam reflector unit  17  is arranged on the vehicle outer side. 
     The high-beam reflector unit  16  is a reflector group that is used to radiate a high beam, and includes three parabolic reflectors, that is, a high-beam diffusion reflector  16   a , a first high-beam condensing reflector  16   b  and a second high-beam condensing reflector  16   c . These three reflectors are integrally formed. Among these three reflectors, the high-beam diffusion reflector  16   a  is provided at the vehicle innermost side, the first high-beam condensing reflector  16   b  is provided on the outer side of the high-beam diffusion reflector  16   a , and the second high-beam condensing reflector  16   c  is provided on the outer side of the first high-beam condensing reflector  16   b.    
     The high-beam diffusion reflector  16   a , the first high-beam condensing reflector  16   b  and the second high-beam condensing reflector  16   c  respectively have reflecting surfaces  19   a  to  19   c  each are formed on the basis of a paraboloid of revolution. The rotation center axis of each paraboloid of revolution coincides with the optical axis of a corresponding one of the reflectors. That is, the high-beam diffusion reflector  16   a  has a first optical axis Ax1, the first high-beam condensing reflector  16   b  has a second optical axis Ax2, and the second high-beam condensing reflector  16   c  has a third optical axis Ax3. The high-beam diffusion reflector  16   a , the first high-beam condensing reflector  16   b  and the second high-beam condensing reflector  16   c  are arranged such that the first optical axis Ax1, the second optical axis Ax2 and the third optical axis Ax3 are directed in the vehicle longitudinal direction (horizontal direction). 
     The first LED  18   a  is arranged at the focal point of the reflecting surface  19   a  of the high-beam diffusion reflector  16   a  (located in the first optical axis Ax1) (see  FIG. 2 ). The second LED  18   b  is arranged at the focal point of the reflecting surface  19   b  of the first high-beam condensing reflector Mb (located in the second optical axis Ax2). The third LED  18   c  is arranged at the focal point of the reflecting surface  19   c  of the second high-beam condensing reflector  16   c  (located in the third optical axis Ax3). Each reflector reflects light from a corresponding one of the LEDs in a direction parallel to its optical axis. 
     The low-beam reflector unit  17  is a reflector group that is used to radiate a low beam, and includes three parabolic reflectors, that is, a low-beam diffusion reflector  17   a , a first low-beam condensing reflector  17   b  and a second low-beam condensing reflector  17   c . These three reflectors are integrally formed. Among these three reflectors, the low-beam diffusion reflector  17   a  is provided at the vehicle innermost side, the first low-beam condensing reflector  17   b  is provided on the outer side of the low-beam diffusion reflector  17   a , and the second low-beam condensing reflector  17   c  is provided on the outer side of the first low-beam condensing reflector  17   b.    
     The low-beam diffusion reflector  17   a , the first low-beam condensing reflector  17   b  and the second low-beam condensing reflector  17   c  respectively have reflecting surfaces  20   a  to  20   c  each formed on the basis of a paraboloid of revolution. The rotation center axis of each paraboloid of revolution coincides with the optical axis of a corresponding one of the reflectors. That is, the low-beam diffusion reflector  17   a  has a fourth optical axis Ax4, the first low-beam condensing reflector  17   b  has a fifth optical axis Ax5, and the second low-beam condensing reflector  17   c  has a sixth optical axis Ax6. The low-beam diffusion reflector  17   a , the first low-beam condensing reflector  17   b  and the second low-beam condensing reflector  17   c  are arranged such that the fourth optical axis Ax4, the fifth optical axis Ax5 and the sixth optical axis Ax6 are directed in the vehicle longitudinal direction (horizontal direction). 
     The fourth LED  18   d  is arranged at the focal point of the reflecting surface  20   a  of the low-beam diffusion reflector  17   a  (located in the fourth optical axis Ax4). The fifth LED  18   e  is arranged at the focal point of the reflecting surface  20   b  of the first low-beam condensing reflector  17   b  (located in the fifth optical axis Ax5). The sixth LED  18   f  is arranged at the focal point of the reflecting surface  20   c  of the second low-beam condensing reflector  17   c  (located in the sixth optical axis Ax6). Each reflector reflects light from a corresponding one of the LEDs in a direction parallel to its optical axis. 
     The high-beam reflector unit  16  and the low-beam reflector unit  17  each are formed by evaporating aluminum onto the inner surface of a resin-molded base member. 
     In the present embodiment, the high-beam reflector unit  16  and the first LED  18   a  to the third LED  18   c  constitute a high-beam lamp unit that radiates a high beam.  FIG. 3  shows a high-beam distribution pattern  30  that is formed by the high-beam lamp unit. The high-beam distribution pattern  30  shown in  FIG. 3  is a distribution pattern that is formed on an imaginary vertical screen arranged at a location 25 m ahead of the vehicular lamp  10 .  FIG. 3  shows a vertical line V-V passing through an H-V point that is a vanishing point in a lamp forward direction, and a horizontal line H-H passing through the H-V point. 
     A high-beam condensed distribution pattern  31  is formed around the H-V point from light reflected from the reflecting surface  19   b  of the first high-beam condensing reflector  16   b  after being emitted from the second LED  18   b  and light reflected from the reflecting surface  19   c  of the second high-beam condensing reflector  16   c  after being emitted from the third LED  18   c . The high-beam condensed distribution pattern  31  is a high light intensity region called “hot zone”. A high-beam diffusion distribution pattern  32  is formed from light reflected from the reflecting surface  19   a  of the high-beam diffusion reflector  16   a  after being emitted from the first LED  18   a  so as to cover the high-beam condensed distribution pattern  31 . The high-beam diffusion distribution pattern  32  is wider in both the horizontal line H-H direction and the vertical line V-V direction than the high-beam condensed distribution pattern  31 . The high-beam condensed distribution pattern  31  may be, for example, a region ranging in the horizontal line H-H direction by about ±10° to 15° and ranging in the vertical line V-V direction by about ±3° to 5°. The high-beam diffusion distribution pattern  32  may be, for example, a region ranging in the horizontal line H-H direction by about ±25° to 35° and ranging in the vertical line V-V direction by about ±8° to 10°. The high-beam distribution pattern  30  is formed by superimposing the high-beam condensed distribution pattern  31  on the high-beam diffusion distribution pattern  32 . 
     The low-beam reflector unit  17  and the fourth LED  18   d  to the sixth LED  18   f  constitute a low-beam lamp unit that radiates a low beam.  FIG. 4  shows a low-beam distribution pattern  40  that is formed by the low-beam lamp unit. The low-beam distribution pattern is a distribution pattern having a cut-off line in a predetermined shape. 
     A low-beam condensed distribution pattern  41  is formed around the H-V point from light reflected from the reflecting surface  20   b  of the first low-beam condensing reflector  17   b  after being emitted from the fifth LED  18   e  and light reflected from the reflecting surface  20   c  of the second low-beam condensing reflector  17   c  after being emitted from the sixth LED  18   f . The low-beam condensed distribution pattern  41  is a high light intensity region called “hot zone”, and has a cut-off line CL in a predetermined shape. A low-beam diffusion distribution pattern  42  is formed from light reflected from the reflecting surface  20   a  of the low-beam diffusion reflector  17   a  after being emitted from the fourth LED  18   d  so as to cover the low-beam condensed distribution pattern  41 . The low-beam diffusion distribution pattern  42  is wider in both the horizontal line H-H direction and the vertical line V-V direction than the low-beam condensed distribution pattern  41 . The low-beam condensed distribution pattern  41  may be, for example, a region ranging in the horizontal line H-H direction by about ±10° to 15° and ranging in the vertical line V-V direction by about 0° to −5°. The low-beam diffusion distribution pattern  42  may be, for example, a region ranging in the horizontal line H-H direction by about ±25° to 45° and ranging in the vertical line V-V direction by about 0° to −10°. The low-beam distribution pattern  40  is formed by superimposing the low-beam condensed distribution pattern  41  on the low-beam diffusion distribution pattern  42 . 
       FIG. 5  is a view that shows a device mounting surface  50  of the high-beam circuit board  15   a .  FIG. 6  is a view for illustrating an assembled structure of the high-beam circuit board  15   a  and the high-beam reflector unit  16 . The device mounting surface  50  shown in  FIG. 5  is directed downward in a state of being mounted on the vehicle as shown in  FIG. 6 . 
     A first LED mounting portion  51   a , a second LED mounting portion  51   b  and a third LED mounting portion  51   c  for respectively mounting the first LED  18   a , the second LED  18   b  and the third LED  18   c  are provided on the device mounting surface  50  of the high-beam circuit board  15   a  in the vehicle width direction. Each LED mounting portion includes lands for soldering the electrodes of a corresponding one of the LEDs. The structure of each LED mounting portion will be described later. 
     As shown in  FIG. 6 , the high-beam reflector unit  16  is mounted on the device mounting surface  50  of the high-beam circuit board  15   a . In the present embodiment, the high-beam reflector unit  16  includes a first positioning pin  52  and a second positioning pin  53 . The high-beam circuit board  15   a  has a first positioning hole  54  and a second positioning hole  55 . The first positioning hole  54  is provided at a portion corresponding to the first positioning pin  52  to receive the first positioning pin  52 . The second positioning hole  55  is provided at a portion corresponding to the second positioning pin  53  to receive the second positioning pin  53 . When the positioning pins  52 ,  53  are respectively inserted to the corresponding positioning holes  54 ,  55 , the high-beam reflector unit  16  is positioned on the device mounting surface  50  of the high-beam circuit board  15   a.    
     The first positioning pin  52  protrudes from a first coupling portion  56 . The first coupling portion  56  couples the high-beam diffusion reflector  16   a  to the first high-beam condensing reflector  16   b . The second positioning pin  53  protrudes from a second coupling portion  57 . The second coupling portion  57  couples the first high-beam condensing reflector  16   b  to the second high-beam condensing reflector  16   c . The first positioning pin  52  and the second positioning pin  53  each may be a cylindrical columnar pin. The size of the first positioning pin  52  may be equal to the size of the second positioning pin  53 . The first positioning pin  52  and the second positioning pin  53  may have a height larger than or equal to the thickness of the high-beam circuit board  15   a.    
     As shown in  FIG. 5  and  FIG. 6 , the first positioning hole  54  is provided at a location inward of the first LED mounting portion  51   a  located at one end side (vehicle inner side) of the high-beam circuit board  15   a  in the vehicle width direction, and the second positioning hole  55  is provided at a location inward of the third LED mounting portion  51   c  located at the other end (vehicle outer side) of the high-beam circuit board  15   a  in the vehicle width direction. More specifically, the first positioning hole  54  is provided between the first LED mounting portion  51   a  and the adjacent second LED mounting portion  51   b , and the second positioning hole  55  is provided between the third LED mounting portion  51   c  and the adjacent second LED mounting portion  51   b.    
     In the present embodiment, the first positioning hole  54  is a long hole extending in the vehicle width direction of the circuit board. When the first positioning pin  52  to be inserted into the first positioning hole  54  has a cylindrical shape, the first positioning hole  54  is a long hole of which the inside diameter in the vehicle width direction is larger than the diameter of the first positioning pin  52  and the inside diameter in the vehicle longitudinal direction is substantially equal to the diameter of the first positioning pin  52  in cross section perpendicular to the vertical direction. On the other hand, the second positioning hole  55  has a shape and a size substantially equal to those of the second positioning pin  53  to be inserted into the second positioning hole  55  in cross section perpendicular to the vertical direction. When the second positioning pin  53  has a cylindrical shape, the second positioning hole  55  is a cylindrical hole of which the inside diameter is equal to the diameter of the second positioning pin  53 . As in the case of the present embodiment, by forming one of the two positioning holes in an long hole, it is possible to allow the tolerance of the high-beam reflector unit  16 . 
     When the high-beam reflector unit  16  is assembled to the high-beam circuit board  15   a , the first positioning pin  52  and second positioning pin  53  of the high-beam reflector unit  16  are respectively inserted into the first positioning hole  54  and second positioning hole  55  of the high-beam circuit board  15   a , as shown in  FIG. 6 . After that, portions of the first positioning pin  52  and second positioning pin  53 , protruded from a back surface  58  across from the device mounting surface  50 , are subjected to thermal caulking. Thus, the high-beam reflector unit  16  is fixed to the high-beam circuit board  15   a . In the present embodiment, the first positioning pin  52  and the second positioning pin  53  serve to both position and fix the high-beam reflector unit  16  to the high-beam circuit board  15   a . Instead, the first positioning pin  52  and the second positioning pin  53  may be used only for positioning, and another member may be used for fixing. For example, screw fixing holes may be respectively provided in the high-beam circuit board  15   a  and the high-beam reflector unit  16 , and the high-beam reflector unit  16  may be fixed to the high-beam circuit board  15   a  by screws. 
     In the above-described embodiment, the second positioning hole  55  formed in a shape and a size substantially equal to those of the second positioning pin  53  is provided at a portion closer to the second LED mounting portion  51   b  and the third LED mounting portion  51   c  on which the condensing second LED  18   b  and third LED  18   c  are mounted than the first LED mounting portion  51   a  on which the diffusing first LED  18   a  is mounted, as shown in  FIG. 5  and  FIG. 6 . This is because the condensing second LED  18   b  and third LED  18   c  require higher positional accuracy than the diffusing first LED  18   a . With such a configuration, it is possible to improve the light distribution performance of the vehicular lamp  10 . 
     In the above description, the assembled structure of the high-beam circuit board  15   a  and the high-beam reflector unit  16  is mainly described; however, this is similar to the assembled structure of the low-beam circuit board  15   b  and the low-beam reflector unit  17 . 
     Next, the mounting structure of the LEDs in the vehicular lamp  10  according to the present embodiment will be described.  FIG. 7  shows the device mounting surface  50  of the printed circuit board  15  and a back surface  70  of each LED  18 .  FIG. 8  shows the cross-sectional structure of the printed circuit board  15  and LED  18 . 
     The LED  18  shown in  FIG. 7  and  FIG. 8  is a surface mount LED. Three electrodes, that is, an anode  72 , a first cathode  73  and a second cathode  74 , are provided on the back surface  70  of the LED  18 . The anode  72  is arranged at the left end of the back surface  70  in the X direction. The first cathode  73  is arranged at the center of the back surface  70  in the X direction. The second cathode  74  is arranged at the right end of the back surface  70  in the X direction. In the present embodiment, the first cathode  73  and the second cathode  74  are provided as separate electrodes; however, the first cathode  73 , and the second cathode  74  are electrically continuous with each other inside the LED. The anode  72 , the first cathode  73  and the second cathode  74  each are formed in a rectangular shape in plain view. 
     The LED mounting portion  51  for mounting the LED  18  is provided on the device mounting surface  50  of the printed circuit board  15 . The LED mounting portion  51  includes three lands, that is, an anode land  75 , a first cathode land  76  and a second cathode land  77 . The anode land  75  is arranged at the left end of the LED mounting portion  51  in the X direction, and is soldered to the anode  72  of the LED  18 . The first cathode land  76  is arranged at the center of the LED mounting portion  51  in the X direction, and is soldered to the first cathode  73  of the LED  18 . The second cathode land  77  is arranged at the right end of the LED mounting portion  51  in the X direction, and is soldered to the second cathode  74  of the LED  18 . 
     Each of the lands of the LED mounting portion  51  has a corresponding one of conductor patterns  79 ,  80 ,  81  and a solder resist  82 . Each of the conductor patterns  79 ,  80 ,  81  is provided on a substrate  78 , such as glass-cloth epoxy resin. In the present embodiment, the shape of each land is defined by two types of methods. The first method is to define each land shape by printing the solder resist on the conductor pattern. The second method is to define each land shape by exposing an etched surface of the conductor pattern. 
     This will be specifically described with reference to  FIG. 7  and  FIG. 8 . The land shape of the second cathode land  77  is defined by covering all around the conductor pattern  81 , provided on the substrate  78 , with a solder resist  82   a . All the side surfaces of the conductor pattern  81 , that is, both the side surfaces of the conductor pattern  81  in the Y direction, the left side surface  81   a  of the conductor pattern  81  in the X direction and the right side surface  81   b  of the conductor pattern  81  in the X direction, are covered with the solder resist  82   a . In the following description, the side surface of the conductor pattern, covered with the solder resist, is termed “resist side surface”. The land shape of the second cathode land  77  is the shape of a region surrounded by the resist side surfaces. 
     On the other hand, in the anode land  75 , part of the side surfaces of the conductor pattern  79  is not covered with a solder resist. That is, both side surfaces of the conductor pattern  79  in the Y direction and the left side surface  79   a  of the conductor pattern  79  in the X direction are covered with the solder resist  82   b ; however, the right side surface  79   b  of the conductor pattern  79  in the X direction is not covered with a solder resist. That is, the right side surface  79   b  of the conductor pattern  79  formed by etching is exposed. In the following description, the side surface of the conductor pattern, not covered with a solder resist, is termed “non-resist side surface”. In the anode land  75 , the shape of a region surrounded by the resist side surfaces and the non-resist side surface is the land shape. 
     Similarly, in the first cathode land  76  as well, part of the side surfaces of the conductor pattern  80  is not covered with a solder resist. That is, both side surfaces of the conductor pattern  80  in the Y direction and the right side surface  80   a  of the conductor pattern  80  in the X direction are covered with the solder resist  82   c ; however, the left side surface  80   b  of the conductor pattern  80  in the X direction is not covered with a solder resist. That is, the left side surface  80   b  of the conductor pattern  80  formed by etching is exposed. In the first cathode land  76  as well, the shape of a region surrounded by the resist side surfaces and the non-resist side surface is the land shape. 
     In the present embodiment, the LED mounting portion  51  includes three lands as described above. The adjacent anode land  75  and first cathode land  76  among the three lands are provided such that the non-resist side surfaces are opposite (adjacent) to each other. That is, the right side surface  79   b  as the non-resist side surface of the anode land  75 , is opposite to the left side surface  80   b  as the non-resist side surface of the first cathode land  76 . 
     A solder resist region  82   d  is provided on the substrate  78  between the adjacent anode land  75  and first cathode land  76 . The solder resist region  82   d  is provided in order to prevent flow of solder between the anode land  75  and the first cathode land  76 . 
     In the present embodiment, the anode land  75  and the first cathode land  76  are respectively formed in the same shapes as the electrodes that are soldered on the anode land  75  and the first cathode land  76 . That is, the anode land  75  and the first cathode land  76  respectively have the same rectangular shapes as the anode  72  and the first cathode  73 . In the present embodiment, the second cathode land  77  also has the same rectangular shape as the second cathode  74  that is soldered on the second cathode land  77 ; however, this is not specifically limited. 
     In the present embodiment, the anode land  75  and the first cathode land  76  respectively has sizes smaller than or equal to the sizes of the electrodes that are soldered on the anode land  75  and the first cathode land  76 . That is, the width LX1 of the anode land  75  in the X direction and the width LY1 of the anode land  75  in the Y direction are respectively smaller than or equal to the width EX1 of the anode  72  in the X direction and the width EY1 of the anode  72  in the Y direction. The width LX2 of the first cathode land  76  in the X direction and the width LY2 of the first cathode land  76  in the Y direction are respectively smaller than or equal to the width EX2 of the first cathode  73  in the X direction and the width EY2 of the first cathode  73  in the Y direction. In the present embodiment, the second cathode land  77  is also smaller than or equal to the second cathode  74  that is soldered on the second cathode land  77 ; however, this is not specifically limited. 
     In the present embodiment, each land is thicker than the solder resist  82  provided on the substrate  78 . The thickness TL of each land is desirably larger than or equal to twice as large as the thickness TR of the solder resist  82  provided on the substrate  78  and smaller than or equal to six times as large as the thickness TR. For example, when the solder resist thickness TR is 20 μm, the land thickness TL is desirably 40 μm to 120 μm. 
       FIG. 9  shows a state where the LED  18  is soldered to the lands of the printed circuit board  15 . As shown in  FIG. 9 , a solder portion  90  is provided between the anode  72  and the anode land  75 , a solder portion  91  is provided between the first cathode  73  and the first cathode land  76 , and a solder portion  92  is provided between the second cathode  74  and the second cathode land  77 . In  FIG. 9 , the solder portions  90 ,  91 ,  92  are molten. 
     While solder is molten, there occurs the tension of solder, and the tension of the solder may move the LED  18  mounted on the printed circuit board  15 .  FIG. 9  shows a solder tension F1 that acts on the LED  18  from the right-side portion of the solder portion  90 , a solder tension F2 that acts on the LED  18  from the left-side portion of the solder portion  91 , a solder tension F3 that acts on the LED  18  from the right-side portion of the solder portion  91 , and a solder tension F4 that acts on the LED  18  from the left-side portion of the solder portion  92 . The solder tensions F1 to F4 are forces that act in the X direction. As shown in  FIG. 9 , the solder tensions F1, F2 equally act in opposite directions. The solder tensions F3, F4 equally act in opposite directions. 
     As shown in  FIG. 9 , because the right side surface  79   b  of the anode  72  and the left side surface  80   b  of the first cathode  73  are non-resist surfaces, solder covers those side surfaces. On the other hand, the right side surface  80   a  of the first cathode land  76  and the left side surface  81   a  of the second cathode land  77  are resist surfaces, so no solder covers those side surfaces. In the present embodiment, each land is thicker than the solder resist  82  provided on the substrate  78 . Therefore, the amount of solder per unit area at the right-side portion of the solder portion  90  or the left-side portion of the solder portion  91  is larger than the amount of solder per unit area at the right-side portion of the solder portion  91  or the left-side portion of the solder portion  92 . As a result, the solder tensions F1, F2 are larger than the solder tensions F3, F4. This means that the solder tensions F1, F2 have larger forces in moving the LED  18  than those of the solder tensions F3, F4, so the solder tensions F1, F2 are more predominant in force moving the LED  18  than the solder tensions F3, F4. 
       FIG. 10A  and  FIG. 10B  are views for illustrating movement of the LED  18  in the X direction due to solder tension. 
       FIG. 10A  shows the way of movement of the LED  18  in the X direction in the case where the sizes of the anode land  75  and first cathode land  76  are respectively equal to the sizes of the anode  72  and first cathode  73  are soldered on the anode land  75  and the first cathode land  76 . In this case, as shown in  FIG. 10A , due to the solder tensions F1, F2, the LED  18  moves in the X direction such that the right side surface  72   a  of the anode  72  and the right side surface  79   b  of the anode land  75  overlap with each other and the left side surface  73   a  of the first cathode  73  and the left side surface  80   b  of the first cathode land  76  overlap with each other. 
       FIG. 10B  shows the way of movement of the LED  18  in the X direction in the case where the sizes of the anode land  75  and first cathode land  76  are respectively smaller than the sizes of the anode  72  and first cathode  73  that are soldered on the anode land  75  and the first cathode land  76 . In this case, as shown in  FIG. 10B , due to the solder tensions F1, F2, the LED  18  moves in the X direction such that a center C1 between the right side surface  72   a  of the anode  72  and the opposite left side surface  73   a  of the first cathode  73  matches with a center C2 between the right side surface  79   b  of the anode land  75  and the opposite left side surface  80   b  of the first cathode land  76 . In this way, in any of the cases shown in  FIG. 10A  and  FIG. 10B , the LED  18  is positioned to the predetermined position in the X direction with respect to the printed circuit board  15 . 
     In this way, according to the present embodiment, by providing the anode land  75  and the first cathode land  76  such that the non-resist faces are opposite to each other, tensions of the solder portions provided on these lands are predominant in movement of the LED  18 . The shapes of the anode land  75  and first cathode land  76  of which the non-resist faces are opposite are respectively the same as the shapes of the anode  72  and first cathode  73  that are soldered on the anode land  75  and the first cathode land  76 , and the sizes of the anode land  75  and first cathode land  76  are respectively smaller than or equal to the sizes of the anode  72  and first cathode  73 . Thus, the LED  18  is positioned to the predetermined position in the X direction with respect to the lands of the printed circuit board  15 , so it is possible to mount the LED  18  at the position of the printed circuit board  15  in the X direction as designed. 
     Improvement in mounting accuracy of the LED  18  in the X direction is described above, and the mounting accuracy in the Y direction also improves according to the present embodiment. As described above, in the present embodiment, the shapes of the anode land  75  and first cathode land  76  are respectively the same as the shapes of the anode  72  and first cathode  73  that are soldered on the anode land  75  and the first cathode land  76 , so the side surfaces of the lands and the side surfaces of the electrodes are parallel to each other at both ends in the Y direction. Thus, the solder tension acts in the direction in which the midpoint of each electrode in the Y direction coincides with the midpoint of the corresponding land in the Y direction, so it is also possible to improve the mounting accuracy of the LED  18  in the Y direction. That is, according to the present embodiment, it is possible to improve the mounting accuracy in the X direction and in the Y direction. 
     By applying the LED mounting structure described in  FIG. 7  to  FIG. 10B  to the vehicular lamp  10  shown in  FIG. 1 , it is possible to mount the LEDs and the reflectors in the positional relationship as designed, so it is possible to prevent or at least suppress a positional deviation of the distribution pattern. 
     As in the case of the vehicular lamp  10  shown in  FIG. 1 , when a plurality of reflectors are integrally formed or when a plurality of LEDs are mounted on a common single circuit board, it is difficult to set the direction of a light beam emitted from each reflector to an ideal direction by adjusting the orientation of each reflector. If the mounting positions of part or all of the LEDs deviate from predetermined positions, the distribution pattern around the H-V point, which should be particularly set to a high light intensity, becomes dark, so there is a concern that distance visibility decreases. In a low-beam lamp unit, a deviation of the mounting positions of the LEDs leads to a deformation of the shape of the cut-off line, with the result that there is a concern that a driver of a host vehicle experiences a feeling of strangeness or a driver of an oncoming vehicle feels too bright. In this respect, with the vehicular lamp  10  in which the LED mounting structure described in  FIG. 7  to  FIG. 10B  is applied, it is possible to suppress a positional deviation of the distribution pattern, so it is possible to prevent these inconveniences. 
     In the above-described embodiment, the adjacent anode land  75  and first cathode land  76  respectively have the same shapes as the electrodes that are soldered on the anode land  75  and the first cathode land  76 ; however, the shape of at least one of the adjacent two lands just needs to have the same shape as the corresponding one of the electrodes, which is soldered on the at least one of the adjacent two lands. In the above-described embodiment, the sizes of the adjacent anode land  75  and first cathode land  76  are respectively smaller than the sizes of the electrodes that are soldered on the anode land  75  and the first cathode land  76 ; however, the size of at least one of the adjacent two lands just needs to be smaller than the size of a corresponding one of the electrodes, which is soldered on the at least one of the adjacent two lands. 
     The invention is described on the basis of the embodiments. These embodiments are only illustrative, and various alternative embodiments are applicable in combinations of the component elements or processes, and the invention also encompasses those alternative embodiments. 
     For example, in the above-described embodiment, the surface mount LEDs are illustrated as electronic devices (surface mount devices) mounted on the printed circuit board. the printed circuit board according to the embodiment of the invention does not limit the surface mount LEDs, and may be applied to any surface mount devices. 
     In the above-described embodiment, the reflectors are illustrated as optical members that radiate light emitted from the LEDs forward; however, the optical members are not limited to the reflectors, and may be, for example, projection lenses.