LED module and LED dot matrix display

The present invention relates to an LED module used for e.g. an electronic message display on a train and designed to emit white light by mixing lights of different colors from three LED chips. The present invention also relates to an LED dot matrix display utilizing such an LED module.

FIG. 16 illustrates an example of conventional LED module (see Patent Document 1, for example). The LED module X illustrated in the figure includes a rectangular module substrate 91 , on which three LED chips 94 R, 94 G, 94 B are mounted. The module substrate 91 is formed with a plurality of electrodes 92 R, 92 G, 92 B, 93 R, 93 G, 93 B. The LED chips 94 R, 94 G and 94 B are bonded to the electrodes 92 R, 92 G and 92 B, respectively. The electrodes 93 R, 93 G and 93 B are electrically connected to the LED chips 94 R, 94 G and 94 B via wires 95 R, 95 G and 95 B, respectively. The three LED chips 94 R, 94 G, 94 B are covered by a light-transmitting sealing resin 96 . The electrodes 92 R, 92 G, 92 B, 93 R, 93 G, 93 B include portions covering the side surfaces and reverse surface of the module substrate 91 . These portions are utilized for mounting of the LED module X. The LED chips 94 R, 94 G and 94 B emit red light, green light and blue light, respectively. By mixing the light from the LED chips 94 R, 94 G and 94 B, the LED module X emits white light. By arranging a plurality of LED modules X in a matrix, an LED dot matrix display for use in an electronic message display is obtained.

There is an increasing demand for size reduction of an LED module X. Further, to properly mix the light of different colors, it is desirable that the LED chips 94 R, 94 G, 94 B are arranged as close to each other as possible. However, the LED module X requires a space for arranging the wires 95 R, 95 G, 95 B and a space for arranging the portions of the electrodes 93 R, 93 G, 93 B to which the wires 95 R, 95 G, 95 B are to be bonded, in addition to a space for arranging the LED chips 94 R, 94 G, 94 B. These parts or portions need to be arranged without mutual contact or short-circuiting. Thus, it is not easy to arrange the LED chips 94 R, 94 G, 94 B close to each other and make the LED module X compact.

Further, in recent years, LED dot matrix displays are required to have high resolution. However, when LED modules X are arranged at a high density, the module substrates 91 occupy a large proportion of the display region of the LED dot matrix display. Generally, the module substrates 91 , which are made of glass fiber-reinforced epoxy resin, are milk white. Thus, even when all the LED modules X are in the OFF state, the display region of the dot matrix display appears white, which leads to a poor contrast relative to the ON state.

Patent Document 1: JP-A-2003-17753

Problems to be Solved by the Invention

The present invention has been proposed under the circumstances described above. It is therefore an object of the present invention to provide an LED module and an LED dot matrix display which are capable of enhancing the contrast and achieving the size reduction and proper color mixing.

Means for Solving the Problems

According to a first aspect of the present invention, there is provided an LED module including a first, a second and a third LED chips, and a module substrate on which the first, the second and the third LED chips are mounted. A first wire is connected to the first LED chip, and the second LED chip and the third LED chip are arranged to face each other across the first wire.

Preferably, a second wire and a third wire are connected to the second LED chip and the third LED chip, respectively, and each of the second wire and the third wire extends away from the first wire.

Preferably, the first LED chip is smaller than the second and the third LED chips.

Preferably, the first LED chip emits red light, one of the second and the third LED chips emits blue light, and the other one of the second and the third LED chips emits green light.

Preferably, the module substrate has a pair of sides extending in parallel to each other. The first wire extends perpendicularly to a direction in which the paired sides extend.

Preferably, the LED module further includes a pair of first electrodes each of which includes a portion covering part of a respective one of the paired sides. The first LED chip is bonded to one of the first electrodes, and the first wire is connected to the other one of the first electrodes.

Preferably, the LED module further includes two pairs of second electrodes including portions covering respective two ends of each of the paired sides. The second LED chip is electrically connected to one of the two pairs of the second electrodes, whereas the third LED chip is electrically connected to the other one of the two pairs of the second electrodes.

According to a second aspect of the present invention, there is provided an LED module including: a first, a second and a third LED chips; a module substrate on which the first, the second and the third LED chips are mounted; and a common electrode formed on the module substrate and electrically connected to the first, the second and the third LED chips. Part of the common electrode is arranged between the third LED chip and each of the first and the second LED chips.

Preferably, the first, the second and the third LED chips are respectively arranged at locations corresponding to vertices of a triangle.

Preferably, the first LED chip emits red light, the second LED chip emits blue light and the third LED chip emits green light.

Preferably, the module substrate has a substantially rectangular shape having a first, a second, a third and a fourth corners. The module substrate is formed with a first, a second and a third individual electrodes electrically connected to the first, the second and the third LED chips, respectively. The first, the second and the third individual electrodes include portions covering the first, the second and the third corners, respectively, whereas the common electrode includes a portion covering the fourth corner.

Preferably, the module substrate has a dark color at least at a portion of a surface on which the LED chips are mounted.

Preferably, the module substrate contains a pigment or dye of a dark color.

Preferably, the module substrate is formed with a wiring pattern at least on the surface on which the LED chips are mounted, and the surface has a dark color at a portion that is not covered with the wiring pattern.

Preferably, the surface of the module substrate entirely has a dark color.

Preferably, the dark color is black.

Preferably, the LED module further includes a sealing resin member covering the LED chips and made of a resin of a dark color that transmits light from the LED chips.

According to a third aspect of the present invention, there is provided LED dot matrix display including a plurality of LED modules provided according to the first aspect of the present invention, and a main board on which the LED modules are mounted in a matrix. At least part of the surface of the main board, on which the LED modules are mounted, has a dark color.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

FIG. 1 is a perspective view illustrating an LED module according to a first embodiment of the present invention.

FIG. 2 is a plan view illustrating the LED module according to the first embodiment of the present invention.

FIG. 3 is a bottom view illustrating the LED module according to the first embodiment of the present invention.

FIG. 4 is a plan view illustrating an LED module according to a second embodiment of the present invention.

FIG. 5 is a plan view illustrating an LED module according to a third embodiment of the present invention.

FIG. 6 is a perspective view illustrating an LED module according to a fourth embodiment of the present invention.

FIG. 7 is a plan view illustrating the LED module according to the fourth embodiment of the present invention.

FIG. 8 is a bottom view illustrating the LED module according to the fourth embodiment of the present invention.

FIG. 9 is a plan view illustrating an LED module according to a fifth embodiment of the present invention.

FIG. 10 is a plan view illustrating an LED module according to a sixth embodiment of the present invention.

FIG. 11 is a perspective view illustrating an LED module according to a seventh embodiment of the present invention.

FIG. 12 is a perspective view illustrating a principal portion of an example of LED dot matrix display utilizing the LED module illustrated in FIG. 11 .

FIG. 13 is a perspective view illustrating a principal portion of the LED dot matrix display utilizing the LED module illustrated in FIG. 11 .

FIG. 14 is a sectional view taken along lines XIV-XIV in FIG. 12 .

FIG. 15 is a sectional view illustrating a principal portion of an example of dot matrix display utilizing a variation of the LED module illustrated in FIG. 11 .

FIG. 16 is a plan view illustrating an example of conventional LED module.

Preferred embodiments of the present invention are described below with reference to the accompanying drawings.

FIGS. 1-3 illustrate an LED module according to a first embodiment of the present invention. The LED module A 1 of this embodiment includes a module substrate 1 , a wiring pattern 2 , LED (light emitting diode) chips 3 R, 3 G, 3 B, wires 4 R, 4 Q, 4 B and a sealing resin 5 . The LED module A 1 is designed to emit white light by mixing red light, blue light and green light. The LED module A 1 of this embodiment has a very small size of about 1.0 mm×1.5 mm in plan view and about 0.2 mm in height. For easier understanding, the sealing resin 5 is illustrated by imaginary lines in FIG. 2 .

The module substrate 1 is an insulating substrate made of e.g. glass fiber-reinforced epoxy resin and has a substantially rectangular shape. The module substrate 1 has an obverse surface on which the LED chips 3 R, 3 G, 3 B are mounted, and a reverse surface which is opposite to the obverse surface in the thickness direction. The reverse surface of the module substrate 1 is utilized as a mount surface for mounting the LED module A 1 . The module substrate 1 is formed with a plurality of grooves 11 R, 11 G, 11 B, 12 R, 12 G, 12 B extending in the thickness direction of the module substrate 1 . The grooves 11 G, 11 B, 12 G, 12 B are provided at the four corners of the module substrate 1 . Each of the grooves 11 R and 12 R is provided at or near the center of a respective one of the long sides of the module substrate 1 . The size of the module substrate 1 may be about 1.0 mm×1.5 mm in plan view and about 0.05 mm in thickness.

The wiring pattern 2 is made of a plating layer of Cu, Ni or Au, for example, and includes electrodes 21 R, 21 G, 21 B, 22 R, 22 G, 22 B. The electrodes 21 R, 21 G, 21 B serve to supply power to the LED chips 3 R, 3 G, 3 B. The electrode 21 R includes a pad 21 Ra, a strip portion 21 Rb, a semi-annular portion 21 Rc, a semi-cylindrical portion 21 Rd and a mount portion 21 Re. The electrodes 21 G and 21 B include pads 21 Ga, 21 Ba, strip portions 21 Gb, 21 Bb, quarter-annular portions 21 Gc, 21 Bc, quarter-cylindrical portions 21 Gd, 21 Bd and mount portions 21 Ge, 21 Be. The electrode 21 R corresponds to a first electrode of the present invention, whereas the electrodes 21 G and 21 B correspond to a second electrode of the present invention.

As illustrated in FIG. 2 , the pads 21 Ra, 21 Ga and 21 Ba are provided on the obverse surface of the module substrate 1 for bonding the LED chips 3 R, 3 G and 3 B, respectively. In this embodiment, the pads 21 Ra, 21 Ga, 21 Ba are substantially X-shaped. The pads 21 Ga and 21 Ba are aligned in parallel to one of long sides of the module substrate 1 which extend in the lateral direction. The pad 21 Ra is arranged at a position deviated from the pads 21 Ga and 21 Ba toward the other long side of the module substrate 1 . In this embodiment, the pads 21 Ra, 21 Ga, 21 Ba are arranged to form an isosceles triangle, with the pad 21 Ra positioned at the vertex.

The strip portions 21 Rb, 21 Gb, 21 Bb extend from the pads 21 Ra, 21 Ga, 21 Ba toward a long side of the module substrate 1 . Specifically, the strip portion 21 Rb extends toward the center of the long side. The strip portions 21 Gb and 21 Bb extend in the form of a crank toward the two ends of the long side. The semi-annular portion 21 Rc surrounds the opening of the groove 11 R in the obverse surface side of the module substrate 1 . The quarter-annular portions 21 Gc and 21 Bc surround the openings of the grooves 11 G and 11 B in the obverse surface side of the module substrate 1 . The semi-cylindrical portion 21 Rd is formed to cover the groove 11 R. The quarter-cylindrical portions 21 Gd and 21 Bd are formed to cover the grooves 11 G and 11 B. As illustrated in FIG. 3 , the mount portions 21 Re, 21 Ge, 21 Be are formed to surround the openings of the grooves 11 R, 11 G, 11 B in the reverse surface side of the module substrate 1 and have a shape obtained by combining a semi-annular or quarter-annular portion and a rectangular portion. The mount portions 21 Re, 21 Ge, 21 Be are utilized for surface-mounting of the LED module A 1 on e.g. a circuit board. The semi-cylindrical portion 21 Rd, the quarter-cylindrical portions 21 Gd, 21 Bd, the semi-annular portion 21 Rc and the quarter-annular portions 21 Gc, 21 Bc are utilized for promoting formation of a solder fillet in surface-mounting the LED module A 1 .

The electrodes 22 R, 22 G, 22 B serve to supply power to the LED chips 3 R, 3 G, 3 B. The electrode 22 R includes a pad 22 Ra, a strip portion 22 RB, a semi-annular portion 22 Rc, a semi-cylindrical portion 22 Rd and a mount portion 22 Re. The electrodes 22 G and 22 B include pads 22 Ga, 22 Ba, strip portions 22 GB, 22 BB, quarter-annular portions 22 Gc, 22 Bc, quarter-cylindrical portions 22 Gd, 22 Bd and mount portions 22 Ge, 22 Be. The electrode 22 R corresponds to a first electrode of the present invention, whereas the electrodes 22 G and 22 B correspond to a second electrode of the present invention.

As illustrated in FIG. 2 , the pads 22 Ra, 22 Ga and 22 Ba are provided on the obverse surface of the module substrate 1 for bonding the wires 4 R, 4 G and 4 B, respectively. In this embodiment, the pads 22 Ra, 22 Ga, 22 Ba are rectangular. The pad 22 Ra is spaced from the pad 21 Ra in the direction in which the short sides of the module substrate 1 extend. Relative to the pads 21 Ga and 21 Ba, the pads 22 Ga and 22 Ba are arranged closer to the two ends of the module substrate 1 in the direction in which the long sides of the module substrate extend.

The strip portions 22 RB, 22 GB, 22 BB extend from the pads 22 Ra, 22 Ga, 22 Ba toward a long side of the module substrate 1 . Specifically, the strip portion 22 RB extends toward the center of the long side. The strip portions 22 GB and 22 BB extend toward the two ends of the long side. The semi-annular portion 22 Rc surrounds the opening of the groove 12 R in the obverse surface side of the module substrate 1 . The quarter-annular portions 22 Gc and 22 Bc surround the openings of the grooves 12 G and 12 B in the obverse surface side of the module substrate 1 . The semi-cylindrical portion 22 Rd is formed to cover the groove 12 R. The quarter-cylindrical portions 22 Gd and 22 Bd are formed to cover the grooves 12 G and 12 B. As illustrated in FIG. 3 , the mount portions 22 Re, 22 Ge, 22 Be are formed to surround the openings of the grooves 12 R, 12 G, 12 B in the reverse surface side of the module substrate 1 and have a shape obtained by combining a semi-annular or quarter-annular portion and a rectangular portion. The mount portions 22 Re, 22 Ge, 22 Be are utilized for surface-mounting of the LED module A 1 on e.g. a circuit board. The semi-cylindrical portion 22 Rd, the quarter-cylindrical portions 22 Gd, 22 Bd, the semi-annular portion 22 Rc and the quarter-annular portions 22 Gc, 22 Bc are utilized for promoting formation of a solder fillet in surface-mounting the LED module A 1 .

Each of the LED chips 3 R, 3 G, 3 B has e.g. a laminated structure made up of a p-type semiconductor layer, an n-type semiconductor layer and an active layer sandwiched between the p-type semiconductor layer and the n-type semiconductor layer. The LED chip 3 R emits red light, the LED chip 3 G emits green light and the LED chip 3 B emits blue light. The LED chips 3 R, 3 G and 3 B are bonded to the pads 21 Ra, 21 Ga and 21 Ba, respectively, via e.g. conductive paste. Thus, in this embodiment, the LED chips 3 R, 3 G, 3 B are arranged to form an isosceles triangle, with the LED chip 3 R for emitting red light positioned at the vertex facing the base of the triangle. The LED chip 3 R has a size of about 0.15×0.15 mm in plan view, whereas the LED chips 3 G and 3 B have a size of about 0.2×0.2 mm to 0.3×0.3 mm in plan view. Thus, the LED chip 3 R for emitting red light is relatively small.

The wires 4 R, 4 G and 4 B are made of e.g. Au and electrically connect the anode electrodes (not shown) of the LED chips 3 R, 3 G and 3 B to the electrodes 22 R, 22 G and 22 B, respectively. The wire 4 R connects the LED chip 3 R and the pad 22 Ra to each other and extends in the short-side direction of the module substrate 1 . The wires 4 G, 4 B connect the LED chips 3 G, 3 B and the pads 22 Ga, 22 Ba to each other. In this embodiment, the wires 4 G, 4 B extend from the LED chips 3 G, 3 B toward the two ends of the module substrate 1 in the long-side direction of the module substrate 1 .

The sealing resin 5 is made of e.g. a transparent resin which transmits light from the LED chips 3 R, 3 G, 3 B and covers the LED chips 3 R, 3 G, 3 B and wires 4 R, 4 G, 4 B. The reverse surface of the module substrate 1 is formed with a resist film 17 . The resist film 17 serves to prevent mounting of the LED module A 1 with wrong polarity.

The advantages of the LED module A 1 are described below.

In this embodiment, the LED chips 3 G and 3 B are arranged to face each other across the wire 4 R so that the LED chips 3 R, 3 G, 3 B form a triangle. No other elements are arranged between the wire 4 R and the LED chip 3 G or 3 B. Thus, it is possible to arrange the LED chips 3 G and 3 B close to each other and hence arrange the LED chips 3 G, 3 B and the LED chip 3 R close to each other. Thus, the arrangement of this embodiment ensures the size reduction of the LED module A 1 while achieving proper mixing of light from the LED chips 3 R, 3 G, 3 B.

Since the LED chip 3 R is smaller than the LED chips 3 G and 3 B, the LED chips 3 G and 3 B can be arranged close to each other. Moreover, the arrangement of the LED chip 3 R, which emits red light, at the vertex of the isosceles triangle formed by the LED chips 3 R, 3 G, 3 B is suitable for balanced mixing of light from the LED chips 3 R, 3 G, 3 B.

The wires 4 G and 4 B are arranged to extend perpendicularly to the wire 4 R. With this arrangement, the pads 22 Ga, 22 Ba, to which the wires 4 G, 4 B are connected, can be arranged compactly in the short-side direction of the module substrate 1 .

The electrodes 21 R, 21 G, 21 B, 22 R, 22 G, 22 B include mount portions 21 Re, 21 Ge, 21 Be, 22 Re, 22 Ge, 22 Be positioned at the four corners or the center of a long side of the module substrate 1 . The strip portions 21 Rb, 21 Gb, 21 Bb, 22 RB, 22 GB, 22 BB extend from the pads 21 Ra, 21 Ga, 21 Ba, 22 Ra, 22 Ga, 22 Ba to the mount portions 21 Re, 21 Ge, 21 Be, 22 Re, 22 Ge, 22 Be through relatively short routes. Thus, an unnecessary space is not created in the surface of the module substrate 1 , which is suitable for the size reduction of the LED module A 1 .

FIGS. 4-15 illustrate other embodiments of the LED module according to the present invention and an LED dot matrix display according to the present invention. In these figures, the elements which are identical or similar to those of the foregoing embodiment are designated by the same reference signs as those used for the foregoing embodiment.

FIG. 4 illustrates an LED module according to a second embodiment of the present invention. The LED module A 2 of this embodiment differs from that of the foregoing embodiment in structure of the LED chips 3 G and 3 B. Specifically, each of the LED chips 3 G and 3 B includes two electrodes on the upper surface. Thus, two wires 4 G and two wires 48 are bonded to the LED chips 3 G and 3 B, respectively. One of the wires 4 G and one of the wires 4 B are bonded to the pads 21 Ga and 21 Ba, respectively. The pads 21 Ga, 21 Ba of the electrodes 21 G, 21 B are aligned with the pads 22 Ga, 22 Ba of the electrodes 22 G, 22 B in the short-side direction of the module substrate 1 , respectively.

According to this embodiment again, mixing of light from the LED chips 3 R, 3 G, 3 B is promoted, and the size reduction of the LED module A 1 is achieved. As will be understood from this embodiment, the present invention is also applicable to an LED module including two-wire type LED chips.

FIG. 5 illustrates an LED module according to a third embodiment of the present invention. The LED module A 3 of this embodiment differs from the foregoing embodiments in structure of the LED chips 3 G and 3 B. Specifically, each of the LED chips 3 B and 3 G of this embodiment have a flip-chip structure including two electrodes on the lower surface. To correspond to this structure, the pads 21 Ga and 21 Ba have a horizontally elongated shape to overlap the LED chips 3 G and 3 B, respectively. The pads 22 Ga and 22 Ba are arranged next to the pads 21 Ga and 21 Ba, respectively, in the short-side direction of the module substrate 1 . The two electrodes of the LED chip 3 G are bonded to the pads 21 Ga and 22 Ga, whereas the two electrodes of the LED chip 3 B are bonded to the pads 21 Ba and 22 Ba.

According to this embodiment again, the size reduction of the LED module A 1 and mixing of light of different colors are promoted. As will be understood from this embodiment, the present invention is also applicable to an LED module including flip-chip type LED chips.

FIGS. 6-8 illustrate an LED module according to a fourth embodiment of the present invention. The LED module A 4 of this embodiment includes a module substrate 1 , a wiring pattern 2 , LED chips 3 R, 3 G, 3 B, wires 4 R, 4 G, 4 B and a sealing resin 5 . The LED module A 4 is designed to emit white light by mixing red light, blue light and green light. The LED module A 4 of this embodiment has a very small size of about 1.0 mm×1.0 mm in plan view and about 0.2 mm in height. For easier understanding, the sealing resin 5 is illustrated by imaginary lines in FIG. 7 .

The module substrate 1 is an insulating substrate made of e.g. glass fiber-reinforced epoxy resin and has a substantially rectangular shape. The module substrate 1 has an obverse surface on which the LED chips 3 R, 3 G, 3 B are mounted, and a reverse surface which is opposite to the obverse surface in the thickness direction. The reverse surface of the module substrate 1 is utilized as a mount surface for mounting the LED module A 4 . The module substrate 1 is formed with a plurality of grooves 11 R, 11 G, 11 B, 11 C. The grooves 11 R, 11 G, 11 B, 11 C extend in the thickness direction of the module substrate 1 at the four corners of the module substrate 1 . The module substrate 1 may be about 1.0 mm×1.0 mm in plan view and about 0.05 mm in thickness.

The wiring pattern 2 includes electrodes 21 R, 21 G, 21 B and a common electrode 22 C and is made of a plating layer of Cu, Ni or Au, for example. The electrodes 21 R, 21 G, 21 B serve to supply power to the LED chips 3 R, 3 G, 3 B. The electrodes 21 R, 21 G, 21 B include pads 21 Ra, 21 Ga, 21 Ba, strip portions 21 Rb, 21 Gb, 21 Bb, quarter-annular portions 21 Rc, 21 Gc, 21 Bc, quarter-cylindrical portions 21 Rd, 21 Gd, 21 Bd and mount portions 21 Re, 21 Ge, 21 Be.

As illustrated in FIG. 7 , the pads 21 Ra, 21 Ga and 21 Ba are provided on the obverse surface of the module substrate 1 for bonding the LED chips 3 R, 3 G and 3 B, respectively. In this embodiment, the pads 21 Ra, 21 Ga, 21 Ba are substantially X-shaped. The pads 21 Ga and 21 Ba are aligned in parallel to one of horizontally-extending sides of the module substrate 1 . The pad 21 Ra is arranged at a position deviated from the pads 21 Ga and 21 Ba toward the other horizontally-extending side of the module substrate 1 . The distance from the pad 21 Ra to the pad 21 Ba is set shorter than the distance from the pad 21 Ra to the pad 21 Ga.

The strip portions 21 Rb, 21 Gb, 21 Bb extend from the pads 21 Ra, 21 Ga, 21 Ba toward three corners of the module substrate 1 . The quarter-annular portions 21 Rc, 21 Gc, 21 Bc surround the openings of the grooves 11 R, 11 G, 11 B in the obverse surface side of the module substrate 1 . The quarter-cylindrical portions 21 Rd, 21 Gd, 21 Bd are formed to cover the grooves 11 R, 11 G, 11 B. As illustrated in FIG. 8 , the mount portions 21 Re, 21 Ge, 21 Be are formed to surround the openings of the grooves 11 R, 11 G, 11 B in the reverse surface side of the module substrate 1 . The mount portions 21 Re, 21 Ge, 21 Be are utilized for surface-mounting of the LED module A 4 on e.g. a circuit board. The quarter-cylindrical portions 21 Rd, 21 Gd, 21 Bd and the quarter-annular portions 21 Rc, 21 Gc, 21 Bc are utilized for promoting formation of a solder fillet in surface-mounting the LED module A 4 .

The common electrode 22 C is electrically connected to all the LED modules 3 R, 3 G, 3 B. The common electrode 22 C includes pads 22 Ca, 22 Cb, strip portions 22 Cc, 22 Cd, a quarter-annular portion 22 Ce, a quarter-cylindrical portion 22 Cf and a mount portion 22 Cg. The pads 22 Ca and 22 Cb are provided on the obverse surface of the module substrate 1 for bonding the wires 4 R, 4 G, 4 B. The pad 22 Ca is in the form of a vertically elongated rectangle and arranged between the pads 21 Ga and 21 Ba. The pad 22 Cb is in the form of a horizontally elongated rectangle and arranged on the left side of the pad 21 Ra and on the upper side of the pad 21 Ga in FIG. 7 . The strip portion 22 Cc connects the pads 22 Ca and 22 Cb to each other. The strip portion 22 Cd extends from the pad 22 Cb toward the groove 11 C of the module substrate 1 . The quarter-annular portion 22 Ce surrounds the opening of the groove 11 C in the obverse surface side of the module substrate 1 . The quarter-cylindrical portion 22 Cf is formed to cover the groove 11 C. As illustrated in FIG. 8 , the mount portion 22 Cg surrounds the opening of the groove 11 C in the reverse surface side of the module substrate 1 and is utilized for surface-mounting of the LED module A 4 on e.g. a circuit board. The quarter-cylindrical portion 22 Cf and the quarter-annular portion 22 Ce are utilized for promoting formation of a solder fillet in surface-mounting the LED module A 4 .

Each of the LED chips 3 R, 3 G, 3 B has e.g. a laminated structure made up of a p-type semiconductor layer, an n-type semiconductor layer and an active layer sandwiched between the p-type semiconductor layer and the n-type semiconductor layer. The LED chip 3 R emits red light, the LED chip 3 G emits green light and the LED chip 3 B emits blue light. The LED chips 3 R, 3 G and 3 B are bonded to the bonding pads 21 Ra, 21 Ga and 21 Ba, respectively, via e.g. conductive paste. In this embodiment, the LED chips 3 R, 3 G, 3 B are arranged to form vertices of a triangle. The LED chip 3 R has a size of about 0.15×0.15 mm in plan view, whereas the LED chips 3 G and 3 B have a size of about 0.2×0.2 mm to 0.3×0.3 mm in plan view. Thus, the LED chip 3 R for emitting red light is relatively small.

The wires 4 R, 4 G, 4 B are made of e.g. Au and electrically connect the anode electrodes (not shown) of the LED chips 3 R, 3 G, 3 B to the electrode 22 C. In this embodiment, the wire 4 B is connected to the LED chip 3 B and the pad 22 Ca. The wires 4 R and 4 G are connected to the LED chip 3 R or 3 G and the pad 22 Cb.

The sealing resin 5 is made of e.g. a transparent resin which transmits light from the LED chips 3 R, 3 G, 3 B and covers the LED chips 3 R, 3 G, 3 B and wires 4 R, 4 G, 4 B. The reverse surface of the module substrate 1 is formed with e.g. a resist film for preventing the LED module A 4 from being mounted with wrong polarity.

The advantages of the LED module A 4 are described below.

In this embodiment, all the wires 4 R, 4 G, 4 B are bonded to the common electrode 22 C. Since the wire 4 B is bonded to the pad 22 Ca arranged between the LED chips 3 G and 3 B, the wire 4 B does not need to be long, and further, the bonding portions of the wires 4 R, 4 G, 4 B are prevented from being positioned too close to each other. Further, the portions for bonding the wires 4 R, 4 G, 4 B do not project largely in the plan-view direction relative to the LED chips 3 R, 3 G, 3 B. Thus, the LED chips 3 R, 3 G, 3 B can be arranged close to each other, which leads to the size reduction of the LED module A 4 .

By arranging the LED chips 3 R, 3 G, 3 B close to each other to form a triangle, red light, green light and blue light from the LED chips 3 R, 3 G, 3 B are properly mixed. The LED chip 3 G, which emits green light, is separated from the LED chips 3 R and 3 B by the common electrode 22 C, and the distance between the LED chip 3 G and the LED chips 3 R, 3 B is relatively long. However, the visual sensitivity of human eyes to green light is relatively high. Thus, the balanced mixing of red light, green light and blue light from the LED chips 3 R, 3 G, 3 B is achieved.

The electrodes 21 R, 21 G, 21 B and the common electrode 22 C are configured and arranged to extend dispersedly toward the four corners of the module substrate 1 . With this arrangement, none of the electrodes 21 R, 21 G, 21 B and the common electrode 22 C does not need to include an unfavorably long strip portion. Further, an unnecessary space is not created in the surface of the module substrate 1 . Thus, the arrangement of this embodiment is suitable for the size reduction of the LED module A 4 .

FIG. 9 illustrates an LED module according to a fifth embodiment of the present invention. The LED module A 5 of this embodiment differs from that of the fourth embodiment in structure of the LED chips 3 G and 3 B. Specifically, each of the LED chips 3 G and 3 B includes two electrodes on the upper surface. Thus, two wires 4 G and two wires 4 B are bonded to the LED chips 3 G and 3 B, respectively. The pad 21 Ga and 21 Ba of the electrodes 21 G and 21 B are spaced from the LED chips 3 G and 3 B in the horizontal direction in FIG. 4 . One of the wires 4 G and one of the wires 4 B are bonded to the pads 21 Ga and 21 Ba, respectively.

According to this embodiment again, mixing of light from the LED chips 3 R, 3 G, 3 B is promoted. Although the LED module A 5 is slightly larger than the LED module A 4 of the fourth embodiment because of the difference in arrangement of the pads 21 Ga and 21 Ba, the LED module A 5 is still small for an LED module including two-wire type LED chips 3 G, 3 B. As will be understood from this embodiment, the present invention is also applicable to an LED module including two-wire type LED chips.

FIG. 10 illustrates an LED module according to a sixth embodiment of the present invention. The LED module A 6 of this embodiment differs from those of the fourth and fifth embodiments in structure of the LED chips 3 G and 3 B. Specifically, the LED chips 3 B and 3 G of this embodiment have a flip-chip structure including two electrodes on the lower surface. To correspond to this structure, the pad 22 Ca has a horizontally elongated shape to overlap the LED chips 3 G and 3 B. The pads 21 Ga and 21 Ba are arranged adjacent to the pads 22 Ca. The two electrodes of the LED chip 3 G are bonded to the pads 22 Ca and 21 Ga, whereas the two electrodes of the LED chip 3 B are bonded to the pads 22 Ca and 21 Ba.

According to this embodiment again, the size reduction of the LED module A 6 and mixing of light of different colors are promoted. As will be understood from this embodiment, the present invention is also applicable to an LED module including flip-chip type LED chips.

FIG. 11 illustrates an LED module according to a seventh embodiment of the present invention. The LED module A 7 of this embodiment has the same structure as that of the LED module A 4 of the fourth embodiment except for the structure of the module substrate 1 .

The module substrate 1 of this embodiment is an insulating substrate which is made of e.g. glass fiber-reinforced epoxy resin containing e.g. a black pigment and hence entirely dark in color. The module substrate 1 is substantially square. In the module substrate 1 , the pigment is contained to such a degree that the entirety of the module substrate 1 be black. However, unlike this embodiment, the module substrate 1 may have a dark color other than black, such as dark gray. To prepare the module substrate 1 having a dark color, a dye may be mixed in a glass fiber-reinforced epoxy resin or a coating of a dark color may be applied to the surface of a glass fiber-reinforced epoxy resin. It is only necessary that, of the module substrate 1 , at least part of the surface on which the LED chips 3 R, 3 G, 3 B are mounted has a dark color.

FIGS. 12-14 illustrate an example of LED dot matrix display which utilizes the LED module A 7 . The LED dot matrix display B illustrated in these figures includes a plurality of LED modules A 7 , main boards 6 , IC chips 61 , connectors 62 and connection modules 7 . For easier understanding, the illustration of the wiring pattern 2 is omitted in FIG. 14 .

Each of the main boards 6 is in the form of an elongated rectangle and made of e.g. glass fiber-reinforced epoxy resin containing a black pigment. Thus, the main boards 6 are entirely black. However, the color of the main boards 6 is not limited to black, and other dark colors may be employed. Further, it is only necessary that, of the main board 6 , at least part of the surface on which the LED modules A 7 are mounted has a dark color. The LED modules A 7 are mounted on the obverse surface of the main board 6 , whereas the IC chips 61 and the connectors 62 are mounted on the reverse surface of the main board 6 . The size of the main board 6 is about 36 mm×72 mm, and the LED modules A 7 are arranged in a matrix of 24×48 with a pitch of 1.5 mm.

The IC chips 61 drive the LED modules A 7 in accordance with inputted display signals. In this embodiment, the IC chips 61 receive display image information as serial signals. The IC chips are small chips having a size of about 5 mm×5 mm in plan view, for example.

The connectors 62 serve to connect a plurality of main boards 6 to each other. The connectors 62 are fitted to the connectors 72 of the connection modules 7 , which will be described later.

The plurality of main boards 6 are connected to each other by the connection modules 7 . Each of the connection modules 7 includes a connection substrate 71 , two connectors 72 and four bosses 73 . The connection substrate 71 is made of e.g. glass fiber-reinforced epoxy resin and in the form of a rectangle of about 15 mm×38 mm in plan view.

The two connectors 72 are mounted on a surface of the connection substrate 71 which faces the main boards 6 . Each of the connectors 72 is connected to a respective one of the connectors 62 .

The bosses 73 are made of an alloy of Cu or Fe, for example, and provided at four corners of the connection substrate 71 . The bosses 73 are utilized for fixing the main boards 6 to e.g. another structural element of the LED dot matrix display B along with the connection module 7 .

The advantages of the LED dot matrix display B will be described below.

According to this embodiment, the main boards 6 and the module substrates 1 , which are black, occupy most part of the display region of the LED dot matrix display B. Thus, when all the LED modules A 7 are in the OFF state, the display region of the LED dot matrix display B shows a deep black color. Thus, the contrast of the LED dot matrix display B is enhanced. This enhanced contrast is obtained if only the main boards 6 and the modules substrates 1 have a dark color.

To increase the resolution of the LED dot matrix display B, LED modules A 7 are mounted at a higher density. Mounting the LED modules at a higher density means that the module substrates 1 occupy a larger proportion of the display region of the LED dot matrix display B. Since the module substrates 1 are black, it is possible to increase the definition of the LED dot matrix display B while achieving an enhanced contrast.

To make the entirety of the module substrate 1 black is suitable for making the display region of the LED dot matrix display B have a deep black color. However, unlike this embodiment, the module substrate 1 may be made of a glass fiber-reinforced epoxy resin to which a coating of dark colors, which include black, is applied. In this case again, the contrast of the LED dot matrix display B is enhanced.

FIG. 15 illustrates an LED dot matrix display B which utilizes a variation of the LED module A 7 . In the illustrated LED dot matrix display B, a plurality of LED modules A 7 are arranged in a matrix. The LED modules A 7 differ from the above-described LED modules A 7 in material of the sealing resin 5 . Specifically, the sealing resin 5 of this variation is made of a light-transmitting resin containing a pigment of a dark black color. When the LED chips 3 R, 3 G, 3 B are in the ON state, the sealing resin 5 transmits the light from the LED chips 3 R, 3 G, 3 B. When the LED chips 3 R, 3 G, 3 B are in the OFF state, the sealing resin shows a substantially black color.

According to this embodiment, when the LED chips 3 R, 3 G, 3 B are in the OFF state, the wiring pattern 6 is prevented from shining due to the reflection of external light. This is suitable for enhancing the contrast of the LED dot matrix display B.

The LED module and LED dot matrix display according to the present invention are not limited to the foregoing embodiments. The specific structure of each part of the LED module and LED dot matrix display of the present invention may be modified in design in many ways.