JP2012160534A - Led light source unit and lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a light source unit which prevents a deformation of a ceramic substrate and an occurence of stress when a strip-like ceramic substrate on which multiple LED are mounted is joined to a frame or a heat sink.SOLUTION: A strip-like ceramic substrate 11 on which multiple LED 13 are mounted is joined to a kovar or ferrous metal substrate 12 having a heat expansion coefficient different from that of the ceramic substrate 11, with a thermosetting resin adhesive 14 including filler.

Description

  Embodiments described herein relate generally to an LED light source unit used as an LED backlight for a liquid crystal television or the like, and an illumination device using the same.

  Conventionally, an edge-light type backlight unit using a light emitting diode (LED) as a light source has a metal substrate such as a high thermal conductivity aluminum or copper alloy on which an LED is mounted, or a ceramic substrate such as aluminum nitride or alumina. It is attached to a frame having a heat dissipation function via a heat dissipation member.

  Also, the direct type backlight unit using LEDs is mounted on a ceramic substrate made of a metal such as aluminum or copper alloy with high thermal conductivity, aluminum nitride, etc. 3 is fixed to the upper surface of the bottom of a unit case formed of a metal having a high thermal conductivity such as an aluminum alloy by screwing or the like.

JP 2009-272451 A JP 2007-335371 A

  The problem to be solved by the present invention is that when a long and narrow strip-shaped ceramic substrate is used as a linear LED light source unit to an aluminum frame or a heat sink, bonding from the curing temperature of the adhesive to room temperature is achieved. Due to the difference in thermal expansion coefficient between the two joined materials, due to the temperature drop and the heat generation and temperature rise due to energization of the LED, the curved deformation, especially in the long direction, while maintaining the joined state as shown in FIG. In the case of a structure in which the center part in the longitudinal direction is lifted and the incident efficiency of LED light to the light guide plate is deteriorated, or an aluminum frame or a heat radiating plate is further joined to a surrounding metal frame to radiate heat, etc. There was a problem that air gaps were formed and heat dissipation was lost.

  As another heat dissipation measure, when screwing with a highly thermally conductive sheet or grease between the aluminum substrate and the ceramic substrate, the heat dissipation becomes worse, the cost becomes higher, and the ceramic substrate There is a problem that a large space is required because it needs to be fixed with screws so that it does not break, and it is not suitable for a liquid crystal television or the like that has a strong demand for thinness.

  Accordingly, an LED light source unit and an illumination device are provided that can suppress the occurrence of distortion and stress of a ceramic substrate even when a long ceramic substrate is attached to an aluminum frame or a heat sink.

  In order to solve the above-described problems, an LED light source unit according to an embodiment is bonded to a long and narrow strip-shaped ceramic substrate on which a plurality of LEDs are mounted, and a back surface side of the ceramic substrate on which the LEDs are mounted. It is characterized by comprising a long and narrow strip-shaped Kovar-type or iron-type metal member.

  In addition, the lighting device of the embodiment includes a long and narrow strip-shaped ceramic substrate on which a plurality of LEDs are mounted, a metal member having a thermal conductivity with a thermal expansion coefficient approximate to the ceramic substrate, An LED light source unit comprising a ceramic substrate and the metal member made of an adhesive, and a light guide plate that allows light emitted from the LED light source unit to enter from one side and to exit from one surface. Features.

It is typical sectional drawing for demonstrating 1st Embodiment regarding an LED light source unit. It is typical sectional drawing for demonstrating 2nd Embodiment regarding an LED light source unit. It is a view for demonstrating the 1st modification of 2nd Embodiment regarding an LED light source unit. It is a perspective view for demonstrating the 2nd modification of 2nd Embodiment regarding an LED light source unit. It is a typical disassembled perspective view for demonstrating 1st Embodiment regarding an illuminating device. 5 is an enlarged perspective view of the main part. FIG. 5 is a sectional view of the assembled state. It is explanatory drawing for demonstrating adhering of a LED light source unit. It is a typical disassembled perspective view for demonstrating 2nd Embodiment regarding an illuminating device. 9 is an enlarged perspective view of the main part. FIG. 9 is a cross-sectional view of the assembled state. It is explanatory drawing for demonstrating the conventional LED light source unit.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view for explaining a first embodiment relating to an LED light source unit.

In FIG. 1, reference numeral 11 denotes a long and narrow strip-shaped ceramic substrate formed of a heat-resistant and insulating material such as alumina (Al ₂ O ₃ ), aluminum nitride (AlN) and silicon nitride (Si ₃ N ₄ ). It is. Reference numeral 12 denotes a Kovar (Fe—Ni—Co alloy) -based or iron-based thermally conductive metal substrate. The ceramic substrate 11 and the metal substrate 12 are bonded with an adhesive 14. As the adhesive 14, an epoxy resin, a silicone resin, an acrylic resin, a double-sided adhesive tape, or the like can be used. In order to improve the thermal conductivity in the adhesive layer, the adhesive may be filled with a filler.

  The adhesive 14 does not necessarily need to be used for joining the ceramic substrate 11 and the metal substrate 12, and may be screwed.

  A wiring pattern (not shown) using a silver conductor or the like is formed on the ceramic substrate 11 along the longitudinal direction of the ceramic substrate 11, and a plurality of LEDs 13 are linearly mounted on the ceramic substrate 11 on the wiring pattern. Yes. The LED 13 may be packaged or in a chip state. In the case of a chip, a transparent sealing resin is molded on the surface of the chip.

  For example, commercial power supply AC100-220V is converted into direct current by an AC-DC converter and supplied to the LED 13 as a lighting power supply. Alternatively, a DC power source such as a battery or a battery may be used as a lighting power source. Furthermore, constant current control is performed using a DC-DC converter so that a constant current flows to the LED even if the ambient temperature of the LED 13 changes when the usage environment temperature of the product equipped with the LED light source unit changes or the LED 13 lights up. It has been broken.

  By the way, the thermal expansion coefficient of the ceramic substrate excellent in thermal conductivity is about 6.5 ppm / K, whereas the thermal expansion coefficient of the aluminum substrate is about 24 ppm / K. The thermal expansion coefficient of the aluminum substrate is an order of magnitude greater than that of the ceramic substrate, and the coefficient difference is as large as 17.5 ppm (about 3.7 times). In order to dissipate the heat generated by lighting of the LED 13 mounted on the ceramic substrate having such a thermal expansion coefficient relationship, in the conventional case where the aluminum substrate is simply bonded, the temperature when both substrates are bonded In contrast, the expansion or contraction dimensions of both bonded substrates differ depending on the difference in thermal expansion coefficient depending on the temperature rise when the LED 13 is lit and the temperature difference when the operating environment temperature changes (rising / falling) occurs. appear. As a result, the substrate is curved and deformed in the long axis direction, and the brightness uniformity of the backlight light emitting surface is reduced or heat is released due to deviation in the optical axis direction of each LED with respect to the light incident surface of the light guide plate. A gap is formed on the contact surface of the external frame, or the bonding is peeled off from the ceramic substrate due to the curvature.

  The thermal expansion coefficient of the alumina ceramic substrate 11 is about 6.5 ppm / K, whereas the Kovar-based metal substrate 12 is about 5.02 ppm / K depending on the composition ratio. Since the ceramic substrate 11 and the metal substrate 12 have the same order of thermal expansion coefficient, and the coefficient difference is also a small approximate value of 1.52 ppm, the amount of deformation and stress due to the temperature difference can be suppressed small.

  Even when the metal substrate 12 is made of Kovar-based iron, the thermal expansion coefficient of the iron substrate is about 12 ppm / K, and the difference in thermal expansion coefficient between the ceramic substrate and the aluminum substrate (about 3.7 times). The thermal expansion coefficient difference of the ceramic substrate 11 (approximately 1.85 times) is a small approximation. In this case, the amount of deformation and stress due to the iron-based metal substrate 12 can be adjusted by setting the metal substrate 12 made of iron to an appropriate thickness according to the following formulas 1 and 2 required for the stress of the three-layer structure. It becomes.

  As for Formula 1 and Formula 2, for example, “Buffer layer effects on residual stress in InP” on pages 1754 to 1756 of the document “Appl. Phys. Left Vol. 54, No. 18” published on May 1, 1989, for example. on Si substrates ".

となる。式１および式２からｉ番目層の平均応力は、Ｐｉ／ｄｉとなる。ただし、
Ｐｉ：ｉ番目の層の平均面内応力 ε_１：界面に垂直な方向の歪
Ｅｉ：ｉ番目の層のヤング率 ｄｉ：ｉ番目の層の厚み
Ｃij：弾性スティフネス Ｒ ：曲率半径
ν ：ボアッソン比 ｆ’：１層目と２層目界面の歪
ｆ ：２層目と３層目界面の歪
である。

It becomes. From Equation 1 and Equation 2, the average stress of the i-th layer is Pi / di. However,
Pi: Average in-plane stress of i-th layer ε ₁ : Strain in the direction perpendicular to the interface Ei: Young's modulus of i-th layer di: Thickness of i-th layer Cij: Elastic stiffness R: Radius of curvature ν: Boisson's ratio f ′: strain at the interface between the first layer and the second layer f: strain at the interface between the second layer and the third layer.

  When the thus configured LED light source unit is joined to a heat radiating plate such as aluminum or a frame having a heat radiating property, an appropriate thickness is provided between the ceramic substrate 11 and the heat radiating plate or the frame in accordance with Equations 1 and 2. The length and width of the Kovar-based or iron-based metal substrate 12 is affixed with a thermosetting resin adhesive 14 containing a filler. Thereby, the deformation amount and stress due to the difference in thermal expansion between the ceramic substrate 11 and the metal substrate 12 having a similar thermal expansion coefficient value can be suppressed.

  According to this embodiment, even when an LED light source unit using a strip-shaped ceramic substrate is manufactured, the heat dissipation characteristics are reduced due to a gap generated between the heat sink and the frame surface due to the deformation curve of the ceramic substrate, and the ceramic substrate is deformed. Therefore, it is possible to obtain an LED light source with high efficiency and reliability without reducing the incident efficiency to the light guide plate.

  FIG. 2 is a schematic cross-sectional view for explaining a second embodiment related to the LED light source unit. The same components as those in the first embodiment will be described with the same reference numerals.

  In this embodiment, an aluminum substrate 15 is sandwiched between the ceramic substrate 11 and the metal substrate 12 of the first embodiment relating to the LED light source unit. One surface of the aluminum substrate 15 is bonded to the ceramic substrate 11 by a highly thermally conductive epoxy resin, silicone resin, or acrylic resin adhesive 14a filled with a filler. The other surface of the aluminum substrate 15 is joined to the Kovar-based or iron-based metal substrate 12 by a highly thermally conductive epoxy resin, silicone resin, or acrylic resin-based adhesive 14b filled with a filler.

  The adhesive 14a for bonding the ceramic substrate 11 and the aluminum substrate 15 and the adhesive 14b for bonding the aluminum substrate 15 and the metal substrate 12 are not necessarily used, and may be screwed. Further, the adhesives 14a and 14b and screwing may be shared.

  On the opposite side of the aluminum substrate 15 to which the ceramic substrate 11 is bonded, a Kovar-based metal substrate 12 having a thermal expansion coefficient of about 5.02 ppm / K or an iron-based metal substrate 12 having a thermal expansion coefficient of about 12 ppm / K is attached by an adhesive 14b. It is joined.

  The aluminum substrate 15 is sandwiched between the Kovar-based or iron-based metal substrate 12 whose thermal expansion coefficient is close to that of the ceramic substrate 11, and the stress due to the difference in thermal expansion coefficient between the ceramic substrate 11 and the aluminum substrate 15 is offset. It can be mitigated.

  Thus, even when the LED light source unit uses the ceramic substrate 11 having excellent thermal conductivity and heat dissipation as an LED mounting substrate and is attached to a heat sink or a metal frame in order to obtain a heat dissipation effect, the thermal expansion coefficient of the ceramic light source unit By joining an approximate metal member to the back side of the ceramic substrate, the stress due to the difference in thermal expansion coefficient can be canceled and relaxed, and deformation of the ceramic substrate 11 on which the LED 13 is mounted can be suppressed.

  According to this embodiment, even when an LED light source unit using a strip-shaped ceramic substrate is manufactured, the heat dissipation characteristics are reduced due to a gap generated between the heat sink and the frame surface due to the deformation curve of the ceramic substrate, and the ceramic substrate is deformed. Therefore, it is possible to obtain an LED light source with high efficiency and reliability without reducing the incident efficiency to the light guide plate. Furthermore, since the aluminum substrate with high heat dissipation is arranged on the ceramic substrate, the heat dissipation effect can be improved.

  FIGS. 3 and 4 are perspective views for explaining a first modification and a second modification of the second embodiment relating to the LED light source unit, respectively.

  First, in the modification of FIG. 3, a plurality of ceramic substrates 11 on which the LEDs 13 are mounted are arranged in the longitudinal direction and further lengthened. A metal substrate 12 is bonded to a plurality of ceramic substrates 11 at positions facing the ceramic substrate 11 with the common aluminum substrate 15 and the aluminum substrate 15 interposed therebetween.

  In the case of this modification, the aluminum substrate 15 is made common to the plurality of ceramic substrates 11, so that the heat radiation area of the aluminum substrate 15 is increased and the temperature rise of the ceramic substrate 11 is suppressed, and the metal substrate 12 is joined. Warpage can be prevented.

  In the modification of FIG. 4, a plurality of ceramic substrates 11 mounted with LEDs 13 are arranged in the longitudinal direction and further elongated. A common metal substrate 12 is bonded to a plurality of ceramic substrates 11 at positions facing the plurality of ceramic substrates 11 with the common aluminum substrate 15 and the aluminum substrate 15 interposed therebetween.

  In the case of this modification, the aluminum substrate 15 and the metal substrate 12 are made common to the plurality of ceramic substrates 11, so that in addition to an increase in the heat radiation area of the aluminum substrate 15, the entire aluminum substrate 15 is made a common metal substrate. By joining at 12, the heat dissipation effect and the effect of warping prevention can be improved.

  FIGS. 5 to 7 are schematic exploded perspective views, FIG. 6 is a perspective view of the main part of FIG. 5, and FIG. FIG. In this embodiment, the LED light source unit according to the first embodiment is applied to a backlight of a liquid crystal television as an example of an edge light type liquid crystal display device.

  That is, the backlight 50 includes a plurality of LED light source units 511 and 512 and a light guide plate 52. One side surface of the light guide plate 52 is a light incident surface 521 in a state where the LEDs 13 of the LED light source units 511 and 512 are linearly opposed to each other. One surface of the light guide plate 52 is a light exit surface 522 that emits light incident from the light incident surface 521. The light guide plate 52 has a transparent plate structure such as an acrylic resin.

  The light guide plate 52 is accommodated in a back frame 53 made of, for example, aluminum having high thermal conductivity, for example. The back frame 53 is configured such that the light incident surface 521 and the light exit surface 522 are open.

  Further, the LED light source units 511 and 512 are attached by fixing means such as screws in a state in which the LED light source units 511 and 512 are in close contact with the metal substrate 12 of the LED light source units 511 and 512 in a frame 54 having a U-shaped cross section and high thermal conductivity. . The frame 54 may have a T-shaped or L-shaped cross section. In short, a flat portion for fixing the LED light source units 511 and 512 and a rib perpendicular to the flat portion for preventing the frame 54 from being warped are integrally formed. If it was done. The frame 54 is attached in a state where it is thermally coupled to the back frame 53.

  The backlight 50 is installed on the back of the liquid crystal television, and the illumination light 55 is optically switched by the liquid crystal display, and the liquid crystal television performs image display. The backlight 50 has a structure in which a back frame 53, a light guide plate 52, a diffusion sheet 56, a lens sheet 57, a polarizing sheet 58, and a front frame 59 are laminated in order from the bottom. The back frame 53, the diffusion sheet 56, the lens sheet 57, the polarizing sheet 58, and the front frame 59 can be omitted as appropriate.

  Here, with reference to FIG. 8, the joining of the LED light source units 511 and 512 and the frame 54 using the thermosetting resin adhesive 14 with filler will be described in more detail.

  As shown in FIG. 8A, in the state where the LED 13 is mounted and the adhesive 14 is applied between the ceramic substrate 11 and the metal substrate 12, the fulcrum b installed at the central portion a and the peripheral portion. , C, the LED light source 511 is attached to the flat portion of the frame 54, and the frame 54 is attached. In a state of being deformed so as to have a convex shape, it is placed in a heating furnace, heated and joined. Thereafter, when the temperature is lowered to room temperature, the deformation disappears as shown in FIG. 8B, and the LED light source unit 511 is joined linearly. The LED 512 is also bonded to the frame 54 in the same manner.

  The temperature at the time of joining the LED light source units 511 and 512 and the frame 54 is set to a temperature as high as possible at 100 ° C. or less, and the adhesive 14 has a joining strength equal to or higher than the stress generated by the difference in thermal expansion coefficient between the joining temperature and room temperature. . The adhesive may have a flexibility that can relieve strain generated due to a difference in thermal expansion coefficient between the bonding temperature and room temperature.

  Further, the thicknesses of the ceramic substrate 11 and the frame 53 are adjusted so that the deformation of the ceramic substrate 11 does not deteriorate the incident efficiency of the light guide plate 52. Since the junction temperature during energization of the LED 13 is normally about 120 ° C., if a temperature history higher than the junction temperature is given, excessive stress is applied. For this reason, it is desirable that the bonding temperature be 100 ° C. or lower.

  Since the illumination device according to this embodiment can suppress deformation of the strip-shaped ceramic substrate on which the LED is mounted, the light of the LED can be reliably guided to the light guide plate, and the incident efficiency can be improved. It becomes possible.

  FIGS. 9 to 11 are schematic exploded perspective views, FIG. 10 is a perspective view of the main part of FIG. 9, and FIG. 11 is an assembled view of FIG. FIG. The same components as those in the first embodiment relating to the lighting device will be described with the same reference numerals. In this embodiment, the second embodiment of the LED light source unit is applied to a backlight of a liquid crystal television as an example of an edge light type liquid crystal display device.

  That is, the backlight 50 includes a plurality of LED light source units 513 and 514 and a light guide plate 52 having a transparent plate structure such as an acrylic resin. One side surface of the light guide plate 52 is a light incident surface 521 in a state where the LEDs 13 of the LED light source units 513 and 514 are linearly opposed to each other. One surface of the light guide plate 52 is a light exit surface 522 that emits light incident from the light incident surface 521.

  The light guide plate 52 is accommodated in a back frame 53 made of, for example, aluminum having high thermal conductivity, for example. The back frame 53 is configured such that the light incident surface 521 and the light exit surface 522 are open.

  Further, the LED light source units 513 and 514 are attached by a fixing means such as an adhesive in a state where the LED light source units 513 and 514 are in close contact with the metal substrate 12 of the LED light source units 513 and 514 in a frame 54 having a U-shaped cross section and high thermal conductivity. The The frame 54 may have a T-shaped or L-shaped cross section. In short, a flat part for fixing the LED light source units 513 and 514 and a rib orthogonal to the flat part that does not warp the frame 54 are integrally formed. If it is. The frame 54 is attached in a state where it is thermally coupled to the back frame 53.

  The backlight 50 is installed on the back of the liquid crystal television, and the illumination light 55 is optically switched by the liquid crystal display, and the liquid crystal television performs image display. The backlight 50 has a structure in which a back frame 53, a light guide plate 52, a diffusion sheet 56, a lens sheet 57, a polarizing sheet 58, and a front frame 59 are laminated in order from the bottom.

  The LED light source units 513 and 514 are attached to the frame 54 by forming a through hole (not shown) on a surface different from the surface where the ceramic substrate 11 and the metal substrate 12 of the aluminum substrate 15 are bonded and screwing. It doesn't matter.

  Also in the illumination device according to this embodiment, since the deformation of the strip-shaped ceramic substrate on which the LED is mounted can be suppressed, the light of the LED can be surely guided to the light guide plate, so that the incident efficiency can be improved. It becomes possible to plan.

  Although several embodiments have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

11 Ceramic substrate 12 Metal substrate 13 LED
14, 14a, 14b Adhesive 15 Aluminum substrate 50 Backlights 511-514 LED light source unit 52 Light guide plate 53 Back frame 54 Frame

Claims (5)

A long and narrow strip-shaped ceramic substrate on which a plurality of LEDs are mounted;
An LED light source unit comprising a long and narrow strip-shaped Kovar-based or iron-based metal member joined to the back side of the ceramic substrate on which the LED is mounted.   2. The LED light source unit according to claim 1, wherein an aluminum substrate is interposed between the ceramic substrate and the metal substrate, and the ceramic substrate and the metal substrate are joined to the aluminum substrate, respectively.   The LED light source unit according to claim 2, wherein the aluminum substrate when the LED light source units according to claim 2 are arranged in a straight line is integrated.   The LED light source unit according to claim 2, wherein the aluminum substrate and the metal substrate when the LED light source units according to claim 2 are arranged in a straight line are integrated. The LED light source unit according to any one of claims 1 to 4,
A light guide plate comprising: a light guide plate that allows light emitted from the LED light source unit to enter from one side and exit from one surface.

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