LED packaging structure

Abstract

The utility model relates to the technical field of LED manufacturing, and provides an LED packaging structure, comprising a substrate; the LED chip is fixed on the front surface of the substrate; the box dam is annular and arranged on the front face of the substrate, the box dam surrounds the periphery of the LED chip, the box dam is made of a polytetrafluoroethylene material, the box dam is provided with an inclined face facing the LED chip, the inclined face inclines from the bottom face of the box dam to the direction away from the LED chip, and the included angle between the inclined face and the bottom face of the box dam ranges from 30 degrees to 60 degrees; and the light-transmitting part is connected to the box dam, and the light-transmitting part, the front surface of the substrate and the box dam enclose to form an accommodating cavity for accommodating the LED chip. According to the utility model, the reflection frequency of light rays on the box dam is reduced, the manufacturing is simple, the problem of light loss is further reduced, the included angle between the inclined plane and the front surface of the substrate is limited to be 30-60 degrees, the angle of the included angle when the light rays are reflected on the light-transmitting piece is limited, and the light-transmitting effect is improved. Therefore, the light transmittance of the light passing through the light-transmitting part can be improved, and the light emitting rate of the product is increased.

Description

Technical Field

[0001] The utility model belongs to the technical field of LED manufacturing, and in particular relates to an LED packaging structure. Background Art

[0002] Ultraviolet light-emitting diodes (UV-LEDs) are a type of semiconductor light source. However, in the LED packaging industry, due to the limited light output of LEDs, especially UV-LEDs with a peak wavelength below 350nm, how to improve the light output efficiency of LED products has always been a key research issue in the industry.

[0003] The existing LED packaging structure usually includes a substrate, an LED chip, a light-transmitting member and a dam. The LED chip is arranged on the front of the substrate, and the dam is arranged on the front of the substrate in a direction perpendicular to the thickness of the substrate. The light-transmitting member is arranged on the dam to form a receiving space for the chip with the substrate and the dam. However, such a setting has the following problems: first, the LED chip often has a strong light output in the transverse TM mode (a propagation mode in which the longitudinal component of the magnetic field is zero and the longitudinal component of the electric field is not zero in the waveguide), and a weak light output in the vertical TE mode (a propagation mode in which the longitudinal component of the electric field in the propagation direction of the electromagnetic wave is zero and the longitudinal component of the magnetic field is not zero). The dam made of copper material is perpendicular to the chip, and the transverse light emitted by the LED chip will be reflected back and forth on the surface of the dam. When the light is finally emitted to the outside through the light-transmitting member, the light loss is relatively large; second, in order to improve the anti-oxidation performance of the dam, the surface of the dam is often plated with nickel gold during the production process. The reflectivity of gold to UV light is low, which further increases the light loss and the light output rate of the product is low. Summary of the invention

[0004] The purpose of the present utility model is to overcome at least one of the above-mentioned deficiencies of the prior art and to provide an LED packaging structure capable of improving the light extraction rate of the LED packaging structure.

[0005] The technical solution of the utility model is: an LED packaging structure, comprising: a substrate; an LED chip fixed on the front side of the substrate; a dam, the dam is annular and arranged on the front side of the substrate, the dam surrounds the periphery of the LED chip, the dam is made of polytetrafluoroethylene, the dam is provided with an inclined surface facing the LED chip, the inclined surface is inclined from the bottom surface of the dam toward a direction away from the LED chip, and the angle between the inclined surface and the bottom surface of the dam is 30° to 60°; a light-transmitting member connected to the dam, and the light-transmitting member, the front side of the substrate and the dam together form a receiving cavity for receiving the LED chip.

[0006] As a further improvement of the present technical solution, the LED chip is a UV chip.

[0007] As a further improvement of the technical solution, the cross-section of the dam is trapezoidal.

[0008] As a further improvement of the technical solution, the angle between the inclined surface and the bottom surface of the dam is 45°

[0009] As a further improvement of the technical solution, the height of the dam is 0.2 to 1.5 mm.

[0010] As a further improvement of the present technical solution, the dam has a relative bottom surface and a top surface, the bottom surface and the top surface of the dam are respectively provided with a first active layer and a second active layer, the bottom surface of the dam is connected to the front surface of the substrate, and the bottom surface of the light-transmitting member is connected to the top surface of the dam.

[0011] As a further improvement of the technical solution, a welding layer is provided on the front side of the substrate, and the dam is connected to the substrate through the welding layer.

[0012] As a further improvement of the technical solution, the bottom surface of the light-transmitting member is bonded to the top surface of the dam by adhesive.

[0013] As a further improvement of the technical solution, the bottom surface of the light-transmitting member is welded to the top surface of the dam by welding material.

[0014] As a further improvement of the technical solution, a first metal layer covering the first active layer is further provided on the bottom surface of the dam, and a second metal layer covering the second active layer is further provided on the top surface of the dam.

[0015] The utility model provides an LED packaging structure comprising: a substrate, an LED chip, a dam and a light-transmitting member. The LED chip is fixed to the front of the substrate, the dam is annular and arranged on the front of the substrate, the dam surrounds the periphery of the LED chip, the dam is made of polytetrafluoroethylene, the dam is provided with an inclined surface facing the LED chip, and the angle between the inclined surface and the bottom surface of the dam is 30° to 60°. The light-transmitting member is connected to the dam, and the light-transmitting member, the front of the substrate and the dam together form a receiving cavity for receiving the LED chip. According to the Fresnel reflection characteristics (when the light is perpendicular to the surface, the reflection is weaker, and when the light is not perpendicular to the surface, the smaller the angle, the more obvious the reflection), it can be known that the smaller the angle when the light is reflected on the light-transmitting member, the higher the transmittance of the light through the light-transmitting member. Since the light is reflected from the inclined surface to the light-transmitting member after being emitted from the LED chip, the angle between the inclined surface and the bottom surface of the dam is limited to 30° to 60°, the angle when the light is reflected on the light-transmitting member can be limited to increase the transmittance of the light through the light-transmitting member. In the prior art, a vertical dam is usually made of copper material, and a nickel-gold layer with low reflectivity is provided on the surface of the dam, which causes the lateral light emitted by the chip to be reflected on the surface of the dam, resulting in a large light loss. The utility model changes the reflection path of the light by providing an inclined plane on the dam, reduces the number of times the light is reflected on the dam, and avoids the light loss problem caused by multiple reflections of the light on the surface of the dam in the vertical dam structure in the prior art. The dam in the utility model is made of polytetrafluoroethylene material with high reflectivity, which is not only simple to manufacture, but also improves the light reflectivity of the dam, further reducing the light loss problem in the prior art. The utility model limits the angle between the inclined plane and the front side of the substrate to 30° to 60°, thereby limiting the angle between the lateral light emitted by the chip and the inclined plane, thereby limiting the angle when the light is reflected on the light-transmitting member, thereby improving the light transmittance of the light through the light-transmitting member and increasing the light output rate of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 is a cross-sectional view of an LED packaging structure provided by an embodiment of the utility model;

[0018] Figure 2 It is a cross-sectional view of a light-transmitting member and a packaging body in an LED packaging structure provided by an embodiment of the utility model;

[0019] Figure 3 is a cross-sectional view of a light-transmitting member and a packaging body in an LED packaging structure provided by another embodiment of the utility model;

[0020] Figure 4 It is a schematic diagram of the refraction of light in the light-transmitting component when α is 15°, 30°, 45°, 60° or 75° in the LED packaging structure provided by one embodiment of the utility model.

[0021] In the figure: 100, LED packaging structure; 10, substrate; 11, front surface; 12, receiving cavity; 20, LED chip; 30, dam; 31, inclined surface; 32, bottom surface; 33, side surface; 40, light-transmitting member. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0023] It should be noted that the terms “setting” and “connection” should be understood in a broad sense. For example, it can be directly setting or connecting, or it can be indirectly setting or connecting through a central component or a central structure.

[0024] In addition, if there are terms such as "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicating orientation or positional relationship in the embodiments of the present invention, they are based on the orientation or positional relationship or the conventional placement state or use state shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the structure, feature, device or element referred to must have a specific orientation or positional relationship, nor must it be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0025] The various specific technical features and embodiments described in the specific implementation methods can be combined in any suitable manner unless there is any contradiction. For example, different implementation methods can be formed by combining different specific technical features / embodiments. In order to avoid unnecessary repetition, the various possible combinations of the specific technical features / embodiments in the present utility model will not be described separately.

[0026] The utility model provides a LED packaging structure, see Figures 1 to 3The LED packaging structure 100 includes: a substrate 10, an LED chip 20, a dam 30 and a light-transmitting member 40. The LED chip 20 is fixed to the front surface 11 of the substrate 10, the dam 30 is annular and arranged on the front surface 11 of the substrate 10, the dam 30 surrounds the outer periphery of the LED chip 20, the dam 30 is made of polytetrafluoroethylene material, the dam 30 is provided with an inclined surface 31 facing the LED chip 20, the inclined surface 31 is inclined from the bottom surface 32 of the dam 30 to the direction away from the LED chip 30, and the angle α between the inclined surface 31 and the bottom surface 32 of the dam 30 is 30° to 60°. The light-transmitting member 40 is connected to the dam 30, and the light-transmitting member 40, the front surface 11 of the substrate 10 and the dam 30 enclose a receiving cavity 12 for receiving the LED chip 20. The front surface 11 of the substrate 10 is the surface of the substrate 10 facing the LED chip 20, the inclined surface 31 of the dam 30 is the surface of the dam 30 facing the LED chip 20, and the bottom surface 32 of the dam 30 is the surface of the dam 30 parallel to the lateral light emitting direction of the LED chip 20 and close to the LED chip 20. According to the Fresnel reflection characteristics (when the light is perpendicular to the surface of the object, the reflection is weak, and when the light is not perpendicular to the light-transmitting surface, the smaller the angle between the light and the surface of the object, the more obvious the reflection), it can be known that when the angle α when the light is reflected on the light-transmitting member 40 is smaller, the light transmittance through the light-transmitting member 40 is higher. Since the light is emitted from the LED chip 20 and reflected to the light-transmitting member 40 through the inclined surface 31, by limiting the angle α between the inclined surface 31 and the bottom surface 32 of the dam 30 to 30° to 60°, the angle when the light is reflected on the light-transmitting member 40 can be limited to improve the light transmittance through the light-transmitting member 40. In the prior art, the vertical dam 30 is usually made of copper material that is resistant to UV light (ultraviolet light), wherein the dam made of copper needs to be plated with nickel and gold on its surface, and nickel and gold have a low reflectivity to ultraviolet light, which causes the lateral light emitted by the chip to be reflected on the surface of the dam 30, resulting in a large light loss. The utility model provides an inclined surface 31 on the dam 30, thereby changing the reflection path of the light, reducing the number of times the light is reflected on the dam 30, and avoiding the light loss problem caused by multiple reflections of the light on the vertical dam 30 surface in the prior art. The dam 30 in the type is made of high-reflectivity polytetrafluoroethylene material, which is not only simple to manufacture, but also improves the light reflectivity of the dam 30, further reducing the problem of light loss in the prior art. The utility model limits the angle α between the inclined surface 31 and the front surface 11 of the substrate 10 to 30° to 60°, thereby limiting the angle between the vertical lateral light emitted by the chip and the inclined surface 31, thereby limiting the angle when the light is reflected on the light-transmitting member 40, thereby improving the transmittance of the light through the light-transmitting member 40 and increasing the light output rate of the product.

[0027] For the substrate 10, preferably, the substrate 10 can be made of ceramic material, which has good insulation and heat dissipation properties, and is convenient for arranging circuits and chips on the surface of the substrate 10. Of course, the present invention does not limit the specific material of the substrate 10, as long as it does not affect the use of the LED packaging structure 100.

[0028] The LED chip 20 may be any one of a flip chip, a face-up chip or a vertical chip. In one example, a flux material is disposed on the front surface 11 of the substrate 10, and then the LED chip 20 is disposed on the flux material to achieve connection between the LED chip 20 and the substrate 10.

[0029] Preferably, the LED chip 20 can be a UV chip, and the polytetrafluoroethylene (also known as Teflon, PTFE or plastic king) used in the dam 30 has a melting point of 327°C and good heat resistance. It not only has good resistance to ultraviolet aging, but also the reflectivity of the polytetrafluoroethylene material to ultraviolet light is more than 90%. Of course, it can be understood that the utility model does not limit the specific material of the dam 30, and the specific material of the dam 30 can be selected according to the light emitted by the LED chip 20 or the manufacturing cost, as long as it can have a good reflectivity to the light emitted by the LED chip 20.

[0030] For the dam 30, preferably, the longitudinal section of the dam 30 is trapezoidal, and the longitudinal section of the dam 30 can be any one of a common trapezoid, a right-angled trapezoid or an isosceles trapezoid. The upper bottom side of the longitudinal section of the dam 30 is parallel to the lower bottom side, that is, the top surface of the dam 30 is parallel to the bottom surface 32, so as to facilitate the installation of the dam 30 on the substrate 10 and the arrangement of the light-transmitting member 40 on the top surface of the dam 30. Preferably, along the height direction of the dam 30, the cross section of the dam 30 is circular, square or rectangular. Of course, the utility model does not limit the specific shape of the dam 30, as long as it does not affect the use of the LED packaging structure 100.

[0031] Preferably, the angle α between the inclined surface 31 and the bottom surface 32 of the dam 30 can be 45°. When α is 15°, 30°, 45°, 60° or 75°, the refraction of light in the light-transmitting member 40 is as follows: Figure 4As shown, according to the Fresnel reflection characteristics (when the light is perpendicular to the surface of an object, the reflection is weaker, and when the light is not perpendicular to the surface, the smaller the angle between the light and the surface of the object, the more obvious the reflection is), it can be known that the smaller the Fresnel reflection of the light at the light-transmitting member 40, the higher the transmittance of the light from the light-transmitting member 40. Therefore, when the angle α between the inclined surface 31 and the bottom surface 32 of the dam 30 is 45°, the Fresnel reflection of the light at the light-transmitting member 40 is the smallest, and the transmittance of the light from the light-transmitting member 40 is the highest, thereby further improving the light output rate of the product.

[0032] In some embodiments, a side surface 33 of the outer periphery of the dam 30 , ie, a surface opposite to the inclined surface 31 , is provided with a light-isolating layer, and the light-isolating layer is used to prevent light from escaping from the side surface 33 of the dam 30 .

[0033] In practical applications, the height H of the dam 30 may be 0.2 to 1.5 mm, and the length of the inclined surface 31 (the length from the bottom to the top of the dam 30 ) may be 0.23 to 3 mm.

[0034] Regarding the light-transmitting member 40, in some embodiments, the light-transmitting member 40 is made of quartz or sapphire material, but the present invention does not limit the specific material of the light-transmitting member 40, as long as it can achieve the light-transmitting effect. For example, the light-transmitting member 40 can be made of plastic such as PMMA (polymethyl methacrylate). In this embodiment, the light-transmitting member 40 can be in the shape of a plate (see Figure 1 and Figure 2 ), but the shape of the light-transmitting member 40 is not limited thereto, for example, it may be a rectangular parallelepiped, a bulb or a hemisphere (such as Figure 3 As shown), etc., as long as it does not affect the light transmission.

[0035] It is understandable that the dam 30 and the light-transmitting member 40 may be integrally formed for ease of use.

[0036] Preferably, the dam 30 has a bottom surface 32 and a top surface opposite to each other, the bottom surface 32 and the top surface of the dam 30 are provided with a first active layer and a second active layer respectively, the bottom surface 32 of the dam 30 is connected to the front surface 11 of the substrate 10, and the bottom surface 32 of the light-transmitting member 40 is connected to the top surface of the dam 30. The first active layer and the second active layer are used to improve the activity of the bottom surface 32 and the top surface of the dam 30, thereby increasing the firmness of the connection between the dam 30 and the substrate 10 or the light-transmitting member 40.

[0037] In some embodiments, a welding layer is provided on the front side 11 of the substrate 10 , and the dam 30 is connected to the substrate 10 through the welding layer, so as to fix the dam 30 .

[0038] In some embodiments, the bottom surface 32 of the light-transmitting member 40 is bonded to the top surface of the dam 30 by adhesive, thereby fixing the light-transmitting member 40. Preferably, the adhesive can be light-resistant glue. When the LED chip 20 is a UV-LED chip, the adhesive is UV-resistant glue, and the adhesive can be made of materials such as silicone resin or fluororesin.

[0039] In other embodiments, the bottom surface 32 of the light-transmitting member 40 is welded to the top surface of the dam 30 by welding material, so as to fix the light-transmitting member 40 .

[0040] Preferably, the welding material may be a gold-tin solder such as a gold-tin alloy. In a specific application, the gold content of the gold-tin alloy may be 80wt%, the tin content may be 20wt%, and the melting temperature of the gold-tin alloy may be greater than 280°C.

[0041] The bottom surface 32 of the dam 30 is further provided with a first metal layer covering the first active layer, and the top surface of the dam 30 is further provided with a second metal layer covering the second active layer, thereby increasing the firmness of the connection between the dam 30 and the substrate 10 or the light-transmitting member 40 .

[0042] In the actual production process, polytetrafluoroethylene powder (the particle size of polytetrafluoroethylene powder can be 20 to 400 microns) can be placed in a mold first, and pressed into a blank of the dam 30 at room temperature. Among them, the preforming pressure can be 18 to 40 MPa, and the holding time can be 5 to 10 minutes. Secondly, the blank is placed in a sintering furnace for sintering, the sintering temperature can be 370 to 380°C, the heating rate can be 50 to 100°C / hour, and the sintering time can be 10 to 30 minutes. Then the sintered blank is cooled down, and the cooling rate can be 15 to 50°C / hour. Then the blank is polished to improve the flatness of the dam 30. Then the first active layer and the second active layer are respectively set on the bottom surface 32 and the top surface of the dam 30. The way to set the active layer can be plasma treatment or sodium naphthalene solution treatment of the top surface and the bottom surface 32, so as to improve the firmness of the connection between the dam 30 and the substrate 10 or the light-transmitting member 40. If it is necessary to bond the dam 30 to the substrate 10 or the light-transmitting member 40, the adhesive is disposed between the dam 30 and the substrate 10 or the light-transmitting member 40, and then the adhesive is cured. The adhesive can be cured by baking or the like.

[0043] If the dam 30 needs to be welded to the substrate 10 or the light-transmitting member 40, it is also necessary to respectively set a first metal layer covering the first active layer and a second metal layer covering the second active layer on the bottom surface 32 and the top surface of the dam 30 before welding. The first metal layer and the second metal layer can be made of metals such as tungsten (W), titanium (Ti), nickel (Ni), chromium (Cr), copper (Cu), gold (Au), silver (Ag) or their alloys. The utility model is preferably a stacked nickel-gold, wherein the thickness of the nickel layer can be greater than 3um, and the thickness of the gold layer can be greater than 0.05um. Secondly, flux or gold-tin solder such as gold-tin alloy is respectively set on the bottom surface 32 and the top surface of the dam 30, and then the dam 30 is placed on the substrate 10 or the light-transmitting member 40 is placed on the dam 30, and finally the welding is performed by eutectic furnace or reflow soldering, and the welding temperature can be 280 to 310°C. Preferably, the edge of the dam 30 does not exceed the edge of the substrate 10 , and the edge of the light-transmitting member 40 does not exceed the edge of the dam 30 .

[0044] The utility model provides an LED packaging structure, the LED packaging structure 100 comprises: a substrate 10, an LED chip 20, a dam 30 and a light-transmitting member 40. The LED chip 20 is fixed to the front surface 11 of the substrate 10, the dam 30 is annular and arranged on the front surface 11 of the substrate 10, the dam 30 surrounds the periphery of the LED chip 20, the dam 30 is made of polytetrafluoroethylene, the dam 30 is provided with an inclined surface 31 facing the LED chip 20, and the angle between the inclined surface 31 and the bottom surface 32 of the dam 30 is 30° to 60°. The light-transmitting member 40 is connected to the dam 30, and the light-transmitting member 40, the front surface 11 of the substrate 10 and the dam 30 enclose a receiving cavity 12 for receiving the LED chip 20. According to the Fresnel reflection characteristics (when the light is perpendicular to the surface, the reflection is weaker, and when the light is not perpendicular to the surface, the smaller the angle, the more obvious the reflection), it can be known that when the reflection angle of the light on the light-transmitting member 40 is smaller, the transmittance of the light through the light-transmitting member 40 is higher. Since the light is reflected from the inclined surface 31 to the light-transmitting member 40 after being emitted from the LED chip 20, the angle between the inclined surface 31 and the bottom surface 32 of the dam 30 is limited to 30° to 60°, the angle of the light when reflected on the light-transmitting member 40 can be limited to increase the transmittance of the light through the light-transmitting member 40. In the prior art, the vertical dam 30 is usually made of copper material, wherein the copper dam needs to be plated with nickel-gold on its surface, and nickel-gold has a low reflectivity to ultraviolet light, which causes the lateral light emitted by the chip to be reflected on the surface of the dam 30, resulting in a large light loss. The utility model provides an inclined surface 31 on the dam 30, changes the reflection path of the light, reduces the number of times the light is reflected on the dam 30, avoids the light loss problem caused by multiple reflections of the light on the vertical dam 30 surface in the prior art, and the utility model The dam 30 in the novel device is made of high-reflectivity polytetrafluoroethylene material, which improves the light reflectivity of the dam 30 and further reduces the problem of light loss in the prior art. The utility model limits the angle between the lateral light emitted by the chip and the bevel 31 by limiting the angle between the bevel 31 and the front surface 11 of the substrate 10 to 30° to 60°, thereby limiting the angle when the light is reflected on the light-transmitting member 40, thereby improving the transmittance of the light through the light-transmitting member 40 and increasing the light output rate of the product.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An LED packaging structure, characterized in that: include: substrate; An LED chip is fixed on the front side of the substrate; A dam, the dam is annular and is disposed on the front side of the substrate, the dam surrounds the periphery of the LED chip, the dam is made of polytetrafluoroethylene, the dam is provided with an inclined surface facing the LED chip, the inclined surface is inclined from the bottom surface of the dam in a direction away from the LED chip, and the angle between the inclined surface and the bottom surface of the dam is 30° to 60°; The light-transmitting member is connected to the dam, and the light-transmitting member, the front surface of the substrate and the dam together form a receiving cavity for receiving the LED chip.

2. The LED packaging structure according to claim 1, characterized in that: The LED chip is a UV chip.

3. The LED packaging structure according to claim 1, characterized in that: The cross section of the dam is trapezoidal.

4. The LED packaging structure according to claim 1, characterized in that: The included angle between the inclined surface and the bottom surface of the dam is 45°.

5. The LED packaging structure according to claim 1, characterized in that: The height of the dam is 0.2 to 1.5 mm.

6. The LED packaging structure according to any one of claims 1 to 5, characterized in that: The dam has a bottom surface and a top surface opposite to each other. The bottom surface and the top surface of the dam are respectively provided with a first active layer and a second active layer. The bottom surface of the dam is connected to the front surface of the substrate. The bottom surface of the light-transmitting member is connected to the top surface of the dam.

7. The LED packaging structure according to claim 6, characterized in that: A welding layer is provided on the front side of the substrate, and the dam is connected to the substrate through the welding layer.

8. The LED packaging structure according to claim 6, characterized in that: The bottom surface of the light-transmitting member is bonded to the top surface of the dam by adhesive.

9. The LED packaging structure according to claim 6, characterized in that: The bottom surface of the light-transmitting member is welded to the top surface of the dam by welding material.

10. The LED packaging structure according to claim 9, characterized in that: A first metal layer covering the first active layer is further provided on the bottom surface of the dam, and a second metal layer covering the second active layer is further provided on the top surface of the dam.

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