TWI775682B - Light source element, preparation method of light source element, and display device - Google Patents

Abstract

The invention belongs to the technical field of display, and provides a light source element, a preparation method of the light source element and a display device. The light source element includes a driving chip, at least one LED chip group, a circuit wire layer, a channel wire, a first metal pad and a second metal pad. Wherein, the first metal pad is arranged on the first surface of the driving wafer, the circuit wire layer and the second metal pad are arranged on the second surface of the driving wafer, and the side surface of the driving wafer is provided with channel wires for connecting the circuit wire layer and the second surface of the driving wafer. The first metal pad, the LED chip is assembled on the second surface of the driver chip and connected to the second metal pad; the circuit wire layer on both sides of the driver chip and the first metal pad are connected by setting channel wires on the side of the driver chip , the size of the light source element is reduced, and the problem that the size of the package body existing in the conventional light source body is large and cannot be reduced is solved.

Description

Light source element, preparation method of light source element, and display device

The present invention relates to the technical field of display, and in particular, to a light source element, a method for preparing the light source element, and a display device.

In the display market, with the rapid development of technology, transparent display has become the mainstream device used in emerging markets, and the main component of transparent display is an integrated light source including driver chips and LED (light-emitting diode) chips. The existing LED light source body adopts the vertical structure packaging technology to fix the driving chip on the circuit carrier board in a flip-chip manner, and fix and adhere the front-emitting LED chip to the top of the driving chip, and then solder the chip. The LED chip is electrically connected with the driving chip and the circuit carrier board by means of a conducting wire, so as to realize a driving-integrated LED light source body.

However, the above-mentioned design has a problem that the size of the package cannot be reduced due to the need to reserve a space for bonding wires on the circuit carrier.

The purpose of the present invention is to provide a light source element, a preparation method of the light source element and a display device, which aims to solve the problem that the size of the package body of the existing light source body is too large and cannot be reduced.

A first aspect of the embodiments of the present invention provides a light source element, comprising: a driving wafer, a first surface of the driving wafer is provided with a plurality of first metal pads, and the first surface of the driving wafer is opposite to the first surface of the driving wafer A circuit line layer and a plurality of second metal pads are provided on both sides, the circuit line layer is connected to a plurality of the second metal pads, and is connected to the first surface of the driving chip and the second surface of the driving chip The side surface of the driving chip is provided with a plurality of channel wires exposed on the driving chip, and the plurality of channel wires are connected to the circuit wire layer and are respectively connected to a plurality of the first metal pads; and at least one The LED chip set is disposed on the second surface of the driving chip and connected to a plurality of the second metal pads.

Preferably, the light source element further comprises: a circuit substrate, the driving chip is disposed on the upper surface of the circuit substrate, and the first surface of the driving chip faces the upper surface of the circuit substrate, the circuit substrate The lower surface of the circuit board is provided with a plurality of electrical contacts; and an outer sealing compound, which covers the driving chip and the LED chip group and is connected to the periphery of the upper surface of the circuit substrate.

Preferably, the LED chip group includes red LED chips, green LED chips and blue LED chips.

Preferably, the LED chip set and the plurality of second metal pads are located in the middle area of the second surface of the driving chip.

Preferably, at least one LED chip group is a plurality of the LED chip groups, and the plurality of the LED chip groups and the plurality of the second metal pads are distributed in the four corners of the second surface of the driving chip.

Preferably, a plurality of the first metal pads are distributed in the surrounding area of the first surface of the driving wafer.

A second aspect of the embodiments of the present invention provides a method for preparing a light source element, the preparation method comprising the following steps: Manufacture a driving chip wafer, the driving chip wafer has a plurality of sub-blocks, a plurality of longitudinal scribe lines and a plurality of transverse scribe lines, and the plurality of the transverse scribe lines and the plurality of the longitudinal scribe lines intersect vertically and are divided into a plurality of said sub-blocks separated from each other; forming a plurality of through holes in a plurality of the longitudinal cutting lines and a plurality of the transverse cutting lines, and filling conductive materials in the through holes to form channel wires; A plurality of first metal pads are arranged on the first side of the sub-block, and a circuit line layer and a plurality of circuit lines are arranged on the second side of the sub-block opposite to the first side of the sub-block. the second metal pad of the layer, and the channel wire is connected to the first metal pad of the two adjacent sub-blocks and the circuit line layer; cutting along the respective centerline positions of the plurality of longitudinal scribe lines and cutting along the respective centerline positions of the plurality of the transverse scribe lines to form the sub-blocks into driving wafers; A circuit carrier board is provided, a plurality of the driving chips are arranged on the upper surface of the circuit carrier board, and the first surface of the driving chips faces the upper surface of the circuit carrier board. The lower surface is provided with a plurality of electrical contacts; at least one LED chip is assembled on the second surface of the driving chip and connected to a plurality of the second metal pads of the driving chip; Making an outer packaging layer, the outer packaging layer covers a plurality of the driving chips and a plurality of the LED chip groups and connects the surrounding area of the upper surface of the circuit carrier board and the plurality of the driving chips with each other the gap area between; and The outer packaging layer and the circuit board are cut and disconnected along the gaps between a plurality of the driving chips to obtain a plurality of light source elements.

Preferably, the circuit line layer and the plurality of second metal pads on the second surface of the sub-block are formed by etching the metal layer.

Preferably, the plurality of the first metal pads of the sub-block are formed in a redistribution layer manner.

The third party aspect of the embodiment of the present invention provides a display device, comprising: a transparent conductive plate and a plurality of light source elements according to any one of the above, wherein a plurality of the light source elements are arranged in an array on the transparent conductive plate And the plurality of first metal pads on the first surface of the driving chip are electrically connected to the transparent conductive plate.

In the light source element and the manufacturing method thereof provided by the embodiments of the present invention, the driving chip realizes the electrical connection design of the double-sided circuit layer by using the space of the wafer dicing road, and the circuit design is performed by avoiding the position of the through hole inside the existing chip. The limitations of the embodiment of the present invention are more flexible, so that the internal circuit design can obtain better density, thereby releasing the area space of the driving chip, so that when the light source body is packaged, it can achieve a single The size is more miniaturized. The driver chip formed in this way is packaged with at least one LED chip set in one piece. Under the same performance conditions, it can achieve miniaturization and maximize the luminous brightness of the product, so that the product can be applied to the transparent display device market. It can meet the needs of smaller dot pitch and high brightness display without affecting the transparency effect.

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

In the description of the present invention, it should be understood that the terms "first" and "second" are only used for description purposes, and cannot be interpreted as indicating or implying relative importance or the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature.

As shown in FIG. 1 , the main component of the current transparent display screen is the LED light source body (including the driving chip and the LED chip). Because the vertical structure packaging technology adopted by the existing LED light source body is to flip the driving chip 11 . The LED chip 13 is fixed and electrically connected to the circuit substrate 10 by means of a method, and the front-emitting LED chip 13 is fixed directly above the driving chip 11, and then the LED chip 13 is electrically connected to the driving chip 11 and the circuit substrate 10 by soldering conductive wires. , and then encapsulated by the molding colloid 12 to realize the integrated light source of the driver chip and the LED chip. The LED light source body realized by this technology is difficult to miniaturize the size of the product, and it needs to be pre-fabricated on the circuit substrate 10. A certain space for soldering wires is reserved, so that the size of the package cannot be reduced.

Although in the prior art, a through silicon via (TSV) technology is also used, as shown in FIG. 2 , the driver chip 21 is fixed and electrically connected to the circuit substrate 20 in a flip-chip manner, and the LED chip 23 is flip-chipped on the driver chip. 21, but when designing the internal structure circuit 22 of the driver chip 21, the circuit inside the chip must avoid the reserved space range required for making through silicon vias. This design structure not only increases the difficulty of the driver chip 21 to realize the internal circuit , and the design cost of the chip is also increased, and the area of the driving chip 21 designed in this way is also difficult to reduce.

In order to solve the above technical problems, an embodiment of the present invention provides a light source element. As shown in FIG. 3 , FIG. 4 , FIG. 5 a , FIG. 5 b and FIG. 6 , a light source element in the embodiment of the present invention includes: a driving chip 40 , a circuit The wire layer 03 , the channel wire 04 , the first metal pad 01 , the second metal pad 02 , and at least one LED chip group 50 .

Specifically, the first surface of the driving wafer 40 is provided with a plurality of first metal pads 01 , and the second surface of the driving wafer 40 opposite to the first surface of the driving wafer 40 is provided with a circuit line layer 03 and a plurality of second metal pads 01 . The pads 02 and the circuit wire layer 03 are connected to a plurality of second metal pads 02 . Channel wires 04, a plurality of channel wires 04 are connected to the circuit wire layer 03 and are respectively connected to a plurality of first metal pads 01; at least one LED chip group 50 is disposed on the second surface of the driving chip 40 and is welded to the plurality of second metals Disk 02 is connected.

In this embodiment, as shown in FIG. 5 b , the circuit wire layer 03 is connected to a plurality of second metal pads 02 , and the plurality of second metal pads 02 are connected to the LED chip set 50 , and the circuit wire layer 03 is used to connect to the LED chips 03 . The chip set 50 provides the driving signal. Since the second surface of the driving chip 40 is provided with the circuit line layer 03, the circuit migration and connection of the plurality of second metal pads 02 can be realized in unlimited positions, thereby reducing the size of the light source element. And a plurality of channel wires 04 exposed to the driver chip 40 are arranged on the side of the driving chip 40, and the through holes 502 of the plurality of channel wires 04 are arranged on the dicing road 501 of the wafer, and after the wafer is cut, a plurality of driving chips are formed. 40. The channel wire 04 is used for the connection between the first metal pad 01 on the first side of the driving chip 40 and the circuit wire layer 03 on the second side of the driving chip 40. This design not only reduces the length of the connecting line, but also The occupation of the lead position is avoided, the size of the light source element is greatly reduced, and the problem that the size of the package body of the existing light source body is large and cannot be reduced is solved.

FIGS. 5 a and 5 b are schematic diagrams of circuit structures on the surface of the driving chip 40 in which at least one LED chip group 50 is one LED chip group 50 and a plurality of LED chip groups 50 , respectively.

In this embodiment, the second surface of the driving chip 40 is provided with a circuit wire layer 03 and a plurality of second metal pads 02 , and a plurality of first metals on the first surface of the driving chip 40 are made through a plurality of channel wires 04 The pads 01 are conductively connected to the circuit line layer 03 on the second side of the driving chip 40, and the plurality of second metal pads 02 on the second side of the driving chip 40 are connected to at least one LED chip group 50, thereby forming a brand new Miniaturized double-sided line driver wafer 40 .

In one embodiment, the aperture size of the through holes 502 provided in the dicing lanes 501 of the wafer is 50-200 μm to achieve higher interconnection density.

In one embodiment, as shown in FIG. 6 a and FIG. 6 b , the light source element further includes: a circuit substrate 10 and an outer sealing compound 60 . Specifically, the driving chip 40 is disposed on the upper surface of the circuit substrate 10, the first surface of the driving chip 40 faces the upper surface of the circuit substrate 10, and the lower surface of the circuit substrate 10 is provided with a plurality of electrical contacts; The driver chip 40 and the LED chip group 50 are covered and connected to the periphery of the upper surface of the circuit board 10 .

In this embodiment, the circuit substrate 10 may be a printed circuit board (Printed Circuit Board) or the like; the LED chip set 50 is fixed directly above the driving chip 40 through a flip-chip process, and is in circuit conduction with the second metal pad 02 , Thus, a light source body in which the driver chip 40 and at least one LED chip group 50 can be integrated with the package body size can be maximized, which saves the space reserved on the circuit substrate 10 for placing the light source body and the welding wire, and greatly reduces the size of the light source body. The size of the packaged product makes the size of the light source element smaller and more refined, so that the product can be applied to the transparent display device market, and it can meet the requirements of smaller dot pitch and high brightness display without affecting the transparent effect. need.

In one embodiment, the LED chip set 50 includes red LED chips, green LED chips, and blue LED chips for combining to emit light of different colors.

In one embodiment, at least one LED chip group 50 is an LED chip group 50, and the plurality of second metal pads 02 are located in the middle area of the second surface of the driving chip 40, thereby forming a brand new miniaturized The double-sided circuit driving chip 40 greatly reduces the size of the light source element, and solves the problem that the size of the package body of the existing light source body is too large and cannot be reduced.

In one embodiment, the at least one LED chip group 50 is a plurality of LED chip groups 50 , and the plurality of LED chip groups 50 and the plurality of second metal pads 02 are all distributed in the four corner regions of the second surface of the driving chip 40 , so that The light source element emits light more uniformly.

In one embodiment, a plurality of first metal pads 01 are distributed in the surrounding area of the first surface of the driving wafer 40, and the surrounding area is the edge position of the first surface close to the channel wire 04, so as to realize the double-sided circuit layer structure design , which is more flexible.

In this embodiment, by making the layout of the channel wires 04 on the surrounding sides of the driving chip 40 to release the inner space of the driving chip 40, the unit size can be further miniaturized when the light source body element is packaged. The space flexibility of the layout channel wires 04 on the sides of the driver chip 40 is flexible. The driver chip 40 with the same unit area can also realize the layout of multiple groups of metal pads on the front and back. The luminous brightness can also be improved even more.

In one embodiment, FIG. 6a is a schematic diagram of one LED chip set 50, and FIG. 6b is a schematic diagram of a plurality of LED chip sets 50. The LED chip sets 50 are connected to a corresponding plurality of second metal pads 02, because multiple LED chip sets 50 are used. The LED chip set 50 fully enhances the luminous effect, makes the emitted light cells uniform, the illumination range is wider, and the color is more uniform.

In this embodiment, the plurality of LED chip groups 50 are arranged in an array, which is neatly arranged and has a better light emitting effect.

In addition, an embodiment of the present invention also provides a method for manufacturing a light source element. Referring to FIG. 7 , the manufacturing method includes steps S10 to S80.

In step S10, a driving chip wafer is manufactured. Referring to FIG. 4, the driving chip wafer has a plurality of sub-blocks, a plurality of longitudinal dicing streets 501 and a plurality of transverse dicing streets 501, and a plurality of transverse dicing streets 501 and a plurality of The longitudinal scribe lines 501 intersect vertically and divide a plurality of sub-blocks separated from each other.

In step S20 , a plurality of through holes 502 are formed in the plurality of longitudinal scribe lines 501 and the plurality of transverse scribe lines 501 , and conductive materials are filled in the through holes 502 to form the channel wires 04 . In one embodiment, the channel wires 04 are fabricated by using TSV (through silicon via) technology, and the TSV technology can realize electrical connection between different metal pads and realize miniaturization of component integration. Since the dicing lane 501 is at the periphery of the sub-block that drives the wafer, the fabrication of the channel wire 04 in the dicing lane 501 will not affect the circuit arrangement inside the sub-block, and there is no need to reserve the channel wire 04 inside the sub-block space, reducing the size of the light source components.

In step S30, a plurality of first metal pads 01 are arranged on the first side of the sub-block, and a circuit line layer 03 and a plurality of connection circuits are arranged on the second side of the sub-block opposite to the first side of the sub-block The second metal pad 02 of the wire layer 03 is connected, and the channel wire 04 is connected to the first metal pad 01 and the circuit wire layer 03 of the two adjacent sub-blocks.

In step S40 , cutting along the respective centerline positions of the plurality of longitudinal scribe lines 501 and cutting along the respective centerline positions of the plurality of transverse scribe lines 501 to form the sub-blocks into the driving wafers 40 , so that the side surfaces of the driving wafers 40 are formed. A plurality of channel wires 04 exposed to the driving wafer 40 are provided.

In step S50, a circuit carrier is provided, a plurality of driving chips 40 are arranged on the upper surface of the circuit carrier, the first surface of the driving chips 40 faces the upper surface of the circuit carrier, and the lower surface of the circuit carrier is provided with a plurality of driving chips 40. Individual electrical contacts.

In step S60 , at least one LED chip group 50 is disposed on the second surface of the driving chip 40 and connected to a plurality of second metal pads 02 of the driving chip 40 .

In step S70 , an outer packaging layer is fabricated, and the outer packaging layer covers the plurality of driving chips 40 and the plurality of LED chip groups 50 and connects the surrounding area of the upper surface of the circuit board and the gaps between the plurality of driving chips 40 area.

In step S80, the outer packaging layer and the circuit carrier are cut and disconnected along the gaps between the plurality of driving chips 40 to obtain a plurality of light source elements. The outer encapsulation layer is cut along the scribe line 501 to form each outer sealant 60 , and the circuit carrier board is cut along the scribe line to form each circuit substrate 10 .

In one embodiment, the circuit line layer 03 and the plurality of second metal pads 02 on the second side of the sub-block are formed by etching the metal layer, as shown in the circuit structure shown in FIG. 5a and FIG. 5b.

In one embodiment, the plurality of first metal pads 01 of the sub-block are formed in a redistribution layer manner.

In this embodiment, the re-wiring layer is adopted to increase the flexibility of design, reduce the difficulty of typesetting and wiring, and also reduce the occupied area, so that it can be arranged in a more compact manner, and the integration of the circuit is improved. and performance; when maximizing the packaging of the light source body in a certain space, the size of the light source element is reduced.

In this embodiment, the circuit wire layer 03 and the plurality of second metal pads 02 are disposed on the second surface of the driving chip 40 , the circuit wire layer 03 is connected to the plurality of second metal pads 02 , and the circuit wire layer 03 can The line migration connection of unlimited positions of the second metal pad 02 is realized, so that the size of the light source element is reduced, and the through hole 502 is arranged in the dicing road 501 of the driving chip wafer, which can avoid the through hole pre-processing inside the driving chip 40. Leaving space, reducing the size of the light source components.

In the light source element and the manufacturing method thereof provided by the embodiments of the present invention, the driving chip 40 realizes the electrical connection design of the double-sided circuit layer by utilizing the space of the wafer dicing road, and the circuit is formed by avoiding the position of the through hole inside the existing chip. Due to the limitation of design, the method of the embodiment of the present invention is more flexible, so that better density is obtained when designing the circuit inside, so as to release the area space of the driving chip 40, so that when the light source body is packaged, it can be The size of a single body is further downsized. The driving chip 40 and at least one LED chip set 50 formed in this way are packaged in one piece, and under the same performance conditions, it can achieve the miniaturization and the luminous brightness of the product can be improved, so that the product can be used in a transparent display device The market can meet the needs of smaller dot pitch and high brightness display without affecting the transparency effect.

The present invention also provides a display device, comprising: a transparent conductive plate and a plurality of light source elements according to any one of the above-mentioned embodiments, the plurality of light source elements are arranged in an array on the transparent conductive plate and drive a plurality of light source elements on the first surface of the chip 40 The first metal pads 01 are electrically connected to the transparent conductive plate.

In the foregoing embodiments, the description of each embodiment has its own emphasis. For parts that are not described or described in detail in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

The unit described as a separate component may or may not be physically separated, and the component displayed as a unit may or may not be a physical unit, that is, it may be located in one place, or may be distributed to multiple network units . Some or all of the units may be selected according to actual needs to achieve the purpose of the solution in this embodiment.

The above-mentioned embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those with ordinary knowledge in the technical field to which the present invention belongs should understand: it can still be Modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, All should be included within the protection scope of the present invention.

01: The first metal pad 02: Second metal pad 03: Circuit line layer 04: Channel Wires 10,20: Circuit board 11, 21, 40: Driver Chip 12: Molded colloid 13,23: LED chip 22: Internal structure circuit 50: LED Chipset 501: Cutting Road 502: Through hole 60: Outer sealing colloid

1 is a schematic structural diagram of a light source element provided in the prior art; 2 is a schematic structural diagram of another light source element provided by the prior art; FIG. 3 is a schematic structural diagram of a driving chip according to an embodiment of the present invention; FIG. 4 is a schematic structural diagram of a driving chip wafer according to an embodiment of the present invention; 5a and 5b are schematic diagrams of the circuit structure on the surface of the driving wafer provided by the embodiment of the present invention; 6a and 6b are schematic exploded views of a light source element provided by an embodiment of the present invention; and FIG. 7 is a schematic flowchart of a preparation method provided in an embodiment of the present invention.

01: The first metal pad

03: Circuit line layer

04: Channel Wires

40: Driver chip

Claims (10)

A light source element, comprising: A driving chip, a first surface of the driving chip is provided with a plurality of first metal pads, and a second surface of the driving chip opposite to the first surface of the driving chip is provided with a circuit line layer and a plurality of first metal pads Two metal pads, the circuit line layer is connected to a plurality of the second metal pads, and a side surface of the driving chip connecting the first surface of the driving chip and the second surface of the driving chip is exposed to the driver a plurality of channel wires of the chip, the plurality of the channel wires are connected to the circuit wire layer and are respectively connected to the plurality of the first metal pads; and At least one LED chip set is disposed on the second surface of the driving chip and connected to a plurality of the second metal pads. The light source element according to claim 1, wherein the light source element further comprises: a circuit substrate, the driving chip is disposed on the upper surface of the circuit substrate, the first surface of the driving chip faces the upper surface of the circuit substrate, and the lower surface of the circuit substrate is provided with a plurality of electrical contacts; and An encapsulant encapsulates the driving chip and the LED chip set and is connected to the periphery of the upper surface of the circuit substrate. The light source element according to claim 1, wherein the LED chip set includes a red LED chip, a green LED chip and a blue LED chip. The light source device of claim 3, wherein the LED chip group and the plurality of second metal pads are located in a middle area of the second surface of the driving chip. The light source device as claimed in claim 3, wherein the at least one LED chip set is a plurality of the LED chip sets, and the plurality of the LED chip sets and the plurality of the second metal pads are all distributed on the first and second metal pads of the driving chip. A four-corner area on two sides. The light source device of claim 3, wherein a plurality of the first metal pads are distributed in a surrounding area of the first surface of the driving chip. A preparation method of a light source element, comprising the following steps: Manufacture a driving chip wafer, the driving chip wafer has a plurality of sub-blocks, a plurality of longitudinal scribe lines and a plurality of transverse scribe lines, and the plurality of the transverse scribe lines and the plurality of the longitudinal scribe lines intersect vertically and are divided and separated from each other a plurality of such sub-blocks; A plurality of through holes are formed in a plurality of the longitudinal cutting lines and a plurality of the transverse cutting lines, and a conductive material is filled in the through holes to form a channel wire; A plurality of first metal pads are arranged on a first side of the sub-block, and a circuit wire layer is arranged on a second side of the sub-block opposite to the first side of the sub-block to connect the circuit wires a plurality of second metal pads of the layer, and make the channel wires connect the first metal pads of the adjacent two sub-blocks and the circuit line layer; cutting along the respective centerline positions of the plurality of longitudinal scribe lines and cutting along the respective centerline positions of the plurality of the transverse scribe lines so that the sub-block forms a driving wafer; A circuit carrier is provided, a plurality of the driving chips are arranged on the upper surface of the circuit carrier, the first surface of the driving chips faces the upper surface of the circuit carrier, and the lower surface of the circuit carrier is provided with a plurality of electrical contacts; at least one LED chip is assembled on the second surface of the driver chip and connected to a plurality of the second metal pads of the driver chip; An outer packaging layer is made, the outer packaging layer covers a plurality of the driving chips and a plurality of the LED chip groups and is connected to a surrounding area of the upper surface of the circuit carrier and a plurality of the driving chips between each other. gap area; and The outer packaging layer and the circuit board are cut and disconnected along the gaps between the plurality of driving chips to obtain a plurality of light source elements. The preparation method of claim 7, wherein the circuit line layer and the plurality of second metal pads on the second surface of the sub-block are formed by etching a metal layer. The preparation method of claim 7, wherein the plurality of first metal pads of the sub-block are formed in a redistribution layer manner. A display device, comprising: a transparent conductive plate and a plurality of the light source elements as described in any one of claims 1-6, the plurality of the light source elements are arranged in an array on the transparent conductive plate and the driving chip The plurality of first metal pads on the first surface are electrically connected to the transparent conductive plate.

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