Patent Application
20240162124
This disclosure claims priority to Chinese Patent Application No. 202211434404.2 filed Nov. 16, 2022, the disclosure of which is incorporated herein by reference in its entirety.
The present disclosure relates to the technical field of optocouplers, and in particular to an optocoupler, a lead frame and a manufacturing method for the optocoupler.
As a safety device for electric-optic-electric conversion and isolation, an optocoupler has a wide range of applications. Generally, an optocoupler mainly includes a light-emitting chip and a light-sensing chip. The light-emitting chip and the light-sensing chip are encapsulated in the same encapsulation body with encapsulating glue. When an electrical signal is applied to an input terminal of the optocoupler, the light-emitting chip, such as an infrared light-emitting diode, will emit infrared light, and the light-sensing chip at a receiving terminal will generate an induced current after receiving the infrared light, thus achieving the conversion between an optical signal and an electrical signal.
The current transfer ratio (CTR) is the main characteristic index of the optocoupler, and the induced current of the optocoupler when operating is directly related to factors such as the energy of light emitted by the diode, the opposed position design and the spacing distance design of the light-emitting chip and the light-sensing chip within the encapsulation body, and the transmittance of materials between the light-emitting chip and the light-sensing chip.
The common internal encapsulation structures of the conventional optocouplers include a vertically opposed type, an obliquely opposed type, a horizontal reflective type and other types, in which the opposed type is the solution with the least light waste. However, the deviation between the opposed positions of the two types of chips under this solution will directly cause the surface of the photosensitive semiconductor tube to receive less infrared light, adversely affecting the induced current generated and ultimately affecting the consistency of the CTR. In conventional opposed-type optocouplers, since the light-emitting chip and the light-sensing chip respectively use lead frames with different structures, the opposed positions are more likely to be deviated from each other. Moreover, it is necessary to develop molds separately for manufacturing respective lead frames for the two types of chips, which significantly increases the manufacturing costs. In addition, in the process of placing and bonding the two types of chips, different machines need to be respectively used to operate at different work stations, which also increases the costs of equipment and personnel, and is not conducive to improving production efficiency.
In view of at least one defect in the conventional technology described above, an object of the present disclosure is to provide a new type of optocoupler lead frame to improve the CTR consistency of the manufactured opposed optocoupler, reduce manufacturing costs and improve production efficiency.
The technical solutions adopted by the present disclosure are as follows:
A lead frame for an optocoupler is provided. The lead frame is a metal sheet and includes multiple frame units and multiple mutually parallel connecting strips. Respective frame units are arranged at intervals on each of the connecting strips. Each frame unit includes two adjacent functional parts, and two pins perpendicularly connected to the connecting strip. The two functional parts are both located on one side of the connecting strip and are respectively connected to the two pins. Ends of the two pins are located on the other side of the connecting strip; and the area of each functional part is sufficient to accommodate a chip to be installed and fixed, and the chip is any one of a light-emitting chip and a light-sensing chip.
In an embodiment, in each frame unit, a positioning point is provided at a center of each of the two functional parts, and a line connecting the positioning points of the two functional parts is perpendicular to the connecting strip.
In an embodiment, in each frame unit, the two functional parts are respectively a first functional part and a second functional part. The first functional part is close to the ends of the two pins, and the second functional part is away from the ends of the two pins. The first functional part has an area sufficient to accommodate one light-sensing chip to be installed and fixed, and the second functional part has an area sufficient to accommodate one light-emitting chip to be installed and fixed.
In an embodiment, in each of the frame units, the first functional part is separated from the second functional part by a curved slit, to allow a protrusion to form on an edge of the first functional part, and a notch complementary to the protrusion in shape to form on an edge of the second functional part.
Another aspect according to the present disclosure is to provide an optocoupler, which includes two frame units disposed opposite to each other, a light-emitting chip, a light-sensing chip and an encapsulation structure. The two frame units are each the frame unit in the lead frame described above. The functional parts of the two frame units are opposite to each other, and the light-emitting chip and the light-sensing chip are respectively disposed in the two frame units. The light-emitting chip is installed and fixed in one functional part in the frame unit where the light-emitting chip is located and is connected to the other adjacent functional part by a conductive wire. The light-sensing chip is installed and fixed in one functional part in the frame unit where the light-sensing chip is located and is connected to the other adjacent functional part by a conductive wire. The light-emitting chip and the light-sensing chip are positioned opposite to each other. The encapsulation structure encapsulates the two frame units, the light-emitting chip and the light-sensing chip into one body.
In an embodiment, in each frame unit, a positioning point is provided at a center of each of the two functional parts, and a line connecting the positioning points of the two functional parts is perpendicular to the connecting strip. The positioning points of the functional parts of the two frame units are aligned with each other. A fixing position point of the light-emitting chip is aligned with the positioning point of the functional part where the light-emitting chip is located. A fixing position point of the light-sensing chip is aligned with the positioning point of the functional part where the light-sensing chip is located. The light-emitting chip and the light-sensing chip are in a through-beam configuration.
In an embodiment, in each of the frame units, the two functional parts are respectively a first functional part and a second functional part. The first functional part is close to the ends of the two pins, and the second functional part is away from the ends of the two pins. The light-emitting chip is fixed in the second functional part of the frame unit where it is located, and the light-sensing chip is fixed in the first functional part of the frame unit where it is located.
In an embodiment, the encapsulation structure includes an outer encapsulation layer at an outermost side and an inner encapsulation layer wrapping the light-emitting chip, and the material of the inner encapsulation layer is a light-transmitting silicon glue containing a colored pigment.
In an embodiment, the outer encapsulation layer includes a first outer encapsulation layer and a second outer encapsulation layer from inside to outside. The first outer encapsulation layer is made of a light-transmitting white epoxy resin, and the second outer encapsulation layer is made of a light-shielding black epoxy resin.
In an embodiment, the pins of the two frame units both protrude out of the encapsulation structure and are bent toward the same side outside the encapsulation structure.
Another aspect according to the present disclosure is to provide a method for manufacturing an optocoupler, which includes a lead frame manufacturing step, a die bond step, a wire bonding step, a glue dispensing step, a stacking step, an encapsulating step, a dicing and pin bending step. The lead frame is the preceding lead frame. In the die bond step, two pieces of lead frames are taken, in one functional part of each frame unit of one piece of lead frame, one light-emitting chip is installed and fixed, and in one functional part of each frame unit of the other piece of lead frame, one light-sensing chip is installed and fixed. In the wire bonding step, a conductive wire is used to connect the light-emitting chip or the light-sensing chip in each frame unit to the other adjacent functional part. In the stacking step, the two pieces of lead frames are stacked to allow the light-emitting chip and the light-sensing chip on the two pieces of lead frames to be opposite to each other.
In an embodiment, in each of the frame units of the lead frame, a positioning point is provided at a center of each of the two functional parts, and a line connecting the positioning points of the two functional parts is perpendicular to the connecting strip. In the die bond step, the two pieces of lead frames are both placed horizontally, and are respectively in two mutually horizontally flipped states, and in fixing the light-emitting chip, the fixing position point of the light-emitting chip is aligned with the positioning point of the corresponding functional part, and in fixing the light-sensing chip, the fixing position point of the light-sensing chip is aligned with the positioning point of the corresponding functional part.
In an embodiment, in each frame unit of the lead frame, the two functional parts are respectively a first functional part and a second functional part. The first functional part is close to the ends of the two pins, and the second functional part is away from the ends of the two pins; in the die bond step, in the second functional part of each frame unit of one piece of lead frame, a light-emitting chip is fixed, and in the first functional part of each frame unit of the other piece of lead frame, a light-sensing chip is fixed.
In an embodiment, in the die bond step, one die bonder is used, one piece of lead frame is horizontally placed, a conductive glue is dispensed at the positioning point in the second functional part of each frame unit, and then the light-emitting chip is placed; the same die bonder is used, the other piece of lead frame is horizontally placed, a conductive glue is dispensed at the positioning point in the first functional part of each frame unit, and then the light-sensing chip is placed.
In the die bond step, a point alignment correction function of a camera of the die bonder is used, and according to the positioning points in the two functional parts of each frame unit, a machine operation arm is guided to place the light-emitting chip and the light-sensing chip, to allow the fixing position points of the light-emitting chip and the light-sensing chip to be aligned with the positioning points of the corresponding functional parts.
In an embodiment, the wire bonding step includes: a wire bonding machine is used, a piece of lead frame with the light-emitting chip bonded thereto after die bond is placed horizontally, and then a conductive wire is used to electrically connect the light-emitting chip to a bonding point in the functional part adjacent to the light-emitting chip by wiring bonding; the same wire bonding machine is used, the other piece of lead frame with the light-sensing chip bonded thereto after the die bond is placed horizontally, and then a conductive wire is used to electrically connect the light-sensing chip to a bonding point in the functional part adjacent to the light-sensing chip by wiring bonding.
In the wire bonding step, the two pieces of lead frames are respectively in two mutually horizontally flipped states, and the wiring directions for the light-emitting chip and the light-sensing chip are the same.
The optocoupler, its lead frame and its manufacturing method according to the present disclosure have at least the following beneficial effects.
Referring to
Frame units 10 are arranged at intervals on each connecting strip 12. Each frame unit 10 includes two adjacent functional parts 101, 102 and two pins 11. The two pins 11 are perpendicularly connected to the connecting strip 12. The two functional parts 101 and 102 are both located on one side of the connecting strip 12 and are respectively connected to the two pins 11. Ends 110 of the two pins 11 are located on the other side of the connecting strip 12; and the area of each functional part is sufficient to accommodate a chip to be installed and fixed, and the chip is any one of a light-emitting chip 21 and a light-sensing chip 22.
In an embodiment, in each frame unit 10, a positioning point 100 is provided at a center of each of the two functional parts 101 and 102, and a line connecting the positioning points 100 of the two functional parts 101 and 102 is perpendicular to the connecting strip 12. As shown in
Specifically, in each frame unit 10, a center mark and a range mark may be provided in a central part of each of the two functional parts 101 and 102. The center mark is used to form the positioning point 100, and the range mark is used to define a preset chip mounting range or a preset wire bonding range. More specifically, the center mark may be a score in the shape of a symbol “+” engraved on both sides of the functional part, then the positioning point 100 is the center point of the score of the symbol “+”; and the range mark may be a score in the shape of a symbol “O” or “□” engraved on both sides of the functional part, and the range mark surrounds the positioning point of the functional part where the range mark is located.
The two functional parts 101 and 102 are respectively a first functional part 101 and a second functional part 102. The first functional part 101 is close to the ends 110 of the two pins 11, and the second functional part 102 is away from the ends 110 of the two pins 11. The first functional part 101 has an area sufficient to accommodate one light-sensing chip 22 to be installed and fixed, and the second functional part 102 has an area sufficient to accommodate one light-emitting chip 21 to be installed and fixed.
Therefore, in the subsequent process of manufacturing the optocoupler, the same die bonder can be used to perform die bond for the two types of chips at the same work station: a light-emitting chip 21 is placed onto a second functional part 102 of a frame unit 10 in one piece of lead frame 1 using an operating arm, as shown in
Similarly, in wire bonding, the same wire bonding equipment can be used to perform wire bonding of the two types of chips at the same work station in the same wiring direction. As shown in
In order to more conveniently identify the two functional parts or to leave a place for arranging a Zener diode chip, the first functional part 101 is separated from the second functional part 102 by a curved slit S, to allow a protrusion to form on an edge of the first functional part 101 and a notch complementary to the protrusion in shape to form on an edge of the second functional part 102. That is, the shapes of the two functional parts are different. The position of the protrusion of the second functional part 101 may be used to place a Zener diode chip when necessary to improve the anti-static and anti-interference capabilities of the input terminal or the output terminal of the device.
The lead frame 1 further includes two frame bars 13 parallel to each other, playing the role of support and connection. The two frame bars 13 are connected perpendicularly to two ends of the multiple connecting strips 12 respectively, and the multiple connecting strips 12 are arranged at intervals between the two frame bars 13.
Each frame bar 13 is provided with multiple through positioning holes 130. Therefore, in the subsequent process of manufacturing the optocoupler, two pieces of lead frames 1 with the light-emitting chips 21 and the light-sensing chips 22 fixed thereon respectively may be positioned facing each other by means of the positioning holes 130, facilitating the stacking, as shown in
Multiple frame units 10 are arranged on the connecting strips 12 at equal intervals.
The connecting strips 12 are arranged between the frame bars 13 at equal intervals, and the interval is just sufficient to accommodate the stacking arrangement of the functional parts of the two frame units 10 facing each other, as shown in
The material of the lead frame 1 may be one of aluminum alloy, iron-nickel alloy or copper alloy. The thickness of the lead frame 1 ranges from 0.2 mm to 0.3 mm.
In order to improve the reflectivity of the light-emitting chip 21, a highly reflective metal plating layer is provided on at least the surface of each functional part. In an embodiment, the material of the highly reflective metal plating layer is gold or silver.
In combination with
The functional parts of the two frame units 10 oppose each other, and the light-emitting chip 21 and the light-sensing chip 22 are respectively disposed in the two frame units 10. The light-emitting chip 21 is installed and fixed in one functional part in the frame unit 10 where the light-emitting chip 21 is located and is connected to the other adjacent functional part by a conductive wire 24. The light-sensing chip 22 is installed and fixed in one functional part in the frame unit 10 where the light-sensing chip 22 is located and is connected to the other adjacent functional part by a conductive wire 24. The light-emitting chip 21 and the light-sensing chip 22 are positioned opposite to each other. The encapsulation structure 23 encapsulates the two frame units 10, the light-emitting chip 21 and the light-sensing chip 22 into one body.
Specifically, the positioning points 100 of the functional parts of the two frame units 10 are aligned with each other; the fixing position point of the light-emitting chip 21 is aligned with the positioning point 100 of the functional part where the light-emitting chip 21 is located; and the fixing position point of the light-sensing chip 22 is aligned with the positioning point 100 of the functional part where the light-sensing chip 22 is located.
More specifically, the first functional part 101 of one frame unit and the second functional part 102 of another frame unit 10 are disposed opposite to each other, and the corresponding positioning points 100 are aligned with each other.
In an embodiment, the light-emitting chip 21 is fixed in the second functional part 102 of the frame unit 10 where the light-emitting chip 21 is located, and the light-sensing chip 22 is fixed in the first functional part 101 of the frame unit 10 where the light-sensing chip 22 is located; and the light-emitting chip 21 and the light-sensing chip 22 are in a through-beam configuration.
The light-emitting chip 21 and the light-sensing chip 22 are specifically fixed to the surfaces of the respective functional parts through conductive glue. The conductive glue may be a conductive paste such as silver glue.
The conductive wire 24 may be a copper wire, an alloy wire or a gold wire.
The encapsulation structure 23 includes an outer encapsulation layer at the outermost side and an inner encapsulation layer 230 wrapping the light-emitting chip 21.
The material of the inner encapsulation layer 230 is a light-transmitting silicon glue containing a colored pigment (such as a red pigment). The main function of doping the colored pigment is to, in a case where the silicon glue is dispensed, allow an apparatus to inspect through an automatic optical inspection (AOI) the inner encapsulation layer 230 coated with the dispensed red silicon glue for example, to determine whether the silicone gel is missed to be dispensed/or whether the shape of the chip or the gel dispensed meets the requirements.
The outer encapsulation layer includes a first outer encapsulation layer and a second outer encapsulation layer from the inside to the outside. The first outer encapsulation layer is made of a light-transmitting white epoxy resin, and the second outer encapsulation layer is made of a light-shielding black epoxy resin.
The pins 11 of both the two frame units 10 protrude out of the encapsulation structure 23 and are bent toward the same side outside the encapsulation structure 23.
In an embodiment, a surface of a part of each of the pins 11 protruding outside the encapsulation structure 23 is plated with a tin layer.
The light-emitting chip 21 is a light-emitting diode, and the light-sensing chip 22 is a photosensitive semiconductor tube. The light-emitting chip 21 may be an infrared light-emitting chip, and the light-sensing chip 22 may correspondingly be an infrared light-receiving chip.
A manufacturing method for the optocoupler 2 according to the second embodiment is provided according to this embodiment, which is roughly the same as the manufacturing method for the conventional optocoupler, and mainly includes steps such as lead frame manufacturing, a die bond, wire bonding, glue dispensing, stacking, encapsulating, pin bending and dicing. The characteristics of the manufacturing method lie in that the lead frame 1 according to the first embodiment is adopted as the lead frame. The manufacturing method is specifically carried out as follows.
In a first step of die bond, two pieces of lead frames 1 are taken, and in one functional part of each frame unit 10 of one piece of lead frame 1, one light-emitting chip 21 is installed and fixed, and in one functional part of each frame unit 10 of the other piece of lead frame 1, one light-sensing chip 22 is installed and fixed.
In this step, the two pieces of lead frames 1 are both placed horizontally and are in two mutually horizontally flipped states. As shown in
More specifically, in this step, one die bonder is used, one piece of lead frame 1 is horizontally placed, and at the positioning point 100 in the second functional part 102 of each frame unit 10, a conductive glue is dispensed and then a light-emitting chip 21 is placed; and the same die bonder is used, the other piece of lead frame 1 is horizontally placed, and at the positioning point 100 in the first functional part 101 of each frame unit 10, a conductive glue is dispensed and then the light-sensing chip 22 is placed.
Specifically, a point alignment correction function of a camera of the die bonder is used, where the camera is specifically a CCD camera. According to the positioning points 100 in two functional parts of each frame unit 10, a machine operation arm is guided to place the light-emitting chip 21 and the light-sensing chip 22, to allow the fixing position points of the light-emitting chip 21 and the light-sensing chip 22 to be aligned with the positioning points 100 of the corresponding functional parts.
In order to improve accuracy, this step further includes an initial inspection and a sampling inspection. In the initial inspection, after die bond of the frame units 10 is performed on several connecting strips 12 (for example, two connecting strips 12) in the lead frame 1, the lead frame 1 is taken and the position value of the chip is measured under a high-power microscope with a measurement function. The deviation between the fixing position point of the chip and the positioning point 100 in the corresponding functional part is determined according to the position value. If the deviation meets preset requirements, the formal die bond operation will be carried out. If the deviation does not meet the preset requirements, the die bonder is adjusted or repaired. In the sampling inspection, during the formal die bond operation, after a fixed interval of operating time or number of operations, a certain proportion of lead frames 1 are selected to repeat the measurement and determination operations in the initial inspection.
In the initial inspection and sampling inspection, the range mark formed by the score in the shape of the symbol “O” or “□” (the score “O” as shown in
The quantitative measurement error inspection carried out in the initial inspection and sampling inspection ensures the accuracy of deviation between the opposed horizontal positions of the light-emitting chip and the light-sensing chip, ultimately ensures the consistency and the rate of falling into a target range of the product parameters and improves product competitiveness.
In a second step of high-temperature baking and curing, a constant-temperature curing oven is used to cure the conductive adhesive so that the chip is bonded to the lead frame 1.
In a third step of wire bonding, a conductive wire 24 is used to connect the light-emitting chip 21 or the light-sensing chip 22 in each frame unit 10 to the other functional part adjacent thereto.
Specifically, in this step, as shown in
Specifically, the two pieces of lead frames 1 are respectively in two mutually horizontally flipped states, and the wiring directions for the light-emitting chip 21 and the light-sensing chip 22 are the same and are specifically from the left to the right as shown in
In order to ensure the quality of the wire bonding, this step further includes initial inspection and sampling inspection. In the initial inspection, after wire bonding is performed for the frame units 10 on several connecting strips 12 (for example, two connecting strips 12) in the lead frame 1, the lead frame 1 is taken, and a bonding force of the bonding ball and a force value for the conductive wire fixed point to be torn off are measured on a push-pull machine with a measuring function to determine the quality of the wire bonding. If the quality of the wire bonding meets the preset requirements, the formal wire bonding operation will be carried out. If the quality of the wire bonding does not meet the preset requirements, then the wire bonding machine will be adjusted or repaired. In the sampling inspection, during the formal wire bonding operation, after a fixed interval of operating time or number of operations, a certain proportion of lead frames 1 are selected repeat the measurement and determination operations in the initial inspection.
In a fourth step of glue dispensing, glue is dispensed on the light-emitting chip 21 to form the inner encapsulation layer 230 that encapsulates the light-emitting chip 21.
Specifically, in this step, a high-precision glue dispensing apparatus is used to dispense in a syringe air pressure extrusion manner, a light-transmitting silicone glue with a colored pigment (such as a red pigment) to the region of the light-emitting chip 21, to completely encapsulate the light-emitting chip 21 for protection. The light-transmitting silicone glue can reduce the stress on the light-emitting chip 21 and the bonded wire on the one hand, and on the other hand, enable the heat of the light-emitting chip 21 to be dispersed to improve the conversion efficiency of the light-emitting chip 21, in addition to facilitating visual inspection of the glue amount and the encapsulating position in the glue dispensing.
In a fifth step of high-temperature baking and curing, a programmable constant-temperature curing oven is used to cure the translucent silicone to achieve good shape and stress buffering effects.
In a sixth step of stacking, as shown in
In this step, specifically, a high-precision automatic chip arrangement machine is used to accurately align the center of the light-emitting chip 21 with the center of the light-sensing chip 22 vertically, to allow the light-emitting chip 21 and the light-sensing chip 22 to form a precise through-beam configuration.
In a seventh step of white glue encapsulating, each pair of frame units 10 disposed opposite to each other is encapsulated with a white epoxy resin to form the first outer encapsulation layer.
In this step, a high-precision encapsulating and molding machine is used to squeeze and fill the white epoxy resin glue, and the internal structure is shaped through high-temperature curing and molding. The white epoxy resin has light-transmitting, pressure resisting and insulating properties, and has silicon oxide (SiO2) and/or titanium dioxide (TiO2) appropriately added therein, to further improve the insulation. The silicon dioxide and/or titanium dioxide account for about 15% to 30% of the total weight, which can ensure that the light-transmitting white epoxy resin glue has an appropriate light transmittance and has a thermal expansion coefficient close to that of the black epoxy resin used in a subsequent step.
In an eighth step of residual glue removing, a high-precision punching mold is used to remove unnecessary glue flow channels and flow limiting frames.
In a ninth step of black glue encapsulating, a light-shielding black epoxy resin is wrapped around the aforementioned light-transmitting white epoxy resin to form the second outer encapsulation layer.
In this step, a high-precision encapsulating molding machine is used to squeeze and fill the black epoxy resin glue, and the external structure is shaped through high-temperature curing molding. The black epoxy resin has light-shielding, pressure resisting and insulating properties and serves as the basic reflection for the appearance of the product.
In a tenth step of high-temperature baking and curing, a constant temperature curing oven is used to thoroughly cure the two kinds of epoxy resins encapsulating in the previous steps, to obtain an encapsulation structure 23 in which each pair of frame units 10 disposed opposite to each other, the light-emitting chip 21 and the light-sensing chip 22 are encapsulated integrally.
In an eleventh step of residual glue removing, a high-precision punching mold is used to remove unnecessary glue flowing channels and flow limiting frames.
In a twelfth step of tin plating operation, a surfaces of a part of each of the pins 11 protruding outside the encapsulation structure 23 is plated with a tin layer for protection.
In this step, stannous sulfate and high-purity tin metal blocks are used to allow the tin layer to be uniformly and stably bonded to the surfaces of the metal pins through electrolytic replacement reaction.
In a thirteenth step of dicing and pin bending, a high-precision bending and shaping mold is used to remove single optocouplers 2 from the lead frames, and then bend and shape the metal pins.
In a fourteenth step of performance test, the obtained single products are tested 100% and are sorted.
In the case where the light-emitting chips and the light-sensing chips with the same parameter range are used and other encapsulating materials are kept completely consistent, the lead frame according to the present disclosure and other conventional lead frames are used respectively, to obtain, through the manufacturing method according to the present disclosure and other conventional methods, the optocoupler product in a vertically opposed encapsulating form and other optocouplers in conventional different encapsulating forms for comparison. Specifically, 1000 pcs are taken to perform comparisons of the concentration ratio (for example, average CTR±10%), the proportion of falling into a target range (CTR: 200%-400%), and the average CTR of the product CTR. The comparison results are as follows:
Moreover, as shown in
In the description according to the present disclosure, it is to be noted that for orientation words, such as the terms “center”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, and “back” , “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside” for indicating orientations and positional relationships are based on the orientations or positional relationships shown in the drawings, is only used to facilitate the description according to the present disclosure and simplify the description, rather than indicating or implying that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation.
In addition, the terms “first” and “second” if used are for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the quantity of technical features. Therefore, features defined as “first” and “second” may explicitly or implicitly include one or more of these features. In the description according to the present disclosure, “several” means two or more, unless otherwise clearly and specifically stated.
It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept according to the present disclosure, and these modifications and improvements all fall into the protection scope according to the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202211434404.2 | Nov 2022 | CN | national |
