JP2020178057A - Circuit board and light emitting device using circuit board - Google Patents

Abstract

To improve heat radiating property and luminous efficiency while maintaining insulation property in a circuit board in which a heat radiating substrate is fitted in an opening of a resin substrate.SOLUTION: A heat radiating substrate 12 includes a metal substrate 12c and ceramic layers 12b and 12d laminated on the metal substrate 12c. A part of a wiring 12a on the ceramic layer 12b is connected to a wiring 11a formed on a resin substrate 11. The ceramic layers 12b and 12d maintain a high insulation withstand voltage. When an LED is mounted on the heat radiating substrate 12, the light emitted from the bottom surface side of the LED is reflected by the surfaces of the ceramic layer 12b and the metal substrate 12c and directed upward, and the heat generated by the LED is sent downward through the metal substrate 12c.SELECTED DRAWING: Figure 2

Description

The present invention relates to a circuit board configured by fitting a heat-dissipating substrate having high thermal conductivity into an opening of a resin substrate, and a light emitting device in which an LED is mounted on the circuit board.

In a high-brightness light emitting device using an LED as a light source, processing of heat generated by the LED has been a continuous issue. If the LED is mounted on a substrate material having a high thermal conductivity such as copper, the problem of heat treatment can be generally solved, but since such a substrate material is expensive, it is required to reduce the amount used.

In order to meet this demand, for example, in FIG. 7A of Patent Document 1, the opening (through hole) formed in the resin substrate (laminated PCB 224) has a higher thermal conductivity than the resin substrate (224) and is insulating. A circuit board in which a heat radiating board (radiator 10) is fitted is described. Further, FIG. 7D shows a light emitting device (LED module) in which an LED is mounted on a heat radiating board (10) included in the circuit board. Further, FIG. 8B shows a light emitting device in which three LEDs are mounted on a heat radiating substrate (10). In addition, () shows a term or a symbol in Patent Document 1.

In the light emitting device described in FIG. 7D of Patent Document 1, most of the heat generated by the LED is a heat conductive electrode (heat conductive bonding pad 73) formed on the heat sink (93) and the heat radiating substrate (10) of the LED. It moves to a large heat sink (not shown) via the heat radiating substrate (10) and the heat radiating pattern (83) formed on the lower surface of the heat radiating substrate (10). The heat radiating substrate (10) is provided with a wiring pattern made of copper (positive electrode bonding pad 71 and negative electrode bonding pad 72) on the surface of a base material made of AlN (aluminum nitride).

A circuit board in which a heat radiating board is fitted in a resin board is a so-called inlay (fitting) board. As described above, the inlay substrate transfers the heat generated by the LED to a large heat sink thermally connected to the heat radiating substrate via the heat radiating substrate. That is, the inlay substrate can efficiently process the heat generated by the LED even though the heat dissipation substrate made of an expensive material is small, and various circuits such as an LED drive circuit can be mounted on the resin substrate. It is easy to use because it can be configured.

JP-A-2017-63177 (FIGS. 7A, 7D, 8B)

However, in the circuit board described in Patent Document 1 and the light emitting device using the circuit board, the heat radiating board (10) is made of AlN, so that high insulation is ensured. Since the reflectance and thermal conductivity of AlN constituting the above are lower than those of materials such as metals, expectations for an increase in the amount of light emission and an improvement in light emission efficiency have not been sufficiently met.

Therefore, the present invention has been made in view of the above problems, and a large number of LEDs are mounted on a circuit board in which a heat radiating board is fitted in an opening of a resin substrate and on the upper surface of the heat radiating board included in the circuit board. It is an object of the present invention to provide a circuit board capable of improving heat dissipation and light emission efficiency while maintaining insulation property, and a light emitting device using the circuit board.

In order to solve the above problems, the circuit board of the present invention is a circuit board in which a heat dissipation board is fitted in an opening of a resin substrate. The heat dissipation board includes a metal substrate and a ceramic layer laminated on the metal substrate, and the ceramic A part of the wiring formed on the upper surface of the layer is connected to the wiring formed on the upper surface of the resin substrate.

The heat radiating substrate included in the circuit board of the present invention includes a metal substrate and a ceramic layer laminated on the metal substrate. A part of the wiring on the ceramic layer is connected to the wiring formed on the resin substrate. The insulation withstand voltage between these wires and the metal substrate is maintained high by the ceramic layer. When the LED is mounted on the heat radiating substrate, the light emitted from the bottom surface of the LED is reflected by the ceramic layer and the surface of the metal substrate and goes upward, and the heat emitted by the LED goes downward through the metal substrate.

The metal substrate may be provided with the ceramic layers on the upper surface and the lower surface, respectively.

The metal substrate may be made of aluminum or copper.

Further, in order to solve the above problems, the light emitting device of the present invention is a light emitting device in which a circuit board in which a heat radiation board is fitted in an opening of a resin substrate is used, and the heat radiation board is laminated on a metal substrate and the metal substrate. A plurality of LEDs are mounted on the upper surface of the ceramic layer, and a part of the wiring formed on the upper surface of the ceramic layer is connected to the wiring formed on the upper surface of the resin substrate. It is a feature.

As described above, in the circuit board of the present invention and the light emitting device using the circuit board, the insulation withstand voltage is secured by the ceramic layer. At this time, since the base material of the heat radiating substrate is metal, the thermal conductivity is improved, and the reflectance is improved by the reflection between the ceramic layer and the surface of the metal substrate. That is, the circuit board of the present invention and the light emitting device using the circuit board have insulating properties even if the circuit board is composed of a resin substrate and a resin substrate and the heat dissipation substrate is fitted in the opening of the resin substrate. It is possible to improve heat dissipation and light emission efficiency while maintaining the above.

It is a top view of the light emitting device shown as the embodiment of this invention. It is sectional drawing of the main part of the light emitting device shown in FIG. It is explanatory drawing of the manufacturing method of the light emitting device shown in FIG. It is explanatory drawing of the manufacturing method of the light emitting device shown in FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicate description will be omitted. The scale of the members is changed as appropriate for explanation.

FIG. 1 is a plan view of a light emitting device 20 shown as an embodiment of the present invention. Note that FIG. 1 shows only a part of the wiring 14 formed on the circuit board 10 included in the light emitting device 20.

As shown in FIG. 1, in the circuit board 10, four heat radiating boards 12 are fitted in the openings 13 of the resin board 11. A circular dam 33 is formed on the upper surface of each heat radiating substrate 12, and the sealing resin 34 is filled and solidified inside the dam 33. Further, from the dam 33 to the resin substrate 1
A wiring 14 extending toward 1 is formed. The wiring 14 includes a wiring 11a formed on the resin substrate 11, a wiring 12a formed on the heat radiating substrate 12, and a wiring 13a connecting the wirings 11a and 12a on the boundary between the resin substrate 11 and the heat radiating substrate 12. Further, electronic components 35 such as a microcomputer, a connector, and a constant current IC are mounted on the resin substrate 11.

FIG. 2 is a cross-sectional view of a main part of the circuit board 10 drawn along the line AA'of FIG. As described above, the heat radiating substrate 12 is fitted in the opening 13 of the resin substrate 11. The resin substrate 11 is a three-layer structure composed of an upper resin plate 11b, a lower resin plate 11d, and a prepreg 11c sandwiched between them. The heat radiating substrate 12 is a three-layer structure having ceramic layers 12b and 12d on the upper and lower surfaces of the metal substrate 12c. The resin substrate 11 and the heat radiating substrate 12 are connected by a prepreg 11c that has exuded from the resin substrate 11.

As described above, the wirings 11a, 12a and 13a are formed on the upper surface of the circuit board 10, and the copper layer 15 which is a solid pattern is formed on the lower surface of the circuit board 10. The copper layer 15 connects the copper layer 11e formed on the lower surface of the resin substrate 11, the copper layer 12e formed on the lower surface of the heat dissipation substrate 12, and the copper layers 11e and 12e on the boundary between the resin substrate 11 and the heat dissipation substrate 12. It is composed of a copper layer 13e.

A plurality of LED dies 31 are mounted on the upper surface of the heat radiating substrate 12. The LED dies 31 are connected to each other or the LED dies 31 and the wiring 12a are connected by a wire 32. The LED die 31 is surrounded by a dam 33. The sealing resin 34 filled and solidified inside the dam 33 covers the LED die 31 and the wire 32. In addition, in FIG. 2, it is simplified and drawn so that four LED dies 31 are connected by a wire 32 in the AA'cross section of FIG. However, in the actual light emitting device 20, a large number of LED dies 31 are arranged in the region inside the dam 33 to form one (or several) series circuits. Here, in the present embodiment, the term "LED" means an LED die. The general term "LED" may be used from an LED die to a light emitting element in which an LED die is packaged.

As described above, the resin substrate 11 is composed of an upper resin plate 11b, a prepreg 11c, and a lower resin plate 11d, and is a three-layer structure having a layer thickness of about 1 mm, and includes wiring 11a on the upper surface and a copper layer 11e on the lower surface. ing. The upper resin plate 11b and the lower resin plate 11d are made by impregnating a glass fiber cloth with an epoxy resin and performing a thermosetting treatment to form a plate. The prepreg 11c is a semi-cured reinforced plastic molding material having a thickness of about 100 μm and containing a fibrous reinforcing material. When the heat radiating substrate 12 is fitted into the opening 13 of the resin substrate 11, the resin substrate 11 is subjected to compression heat treatment. Hardens with. The wirings 11a and the copper layer 11e are the copper layers 11a1 and 11e1 (see FIG. 3C) originally formed on the resin substrate 11 and the copper layers 12a1 and 12e1 originally formed on the heat dissipation substrate 12 (FIG. 3 (b)). )) Is a laminate with the copper layer formed when connecting.

As described above, the heat radiating substrate 12 is a three-layer structure having ceramic layers 12b and 12d on the upper and lower surfaces of the metal substrate 12c, and has wiring 12a on the upper surface and copper layers 12e on the lower surface. The metal substrate 12c used as the base material of the heat radiating substrate 12 is made of aluminum. The ceramic layers 12b and 12d are white inorganic materials in which highly reflective white inorganic fine particles such as alumina and titanium oxide are dispersed in glass (network of silicon dioxide), and are strongly connected to the metal substrate 12c by chemical bonds. doing. Like the wiring 11a and the copper layer 11e, the wiring 12a and the copper layer 12e originally existed in the ceramic layers 12b and 12d, and the copper layers 12a1 and 12e1 (see FIG. 3B) and the copper originally present in the resin substrate 11 were present. It is a laminate with a copper layer formed when the layers 11a1 and 11e1 (see FIG. 3C) are connected.

The LED die 31 is a blue light emitting diode having a plane size of about 0.4 mm × 0.4 mm, has a light emitting layer and an electrode for wire bonding on the upper surface side, and the lower surface is bonded to the ceramic layer 12b with a die bond paste. .. The wire 32 is a gold wire. The dam 33 is made of a white silicone resin containing titanium oxide, and has a thickness of 0.7 to 1.0 mm and a height of 0.5 to 0.8 mm. The sealing resin 34 is a silicone resin containing a phosphor.

A method of manufacturing the light emitting device 20 will be described with reference to FIGS. 3 and 4. 3 and 4 are explanatory views of a method of manufacturing the light emitting device 20, and show a simplified cross section of the light emitting device 20 symbolizing each process. In FIG. 3, (a) to (c) show the steps of preparing the resin substrate 11 and the heat radiating substrate 12. In FIG. 4, (d) is a step of forming a circuit board 10, (e) is a step of forming a wiring 14 on the upper surface of the circuit board 10, and (f) is an LED die 31 on the upper surface of the heat dissipation board 12. The mounting step, (g) is a wire bonding step, (h) is a step of forming a dam 33, (i) is a step of filling the sealing resin 34, and (j) is an electron in the circuit board 10. The process of mounting the component 35 is shown.

As shown in FIG. 3A, first, a large-sized heat-dissipating substrate is manufactured, in which the heat-dissipating substrate 12 can be obtained by individualizing. When manufacturing a large-format heat-dissipating substrate, first, a ceramic copper-pasted sheet 41 in which a ceramic layer 43 is attached to a copper foil 42, a ceramic copper-attached sheet 47 in which a ceramic layer 45 is attached to a copper foil 46, and An aluminum substrate 44 (metal substrate) is prepared. The ceramic copper pasting sheet 47 has a layer thickness of about 100 μm, and the copper layers 42 and 46 have a thickness of about 35 μm. Subsequently, the aluminum substrate 44 and the ceramic copper pasting sheets 41 and 47 are laminated so that the ceramic layers 43 and 45 come into contact with the upper and lower surfaces of the aluminum substrate 44. Finally, by hot-pressing this laminate in vacuum, the surface of the aluminum substrate 44 and the surfaces of the ceramic layers 43 and 45 are firmly connected by a dehydration polymerization reaction.

When the large-sized heat-dissipating board is completed, as shown in FIG. 3B, the large-sized heat-dissipating board is separated into pieces having a predetermined size to obtain the heat-dissipating board 12. At this time, copper layers 12a1 and 12e1 which are solid patterns remain on the upper and lower surfaces of the heat radiating substrate 12.

In parallel with the preparation of the heat radiating substrate 12, the resin substrate 11 is prepared as shown in FIG. 3C. The resin substrate 11 is provided with an opening 13, and copper layers 11a1 and 11e1 which are solid patterns are present on the upper and lower surfaces. In this step, the prepreg 11c is uncured.

Next, as shown in FIG. 4D, the heat radiating substrate 12 is fitted into the opening 13 of the resin substrate 11 to form the circuit board 10. After the heat radiating substrate 12 is fitted, the resin substrate 11 is compressed, the prepreg 11c is exuded to the boundary portion between the resin substrate 11 and the heat radiating substrate 12, and the boundary portion is filled with the prepreg 11c. At this time, the prepreg 11c protrudes from the copper layers 12a1 and 11a1 (see FIGS. 3B and 3c) (the same applies to the lower side). The prepreg 11c is cured by heating to join the upper resin plate 11b and the lower resin plate 11d, and fix the heat radiating substrate 12 to the resin substrate 11.

Next, as shown in FIG. 4 (e), the wiring 14 is formed on the upper surface of the circuit board 10. First, in the previous step, the upper surfaces of the copper layers 11a1 and 12a1 are polished together with the prepreg 11c protruding from the boundary portion by pressurizing the resin substrate 11. When the respective upper surfaces match, a copper layer is formed on the entire upper surfaces of the prepreg 11c and the copper layers 11a1 and 12a1. When the copper layers 11a1 and 12a1 are connected by the copper layer, the copper layer on the upper surface of the circuit board 10 including the copper layers 11a1 and 12a1 is patterned by a photolithography method to form wirings 11a, 12a and 13a. Finally, the wirings 11a, 12a, 13a are gold-plated. Copper layers 11e, 12e, and 13e are similarly formed on the lower surface of the circuit board 10.

Next, as shown in FIG. 4 (f), the LED die 31 is mounted on the upper surface of the heat radiating substrate 12. The LED die 31 and the Zener diode (not shown) are bonded to the heat radiating substrate 12 with a die bond paste. When the LED die 31 and the Zener diode are mounted on the heat radiating substrate 12, the die bond paste is applied in advance at the position where each element is arranged. After arranging each element at a predetermined position with a picker, the circuit board 10 is heated to cure the die bond paste.

Next, as shown in FIG. 4 (g), wire bonding is performed between the elements. The wire 32 connects the cathode of one LED die 31 and the anode of the other LED die 31, and also connects the LED 31 at the end of the LED row to which the LED die 31 is connected in series and the wiring 11a. Similarly, the wire 32 connects the Zener diode and the wiring 11a.

Next, as shown in FIG. 4 (h), the dam 33 is formed. The dam 33 is formed so as to surround the assembly of the LED dies 31 by discharging the white silicone resin in a highly viscous state onto the heat radiating substrate 12 while moving the nozzles of the dispenser. At this time, the Zener diode, a part of the wiring 12a, and a part of the wire 32 are embedded in the dam 33. Finally, the circuit board 10 is heated to cure the dam 33.

Next, as shown in FIG. 4 (i), the sealing resin 34 is filled in the inner region of the dam 33. When the sealing resin 34 containing the fluorescent resin is dropped on the inner region of the dam 33 by the dispenser, the sealing resin 34 is heated and cured. The sealing resin 34 covers the surface of the heat radiating substrate 12, the LED die 31 and the wire 32.

Finally, as shown in FIG. 4J, the electronic component 35 is mounted on the circuit board 10. The electronic component 35 is fixed to the resin substrate 11 in a normal reflow process.

As described above, in the light emitting device 20, the insulation withstand voltage is secured by the ceramic layers 12b and 12d. At this time, since the base material of the heat radiating substrate 12 is aluminum as compared with the conventional heat radiating substrate made of AlN, the thermal conductivity is improved, and the reflectance is improved by the reflection between the ceramic layer 12b and the aluminum surface. .. That is, the light emitting device 20 using the circuit board 10 and the circuit board 10 has a configuration in which the circuit board 10 is composed of the resin board 11 and the heat radiating board 12, and the heat radiating board 12 is fitted in the opening 13 of the resin board 11. However, it is possible to improve heat dissipation and light emission efficiency while maintaining insulation.

The light emitting device 20 was provided with ceramic layers 12b and 12d on the upper and lower surfaces of the heat radiating substrate 12. Since the wirings 11a, 12a, 13a constituting the electric circuit exist only on the upper surface of the circuit board 10, the ceramic layer 12d and the copper layers 11e, 12e, 13e on the lower surface can be omitted. However, since the heat radiating substrate 12 includes the metal substrate 12c, if the ceramic layer 12d is present on the lower surface side of the heat radiating substrate 12, the corners of the metal substrate 12c are coated, so that the insulation withstand voltage is improved. That is, it is preferable that the heat radiating substrate 12 is provided with ceramic layers 12b and 12d on the upper surface and the lower surface of the metal substrate 12c. Further, the copper layers 11e, 12e and 13e improve heat dissipation.

In the light emitting device 20, the light radiated downward from the LED die 31 is reflected by the upper surface of the ceramic layer 12a or the metal substrate 12c and is directed upward. Since the aluminum constituting the metal substrate 12c has a high reflectance, the light emitting device 20 provided with the metal substrate 12c has a high luminous efficiency. On the other hand, as for aluminum, copper having high thermal conductivity may be used as a material for the metal substrate 12c. That is, it is preferable that the material of the metal substrate 12c is aluminum when the luminous efficiency is important, and the material of the metal substrate 12c is copper when the heat dissipation is important. In order to achieve both high reflectance and thermal conductivity, for example, the surface of the copper plate constituting the metal substrate 12 may be coated with a metal layer having high reflectance.

In the light emitting device 20, a laminate of the ceramic layers 43 and 45 and the copper layers 42 and 46 (ceramic copper pasting sheets 41 and 47) is attached to the metal substrate 44 and individualized to form the ceramic layers 12b and 12d. It was. However, the formation of the ceramic layer is not limited to this method. For example, the metal substrate 44 is coated with an ink-like material in which a filler such as titanium oxide, which is white inorganic fine particles, is dispersed or mixed with a silica sol or an organopolysiloxane that functions as an inorganic binder, and the metal substrate 44 is heated. A white ceramic layer may be formed.

In the light emitting device 20, the LED die 31 was used as the LED, and the plurality of LED dies 31 were covered with the sealing resin 34 containing the fluorescent resin. However, in the light emitting device of the present invention, the LED is not limited to the LED die, and for example, a plurality of chip size packages may be mounted on the heat radiating substrate 12. Further, in the light emitting device 20, the resin substrate 11 is provided with wiring 11a only on the upper surface, but for example, wiring may be formed on both sides of the upper resin plate 11b, and the resin substrate 11 may be multi-layered for wiring.

10 ... Circuit board,
11 ... Resin substrate,
11a, 12a, 13a, 14 ... Wiring,
11a1, 11e, 11e1, 12a1, 12e, 12e1,
13e, 15, 42, 46 ... Copper layer,
11b ... Upper resin plate,
11c ... prepreg,
11d ... Lower resin plate,
12 ... Heat dissipation board,
12b, 12d, 43, 45 ... Ceramic layer,
12c, 44 ... Metal substrate,
13 ... Opening,
20 ... Light emitting device,
31 ... LED die,
32 ... Wire,
33 ... Dam,
34 ... Sealing resin,
35 ... Electronic components,
41, 47 ... Ceramic copper pasting sheet.

Claims (4)

In a circuit board in which a heat dissipation board is fitted in the opening of a resin board,
The heat radiating substrate includes a metal substrate and a ceramic layer laminated on the metal substrate.
A circuit board characterized in that a part of the wiring formed on the upper surface of the ceramic layer is connected to the wiring formed on the upper surface of the resin substrate. The circuit board according to claim 1, wherein the metal substrate is provided with the ceramic layers on the upper surface and the lower surface, respectively. The circuit board according to claim 1 or 2, wherein the metal substrate is made of aluminum or copper. In a light emitting device in which a circuit board in which a heat radiating board is fitted in an opening of a resin board is used.
The heat radiating substrate includes a metal substrate and a ceramic layer laminated on the metal substrate.
A plurality of LEDs are mounted on the upper surface of the ceramic layer, and at the same time,
A light emitting device characterized in that a part of the wiring formed on the upper surface of the ceramic layer is connected to the wiring formed on the upper surface of the resin substrate.