JP2011210974A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that a crack occurs in brazing material resulting from difference in thermal expansion coefficients between a metal substrate and an LED package, wherein an LED is a heat-generating light-emitting device, and a metal substrate made of a metal material is adopted to suppress temperature rise of the LED since drive current of the LED cannot be increased without dissipating the heat.SOLUTION: In the lighting device disclosed herein, n LED packages 22 are arranged on a thin and long metal substrate 21 made of aluminum along the long sides thereof, wherein a groove is formed in a first electrode 6a by half etching from a side more inside than the perimeter of an anode electrode 23a.

Description

  The present invention relates to a lighting device in which light emitting diodes (hereinafter referred to as LEDs) are provided in a row.

  In recent years, prevention of global warming has been screamed, and various countermeasures have been taken around the world. In particular, each company has been developing technologies to suppress the generation of carbon dioxide, such as so-called energy generation such as solar cells and wind power generation, energy storage such as fuel cells, and high-efficiency energy saving such as inverters. Yes.

  And as one of this energy saving, LED attracts attention. In other words, this LED can be driven with much lower power than that of incandescent bulbs and fluorescent lamps. Therefore, it is used as a backlight of a large-sized liquid crystal TV, used for home lighting, and further used as a headlight of a car.

  However, this LED has a troublesome temperature characteristic. For example, it is discussed in FIG. 5 of Japanese Patent Laid-Open No. 2001-203395.

  According to the explanation, as shown in FIG. 9, when the surface temperature of the LED chip (the temperature of the operation region) exceeds about 80 to 95 degrees C, the light quantity of the LED is increased even if the drive current is increased. Does not increase, but conversely decreases.

The curve plotted with x at the bottom is the current vs. surface temperature curve of the Al substrate, the curve plotted with the middle triangle is the current vs. surface temperature curve of the PCB substrate, and the curve with the upper peak is the current Therefore, if the temperature of the LED is lowered as much as possible and the amount of light is not increased with respect to the drive current, no further increase in the amount of light can be expected. For example, when a printed circuit board is used as an LED mounting board, the surface temperature rises as much as 230 degrees because the thermal conductivity is small, and the amount of light does not increase even when a large amount of current is passed. However, since the metal substrate has a high thermal conductivity, the surface temperature of the LED can be maintained at about 85 degrees. This effectively works as a heat sink and as a heat sink, and the metal substrate effectively works to lower the surface temperature of the LED, thereby increasing the drive current and increasing the amount of light. As described above, in order to realize a reduction in the surface temperature of the LED, it is necessary to dissipate the heat generated in the LED to the outside as much as possible.

  Candidates such as Al, Cu and other metals, alloys, alumina, AlN, and other ceramics are candidates for mounting substrates with excellent heat dissipation. However, due to recent ecological considerations, weight-weight Al is attracting attention. ing. Compared to Cu, the thermal conductivity is slightly inferior, but the cost is low, and the most important point is that it is lightweight.

JP 2001-203395 A

  However, this metal substrate has a difficult point. That is a problem with the coefficient of thermal expansion. Specific numerical values are listed below.

Al: 23-25 ppm / degree C
Semiconductor element: 3.5 ppm / degree C
Chip resistance: 7.0 ppm / degree C
Chip capacitor: 10.0 ppm / degree C
Solder: 23 ppm / degree C
In other words, it is possible to mount the LED on a metal substrate and release the heat generated from the LED. A large load is applied to the weak part.

  For example, FIG. 8 shows the principle, and shows a state where a chip element is mounted on a metal substrate. The arrows shown therein indicate the thermal expansion coefficient, that is, the expansion and contraction with respect to temperature. Since the elongation of the metal substrate is large, a load is applied to the solder, and the load applied to the solder becomes larger as the angle between the part indicated by a circle, that is, the solder extended surface and the element back surface is an acute angle.

  Specifically, LED packages in which LEDs are sealed with a ceramic package and LED packages that are mounted on a lead frame and resin-sealed are mounted via solder from the viewpoint of mountability, but because the thermal expansion coefficient of the Al substrate is large A large load is applied to the solder. Although it is still able to withstand at the beginning, the number of temperature cycles applied to the solder increases with the passage of time. Eventually, a solder crack may occur, the circuit may be in an open state, and the LED may not emit light. . In the lead frame, the stress can be relaxed due to the flexibility of the lead, but when sealed with a ceramic substrate, the back surface of the electrode is generally adopted because the electrode is attached to the back surface of the ceramic substrate. There is a possibility that a load is directly applied to the solder provided in the solder and induces a solder crack.

The present invention, first,
A ceramic substrate, an LED chip mounted on the ceramic substrate, an anode electrode (or cathode electrode), a cathode electrode (or anode electrode) electrically connected to the LED chip and provided on the back surface of the ceramic substrate And n LED packages having heat radiation electrodes;
A metal substrate mainly composed of slender Al capable of arranging the n LED packages;
An insulating layer made of a resin provided on the entire surface of the metal substrate;
A first electrode, a second electrode, and a third electrode provided on the surface of the insulating layer and corresponding to the anode electrode (or cathode electrode), the cathode electrode (or anode electrode), and the heat dissipation electrode And
The first electrode and the anode electrode (or cathode electrode), the second electrode and the cathode electrode (or anode electrode), the third electrode, and the heat dissipation electrode are fixed by a brazing material, and the length of the metal substrate This is solved by mounting the n LED packages along the side.

  In the present invention, first, in the LED package containing the LED chip, an electrode for heat dissipation is provided in addition to the electrode, so that heat generated from the LED is positively transmitted to the mounting substrate. The back surface of the LED chip is connected to the electrode of the ceramic substrate and adopts a structure that is transmitted to the heat dissipation electrode on the back surface of the ceramic substrate through a thermal via.

  Moreover, the stress applied to the brazing material is reduced by processing the conductive pattern on the mounting substrate on which the light emitting diode is mounted.

  Specifically, by half-etching the periphery of the electrode, the amount of solder in a portion where stress is likely to concentrate is increased and solder cracks are suppressed.

It is a figure explaining the illuminating device of this invention. It is a figure explaining the illuminating device of this invention. It is a figure explaining the illuminating device of this invention. It is a figure explaining the illuminating device of this invention. It is a figure explaining the illuminating device of this invention. It is a figure which shows the manufacturing method of the illuminating device of this invention. It is a figure explaining the illuminating device of this invention. It is a figure explaining the conventional illuminating device. It is a figure explaining the surface temperature of light quantity with respect to current when LED is mounted on an Al substrate and a printed circuit board.

  As shown in FIG. 1A, the present invention is a technique related to an LED module 3 in which an LED package 1 which is a package in which an LED chip 7 is sealed is mounted on a metal substrate 2, and particularly represents solder. This relates to exhaustion and deterioration of the brazing material.

  In particular, the metal substrate 2 may be composed of Cu or Al as a main component or a metal alloy. However, considering mounting on a vehicle or LCD TV, etc., the description will be made with Al or Al as the main material because of its light weight. The Al substrate 2 has a thickness of approximately 1.0 mm to 2.0 mm (for example, 1.5 mm), and both main surfaces are covered with an inorganic insulating film (alumite film) 4 mainly composed of an aluminum oxide film. . Further, the upper surface of the substrate 2 is entirely covered with an insulating layer 5 made of a resin filled with a filler, and a conductive pattern 6 made of Cu is formed on the upper surface of the insulating layer. Note that the inorganic insulating film may be omitted. As a matter of course, the insulating layer 5 itself has a large thermal resistance, but the thermal resistance can be reduced by the filling amount of the filler.

  Next, the LED package 1 will be described. The bare LED chip 7 is mounted on a ceramic substrate 8. The ceramic substrate 8 is provided with conductive patterns 9a to 9c on the front surface for the bare chip mounting, and correspondingly conductive patterns 10a to 10c on the back surface. Here, 9a and 10a are anode (or cathode) electrodes (hereinafter referred to as A electrodes) of LEDs, and 9b and 10b are cathode (or anode) electrodes (hereinafter referred to as C electrodes), each of which is a through hole. It is electrically connected via via. Furthermore, the island 9c thermally coupled to the back surface of the bare chip is thermally coupled to a heat radiation electrode (hereinafter referred to as Rd electrode) 10c provided on the back surface of the ceramic substrate 8 through a thermal via 11. . The thermal via 11 is obtained by firing a metal paste having a high thermal conductivity, and in particular, Ag or Cu is adopted. Further, considering the simplification of the manufacturing method, the same material as the through hole via is preferable. The electrodes 10a and 10b extend upward from the back surface of the ceramic substrate 8 along the side surfaces. In the cross-sectional view, the L-shape is horizontal.

  Subsequently, a frame body 12 serving as four side surfaces of the LED package 1 is provided around the ceramic substrate 8, and an inner side of the frame body 12 serves as a cavity 13 for mounting the bare chip 7. Further, considering the sealing of the cavity 13 and the transmission of LED light, the light-transmitting lid 14 is fixed to the head of the frame body with an adhesive.

  In the present invention, the heat generated from the bare chip 7 is released to the metal substrate 2 through the thermal via 11, so that the temperature rise of the bare chip 7 can be suppressed, and the drive current of the LED can be increased accordingly. Furthermore, as shown in FIG. 7, since ten or more LED packages 1 are mounted on the LED bar, the temperature of the entire LED module 3 inevitably rises. However, since the metal substrate 2 that functions as a heat sink or a heat sink is employed, it is possible to suppress defects due to temperature rise. In particular, if an underfill is provided, the periphery of the solder can be covered with resin, and a compressive stress can always be applied to the solder.

  Furthermore, the present invention employs a structure in which the solder of the Rd electrode 10c is sacrificed for the patterns of the back electrodes 10a and 10b and the Rd electrode 10c. That is, the electrodes 6a and 6b are conductive patterns attached to the metal substrate 2, and correspondingly, the anode electrode and the cathode electrodes 10a and 10b on the LED package 1 side are fixed via the brazing material. Similarly, the electrode 6c is a conductive pattern adhered to a metal substrate, and is fixed to the Rd electrode 10c provided on the back side of the ceramic substrate 8 via a brazing material. The structure is such that cracks are generated in the solder of the heat radiation electrode 10c. As a result, the stress applied to the solder of the electrodes 10a and 10b at both ends is relaxed to suppress cracks.

  Specifically, the angle between the solder extended surface and the back surface of the metal substrate 2 will be described below. First, some definitions will be made with reference to FIG.

  The surface where the solder is melted generally draws a curved curve. For example, FIG. 1B schematically shows the solder state of the heat radiation electrode 10c in FIG. 1A and the electrode 6c on the metal substrate side. The line L1 is the bottom surface of the ceramic substrate 8, and the line L2 indicates the surface on the metal substrate 2 side. An Rd electrode 10c is provided on the ceramic substrate 8 side, and an electrode 6c is provided on the metal substrate 2 side. The solder is wet between the two and is electrically connected.

  Here, the angle between the extended surface of the solder and the ceramic substrate is discussed, but here it is as follows. That is, the solder starts from the point B ′ of the heat radiation electrode 10c and ends at the point A of the electrode 6c of the metal substrate, and is bent and wetted between them, or the contact point B between the outer periphery of the heat radiation electrode 10c and the ceramic substrate is soldered. It is assumed that the surface is wet and draws a curve with the end point A. The former solder surface is regarded as a straight line A-B ', and the latter solder surface is regarded as a straight line AB. Since the solder draws a curve at any position between the two extended surfaces, the angle between the two straight lines and the horizontal line is collectively defined as α3. This point is also described in FIG. 1A, and α3 shown on both sides of the heat radiating electrode 10c is substantially symmetric and thus α3. In the same manner, the solder extending surface inside the anode electrode and the cathode electrode was set to α1. On the other hand, α2 is a generic term for α2 and the angle between the line L3 parallel to the side wall of the ceramic substrate or the side wall of the package and the straight line AB or straight line A-B ′.

  Originally, as described in the conventional example, the angles α1 to α3 are preferably obtuse angles. However, in the present invention, the electrode 6c is made slightly larger than the heat radiation electrode 10c, and is provided so that the entire heat radiation electrode 10c enters the electrode 6C in plan view, and α3 is an acute angle.

  The LED module 3 is constantly subjected to a temperature cycle, and the solder is exhausted over time. Eventually, there is a difference in time, but finally, a solder crack may occur. Therefore, at that time, the stress applied to the portions α1 and α2 is relieved by generating a crack in this portion that is α3. Moreover, there are two paths that are conducted downward from the heat radiation electrode, one that is directed downward, and another that is radiated in a skirt shape with an angle. Therefore, since the heat radiation electrode 6c on the metal substrate side is one size larger, more efficient heat radiation is possible.

Although the present embodiment has been described with a ceramic package, it can be applied to a resin package as long as it has the same structure.
<< Second Embodiment >>
Subsequently, a second embodiment will be described with reference to FIGS. As shown in FIG. 7, this embodiment is based on the LED bar 20 that is attached to the side of the LCDTV and constitutes one backlight, and the metal substrate 21 and the LED package 22 are the same as those in the previous embodiment. It is the same composition as. In the previous embodiment, the angle with the solder surface was discussed, but now the thickness of the solder will be discussed.

  First, as in the previous embodiment, this substrate employs Al or a metal substrate 21 whose main material is Al, has a thickness of about 1.0 mm to about 2.0 mm, and has a planar size of width. The length is about 0.5 cm and the length is about 50 cm. Although this length varies depending on the size of the TV, in principle, it has an elongated shape as shown in FIG. The width of the LED bar is essentially the same as the thickness of the light guide plate attached to the LCDTV. In recent years, since the thickness of the LCDTV has been reduced, this width tends to be narrower from 0.5 mm.

  The elongated metal substrate 21 is provided with LED packages 22 arranged in a line as shown in FIG. 7A. In particular, the LED packages are generally connected in series as shown in the equivalent circuit at the bottom of FIG. Further, in order to disperse the elongation resulting from the thermal expansion coefficient as much as possible, several LED bars may be used and connected in parallel as shown in the equivalent circuit diagram in FIG. One LED bar is formed by connecting three LEDs in series, and the LED bars are connected in parallel. Here, there are three LEDs, but this number is not limited. This can be done by replacing any of the LED bars connected in parallel even if the voltage applied to both ends is lowered, or if any LED chip malfunctions.

  Therefore, electrodes and wirings are formed on the metal substrate 21 corresponding to the equivalent circuit. In particular, the LED package 22 is provided with an A electrode, a C electrode, and an Rd electrode as described with reference to FIG. 1A. In FIG. 7C, reference numerals 23a, 23b, and 23c correspond to the LED package 22; Itself is indicated by a dotted line.

  FIG. 7B is an enlarged view of a portion indicated by a circle in FIG. 7A, and illustrates a conductive pattern provided in a mounting region of one LED package. 7C is a cross-sectional view taken along the line YY, and FIG. 7D is a cross-sectional view taken along the line XX.

The point of the present invention is that the thickness of the conductive patterns 6a, 6b, 6c on the metal substrate 2 side is controlled as shown in FIG. (The conductive pattern 6a corresponding to the anode electrode is the first electrode, the conductive pattern 6b corresponding to the cathode electrode is the second electrode, and the conductive pattern 6c corresponding to the heat dissipation electrode is the third electrode.)
That is, the thickness of the heat radiation electrode 6c is d1, the thickness of the first and second electrodes 6a and 6b is d2, and the thickness of the brazing material between the C electrode 10a and the third electrode 6c is t1. When the thickness of the brazing material between the A electrode 10a and the first electrode 6a and the thickness of the brazing material between the C electrode 10b and the second electrode 6b are t2,
Since d1> d2, the thickness relationship of the brazing material is t2> t1.

  That is, since the thickness t2 of the brazing material that functions as an electrode is formed thick, the strength of the brazing material is improved accordingly. Further, since t2 is thin, stress is easily concentrated here, and fatigue of the thin portion proceeds first, so that cracking of the brazing material that functions as an electrical connection can be suppressed. On the other hand, if the periphery of the brazing material is applied with underfill or the like, a compressive stress is always applied, and cracks are further suppressed. In addition, since compressive stress is applied, even if a crack occurs in the brazing material at the heat radiation electrode, the thermal coupling is not broken, and a heat radiation function can be provided.

  Next, FIG. 2B will be described. In this different part, the A electrode 10 a and the C electrode 10 b extend on the side surface of the ceramic substrate 8. Or it is the structure extended to the side surface of the LED package 1. The rest is the same as FIG. As described with reference to FIG. 1A, the portion of the angle α2 at the A electrode 10a and the C electrode 10b becomes an obtuse angle, so that the strength of the brazing material is further improved.

  The conductive pattern 6 bonded to the metal substrate 2 has a uniform film thickness at the beginning. Therefore, the first electrode and the second electrode may be thinned by etching or the like to provide a difference in film thickness between the first electrode and the third electrode. Conversely, a Cu foil or the like may be bonded to the third electrode to make a difference in film thickness.

  Next, FIG. 3 and FIG. 4 will be described. This case is the same as FIG. 2A and FIG. 2B except for the shapes of the A electrode 6a and the C electrode 6b, and only different parts will be described.

  In FIG. 3, the A electrode 6a and the C electrode 6b are half-etched to form grooves. Although two types are illustrated on the right and left, in actuality, either one is selected and the same shape is applied to the left and right electrodes. The depth of the groove is shallower than the thickness of the electrode. In the plan view of the A electrode 6a indicated by the tip of the arrow, the LED package 1 is illustrated by a dotted line. That is, the groove is formed so that the side wall outside the groove is located outside the LED package and inside the electrode 6 a, and the side wall inside the groove is formed inside the LED package 1. Furthermore, when the outer side wall or the middle of the groove is covered with an insulator such as a solder resist, the outer extended surface of the brazing material can be positioned in the groove. Therefore, the thickness of the brazing material that the side wall of the heat radiation electrode 10a extends by being wetted downward is increased, and the strength of the brazing material can be improved.

  On the other hand, the groove shape of the C electrode has no outer side wall, and a groove having a certain depth is formed from the inner side wall to the outer periphery. This can also secure the thickness of the brazing material and suppress the exhaustion of the brazing material.

  FIG. 4 shows that the A electrode 10a and the C electrode 10b extend on the side wall of the ceramic substrate 8 or on the side wall of the LED package as compared with the structure of FIG. Also in this case, the angle α2 becomes an obtuse angle, and the reliability can be further improved.

  Finally, the case of FIGS. 5 and 6 will be described. Here, the bare chip 7 mounted on the LED package is different from the conventional chips. That is, the back surface of the chip 7 has a structure that functions as a C electrode and a heat dissipation electrode. Therefore, it can be realized with two electrodes, and the original heat radiation electrode can be deleted. The patterns of the A electrode and the C electrode provided on the metal substrate are the same as those in FIG. Again, either one is selected and formed.

  In FIG. 6, the A electrode and the C electrode extend to the side wall of the ceramic substrate, or extend to the side wall of the LED package.

1: LED package 2: Metal substrate 3: LED module 4: Inorganic insulating film 5: Insulating layer 6: Conductive pattern 7: LED bare chip 8: Ceramic substrate 9a, 10a: A electrode 9b, 10b: B electrode 9c, 10c : Rd electrode 11: Thermal via
12: Frame 13: Hollow part 14: Lid

Claims (5)

A ceramic substrate, an LED chip mounted on the ceramic substrate, an anode electrode (or cathode electrode), a cathode electrode (or anode electrode) electrically connected to the LED chip and provided on the back surface of the ceramic substrate And n LED packages having heat radiation electrodes;
A metal substrate mainly composed of slender Al capable of arranging the n LED packages;
An insulating layer made of a resin provided on the entire surface of the metal substrate;
A first electrode, a second electrode, and a third electrode provided on the surface of the insulating layer and corresponding to the anode electrode (or cathode electrode), the cathode electrode (or anode electrode), and the heat dissipation electrode And
The first electrode and the anode electrode (or cathode electrode), the second electrode and the cathode electrode (or anode electrode), the third electrode, and the heat dissipation electrode are fixed by a brazing material, and the length of the metal substrate An illumination device, wherein the n LED packages are mounted along a side. The lighting device according to claim 1, wherein wiring is further provided on the metal substrate, and the n LED packages are electrically connected in series along a long side of the metal substrate. The lighting device according to claim 1, wherein the lighting device is an LED package that serves as both the C electrode and the heat dissipation electrode. The thickness of the said thermal radiation electrode is formed thicker than the film thickness of the said anode electrode (or cathode electrode), or it is formed thicker than the film thickness of the said cathode electrode (or anode electrode). The lighting device according to claim 2 or claim 3. The first electrode is formed with a groove shallower than the thickness of the first electrode from the inner periphery to the outer periphery of the anode electrode (or cathode electrode). Or the illuminating device of Claim 3.

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