JP2009032943A - Printed circuit board for light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed circuit board for a light-emitting element that can simultaneously satisfy control of resin flow and improvement of gap fill behavior that are mutually conflicting requirements when laminating a porous PTFE sheet as a light reflecting member onto a circuit board, the porous PTFE sheet that is not only excellent in chemical stability and thermal resistance but has high light reflecting efficiency. <P>SOLUTION: A printed circuit board for a light-emitting element has a circuit board on which a circuit for mounting a light-emitting element is formed at least on one side and a light reflecting member having a light reflecting member on the circuit through an adhesive resinous layer. The light reflecting member is composed of a porous PTFE sheet, the adhesive resinous layer is composed of a porous PTFE sheet internally impregnated with adhesive resin, and part of the circuit is exposed for mounting a light-emitting element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a printed wiring board for a light emitting element and a light emitting device in which the light emitting element is mounted on the printed wiring board for the light emitting element.

Light-emitting diodes (LEDs) and other light-emitting elements are used in mobile phones, liquid crystal display backlights, lightning boards, signals, car tail lamps, etc., and will be put to practical use in various fields such as car headlights and lighting. It is expected that In a substrate on which such a light-emitting element is mounted, the light-emitting element itself does not emit light in a specific direction but emits light in all directions, so that there is light emitted not only toward the front surface of the substrate but also toward the substrate side. Further, part of the light emitted from the light emitting element is reflected by the upper screen, the side surface, etc., and returns to the substrate side. By reflecting these lights toward the front surface of the substrate, the light emission efficiency as the light emitting device is improved. Conventionally, the following methods are known as such methods.
1. 1. A method of whitening a substrate by mixing the substrate itself with a white powder such as titanium. 2. A method of making the substrate material itself a material close to white that easily reflects light, such as a liquid crystal polymer. A method of using a white solder resist on the surface of a normal substrate.

  However, in the method 1 described above, when the white powder is increased, the strength of the substrate is lowered or the powder is easily dropped, so the amount of addition must be limited. Therefore, the light reflectance in the technique can be expected only to about 85%. In the above method 2, various substrate materials have been studied, but the reflectance is generally up to about 85%. In addition, a foam made of PET or the like can be considered as a material for the white substrate, but a general resin does not have the heat resistance required for soldering or the like, so that it is difficult to make a material for the substrate. In the above method 3, a solder resist must be used, and it is necessary to add a drying step and the like.

  In addition, the above method has a problem that the color of the substrate surface is easily changed by ultraviolet rays contained in the light emitted from the light emitting element.

Therefore, in the techniques described in Patent Documents 1 and 2, a sheet made of porous PTFE (polytetrafluoroethylene) is used as a light reflecting member as a substrate material. Porous PTFE can efficiently scatter light in multiple directions due to its fine porous structure, and has high resistance to ultraviolet rays and no problem of discoloration. Moreover, since it is excellent in heat resistance, there is also an advantage that it is difficult to be altered even if it receives heat by soldering or the like in the manufacturing process.
Japanese National Patent Publication No. 10-511784 JP 2002-124111 A

  As described above, porous PTFE is already known as an excellent material for a light reflecting member in a light emitting device. However, Patent Document 1 merely shows that a porous PTFE sheet is excellent as a light reflecting member. Patent Document 2 shows a light reflecting member installed around an arc tube such as a fluorescent tube. Therefore, it has not been directly applicable to recent light emitting devices such as those equipped with LEDs.

  More specifically, when the porous PTFE sheet is laminated on the circuit surface of the substrate to serve as a light reflecting member of the light emitting element circuit substrate, in order to suppress deterioration of the circuit portion due to the ingress of moisture or gas, It is necessary to prevent a void from being generated between the substrate and the porous PTFE sheet. Therefore, when the adhesive is simply applied to the surface or circuit surface of the porous PTFE sheet and bonded to each other, the amount of the adhesive must be increased or the melt viscosity of the adhesive must be lowered. However, since light emitting elements such as LEDs are usually mounted directly on the circuit surface, it is necessary to provide a hole in the porous PTFE sheet, which is a light reflecting member, in order to expose the circuit surface in the portion where the light emitting element is mounted. . In that case, if an adhesive is used excessively or its melt viscosity is lowered, a phenomenon called a resin flow in which the adhesive flows in a plane direction due to the pressure during bonding occurs, and the mounting portion of the light emitting element is covered with the adhesive. Can occur. On the other hand, if the adhesive is reduced or the melt viscosity is increased in order to suppress the resin flow, the unevenness of the substrate surface cannot be embedded sufficiently, and voids are generated in the substrate, resulting in heat resistance and the like. descend.

  In recent years, the circuit has become very fine due to the high density of circuit boards, and the problem of the resin flow has become very severe. At the same time, since the demand for extending the lifetime of electronic devices is increasing, it is necessary to improve the embedding property. However, as described above, it has been impossible to satisfy these two requirements at the same time by means such as adjusting the amount of adhesive and adjusting the melt viscosity.

  Therefore, the problem to be solved by the present invention is that, when laminating a porous PTFE sheet having excellent chemical stability and heat resistance and high light reflection efficiency on a circuit board as a light reflection member, the resin flow is suppressed and the embedding property is improved. It is an object of the present invention to provide a printed wiring board for a light emitting element that can simultaneously satisfy the mutually contradictory demands for improvement.

  The present inventor has intensively studied to solve the above problems. As a result, it has been found that the above-mentioned problems can be solved by using an adhesive resin layer made of a porous PTFE sheet that is internally impregnated with an adhesive resin when adhering a light reflecting member made of a porous PTFE sheet and a circuit board. The present invention has been completed. More specifically, the porous PTFE impregnated with the adhesive resin can retain the adhesive resin having a low melt viscosity in the porous structure in addition to the flexibility due to the porousness, thereby suppressing the resin flow. It is possible to simultaneously satisfy mutually conflicting demands for improving embedding.

  A printed wiring board for a light-emitting element according to the present invention includes a circuit board on which a circuit for mounting the light-emitting element is formed on at least one surface, and a light reflecting member on the circuit surface via an adhesive resin layer. A light-reflecting member made of a porous PTFE sheet; an adhesive resin layer made of a porous PTFE sheet impregnated with an adhesive resin; and a part of a circuit being a light-emitting element It is exposed because it is mounted.

  The porosity of the porous PTFE sheet constituting the adhesive resin layer of the light emitting element printed wiring board according to the present invention is preferably 40% or more and 70% or less. If the porosity is less than 40%, it may be difficult to achieve the above-described effects of improving the embedding property and holding the adhesive resin. On the other hand, when the porosity exceeds 70%, the adhesive resin cannot be sufficiently retained, and the resin flow may not be suppressed when an adhesive resin having a low melt viscosity is used.

  The light emitting device of the present invention is characterized in that a light emitting element is mounted on an exposed circuit in a printed wiring board for a light emitting element.

  The printed wiring board for a light emitting device of the present invention exhibits high light reflectivity due to porous PTFE, and simultaneously satisfies the mutually contradictory requirements of suppressing resin flow and improving embedding property, and thus has high quality and long life. is there. Therefore, the present invention is extremely useful industrially as being capable of satisfying demands for light emitting elements that have been increasing in recent years.

  A printed wiring board for a light-emitting element according to the present invention includes a circuit board on which a circuit for mounting the light-emitting element is formed on at least one surface, and a light reflecting member on the circuit surface via an adhesive resin layer. A light-reflecting member made of a porous PTFE sheet; an adhesive resin layer made of a porous PTFE sheet impregnated with an adhesive resin; and a part of a circuit being a light-emitting element It is exposed because it is mounted.

  The printed wiring board for a light emitting element of the present invention has a circuit board on which a circuit for mounting the light emitting element is formed on at least one surface, and a light reflecting member on the circuit surface via an adhesive resin layer. Conventionally known materials can be used for the circuit board without particular limitation. For example, in addition to a glass substrate or a glass epoxy substrate, a flexible substrate made of a polymer such as a polyimide substrate or a liquid crystal polymer substrate can also be used. Further, the circuit material is not particularly limited, and copper, copper alloy, or the like can be used.

  Circuit boards include a single-sided board with a circuit formed on one side, a double-sided board with a circuit formed on both sides, and a multi-layer board having a plurality of single-sided boards or a double-sided board and having three or more circuit faces. In the present invention, any of these substrates can be used, but the light emitting element is mounted on at least a part of the circuit formed on the outermost surface. Note that a conventionally known method can be used as a circuit formation method and a substrate lamination method.

  The light reflecting member constituting the printed wiring board for a light emitting device of the present invention is made of a porous PTFE sheet. The porous PTFE sheet has a porous structure in which PTFE fibrils connect a plurality of PTFE nodules, and can efficiently diffuse the irradiated light. In addition, since the material PTFE itself has excellent heat resistance and chemical stability, it is resistant to high heat and ultraviolet rays.

  The thickness of the porous PTFE as the light reflecting member may be adjusted as appropriate, but it is usually preferable to set the thickness of the printed wiring board to about 50 μm or more and 500 μm or less. If the thickness is less than 50 μm, the light reflection efficiency may be lowered. On the other hand, if it exceeds 500 μm, the cost may increase and it may be difficult to mount the light emitting element.

  Such a porous PTFE sheet may be purchased and used as long as it is commercially available. For example, PTFE powder is molded into a sheet and further stretched uniaxially or biaxially to make it porous. For example, it may be produced by a known method.

  The circuit board and the light reflecting member in the printed wiring board for a light emitting element of the present invention are bonded to each other with an adhesive resin layer made of a porous PTFE sheet impregnated with an adhesive resin. Here, “impregnation” refers to a state in which the adhesive resin is sufficiently infiltrated into the porous structure of the porous PTFE sheet. For example, the adhesive resin is simply applied to the surface of the porous PTFE sheet. In such cases, the definition of impregnation shall not be included. If the adhesive resin is simply applied, the adhesive resin cannot sufficiently penetrate into the porous structure, and there is a possibility that a void may be generated in the peripheral portion of the circuit board when the adhesive resin layer is thermocompression bonded to the circuit board.

  The porous PTFE sheet constituting the adhesive resin layer can be the same as the porous PTFE sheet as the light reflecting member, but its thickness is the state before bonding the circuit board and the light reflecting member. In this case, the thickness is preferably about 10 μm or more and 50 μm or less. When the thickness is less than 10 μm, the circuit surface cannot be sufficiently covered, and there is a possibility that voids are generated around the circuit. On the other hand, when the thickness exceeds 50 μm, the cost increases and the resin flow may increase.

  The porosity of the porous PTFE sheet is preferably 40% or more and 70% or less. If the porosity is less than 40%, it may be difficult to achieve the above-described effects of improving the embedding property and holding the adhesive resin. On the other hand, when the porosity exceeds 70%, the adhesive resin cannot be sufficiently retained, and the resin flow may not be suppressed when an adhesive resin having a low melt viscosity is used.

  As the adhesive resin impregnated into the porous PTFE sheet, it is preferable to use a resin having a relatively low melt viscosity. The adhesive resin having a low melt viscosity has a high embedding property, but may reach a circuit on which a light emitting element is mounted when thermocompression bonding each layer. However, in the present invention, since porous PTFE is impregnated with an adhesive resin, even if the adhesive resin has a relatively low melt viscosity, the molten resin can be retained during thermocompression bonding. It is possible to improve the performance.

  The melt viscosity of the adhesive resin is usually defined as the viscosity in a completely dissolved state. However, in the present invention, the adhesive resin is impregnated into the porous PTFE sheet and then used by a relatively short time hot pressing. Therefore, the melt viscosity of the adhesive resin in the present invention refers to the viscosity when the adhesive resin is heated for a short time. For example, the melt viscosity in the present invention can be defined as the viscosity of a resin when heated from room temperature to about 100 to 180 ° C. within 1 minute.

  The adhesive resin layer may be appropriately selected from those having adhesiveness to the circuit board and having an appropriate melt viscosity. For example, one type can be selected and used from an epoxy resin, a phenol resin, a polyimide resin, a BT resin, etc., or two or more types can be selected and mixed for use. Preferably, an epoxy resin is used from the viewpoints of heat resistance, stability after semi-curing, hardness after processing, cost, and the like.

  As a method for impregnating the porous PTFE sheet with an adhesive resin to form an adhesive resin layer, a conventional method can be used. For example, the adhesive resin may be dissolved in methyl ethyl ketone or toluene, impregnated in a porous PTFE sheet, and then dried. Alternatively, a porous PTFE sheet product impregnated with an adhesive resin may be used as it is. An example of such a product is FLEXBOND Leaf of Japan Gore-Tex.

  In addition, as a raw material porous PTFE sheet used as a light reflecting member, a relatively thick material such as about 100 to 500 μm is used, and only one side thereof is impregnated with an adhesive resin to integrally form the light reflecting member and the adhesive resin layer. May be. However, in this case, the adhesive resin layer solution is sucked up by capillary action, and the adhesive resin layer becomes excessively thick and the light reflection efficiency may decrease. Therefore, an embodiment in which the light reflecting member and the adhesive resin layer are separately manufactured and then thermocompression bonded is preferable. This is because if the light reflecting member and the adhesive resin layer are produced separately, the thicknesses of the light reflecting member and the adhesive resin layer in the printed wiring board can be easily controlled.

  In the present invention, the circuit board and the light reflecting member are thermocompression bonded via the adhesive resin layer. Therefore, an adhesive resin layer may be laminated on the circuit surface side on which the light emitting element of the circuit board is mounted, and a light reflecting member may be further laminated thereon, and then thermocompression bonding may be performed integrally. However, in the present invention, since it is necessary to mount the light emitting element in a part of the circuit, it is necessary to provide a hole in the adhesive resin layer and the light reflecting member at a position corresponding to the light emitting element mounting portion. Therefore, first, after thermocompression bonding of the light reflecting member and the adhesive resin layer, a hole is formed at a position corresponding to the light emitting element mounting portion, and then the adhesive resin layer side of this laminate is mounted with the light emitting element of the circuit board. It is preferable to laminate on the circuit surface side and perform thermocompression bonding.

  What is necessary is just to adjust the conditions of thermocompression bonding suitably by the kind etc. of adhesive resin to be used. For example, in the case where the light reflecting member and the adhesive resin layer are thermocompression bonded, after laminating them, a release sheet such as a PET sheet is inserted above and below, and the temperature: 50 to 150 ° C., pressure: 0.1 ˜1 MPa, thermocompression bonding time: thermocompression bonding under relatively mild conditions of 30 seconds to 5 minutes. Next, the circuit surface side on which the light emitting element of the circuit board is mounted is superimposed on the adhesive resin layer side, for example, conditions such as temperature: 100 to 200 ° C., pressure: 0.5 to 2 MPa, thermocompression bonding time: 30 to 120 minutes. Thermocompression with.

  In the printed wiring board for a light emitting element, the circuit of the portion where the light emitting element is to be mounted is exposed, and thus the adhesive resin melted at the time of thermocompression protrudes into the exposed portion. Such a phenomenon is called a resin flow. To suppress this resin flow, the amount of the adhesive resin may be reduced or the melt viscosity may be increased. However, since the peripheral portion of the circuit is not filled with the adhesive resin, a gap is formed, and the life of the substrate is shortened. Therefore, a sufficient amount of the adhesive resin must be used. Therefore, it should be considered that resin flow always occurs at present.

  Conventionally, such resin flow was allowed even at 500 μm. However, in recent years, the miniaturization and high density of circuits have progressed, and the adhesive resin sometimes protrudes over the circuit on which the light emitting element is to be mounted according to the conventional standard. Therefore, the present invention aims to make the resin flow amount 100 μm or less.

  Thus, since the resin flow is suppressed in the printed wiring board of the present invention, there is no possibility that the resin leaks onto the circuit surface on which the light emitting element is to be mounted. At the same time, it exhibits high embedding properties. Therefore, the light emitting device in which the light emitting element is mounted on the exposed circuit of the printed wiring board of the present invention has high quality and long life. In addition, since the printed wiring board of the present invention includes a PTFE sheet having excellent heat resistance as a constituent element, the printed wiring board is stable against heat necessary for mounting a light emitting element. Therefore, it becomes possible to manufacture a light emitting device efficiently with a high yield.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  The details of each test method are as follows.

Method for Measuring Porosity The porosity of the porous PTFE sheet was calculated from the following equation from the apparent density ρ measured according to the apparent density measuring method defined in JIS K6885.
Porosity (%) = [(2.2−ρ) /2.2] × 100

Measuring method of resin flow amount An adhesive sheet serving as an adhesive resin layer was punched out with a punch having a diameter of 10 mm, and the adhesive sheet and the glossy surface of the electrolytic copper foil were pressed for 10 minutes under the conditions of temperature: 170 ° C. and pressure: 1 MPa. Observe the punched surface with a stereomicroscope (Nikon, SMZ-1500, 50 ×, using ring illumination), and out of the resin flowing out from the adhesive resin layer, the tip and punched portions The distance was measured at several points where the distance to the periphery of the resin was the largest, and the average value was taken as the resin flow amount. A schematic view of the sample as viewed from the punched surface is shown in FIG. 1, and a cross-sectional view thereof is shown in FIG. In the case where the resin flow amount is expected to be large, the protruding resin may adhere to the press, so a polyimide film having a thickness of 12.5 μm was used as the cover film on the adhesive sheet surface.

Circuit surface embedding By cutting the sample used in the measurement of the resin flow amount at a position where the cross section of the circuit can be observed, and magnifying with a stereomicroscope (Nikon, SMZ-1500, 50 times, using ring illumination) It was determined whether or not the periphery of the circuit cross section was sufficiently filled with porous PTFE or an adhesive.

Example 1 Production of Printed Wiring Board for Light Emitting Element According to the Present Invention A porous PTFE sheet (made by Japan Gore-Tex) having a thickness of 200 μm and a porosity of 75% as a light reflecting member, and a thickness as an adhesive resin layer Length: 25 μm epoxy resin-impregnated porous PTFE prepreg (manufactured by Japan Gore-Tex, FLEXIBONd Leaf) is stacked, and the upper and lower sides are sandwiched between release films (manufactured by Toray Film Processing Co., Ltd., HP-4C), temperature 90 ° C., pressure 0 An integrated adhesive film was produced by pressing at 5 MPa for 2 minutes. The release film was peeled off, a printed circuit board for test was stacked on the adhesive resin layer side, and the adhesive resin was cured by pressing at a temperature of 170 ° C. and a pressure of 1 MPa for 60 minutes. In addition, the circuit board was formed in the grid | lattice form with the line space of 2 mm and the line width of 0.5 mm, and the test printed circuit board used the thickness of the copper foil which forms the circuit pattern of 18 micrometers.

  The resin flow amount in the exposed circuit portion of the obtained printed wiring board for light emitting element was 70 μm. In addition, as shown in the cross-sectional photograph of the sample shown in FIG. 3, the adhesive resin layer that looks white and translucent fills the space between the substrate or the circuit surface and the light reflecting member without gaps, and the embedding property around the circuit portion is excellent. It is observed to be good.

Comparative Example 1 Production of Printed Circuit Board for Light-Emitting Element In Example 1 above, an epoxy resin prepreg (SAFD manufactured by Nikkan Kogyo Co., Ltd.) having a thickness of 25 μm was used as the adhesive resin layer instead of the epoxy resin-impregnated porous PTFE prepreg. A printed wiring board for a light emitting element was produced in the same manner except for the above.

  As shown in the cross-sectional photograph of the sample shown in FIG. 4, the space between the substrate or the circuit surface and the light reflecting member is filled with an adhesive resin layer containing an epoxy resin without a gap, and the embedding property around the circuit portion is good. It is observed. However, the resin flow amount in the exposed part of the circuit was as large as 450 μm.

Comparative Example 2 Production of Printed Wiring Board for Light Emitting Element For the purpose of suppressing the resin flow amount, the epoxy resin prepreg used in Comparative Example 1 is heated in an oven at 40 ° C. for 30 minutes to cure the epoxy resin to some extent. I let you. A printed wiring board for a light emitting device was produced in the same manner as in Example 1 except that the epoxy resin prepreg was used instead of the epoxy resin-impregnated porous PTFE prepreg as the adhesive resin layer.

  The resin flow amount in the circuit exposed portion of the obtained printed wiring board for light emitting device was suppressed to 70 μm. However, as shown in the cross-sectional photograph of the sample shown in FIG. 5, a white-colored gap is observed at the boundary between the edge of the circuit surface and the substrate, indicating that the embedding is not sufficient (inside the black circle in FIG. 5). See).

  As described above, when an epoxy resin prepreg that has been widely used as an adhesive resin layer is used, the epoxy resin may flow out during hot pressing and cover the circuit surface on which the light emitting element is to be mounted. Therefore, if the epoxy resin of the prepreg is used after being cured to some extent, the circuit surface may not be sufficiently covered and a gap may be generated on the substrate in the vicinity of the circuit end.

  On the other hand, in the printed wiring board of the present invention using the porous PTFE sheet impregnated with the adhesive as the adhesive resin layer, the circuit surface is sufficiently covered and the resin flow amount is also suppressed and protruded. The circuit surface on which the light emitting element is to be mounted is not covered with the resin. Therefore, the printed wiring board of the present invention is very useful as a component of the light emitting device.

It is the schematic diagram which looked at the sample used by the measurement of the resin flow amount from the punching surface. It is sectional drawing of the sample used by the measurement of the resin flow amount. 3 is a photograph showing the embedding property in the printed wiring board for light emitting device of Example 1. FIG. 6 is a photograph showing the embedding property in a printed wiring board for a light emitting element of Comparative Example 1. 6 is a photograph showing the embedding property in a printed wiring board for a light emitting element of Comparative Example 2.

Explanation of symbols

  1: light reflecting member, 2: light emitting element mounting portion, 3: circuit board, 4: electrolytic copper foil, 5: adhesive resin layer, 6: resin flow

Claims (3)

A circuit board on which a circuit for mounting a light-emitting element is formed on at least one surface, and a printed wiring board for a light-emitting element having a light reflecting member on the circuit surface via an adhesive resin layer;
The light reflecting member comprises a porous PTFE sheet;
A printed wiring board for a light emitting element, wherein the adhesive resin layer is made of a porous PTFE sheet impregnated with an adhesive resin inside; and a part of the circuit is exposed for mounting the light emitting element.   The printed wiring board for a light emitting element according to claim 1, wherein the porosity of the porous PTFE sheet constituting the adhesive resin layer is 40% or more and 70% or less.   3. The light emitting device according to claim 1, wherein the light emitting element is mounted on the exposed circuit.