JP2009295648A - Printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both of heat radiation and light reflection in a printed wiring board wherein light emitting components such as LEDs are mounted on the surface of a substrate. <P>SOLUTION: The printed wiring board P1 is provided with a conductor layer 2 formed as a circuit at least on one surface and mounts a heating and light-emitting element 5 and/or a substrate mounting the heating and light-emitting element 5 on the conductor layer 2 formed as the circuit. Heat conductive insulating resin 3 having electrical insulation properties is filled between conductor patterns of the conductor layer 2 formed as the circuit, and at least a part of the surface of the conductor layer 2 and/or the heat conductive insulating resin 3 is coated with light reflective resin 4a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a printed wiring board that diffuses and dissipates heat generated by a heat-emitting body such as an LED (light-emitting diode) mounted on a conductor layer formed with a circuit.

  In recent years, LEDs have been attracting attention not only as display functional parts but also as lighting functional parts due to improvements in performance and quality, and lighting systems using LEDs are used in various applications such as home, medical care, transportation, etc. Yes.

  Since the insulating base material used for the conventional printed wiring board is not high in thermal conductivity, only the periphery of the heat-generating component mounting area is locally high in temperature.

  The LED has a problem that its life and performance are lowered as the LED itself and the surrounding environment (for example, a printed wiring board on which the LED is mounted) are heated.

  Also, in order to obtain an illumination function using LEDs that are easily deteriorated by heat, it is difficult to use an insulating substrate alone as a printed wiring board that is the foundation, and it is often used in combination with a heat sink or the like. There was a problem that the wiring board itself was enlarged and its use and use range had to be limited.

  Therefore, a measure for quickly diffusing and radiating heat from the LED is essential for the printed wiring board on which the LED is mounted so that the LED itself can stably operate.

  The material used for a general printed wiring board is harder to transmit heat as the insulation is better, and the insulating resin hinders the propagation of heat. However, as a method of improving the heat dissipation of the printed wiring board, A method is known in which a thick metal plate is provided in the outer layer, a heat dissipation path is provided between the LED mounting portion, and heat is diffused to avoid local high temperature of the substrate (for example, see Patent Document 1).

  However, in many cases, an insulating resin is generally provided between the circuit on which the LED is mounted and the metal plate so as to be electrically insulated, and the insulating resin deteriorates the propagation of heat that is a problem. In some cases, a sufficient heat dissipation effect may not be obtained by simply bonding metal plates.

  In addition, as another method for improving the heat dissipation of the printed wiring board, a method of dissipating heat by providing a heat dissipation path in the remaining copper on the outer layer of the board is also known, but a sufficient heat dissipation path is secured due to electrical restrictions of the circuit etc. There was a case where it was not possible.

  An example of a conventional printed wiring board is shown in FIG.

  FIG. 4 shows an example of an LED substrate used for general illumination. FIG. 4A is a cross-sectional view, and FIG. 4B is an enlarged view of a part F4 of the LED mounting region of FIG.

  The printed wiring board P4 includes a core layer 1, a conductor layer 2 provided on the core layer 1 and formed with a circuit, and a solder disposed in an area excluding the core layer 1 and the area where the conductor layer 2 is exposed. It consists of a resist 6 and an LED 5 that is partly electrically connected to the exposed region of the conductor layer 2.

  In general, the amount of heat radiation depends on the cross-sectional area of the conductor (heat radiation path) connecting the heat generating part and the remaining copper, so heat radiation is insufficient just by connecting patterns as a circuit (heat propagates as necessary and sufficient) In some cases, it is necessary to secure a heat dissipation path in a larger area (make the cross-sectional area as large as possible), but LED boards for lighting applications may be mounted closely to increase the amount of light. In many cases, it is difficult to provide the remaining copper around the LED mounting region (to provide sufficient remaining copper and a heat dissipation path).

  As a result, as shown in FIG. 4, the conductor pattern connected to the LED 5 in the conductor layer 2 is separated from the conductor pattern not connected to the LED 5, and the heat generated from the LED 5 is connected to the LED 5. There is no heat dissipation path to be transmitted to the conductor pattern that is not done.

  Therefore, the structure such as the printed wiring board P4 has poor heat dissipation efficiency, and as a result, there is a problem that the printed wiring board cannot operate stably.

  Moreover, in order to efficiently use the light emitted from the mounted LED, the substrate on which the LED is mounted is required to have high light reflectivity, and the printed wiring board must have high heat reflectivity as well as high light reflectivity. Has been.

  However, since conventional solder resists generally have poor light reflectivity, there is a problem that they cannot be applied to means for increasing the light reflectivity of a printed wiring board.

  Here, as a method for increasing the light reflectivity of the printed wiring board, a structure in which a white solder resist is disposed on the surface of the printed wiring board of the LED mounting portion may be used. Therefore, it has not been a means for achieving both high heat dissipation and high light reflectivity as described above.

Therefore, in particular, as the main problems of the solder resist used for the LED mounting portion of the printed wiring board on which the LED is mounted as an illumination function component, there are two problems, namely, “heat dissipation” and “light reflectivity” as described above. However, there is no solder resist that is currently generally available and can handle both of the above two problems, and as a result, the LED mounting part of the printed wiring board cannot have a structure suitable for mounting light emitting components. It was.
JP 2002-217508 A

  The present invention has been made in view of the above problems and actual conditions, and in a printed wiring board in which light-emitting components such as LEDs are mounted on a substrate surface, a solder resist that is currently generally available without using a special solder resist. It is an object to achieve both heat dissipation and light reflectivity by using.

  That is, the present invention according to claim 1 is a printed wiring board having a conductor layer formed with a circuit on at least one surface and mounting a heat generating light emitter and / or a substrate on which the heat generating light emitter is mounted on the circuit formed conductor layer. In the above, a conductive conductive resin having electrical insulation is filled between conductive patterns of the conductive layer in which the circuit is formed, and at least a part of the surface of the conductive layer and / or the thermal conductive insulating resin is filled. The above-mentioned problems are solved by a printed wiring board that is coated with a light-reflective resin.

  As a result, in the printed wiring board on which the heat-emitting light emitter is mounted, it is possible to stably dissipate heat efficiently without being restricted by the electrical limitation of the circuit, and the light reflectivity is improved compared to the conventional one. A printed wiring board can be obtained.

  The invention according to claim 2 is characterized in that the thermal conductivity of the thermal conductive resin is 1 W / m · K or more.

  The invention according to claim 3 is characterized in that the light reflective resin has a light reflectance of 70% or more with respect to visible light.

  Moreover, the present invention according to claim 4 is characterized in that the light-reflective resin has discoloration resistance.

  The present invention according to claim 5 is a curable resin composition in which the light-reflective resin contains titanium oxide and contains a substance that suppresses activation of the titanium oxide by exposure to ultraviolet rays. It is characterized by being.

  As described above, it is possible to obtain a printed wiring board that maintains a heat dissipation function and a light reflection function that are superior to those of the conventional art over a long period of time, and that continues to operate efficiently and stably.

  According to the present invention, in a printed wiring board in which a light emitting component such as an LED is mounted on the substrate surface, both heat dissipation and light reflectivity can be achieved.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic cross-sectional explanatory view showing a printed wiring board according to an embodiment of the present invention, where (a) is a cross-sectional view, and (b) is an enlarged view of a part F1 of the LED mounting region of (a). .

  The printed wiring board P1 includes a core layer 1, a conductor layer 2 provided on the core layer 1 and formed with a circuit, an LED 5 partially electrically connected to an exposed region of the conductor layer 2, The heat conductive insulating resin 3 filled between the conductor patterns of the conductor layer 2 and the light reflective insulating resin 4a disposed on the surface of the conductor layer 2 and / or the heat conductive insulating resin 3 are included.

  As shown in FIG. 1, the conductor pattern connected to the LED 5 in the conductor layer 2 has a heat dissipation path by the heat conductive insulating resin 3 provided between the adjacent LED 5 and the conductor pattern not connected. While being formed, it is covered with a light-reflective insulating resin 4 a disposed on the surface of the conductor layer 2 and / or the heat conductive insulating resin 3.

  Here, the greatest feature of the present invention is focusing on the thickness (Z-axis) direction of the conductor layer 2, and by embedding the heat conductive insulating resin 3 between the conductor patterns, heat is dissipated using the side of the conductor pattern. It is possible to perform.

  Specifically, by embedding the heat conductive insulating resin 3 between the conductor patterns, it is not necessary to dispose the heat dissipation path across the layers, and the heat dissipation path is bypassed and the connection point is lost without reducing the circuit design efficiency. The heat dissipation efficiency can be improved by omitting

  As a result, the printed wiring board P1 can efficiently dissipate heat without being restricted by the electrical restrictions of the circuit, and can operate stably, and has a structure with improved light reflectivity compared to the conventional printed wiring board. It becomes a board.

  In the present invention, as in the second embodiment shown in FIG. 2, the light reflective insulating resin 4 b may be provided with a clearance with respect to the conductor pattern connected to the LED 5.

  Further, the present invention is a state (over resist state) in which the light-reflective insulating resin 4c is applied to a part of the conductor pattern connected to the LED 5, as in the third embodiment shown in FIG. Also good.

  The thermal conductivity of the thermally conductive insulating resin 3 is preferably 1 W / m · K or more in consideration of the heat radiation amount of LED mounting products that require a larger amount of light. For example, the thermal conductivity Thermally conductive white solder resist having a thermal conductivity of 2 W / m · K, comprising a curable resin composition containing spherical aluminum oxide particles of 15 W / m · K or higher in a volume fraction of cured product of 60% by volume or more Are preferably used.

  The light reflective resins 4a to 4c preferably have a light reflectance of 70% or more with respect to visible light (420 nm to 740 nm). In particular, among the three primary colors of light constituting white light used as a general visible light source, it is important to have a light reflectance of 70% or more for the blue region (435 nm to 480 nm). . Furthermore, in the case of a development-type resin, sagging and bleeding at the application region interface are less likely to occur than other curable resins. Further, it is particularly desirable to have discoloration resistance, for example, composed of a curable resin composition containing titanium oxide and containing a substance that suppresses activation of the titanium oxide by exposure to ultraviolet rays. A discoloration-resistant white solder resist is preferably used. Examples of such a discoloration-resistant white solder resist include “PSR-4000LEW1” manufactured by Taiyo Ink Manufacturing Co., Ltd.

  Incidentally, the discoloration-resistant white solder resist reduces deterioration due to ultraviolet rays by mixing a substance that suppresses activation of titanium oxide used as a coloring matter (pigment) for producing white, and as a result, It suppresses discoloration (yellowing) due to heating and light exposure due to long-term use.

  In the above embodiment, the printed wiring boards P1 to P3 are described using a single-sided board with a circuit on one side for convenience, but the printed wiring boards P1 to P3 are particularly limited to this. Instead, it may be a double-sided board or a multilayer board.

  The substrate having the shape used in the description of the above embodiment may be provided with heat transfer and heat dissipation means such as a metal plate in order to further increase the heat dissipation efficiency.

  In describing the present invention, the above embodiment has been described. However, the configuration of the present invention is not limited to these, and is not limited to these examples, and various modifications are possible within the scope of the present invention. It can be changed.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing which shows 1st embodiment of this invention. The schematic explanatory drawing which shows 2nd embodiment of this invention. The schematic explanatory drawing which shows 3rd embodiment of this invention. Schematic explanatory drawing which shows the conventional printed wiring board.

Explanation of symbols

1: Core layer 2: Conductor layer 3: Thermally conductive insulating resins 4a to 4c: Light reflecting resin 5: Heat-emitting phosphor (LED)
6: Solder resist P1-P4: Printed wiring board

Claims (5)

  In a printed wiring board having a conductor layer formed with a circuit on at least one side and mounting a heat generating light emitter and / or a substrate on which the heat generating light emitter is mounted on the circuit formed conductor layer, the conductor of the conductor layer formed with the circuit The pattern is filled with a heat conductive insulating resin having electrical insulation, and at least a part of the surface of the conductor layer and / or the heat conductive insulating resin is covered with a light reflecting resin. Printed wiring board characterized by   The printed wiring board according to claim 1, wherein the thermal conductivity of the thermal conductive resin is 1 W / m · K or more.   The printed wiring board according to claim 1, wherein the light reflective resin has a light reflectance of 70% or more with respect to visible light.   The printed wiring board according to claim 1, wherein the light-reflective resin has discoloration resistance.   5. The curable resin composition, wherein the light-reflective resin contains titanium oxide and contains a substance that suppresses activation of the titanium oxide by exposure to ultraviolet rays. The printed wiring board according to any one of the above.