Micro-miniature high-stability quartz resonator and preparation method thereof

Abstract

The invention relates to the technical field of resonators, and discloses a microminiature high-stability quartz resonator and a preparation method thereof.The microminiature high-stability quartz resonator comprises a base, a metal cover plate and a quartz vibrator, at least two leading-out ends are arranged on one face of the base, a containing groove is formed in the other face of the base, and at least two leading-out platforms are arranged at the bottom of the containing groove; each leading-out platform is connected with one leading-out end; the quartz vibrator is located in the containing groove and comprises a quartz wafer and a metal electrode arranged on the quartz wafer, the metal electrode is provided with two connecting ends extending to the edge of the quartz wafer, each connecting end is bonded to one leading-out platform through a conductive adhesive, the length of the quartz wafer is 1.9-2.1 mm, and the width of the quartz wafer is 1.2-1.4 mm; and the metal cover plate hermetically covers one surface of the base provided with the accommodating groove. The small size is ensured, the frequency jump point in the working temperature range is reduced, and the frequency and temperature stability of an application circuit is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of resonators, and in particular to a miniature high-stability quartz resonator and a preparation method thereof. Background Art

[0002] Quartz resonators are widely used in electronic circuits as frequency sources of electronic devices based on their piezoelectric effect. When used in circuits with higher requirements for frequency temperature stability, such as temperature compensation circuits, constant temperature oscillation circuits, etc., higher requirements are also placed on the frequency jump characteristics of quartz resonators as core frequency selection components during temperature changes. Under ideal conditions, the frequency-temperature relationship of AT-cut quartz resonators is a cubic curve. In practice, the measured frequency-temperature characteristic curve may have jumps, no inflection points, or even irregular curves. As the size of the quartz resonator decreases, the frequency jump will also deteriorate due to the influence of various coupled vibrations, and the difficulty of achieving the frequency jump index will increase greatly. For example, the length, width, and thickness of the existing miniature quartz resonator are 5mm×3.2mm×1mm. If the size of the quartz resonator needs to be further reduced, its performance will be difficult to meet the working requirements. Taking the temperature compensation circuit as an example, the sudden jump of the resonator attached to the smooth curve cannot be compensated. When the frequency jump point of the quartz resonator can only reach ±0.8ppm in the entire temperature range, even if the compensation curve perfectly adapts to the quartz resonator and the compensation effect is optimal, the frequency fluctuation of the temperature compensation circuit can still only reach ±0.8ppm. Summary of the invention

[0003] Based on the above, the purpose of the present invention is to provide a miniature high-stability quartz resonator and a preparation method thereof, which can reduce its frequency jump point within the operating temperature range while ensuring a small size, which is beneficial to improving the frequency-temperature stability of the application circuit.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A miniature high-stability quartz resonator comprises a base, a metal cover plate and a quartz oscillator;

[0006] One side of the base is provided with at least two lead-out terminals, and the other side is formed with a receiving groove, the bottom of the receiving groove is provided with at least two lead-out platforms, and each lead-out platform is connected to one of the lead-out terminals;

[0007] The quartz oscillator is located in the receiving groove, and the quartz oscillator includes a quartz wafer and a metal electrode arranged on the quartz wafer, the metal electrode has two connection ends extending to the edge of the quartz wafer, each of the connection ends is bonded to one of the lead-out platforms by a conductive adhesive, and the length of the quartz wafer is 1.9 mm-2.1 mm, and the width is 1.2 mm-1.4 mm;

[0008] The metal cover plate sealing cover is arranged on one side of the base where the receiving groove is arranged.

[0009] As a preferred solution for a miniature high-stability quartz resonator, the metal electrode includes a main body and two connecting ends extending outward from the edge of the main body, the quartz wafer and the main body are both rectangular, and the main body is concentrically arranged with the quartz wafer.

[0010] As a preferred solution for a miniature high-stability quartz resonator, the connecting end extends from the main body to the wide side edge of the quartz wafer.

[0011] As a preferred solution for a miniature high-stability quartz resonator, the length of the main body is 0.7 mm-1.1 mm, and the width is 0.6 mm-1 mm.

[0012] As a preferred solution for a miniature high-stability quartz resonator, the conductive adhesive is a silicon-based conductive adhesive.

[0013] As a preferred solution for a miniature high-stability quartz resonator, a chromium layer is plated between the quartz wafer and the metal electrode.

[0014] A method for preparing a miniature high-stability quartz resonator, used to prepare the miniature high-stability quartz resonator as described in any of the above technical solutions, the preparation method comprising:

[0015] Prepare a quartz wafer blank, a base and a metal cover plate, wherein one side of the base is provided with at least two lead-out terminals, and the other side is formed with a receiving groove, and the bottom of the receiving groove is provided with at least two lead-out platforms, and each lead-out platform is connected to one of the lead-out terminals;

[0016] The quartz wafer blank is AT cut according to a preset wafer cutting angle, and then machined and finished to a rectangular quartz wafer of a first preset size, wherein the first preset size includes a first preset length and a first preset width, wherein the first preset length is 1.9 mm-2.1 mm, and the first preset width is 1.2 mm-1.4 mm;

[0017] Plating a metal electrode of a second preset size at a preset position of the quartz wafer, and extending part of the metal electrode to the edge of the quartz wafer to form two connection ends, thereby obtaining a quartz oscillator;

[0018] After applying a certain amount of conductive glue on the two connecting ends, the quartz resonator is placed in the base so that the two connecting ends are bonded and combined with the two lead-out platforms respectively;

[0019] The metal cover plate is covered on one side of the base having the accommodating groove and fixed by welding to obtain a miniature high-stability quartz resonator of a second preset size. The second preset size includes a second preset length, a second preset width and a preset height. The second preset length is 3.1mm-3.3mm, the second preset width is 2.4mm-2.6mm, and the preset height is 0.62mm-0.78mm.

[0020] As a preferred solution of a method for preparing a miniature high-stability quartz resonator, the preset wafer cutting angle is 35°7'-35°17'.

[0021] As a preferred solution for the preparation method of a miniature high-stability quartz resonator, when plating the metal electrode, a rectangular main body portion concentric with the quartz wafer is plated on the quartz wafer according to a third preset size, and the two connecting ends are plated extending from the main body portion to the wide edge of the quartz wafer; the third preset size includes a third preset length and a third preset width, the second preset length is 0.7mm-1.1mm, and the third preset width is 0.6mm-1mm.

[0022] As a preferred solution of a method for preparing a miniature high-stability quartz resonator, before plating the metal electrode, a chromium layer is first plated at the preset position of the quartz wafer, and the metal electrode is plated on the chromium layer.

[0023] The beneficial effects of the present invention are:

[0024] The present invention provides a miniature high-stable quartz resonator. A quartz resonator made of a quartz wafer of a specific size and a metal electrode is encapsulated in a base and a metal cover plate, so that the miniature high-stable quartz resonator has a lower frequency jump point during temperature changes; and a connecting end is bonded to a lead-out platform by a conductive adhesive to achieve electrical connection between the quartz resonator and the lead-out end, and the connection stability is better.

[0025] The present invention also provides a method for preparing a miniature high-stable quartz resonator. The prepared miniature high-stable quartz resonator has a lower frequency jump point during temperature changes, which can meet the requirement of the application circuit for the frequency fluctuation to be as small as possible during temperature changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the contents of the embodiments of the present invention and these drawings without paying any creative work.

[0027] Figure 1 is a side partial cross-sectional view of a miniature high-stability quartz resonator provided by an embodiment of the present invention;

[0028] Figure 2 is a top view of a partial cross-sectional view of a miniature high-stability quartz resonator provided by an embodiment of the present invention;

[0029] Figure 3 It is a bottom view of a miniature high-stability quartz resonator provided by an embodiment of the present invention;

[0030] Figure 4 It is a flow chart of a method for preparing a miniature high-stability quartz resonator provided by an embodiment of the present invention.

[0031] In the figure:

[0032] 1. Base; 11. Lead-out terminal; 12. Lead-out platform; 2. Metal cover; 3. Quartz resonator; 31. Quartz wafer; 32. Metal electrode; 321. Main body; 322. Connection terminal; 4. Conductive adhesive. DETAILED DESCRIPTION

[0033] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0034] In the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, "plurality" means two or more.

[0035] The term "at least one" in this application means one or more, and the term "multiple" in this application means two or more, for example, multiple second messages means two or more second messages. The terms "system" and "network" are often used interchangeably herein.

[0036] It should be understood that the terms used in the description of the various examples herein are only for describing specific examples and are not intended to be limiting. As used in the description of the various examples and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0037] It should also be understood that the term "and / or" used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term "and / or" is a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this application generally indicates that the associated objects before and after are in an "or" relationship.

[0038] It should also be understood that in the various embodiments of the present application, the size of the serial number of each process does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0039] It should be understood that determining B based on A does not mean determining B only based on A. B can also be determined based on A and / or other information.

[0040] It should also be understood that the term “comprise” (also known as “includes,” “including,” “comprises” and / or “comprising”) when used in this specification specifies the presence of stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0041] It should also be understood that the term "if" may be interpreted to mean "when" or "upon" or "in response to determining" or "in response to detecting." Similarly, the phrase "if it is determined that ..." or "if [a stated condition or event] is detected" may be interpreted to mean "upon determining that ..." or "in response to determining that ..." or "upon detecting [a stated condition or event]" or "in response to detecting [a stated condition or event]," depending on the context.

[0042] It should be understood that the references to "one embodiment", "an embodiment", or "a possible implementation" throughout the specification mean that specific features, structures, or characteristics related to the embodiment or implementation are included in at least one embodiment of the present application. Therefore, the references to "in one embodiment" or "in an embodiment", or "a possible implementation" appearing throughout the specification do not necessarily refer to the same embodiment. In addition, these specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0043] like Figures 1 to 3As shown, the present embodiment provides a miniature high-stability quartz resonator, which includes a base 1, a metal cover plate 2 and a quartz resonator 3. One side of the base 1 is provided with at least two lead-out terminals 11, preferably gold-plated lead-out terminals 11, and the other side is formed with a receiving groove, and the bottom of the receiving groove is provided with at least two lead-out platforms 12, preferably gold-plated lead-out platforms 12, each lead-out platform 12 is connected to a lead-out terminal 11; the quartz resonator 3 is located in the receiving groove, and the quartz resonator 3 includes a quartz wafer 31 and a metal electrode 32 arranged on the quartz wafer 31, the metal electrode 32 has two connecting terminals 322 extending to the edge of the quartz wafer 31, each connecting terminal 322 is bonded to a lead-out platform 12 by a conductive adhesive 4, and the length of the quartz wafer 31 is 1.9mm-2.1mm, and the width is 1.2mm-1.4mm; the metal cover plate 2 sealing cover is arranged on one side of the base 1 where the receiving groove is arranged. By encapsulating a quartz resonator 3 made of a quartz wafer 31 of a specific size and a metal electrode 32 in a base 1 and a metal cover 2, the miniature high-stability quartz resonator has a lower frequency jump point during temperature changes; and the connecting end 322 is bonded to the lead-out platform 12 through a conductive adhesive 4 to achieve electrical connection between the quartz resonator 3 and the lead-out end 11, and the connection stability is better.

[0044] Among them, under the above structure, the length of the miniature high-stability quartz resonator formed by the package is 3.1mm-3.3mm, the width is 2.4mm-2.6mm, and the height is 0.62mm-0.78mm, with a smaller external size. By setting a quartz resonator 3 of a specific size, it can ensure that the quartz resonator has a lower frequency jump point in a tiny size, thereby achieving high stability of the tiny quartz resonator.

[0045] Preferably, a sealing ring is provided between the metal cover plate 2 and the packaging surface of the base 1, the size of the metal cover plate 2 and the sealing ring are adapted, and the metal cover plate 2 and the base 1 are integrated by parallel resistance welding to reduce the leakage rate and improve the performance of the micro-sized high-stability quartz resonator. Among them, the outer surface of the metal cover plate 2 can be used as a marking surface.

[0046] Exemplarily, the base 1 and the metal cover plate 2 are packaged in the form of SMD3225. The base 1 includes a multi-layer stacked ceramic substrate, for example, the base 1 includes two layers of ceramic substrates stacked in sequence and a lead-out platform 12, and at least two lead-out terminals 11 are arranged on the first layer of ceramic substrate, which are arranged specifically according to actual needs, and each lead-out terminal 11 penetrates the second layer of ceramic substrate along the thickness direction of the second layer of ceramic substrate and is connected to a lead-out platform 12, so as to realize the electrical connection between the lead-out platform 12 and the lead-out terminal 11. Four lead-out terminals 11 may also be arranged on the first layer of ceramic substrate, wherein two lead-out terminals 11 are connected to two lead-out platforms 12, and the other two lead-out terminals 11 are connected to the quartz wafer 31.

[0047] Specifically, the metal electrode 32 includes a main body 321 and two connection ends 322 extending outward from the edge of the main body 321. The quartz wafer 31 and the main body 321 are both rectangular, and the main body 321 is concentrically arranged with the quartz wafer 31. That is, the spacing between the two wide sides of the main body 321 and the two wide sides of the quartz wafer 31 is equal, and the spacing between the two narrow sides of the main body 321 and the two narrow sides of the quartz wafer 31 is equal. Among them, the metal electrode 32 can be selected from gold, silver or aluminum as an electrode material, which has good conductivity and stability. The concentric arrangement of the main body 321 and the quartz wafer 31 can effectively reduce coupling resonance, thereby reducing frequency jump points.

[0048] Preferably, the connection end 322 extends from the main body 321 to the edge of the wide side of the quartz wafer 31. The conductive glue 4 points are set at the two end points of the wide side of the quartz wafer 31, and the connection end 322 is led to the edge of the wide side of the quartz wafer 31 to achieve connection with the conductive glue 4 at the two end points. First to the edge and then to the end point can improve the process consistency and avoid the possibility that the inclined electrode cannot be led to the end point during mass production.

[0049] Preferably, a chromium layer is plated between the quartz wafer 31 and the metal electrode 32 to enhance the bonding force between the metal electrode 32 and the quartz wafer 31 .

[0050] In this embodiment, the length of the main body 321 is 0.7mm-1.1mm, and the width is 0.6mm-1mm. The length, width, and height of the packaged micro-miniature high-stability quartz resonator are 3.1mm-3.3mm, 2.4mm-2.6mm, and 0.62mm-0.78mm, respectively.

[0051] By using a quartz crystal 31 and a metal electrode 32 of a specific size, the frequency jump point of a miniature high-stability quartz resonator during temperature changes can be effectively reduced, thereby improving the frequency temperature stability of the application circuit.

[0052] More specifically, the conductive adhesive 4 is a silicon-based conductive adhesive with low volatility, low stress, high bonding strength and excellent conductivity. When the conductive adhesive 4 has better conductivity, the resonator equivalent resistance is smaller and the resonance is more stable within the operating temperature range.

[0053] The frequency jump point of the miniature high-stability quartz resonator provided in this embodiment can reach ±0.5ppm, which can effectively meet the requirements of application circuits (such as temperature compensation circuits, etc.) for the frequency fluctuation to be as small as possible during temperature changes.

[0054] like Figure 4 As shown, this embodiment also provides a method for preparing a micro-sized high-stability quartz resonator, which is used to prepare the above-mentioned micro-sized high-stability quartz resonator. The method for preparing a micro-sized high-stability quartz resonator includes:

[0055] S1: Prepare a quartz wafer 31 blank, a base 1 and a metal cover plate 2. One side of the base 1 is provided with at least two lead terminals 11, and the other side is formed with a receiving groove. The bottom of the receiving groove is provided with at least two lead platforms 12, and each lead platform 12 is connected to one lead terminal 11;

[0056] S2: cutting the quartz wafer 31 blank by AT according to the preset wafer cutting angle, and then machining and finishing it to a rectangular quartz wafer 31 of a first preset size, wherein the first preset size includes a first preset length and a first preset width, wherein the first preset length is 1.9 mm-2.1 mm, and the first preset width is 1.2 mm-1.4 mm;

[0057] Among them, the preset wafer cutting angle is 35°7'-35°17', for example, the preset wafer cutting angle is 35°7', 35°10', 35°12', 35°14', 35°17', etc.

[0058] S3: Plating a metal electrode 32 of a second preset size at a preset position of the quartz wafer 31 , and extending part of the metal electrode 32 to the edge of the quartz wafer 31 to form two connecting ends 322 , thereby obtaining a quartz oscillator 3 ;

[0059] Specifically, when the metal electrode 32 is plated, a rectangular main body part 321 concentric with the quartz wafer 31 is plated on the quartz wafer 31 according to the third preset size, and two connection ends 322 are plated extending from the main body part 321 to the wide edge of the quartz wafer 31; the third preset size includes a third preset length and a third preset width, the second preset length is 0.7mm-1.1mm, and the third preset width is 0.6mm-1mm. The concentric arrangement of the main body part 321 and the quartz wafer 31 can effectively reduce coupling resonance, thereby reducing frequency jump points.

[0060] It can be understood that the sum of the thickness of the quartz crystal 31 and the metal electrode 32 is the thickness of the quartz oscillator 3 . The thickness of the quartz oscillator 3 is inversely proportional to the resonance frequency of the quartz oscillator 3 . The specific thickness is set according to the required frequency.

[0061] In order to improve the bonding force between the metal electrode 32 and the quartz wafer 31 , before plating the metal electrode 32 , a chromium layer is firstly plated at a preset position of the quartz wafer 31 , and then the metal electrode 32 is plated on the chromium layer.

[0062] S4: After applying a certain amount of conductive glue 4 on the two connection ends 322, the quartz resonator 3 is placed in the base 1, so that the two connection ends 322 are bonded to the two lead-out platforms 12 respectively;

[0063] The conductive glue 4 is a silicon-based conductive glue. Before dispensing, the conductive glue 4 is first fully stirred to degas and then dispensed on the connection end 322 to form a conductive glue dot, and the amount of dispensing is controlled. The amount of dispensing is set according to actual needs and is not limited here. When the conductive glue 4 has better conductivity, the resonator equivalent resistance is smaller, and the resonance is more stable within the operating temperature range.

[0064] S5: Cover the metal cover plate 2 on the side of the base 1 having the accommodating groove and weld it to obtain a miniature high-stability quartz resonator of a second preset size. The second preset size includes a second preset length, a second preset width and a preset height. The second preset length is 3.1mm-3.3mm, the second preset width is 2.4mm-2.6mm, and the preset height is 0.62mm-0.78mm.

[0065] The metal cover plate 2 and the base 1 are fixed by parallel sealing welding.

[0066] The miniature high-stable quartz resonator prepared by the above-mentioned preparation method of the miniature high-stable quartz resonator has a lower frequency jump point during temperature changes, which can meet the requirements of the application circuit for the frequency fluctuation to be as small as possible during temperature changes.

[0067] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A miniature high-stability quartz resonator, characterized in that: Including a base, a metal cover and a quartz oscillator; One side of the base is provided with at least two lead-out terminals, and the other side is formed with a receiving groove, the bottom of the receiving groove is provided with at least two lead-out platforms, and each lead-out platform is connected to one of the lead-out terminals; The quartz oscillator is located in the receiving groove, and the quartz oscillator includes a quartz wafer and a metal electrode arranged on the quartz wafer, the metal electrode has two connection ends extending to the edge of the quartz wafer, each of the connection ends is bonded to one of the lead-out platforms by a conductive adhesive, and the length of the quartz wafer is 1.9 mm-2.1 mm, and the width is 1.2 mm-1.4 mm; The metal cover plate sealing cover is arranged on one side of the base where the receiving groove is arranged.

2. The miniature high-stability quartz resonator according to claim 1 is characterized in that: The metal electrode comprises a main body and two connecting ends extending outward from the edge of the main body. The quartz wafer and the main body are both rectangular, and the main body is concentrically arranged with the quartz wafer.

3. The miniature high-stability quartz resonator according to claim 2 is characterized in that: The connection end extends from the main body portion to a broadside edge of the quartz wafer.

4. The miniature high-stability quartz resonator according to claim 2 is characterized in that: The main body has a length of 0.7 mm to 1.1 mm and a width of 0.6 mm to 1 mm.

5. The miniature high-stability quartz resonator according to claim 1 is characterized in that: The conductive adhesive is a silicon-based conductive adhesive.

6. The miniature high-stability quartz resonator according to claim 1 is characterized in that: A chromium layer is plated between the quartz wafer and the metal electrode.

7. A method for preparing a miniature high-stability quartz resonator, for preparing the miniature high-stability quartz resonator as claimed in any one of claims 1 to 6, characterized in that: The preparation method comprises: Prepare a quartz wafer blank, a base and a metal cover plate, wherein one side of the base is provided with at least two lead-out terminals, and the other side is formed with a receiving groove, and the bottom of the receiving groove is provided with at least two lead-out platforms, and each lead-out platform is connected to one of the lead-out terminals; The quartz wafer blank is AT cut according to a preset wafer cutting angle, and then machined and finished to a rectangular quartz wafer of a first preset size, wherein the first preset size includes a first preset length and a first preset width, wherein the first preset length is 1.9 mm-2.1 mm, and the first preset width is 1.2 mm-1.4 mm; Plating a metal electrode of a second preset size at a preset position of the quartz wafer, and extending part of the metal electrode to the edge of the quartz wafer to form two connection ends, thereby obtaining a quartz oscillator; After applying a certain amount of conductive glue on the two connecting ends, the quartz resonator is placed in the base so that the two connecting ends are bonded and combined with the two lead-out platforms respectively; The metal cover plate is covered on one side of the base having the accommodating groove and fixed by welding to obtain a miniature high-stability quartz resonator of a second preset size. The second preset size includes a second preset length, a second preset width and a preset height. The second preset length is 3.1mm-3.3mm, the second preset width is 2.4mm-2.6mm, and the preset height is 0.62mm-0.78mm.

8. The method for preparing a miniature high-stability quartz resonator according to claim 7, characterized in that: The preset wafer cutting angle is 35°7'-35°17'.

9. The method for preparing a miniature high-stability quartz resonator according to claim 7, characterized in that: When plating the metal electrode, a rectangular main body portion concentric with the quartz wafer is plated on the quartz wafer according to a third preset size, and the two connecting ends are plated extending from the main body portion to the wide edge of the quartz wafer; the third preset size includes a third preset length and a third preset width, the second preset length is 0.7mm-1.1mm, and the third preset width is 0.6mm-1mm.

10. The method for preparing a miniature high-stability quartz resonator according to claim 7, characterized in that: Before plating the metal electrode, a chromium layer is firstly plated at the preset position of the quartz wafer, and the metal electrode is plated on the chromium layer.

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