An absolute pressure sensor and method of fabrication

Abstract

The application relates to the technical field of absolute pressure sensors, and discloses an absolute pressure sensor and a manufacturing method, wherein the absolute pressure sensor comprises a silicon cup, a base, a circuit board and a shell; the top surface of the silicon cup is etched with a Wheatstone bridge and a modulation amplification circuit; the bottom of the silicon cup is connected with the base; the bottom surface of the base is connected with the shell through a transition layer; the bottom surface of the shell is provided with a medium channel; in use, the Wheatstone bridge and the modulation amplification circuit are etched on the silicon cup, and only signal transmission contacts are arranged on the circuit board, so that the area of the circuit board is reduced, the volume of the absolute pressure sensor is reduced, and the absolute pressure sensor can be applied to more occasions; secondly, during assembly, the pin does not need to be welded with the circuit board, the assembly process is reduced, and the assembly speed is improved; finally, when the shell is sealed, a stainless steel ball is placed in the air permeation channel and the upper opening of the air permeation channel is extruded, the process is simple, the inside of the shell and the top surface of the silicon cup are isolated from the atmosphere after sealing, and absolute pressure measurement is realized.

Description

Technical Field

[0001] This invention relates to the field of absolute pressure sensor technology, specifically to an absolute pressure sensor and its manufacturing method. Background Technology

[0002] An absolute pressure sensor is a physical sensor used to measure absolute pressure. It can directly convert the absolute pressure of a gas or liquid into an equivalent electrical signal output. It is widely used in engine control and safety monitoring in the automotive field, flight altitude measurement in the aerospace field, process control and hydraulic systems in the industrial automation field, and diagnosis and monitoring in the medical field.

[0003] The existing absolute pressure sensor structure mainly includes a silicon cup, a circuit board, a housing, and a signal transmission pin. The silicon cup and the circuit board are both located inside the housing. A Wheatstone bridge is installed on the silicon cup, and a modulation and amplification circuit is installed on the circuit board. The modulation and amplification circuit processes the output signal of the Wheatstone bridge. The signal transmission pin is soldered to the signal output contact on the circuit board. In actual use, external devices can be connected to the signal transmission pin to obtain the pressure detection value.

[0004] The existing pressure sensor structure is large in size because the modulation amplifier circuit and Wheatstone bridge are set separately, and the signal transmission pins need to be soldered to the circuit board, making the manufacturing process complicated. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides an absolute pressure sensor and a method for manufacturing it. The technical problem to be solved is that the existing absolute pressure sensors are large in size and complex to manufacture.

[0006] To solve the above technical problems, in a first aspect, the present invention provides the following technical solution: an absolute pressure sensor, comprising a silicon cup, a base, a circuit board, and a housing;

[0007] The top surface of the silicon cup is etched with a Wheatstone bridge and a modulation amplifier circuit. The modulation amplifier circuit is electrically connected to the Wheatstone bridge and processes the output signal of the Wheatstone bridge.

[0008] The bottom of the silicon cup is connected to the base; the silicon cup and the base are located inside the housing, and the bottom surface of the base is sealed to the housing through a transition layer;

[0009] The bottom surface of the housing has an inwardly formed medium channel, and the medium channel passes through the transition layer and the base in sequence and then communicates with the pressure detection chamber of the silicon cup;

[0010] The circuit board is fixed inside the housing and sleeved on the base. The modulation and amplification circuit is electrically connected to the signal transmission contacts on the circuit board via a binding wire. Each signal transmission contact is electrically connected to a pin assembly. The pin assembly includes a pin and a spring. The pin passes through the housing, and the two ends of the spring abut against the lower ends of the signal transmission contact and the pin, respectively.

[0011] The housing has a ventilation channel communicating with the inner cavity of the housing. A stainless steel ball is placed inside the ventilation channel, and a positioning block is placed above the stainless steel ball inside the ventilation channel.

[0012] In one embodiment of the first aspect, the housing includes an upper housing and a lower housing, the upper housing and the lower housing being sealed together;

[0013] The top surface of the lower housing is provided with a mounting cavity, the base is sealed to the bottom surface of the mounting cavity through the transition layer, the circuit board is located in the mounting cavity, and the bottom surface of the lower housing is provided with the medium channel.

[0014] The pin passes through the upper housing, and the ventilation channel is formed on the upper housing.

[0015] In one embodiment of the first aspect, the transition layer is formed by soldering the base and the housing.

[0016] In one embodiment of the first aspect, the connection area between the bottom surface of the mounting cavity and the base is provided with a gold-plated layer.

[0017] In one embodiment of the first aspect, the circuit board is provided with three signal transmission contacts.

[0018] In one embodiment of the first aspect, the aperture of the medium channel is less than 0.5 mm.

[0019] In one embodiment of the first aspect, the binding thread is gold thread.

[0020] In one embodiment of the first aspect, the pin is fitted with an insulating glass sleeve and is connected to the housing via the insulating glass sleeve.

[0021] In one embodiment of the first aspect, the base contains a glass material or the ratio of the coefficient of thermal expansion of the base to that of the glass is between 1.05 and 1.25.

[0022] Secondly, the present invention provides a method for manufacturing an absolute pressure sensor, comprising the following steps:

[0023] S1: First, the bottom surface of the silicon substrate and the top surface of the base plate are connected together by anodizing. The base plate is provided with multiple cavities that penetrate the base plate in the vertical direction. The base plate contains glass material or the ratio of the coefficient of thermal expansion of the base plate to the coefficient of thermal expansion of the glass is between 1.05 and 1.25. The bottom surface of the base plate is plated with a metal alloy layer including nickel, vanadium and gold.

[0024] Then, the top surface of the silicon substrate is etched with potassium hydroxide solution to thin the silicon substrate to a preset thickness. At the same time, a pressure detection cavity is formed along the bottom surface of the silicon substrate in the cavity, and the bottom surface of the pressure detection cavity is etched with a chamfer.

[0025] Next, pressure detection circuits are etched on the top surface of the silicon substrate in the corresponding area of ​​each cavity. The pressure detection circuit includes a Wheatstone bridge and a modulation amplifier circuit. The modulation amplifier circuit is electrically connected to the Wheatstone bridge and processes the output signal of the Wheatstone bridge.

[0026] Finally, the silicon substrate and the base plate are cut to make each cavity independent. At this time, the sidewalls of each independent cavity form a base, the silicon substrate on each base forms a silicon cup, and each cavity is a first medium transmission channel connected to the pressure detection cavity of the silicon cup.

[0027] S2: The base is connected to the lower housing by soldering, wherein the lower housing has a second medium channel corresponding to the first medium channel;

[0028] S3: Fix the circuit board to the lower housing, with the base passing through the circuit board;

[0029] S4: Connect the modulation amplifier circuit to the signal transmission contacts on the circuit board by binding wire;

[0030] S5: The lower housing and the upper housing are connected by laser welding. The upper housing is provided with a pin corresponding to each signal transmission contact. The pin is electrically connected to the corresponding signal transmission contact through a spring. A ventilation channel is provided on the upper housing.

[0031] S6: The stainless steel ball is placed in the ventilation channel by means of an interference fit;

[0032] S7: The upper opening of the ventilation channel is squeezed to form a positioning block that restricts the stainless steel ball.

[0033] The beneficial effects of this invention compared to the prior art are:

[0034] First, the Wheatstone bridge and modulation amplifier circuit are etched onto the silicon cup, so that there are only signal transmission contacts on the circuit board. This reduces the area of ​​the circuit board, thereby reducing the size of the absolute pressure sensor, which lowers the installation size limit and can be used in more applications.

[0035] Secondly, during assembly, there is no need to solder the pins to the circuit board, which reduces the assembly process and thus improves the assembly speed.

[0036] In addition, when sealing the shell, simply place the stainless steel ball in the venting channel and squeeze the top of the venting channel; the process is simple.

[0037] Finally, the silicon cup is connected to the lower housing through the base and transition layer. The expansion coefficient between the silicon cup and the lower housing transitions slowly, which can reduce the pressure of the pressure sensor at temperature and improve the detection accuracy of the pressure sensor. After sealing, the inside of the housing and the top surface of the silicon cup are isolated from the atmosphere, which plays the role of absolute pressure measurement. Attached Figure Description

[0038] Figure 1 This is a cross-sectional view of the present invention in Embodiment 1;

[0039] Figure 2 This is a three-dimensional schematic diagram of the present invention in Embodiment 1;

[0040] Figure 3 This is a schematic diagram of the stainless steel ball and positioning block in the ventilation channel of Example 1;

[0041] Figure 4 This is a schematic diagram showing the connection between the silicon cup, base, and lower housing in Embodiment 2;

[0042] Figure 5 This is a schematic diagram of the circuit board being fixed on the lower housing in Embodiment 2;

[0043] Figure 6 This is a schematic diagram of the welding of the upper and lower shells in Embodiment 2;

[0044] Figure 7 This is a schematic diagram illustrating the process of fabricating a silicon cup and base from a silicon substrate and a base plate. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0046] Example 1

[0047] like Figure 1-3 As shown, this embodiment provides an absolute pressure sensor, including a silicon cup 2, a base 3, a circuit board 5, and a housing 1;

[0048] The top surface of the silicon cup 2 is etched with a Wheatstone bridge and a modulation amplifier circuit. The modulation amplifier circuit is electrically connected to the Wheatstone bridge and processes the output signal of the Wheatstone. It should be noted that the Wheatstone bridge and the modulation amplifier circuit are existing technologies in the field of pressure detection and will not be described here. One inventive point of this application is that both the Wheatstone bridge and the modulation amplifier circuit are fabricated on the silicon cup 2.

[0049] exist Figure 1 In the middle, the bottom of the silicon cup 2 is connected to the base 3; the silicon cup 2 and the base 3 are located inside the housing 1, and the bottom surface of the base 3 is sealed to the housing 1 through the transition layer 4;

[0050] A medium channel 12 is provided on the bottom surface of the housing 1, and the medium channel 12 passes through the transition layer 4 and the base 3 in sequence and then communicates with the pressure detection chamber 20 of the silicon cup 2.

[0051] The circuit board 5 is fixed inside the housing 1 and fitted onto the base 3. The modulation amplifier circuit is electrically connected to the signal transmission contacts on the circuit board 5 via a binding wire 50. Each signal transmission contact is electrically connected to a pin assembly, which includes a pin 61 and a spring 60. The pin 61 passes through the housing 1, and the two ends of the spring 60 abut against the signal transmission contact and the lower end of the pin 61, respectively. The lower end of the pin 61 is stepped, with a step, and the lower end of the pin 61 is inserted into the spring 60, so that the spring 60 is in a compressed state.

[0052] The housing 1 has a ventilation channel 14 that communicates with the inner cavity 13 of the housing 1. A stainless steel ball 7 is provided in the ventilation channel 14, and a positioning block 8 is provided above the stainless steel ball 7 in the ventilation channel 14.

[0053] The absolute pressure sensor in this embodiment has the following advantages over existing pressure sensors:

[0054] First, the Wheatstone bridge and modulation amplifier circuit are etched onto the silicon cup 2. This way, there are only signal transmission contacts on the circuit board, reducing the area of ​​the circuit board and thus reducing the size of the absolute pressure sensor. This lowers the installation size limit and allows it to be used in more applications.

[0055] Secondly, during assembly, since the spring 60 electrically connects the pin 61 to the circuit board 5, it is not necessary to solder the pin 61 to the circuit board 5, which reduces the assembly process and thus improves the assembly speed.

[0056] In addition, when sealing the shell 1, simply place the stainless steel ball 7 in the venting channel 14 and squeeze the upper opening of the venting channel 14; the process is simple.

[0057] In this embodiment, the structure of the housing 1 is as follows:

[0058] The housing 1 includes an upper housing 11 and a lower housing 10, which are sealed together. The upper housing 11 and the lower housing 10 can be reliably sealed together by laser welding. In addition, since the upper housing and the lower housing are connected by laser welding, the gas pressure in the inner cavity 13 is affected by temperature changes during the welding process. At this time, the inner cavity 13 is connected to the outside through the venting channel 14. This can ensure that the pressure in the inner cavity is consistent with the outside pressure after the laser welding is completed, and also prevent pressure damage to the silicon cup 2.

[0059] The top surface of the lower housing 10 is provided with a mounting cavity, and the base 3 is sealed to the bottom surface of the mounting cavity through a transition layer 4. The circuit board 5 is located in the mounting cavity, and a medium channel 12 is formed inward on the bottom surface of the lower housing 10. It should be noted that, although Figure 1 The mounting cavity was not labeled, but its location can be determined from the position of circuit board 5.

[0060] The pin 61 passes through the upper housing 11, and the ventilation channel 14 is opened on the upper housing 11.

[0061] It should be noted that, in the automotive field, when it comes to engine control, the shifting process of an automatic transmission is achieved by controlling the shift solenoid valve. The absolute pressure sensor monitors the oil pressure changes in the transmission in real time, allowing the transmission controller to understand the working status of the transmission in a timely manner.

[0062] Because vehicles have different oil pressure requirements for the transmission under different driving conditions, such as acceleration, deceleration, climbing hills, and descending hills, the pressure sensor feeds back real-time oil pressure information to the transmission control unit. The control unit can comprehensively judge and adjust the transmission oil pressure based on information from other sensors such as vehicle speed, engine load, throttle position, and current driving needs, ultimately achieving closed-loop control of the transmitter. The pressure sensor operates in a high-temperature, high-pressure environment and is immersed in transmission fluid.

[0063] In order to enable the present invention to perform accurate pressure detection in high temperature, high pressure and immersion in transmission oil environment, in this embodiment, the transition layer 4 is formed by soldering the base 2 and the lower housing 10, and the silicon cup 2 and the base 3 are connected by anodic bonding. The base 3 contains glass material or the ratio of the coefficient of thermal expansion of the base to the coefficient of thermal expansion of the glass is between 1.05 and 1.25.

[0064] In the pressure sensor structure of this embodiment, the silicon cup 2 is connected to the lower housing 10 through the base 3 and the transition layer 4. The expansion coefficient between the silicon cup 2 and the lower housing 10 transitions slowly, which can reduce the pressure of the pressure sensor at temperature and improve the detection accuracy of the pressure sensor.

[0065] In addition, in this embodiment, the connection area between the bottom surface of the mounting cavity and the base 3 is provided with a gold plating layer, wherein the thickness of the gold plating layer can be between 3 micrometers and 6 micrometers; in actual use, the gold plating layer can effectively increase the bonding strength, improve the sensor's resistance to pressure and impact, and thus improve the sensor's overload capacity.

[0066] Specifically, in this embodiment, the circuit board 5 is provided with three signal transmission contacts. In some applications, the three signal transmission contacts can be used to connect to power, ground, and transmit pressure signals, respectively.

[0067] In one implementation, the remaining number of signal transmission contacts can be set according to actual needs. In this case, only the corresponding number of pin assemblies need to be set on the housing 1.

[0068] Specifically, in this embodiment, the aperture of the medium channel 12 is less than 0.5 mm. It should be noted that the medium channel 12 with such an aperture can act as a damping agent, so that the pressure of the liquid reaching the pressure detection surface of the silicon cup 2 is stable, and it is protected from water hammer impact on the pressure detection surface of the silicon cup 2 caused by rapid changes in the liquid medium pressure.

[0069] Specifically, in this embodiment, the binding wire 50 is a gold wire, which is compatible with the modulation amplifier circuit and the solder joints on the circuit board 5.

[0070] Specifically, in this embodiment, as Figure 1 As shown, the pin 61 is fitted with an insulating glass sleeve 62, and is connected to the housing 1 through the insulating glass sleeve 62. This makes the pin 61 securely connected, provides a strong seal, and prevents leakage.

[0071] Example 2

[0072] This embodiment provides a method for manufacturing an absolute pressure sensor, including the following steps:

[0073] S1: As Figure 7 As shown, the bottom surface of the silicon substrate 201 and the top surface of the base plate 202 are first connected together by anodic bonding. The base plate 202 is provided with a plurality of cavities 204 that penetrate the base plate in the vertical direction. The base plate 202 contains glass material or the ratio of the coefficient of thermal expansion of the base plate 202 to the coefficient of thermal expansion of glass is between 1.05 and 1.25. The bottom surface of the base plate 202 is plated with a metal alloy layer 203 including nickel, vanadium and gold.

[0074] Then, the top surface of the silicon substrate 201 is etched with potassium hydroxide solution to thin the silicon substrate 201 to a preset thickness. At the same time, a pressure detection cavity 205 is formed along the bottom surface of the silicon substrate 201 in the cavity 202. A chamfer 206 is etched between the bottom surface of the pressure detection cavity 205 and its own sidewall.

[0075] Next, pressure detection circuits are etched on the top surface of the silicon substrate 201 in the corresponding areas of each cavity 204. The pressure detection circuit includes a Wheatstone bridge and a modulation amplifier circuit. The modulation amplifier circuit is electrically connected to the Wheatstone bridge to process the output signal of the Wheatstone bridge.

[0076] Finally, the silicon substrate 201 and the base plate 202 are cut to make each cavity 204 independent. At this time, the sidewalls of each independent cavity 204 form the base 3, the silicon substrate on each base 3 forms the silicon cup 2, and each cavity 204 is the first medium transmission channel connected to the pressure detection cavity 20 of the silicon cup 2.

[0077] In step S1 of this embodiment, the metal alloy layer 203 can improve soldering performance and enhance pressure impact resistance. The chamfer 206 can reduce the stress at this point and protect the silicon cup 2.

[0078] S2: The base 3 is connected to the lower housing 10 by soldering, wherein the lower housing 10 is provided with a second medium channel corresponding to the first medium channel;

[0079] Specifically, the connection process of the silicon cup 2, the base 3, and the lower housing 10 is shown in the diagram below. Figure 4 As shown; for steps S1 and S2, the expansion coefficient between the silicon cup 2 and the lower housing 10 transitions slowly, which can reduce the pressure of the pressure sensor at temperature and improve the detection accuracy of the pressure sensor.

[0080] In one embodiment, in order to increase the bonding strength and improve the sensor's resistance to pressure and shock, a gold plating layer can be provided in the connection area between the lower housing 10 and the base 3;

[0081] S3: Fix the circuit board 5 onto the lower housing 10, with the base 3 passing through the circuit board 5; the schematic diagram of the circuit board 5 is shown below. Figure 5 As shown;

[0082] S4: The modulation amplifier circuit is electrically connected to the signal transmission contacts on the circuit board 5 via the binding wire 50; wherein the binding wire 50 can be a gold wire.

[0083] S5: The lower housing 10 and the upper housing 11 are connected by laser welding. The upper housing 11 is provided with a pin 61 corresponding to each signal transmission contact. The pin 61 is electrically connected to the corresponding signal transmission contact through a spring 60. The upper housing 11 is provided with a ventilation channel 14.

[0084] S6: The stainless steel ball 7 is placed in the ventilation channel 14 by means of interference fit;

[0085] S7: The upper opening of the ventilation channel 14 is squeezed to form a positioning block 8 that restricts the stainless steel ball 7.

[0086] In the manufacturing method described in this embodiment, the pin 61 and the signal transmission contact on the circuit board 5 do not need to be soldered, and the process is simple. When sealing the housing 1, it is only necessary to place the stainless steel ball 7 in the ventilation channel 14, which is easy to operate and greatly simplifies the manufacturing process of the absolute pressure sensor.

[0087] Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An absolute pressure sensor, characterized in that, Includes a silicon cup (2), a base (3), a circuit board (5), and a housing (1); The top surface of the silicon cup (2) is etched with a Wheatstone bridge and a modulation amplifier circuit. The modulation amplifier circuit is electrically connected to the Wheatstone bridge and processes the output signal of the Wheatstone bridge. The bottom of the silicon cup (2) is connected to the base (3); the silicon cup (2) and the base (3) are located inside the housing (1), and the bottom surface of the base (3) is sealed to the housing (1) through a transition layer (4); The bottom surface of the housing (1) is provided with a medium channel (12), and the medium channel (12) passes through the transition layer (4) and the base (3) in sequence and communicates with the pressure detection chamber (205) of the silicon cup (2); The circuit board (5) is fixed inside the housing (1) and sleeved on the base (3). The modulation amplifier circuit is electrically connected to the signal transmission contacts on the circuit board (5) through the binding wire (50). Each signal transmission contact is electrically connected to a pin assembly. The pin assembly includes a pin (61) and a spring (60). The pin (61) passes through the housing (1), and the two ends of the spring (60) abut against the lower ends of the signal transmission contact and the pin (61), respectively. The housing (1) has a ventilation channel (14) communicating with the inner cavity (13) of the housing (1). A stainless steel ball (7) is provided in the ventilation channel (14), and a positioning block (8) is provided above the stainless steel ball (7) in the ventilation channel (14). The housing (1) includes an upper housing (11) and a lower housing (10), and the upper housing (11) and the lower housing (10) are sealed together. The top surface of the lower housing (10) is provided with an installation cavity. The base (3) is sealed to the bottom surface of the installation cavity through the transition layer (4). The circuit board (5) is located in the installation cavity. The bottom surface of the lower housing (10) is provided with the medium channel (12). The pin (61) passes through the upper housing (11), and the ventilation channel (14) is formed on the upper housing (11); The transition layer (4) is formed by soldering the base (3) and the shell (1); The circuit board (5) is provided with three signal transmission contacts; The base (3) contains glass material or the ratio of the coefficient of expansion of the base (3) to the coefficient of expansion of glass is between 1.05 and 1.

25.

2. An absolute pressure sensor according to claim 1, characterized in that, The bottom surface of the mounting cavity and the connection area of ​​the base (3) are provided with a gold plating layer.

3. An absolute pressure sensor according to any one of claims 1-2, characterized in that, The aperture of the medium channel (12) is less than 0.5 mm.

4. An absolute pressure sensor according to any one of claims 1-2, characterized in that, The binding thread (50) is gold thread.

5. An absolute pressure sensor according to any one of claims 1-2, characterized in that, The pin (61) is fitted with an insulating glass sleeve (62) and is connected to the housing (1) through the insulating glass sleeve (62).

6. A method for manufacturing an absolute pressure sensor according to any one of claims 1-5, characterized in that, Includes the following steps: S1: First, the bottom surface of the silicon substrate (201) and the top surface of the base plate (202) are connected together by anodic bonding. The base plate (202) is provided with a plurality of cavities (204) that penetrate the base plate in the vertical direction. The base plate (202) contains glass material or the ratio of the coefficient of thermal expansion of the base plate (202) to the coefficient of thermal expansion of glass is between 1.05 and 1.

25. The bottom surface of the base plate (202) is plated with a metal alloy layer (203) including nickel, vanadium and gold. Then, the top surface of the silicon substrate (201) is etched with potassium hydroxide solution to thin the silicon substrate (201) to a preset thickness. At the same time, the bottom surface of the silicon substrate (201) is etched along the cavity (204) to form a pressure detection cavity (205). A chamfer (206) is etched between the bottom surface of the pressure detection cavity (205) and its own sidewall. Next, pressure detection circuits are etched on the top surface of the silicon substrate (201) in the corresponding area of ​​each cavity (204). The pressure detection circuit includes a Wheatstone bridge and a modulation amplifier circuit. The modulation amplifier circuit is electrically connected to the Wheatstone bridge and processes the output signal of the Wheatstone bridge. Finally, the silicon substrate (201) and the base plate (202) are cut to make each cavity (204) independent. At this time, the sidewalls of each independent cavity (204) form a base (3), and the silicon substrate on each base (3) forms a silicon cup (2). Each cavity (204) is a first medium transmission channel connected to the pressure detection cavity (205) of the silicon cup (2). S2: The base (3) is connected to the lower housing (10) by soldering, wherein the lower housing (10) is provided with a second medium channel corresponding to the first medium channel; S3: Fix the circuit board (5) on the lower housing (10) and the base (3) passes through the circuit board (5); S4: Connect the modulation amplifier circuit to the signal transmission contacts on the circuit board (5) by means of a binding wire (50); S5: The lower housing (10) and the upper housing (11) are connected by laser welding. The upper housing (11) is provided with a pin (61) corresponding to each signal transmission contact. The pin (61) is electrically connected to the corresponding signal transmission contact through a spring (60). The upper housing (11) is provided with a ventilation channel (14). S6: The stainless steel ball (7) is placed in the ventilation channel (14) by means of interference fit; S7: The upper opening of the ventilation channel (14) is squeezed to form a positioning block (8) that restricts the stainless steel ball (7).

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