Pre-welding device and pre-welding method

Abstract

The invention provides a pre-welding device and a pre-welding method. The pre-welding device is used for pre-welding a welding flux on a wafer, and the wafer is provided with a welding area used for being pre-welded with the welding flux. The pre-welding device comprises a bearing table, a silk screen, a positioning structure and a heating device. The bearing platform is provided with a bearing platform surface for bearing a wafer; the silk screen is provided with a first surface and a second surface which are deviated from each other, one or more hollowed-out limiting structures penetrating through the first surface and the second surface are arranged in a preset area, opposite to the welding area, of the silk screen, and the hollowed-out limiting structures are used for laying welding flux and limiting the welding flux; the positioning structure is at least partially supported between the silk screen and the bearing table top, so that a preset distance is formed between the wafer on the bearing table top and the silk screen; and the heating device is used for heating and pre-welding the welding flux, so that the welding flux is melted in the heating and pre-welding process and is welded to the welding area of the wafer to form a welding ring, and the welding ring is separated from the silk screen.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS devices, and particularly relates to a pre-welding device and a pre-welding method. Background Art

[0002] The electronic packaging technology has been continuously developed along with the development of integrated circuits. As the performance of integrated circuits has been continuously improved and the system has been gradually miniaturized, the requirements for electronic packaging processes have been continuously increased. The integrated circuit packaging industry has lagged far behind the development of the integrated circuit industry due to the complexity of the process and manufacturing requirements.

[0003] MEMS devices adopt production technologies similar to those of integrated circuits and can be mass-produced using IC production methods. After the devices on the wafer surface have completed the MEMS process, and after the wafer electrical test and confirmation that the circuit functions are operating normally, the MEMS devices need to be packaged into a separate packaging protection body. The packaging of MEMS devices is achieved by closely fitting the device wafer and the window wafer pre-welded with solder in a high-temperature vacuum environment to form a protection body with high vacuum isolation of water and oxygen.

[0004] The process of solder processing on the window wafer is an important process before achieving complete packaging. With the miniaturization design of devices, the device size is getting smaller and the number of devices on a single wafer is increasing. Based on the requirement of solder thickness, the solder formed by sputtering, electroplating, etc. is not easy to meet the solder thickness requirement and needs to be repeatedly operated multiple times to achieve, which affects the production efficiency of products. Summary of the Invention

[0005] According to the first aspect of the embodiments of the present invention, a pre-welding device is provided for pre-welding solder onto a wafer, where the wafer has a welding area for pre-welding with the solder, and it includes:

[0006] A carrier table having a carrier table surface for carrying the wafer;

[0007] A wire mesh having a first surface and a second surface facing away from each other, and one or more hollow limiting structures penetrating the first surface and the second surface are provided in a preset area of the wire mesh opposite to the welding area, and the hollow limiting structures are used for solder laying and limiting the solder;

[0008] A positioning structure is at least partially supported between the wire mesh and the carrier table surface, so that a preset distance is spaced between the wafer on the carrier table surface and the wire mesh;

[0009] A heating device is used for heating and pre-welding the solder, so that the solder melts and is welded to the welding area of the wafer to form a welding ring during the heating and pre-welding process, and the welding ring is separated from the wire mesh.

[0010] In some embodiments, the positioning structure is disposed on the screen, and at least a portion of the positioning structure protrudes out of the first surface.

[0011] In some embodiments, the positioning structure includes a positioning post.

[0012] In some embodiments, a portion of the carrying table is concave to form a carrying groove for carrying wafers, and the positioning structure is supported on an area of ​​the carrying table outside the carrying groove.

[0013] In some embodiments, the depth of the bearing groove is the same as the thickness of the wafer, and the height of the positioning pillar protruding from the first surface of the screen is equal to a preset distance.

[0014] In some embodiments, the solder has a first height in the thickness direction of the pre-welding device, the first height is H3, the thickness of the wire mesh is H1, and the preset distance is H2, wherein the first height H3, the thickness H1 of the wire mesh and the preset distance H2 satisfy the following conditions:

[0015] 0.9(H1+H2)≤H3≤1.1(H1+H2).

[0016] In some embodiments, the orthographic projection of the positioning structure in the thickness direction of the pre-welding device is located outside a preset area of ​​the wire mesh.

[0017] In some embodiments, the solder has a first height in the thickness direction of the pre-soldering device, the first height is H3, the welding area is an annular area, and the ring width of the annular area is greater than or equal to 0.5H3.

[0018] In some embodiments, the solder is in the form of balls, blocks or sheets.

[0019] In some embodiments, the solder is a metal solder, the welding area is provided with a metal welding layer, and the welding ring includes an intermetallic compound generated by the reaction between the metal welding layer and the metal solder during the heating pre-welding process.

[0020] In some embodiments, the thickness of the screen is less than or equal to the preset distance.

[0021] In some embodiments, the wafer is a window wafer.

[0022] According to a second aspect of an embodiment of the present invention, a pre-welding method is provided, using the pre-welding device described above, comprising:

[0023] Placing a wafer on a carrying table of a carrying table;

[0024] A wire mesh is disposed on a side of the wafer away from the carrier stage, and at least a part of the positioning structure is supported between the wire mesh and the carrier stage surface, so that there is a gap between the wire mesh and the carrier stage surface;

[0025] Solder is provided, and the solder is located in the hollow limiting structure and correspondingly located above the welding area;

[0026] The wafer and the solder are heated and pre-welded, so that the solder melts during the heating and pre-welding process and is welded to the welding area of the wafer to form a welding ring, and the welding ring is separated from the wire mesh.

[0027] Based on the above technical solution, the wire mesh of the above pre-welding device is supported between the wire mesh and the carrier stage surface by at least a part of the positioning structure, so that a preset distance is provided between the wafer on the carrier stage surface and the wire mesh. And under the action of the heating device, the solder melts during the heating and pre-welding process and can be laid on the welding area of the wafer, and the solder is separated from the wire mesh after melting, that is, the initial limiting of the solder is realized through the hollow limiting structure of the wire mesh, and the solder is melted and welded to the welding area under heating, and the solder is separated from the wire mesh when heated and melted, without sticking to the wire mesh, forming a welding ring separated from the wire mesh. The pre-welding device can complete the pre-welding process of the wafer and the solder in a short time, which is beneficial to improving the production efficiency of the product. Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of a pre-welding device provided by an embodiment of the present invention;

[0029] Figure 2 It is a schematic structural diagram of a wafer provided by an embodiment of the present invention;

[0030] Figure 3 It is a schematic structural diagram of a wire mesh provided by an embodiment of the present invention;

[0031] Figure 4 It is a partial schematic diagram of a combination of a pre-welding device, a wafer and solder provided by an embodiment of the present invention; wherein Figure 4 It shows a part corresponding to one hollow limiting structure;

[0032] Figure 5 is Figure 4 A cross-sectional view of the shown combination;

[0033] Figure 6 It is a schematic flow diagram of a pre-welding method provided by an embodiment of the present invention;

[0034] Figures 7 to 12 It is a preparation process diagram of a pre-welding method provided by an embodiment of the present invention;

[0035] Figure 13 A schematic top view of a welding ring provided in one embodiment of the present invention;

[0036] Figure 14 A schematic structural diagram of another screen provided by an embodiment of the present invention;

[0037] Figure 15 A schematic structural diagram of another screen provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0038] Here, exemplary embodiments will be described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0039] The present application provides a pre-welding device and a pre-welding method. The pre-welding device is used to pre-weld solder on a wafer. The solder is in the shape of a ball, a block or a sheet. The wafer has a welding area for pre-welding with the solder. The pre-welding device includes a carrier, a screen, a positioning structure and a heating device. The carrier has a carrier surface for carrying the wafer; the screen has a first surface and a second surface that are separated from each other, and a preset area on the screen opposite to the welding area is provided with one or more hollow limiting structures that penetrate the first surface and the second surface, and the hollow limiting structure is used for solder laying and limiting the solder; the positioning structure is at least partially supported between the screen and the carrier surface, so that there is a gap between the screen and the carrier surface; the heating device is used to heat the solder for pre-welding, so that the solder melts during the heating pre-welding process and is welded to the welding area of ​​the wafer to form a welding ring, and the welding ring is separated from the screen. The above-mentioned hollow limiting structure in the wire mesh can realize the initial limiting of the solder, and the solder melts under heating and is welded in the welding area, and the solder separates from the wire mesh when heated and melted, and does not stick to the wire mesh, forming a welding ring separated from the wire mesh. When the pre-welding device is used for the specific pre-welding operation, it can not only ensure the positioning function of the wire mesh, but also prevent the wire mesh from being adhered by the solder, which is convenient and quick to remove. It can be seen that the pre-welding device can complete the wafer and solder pre-welding process in a short time, which is beneficial to improving product production efficiency.

[0040] Combine the following Figures 1 to 15 The pre-welding device and the pre-welding method are described in detail.

[0041] Please refer to Figure 1 , and when necessary, combine Figures 2 to 5 as well as Figures 12 to 15As shown, the pre-welding device 100 can be used to pre-weld the solder 300 onto the wafer 200, and the wafer 200 has a welding area 201 for pre-welding with the solder 300 (see Figure 2 as shown).

[0042] The pre-welding device 100 includes a carrier table 10, a wire mesh 20, a positioning structure 30, and a heating device (not shown).

[0043] The carrier table 10 has a carrier table surface S3 for carrying the wafer 200.

[0044] The wire mesh 20 has a first surface S1 and a second surface S2 facing away from each other. One or more hollow limiting structures 210 penetrating through the first surface S1 and the second surface S2 are provided in a preset area 21 of the wire mesh 20 opposite to the welding area 201. The hollow limiting structures 210 are used for laying the solder 300 and limiting the solder 300.

[0045] The positioning structure 30 is at least partially supported between the wire mesh 20 and the carrier table surface S3, so that a preset distance is spaced between the wafer 200 located on the carrier table surface S3 and the wire mesh 20.

[0046] The heating device is used to heat and pre-weld the solder 300, so that the solder 300 melts and is welded to the welding area of the wafer 200 to form a welding ring 301 during the heating and pre-welding process, and the welding ring 301 is separated from the wire mesh 20. Specifically, when the heating device heats and pre-welds the solder 300, the solder melts and can be laid on the welding area of the wafer during the heating and pre-welding process, and the solder is separated from the wire mesh after melting, thereby forming the welding ring 301.

[0047] The heating and pre-welding of the solder 300 by the heating device mentioned here is carried out in a vacuum chamber. Specifically, the preset device 100 and the combined structure of the wafer 200 and the solder 300 arranged on the carrier table surface S3 are both placed in the vacuum chamber, and the solder 300 is melted by heating (such as baking) by the heating device.

[0048] When the pre-welding device 100 specifically performs the pre-welding operation, it can not only ensure the positioning function of the hollow limiting structure 210 in the wire mesh 20, but also the wire mesh 20 is not adhered by the solder 300 and is convenient to remove quickly. It can be seen that the pre-welding device 100 can complete the pre-welding process of the wafer 200 and the solder 300 in a short time, which is beneficial to improving the production efficiency of products.

[0049] It can be understood that the solder 300 is in a solid state under natural conditions.

[0050] In some embodiments, the solder 300 is spherical, block-shaped (including regular or irregular blocks), or flake-shaped.

[0051] For example, the solder 300 can be Figure 5 the spherical shape as shown. For another example, the solder can be Figure 15 the flake shape as shown.

[0052] The preset area 21 mentioned here can be an annular area, for example Figure 4 and Figure 14 as shown.

[0053] As Figure 3 shown, in some embodiments, a plurality of spaced-apart hollow limiting structures 210 can be provided in the preset area 21.

[0054] As Figure 14 shown, in some other embodiments, the preset area 21 can also be provided with a connected hollow limiting structure. In the Figure 14 shown wire mesh 20’, the area inside the preset area 21 can also be set as an area integrally connected to the hollow limiting structure, forming a larger hollow limiting structure. This hollow limiting structure can be used for solders in the form of flakes or similar annular solders, for example Figure 15 the solder 300’ as shown.

[0055] It can be understood that when the solder is the spherical or block-shaped solder 300, the wire mesh 20 as Figure 3 or similar Figure 3 shown can be used. When the solder is the Figure 15 flake-shaped solder 300’ as shown, the wire mesh 20’ as Figure 13 or similar Figure 14 shown can be used.

[0056] In some embodiments, the thickness of the wire mesh 20 is less than or equal to the preset distance, so that while the wire mesh can limit the solder 300, it is beneficial to ensure that the solder 300 can be separated from the wire mesh 20 after melting.

[0057] In some embodiments, the positioning structure 30 is provided on the wire mesh 20, and at least part of the positioning structure 30 protrudes outside the first surface S1.

[0058] Of course, in some other embodiments, the positioning structure can also be provided on the bearing surface S3 of the bearing platform 10, or be provided independently of the bearing platform and the wire mesh 20.

[0059] In some embodiments, the positioning structure 30 includes positioning pillars, such as Figure 1 the structure as shown.

[0060] In some embodiments, a part of the bearing tabletop S3 is recessed to form a bearing groove 101 for bearing the wafer 200, and the positioning structure 30 is supported on the area of the bearing tabletop S3 outside the bearing groove so as not to affect the wafer 200.

[0061] For example Figure 1 The shown bearing tabletop S3 includes a first part S31 that is recessed to form the bearing groove 101 and a second part S32 outside the bearing groove 101. Correspondingly, the positioning structure 30 is supported on the area of the bearing tabletop S3 outside the bearing groove 101, that is, the area included in the second part S32.

[0062] Of course, in some other embodiments, the bearing tabletop can also be a flat surface, which can include a bearing area for bearing the wafer and other areas outside the bearing area. Correspondingly, the support structure can be supported on the other areas outside the bearing area.

[0063] In some embodiments, the depth H4 of the bearing groove 101 is the same as the thickness of the wafer 200, and the height by which the positioning pillar protrudes from the first surface S1 of the wire mesh 20 is equal to the preset distance.

[0064] In some embodiments, the solder 300 has a first height in the thickness direction of the pre-soldering device 100, the first height is H3, the thickness of the wire mesh 20 is H1, and the preset distance is H2. Among them, the following conditions are satisfied among the first height H3, the thickness H1 of the wire mesh 20 and the preset distance H2:

[0065] 0.9(H1 + H2) ≤ H3 ≤ 1.1(H1 + H2).

[0066] In this way, when laying the solder, it will not cause multiple solders to fall into the same hollow limiting structure 210 due to too large H1 + H2, nor will it hinder the laying of the solder due to too small H1 + H2.

[0067] Preferably, H1 + H2 = H3.

[0068] In some embodiments, the orthographic projection of the positioning structure 30 in the thickness direction of the pre-soldering device 100 is located outside the preset area 21 of the wire mesh 20.

[0069] With such a setting, the positioning structure will not affect the soldering of the solder, and thus affect the continuity of the welding ring, thereby affecting the sealing performance of the welding ring in subsequent products.

[0070] In some embodiments, please combine Figure 4 and Figure 5As shown, the solder 300 has a first height H3 in the thickness direction of the pre-welding device 100. The welding area 201 is an annular area, and the width W of the annular area is greater than or equal to 0.5H3.

[0071] With such a setting, it is beneficial to ensure the spreading area of the solder 300 after melting, and it is more beneficial to ensure the separation of the solder 300 from the wire mesh 20.

[0072] It can be understood that in this application, the solder 300 spreads along the welding area after being heated and melted.

[0073] Please refer to Figure 2 and Figure 5 and Figure 12 and Figure 13 As shown, in some embodiments, the solder 300 is a metal solder, and the welding area 201 is provided with a metal welding layer 2011. The fact that the solder 300 spreads along the welding area after being heated and melted can actually be understood as spreading along the area where the metal welding layer 2011 is provided. Correspondingly, the welding ring 301 includes an intermetallic compound (IMC) generated by the reaction between the metal welding layer 2011 and the metal solder during the heating and pre-welding process.

[0074] The proportion of this intermetallic compound is relatively small and is mainly located in the part of the welding ring 301 close to the wafer 200. Most of the welding ring 301 is a solder structure formed by curing the solder 300.

[0075] The solder 300 can be indium-based solder, tin-based solder, etc. The welding layer can be a metal material such as gold, silver, or an alloy material including gold, silver, etc.

[0076] It should be noted that for the welding area 201 provided with a metal welding layer 2011, and the solder is Figure 15 As shown, for the sheet-shaped solder 300', the height of the sheet-shaped solder 300' in the thickness direction of the pre-welding device 100 can still be H3, which can correspondingly meet the conditions satisfied by the first height H3 of the solder 300. For details, please refer to the above relevant description. The difference is that for the wire mesh used for the sheet-shaped solder 300', the outer edge contour of the hollow limiting structure is smaller than the outer edge contour of the metal welding layer 2011 and larger than the inner edge contour of the metal welding layer 2001, so that the area covered by the sheet-shaped solder 300' before heating is smaller than the area of the metal welding layer 2011, and the welding ring formed after heating can be well separated from the wire mesh.

[0077] It should be noted that the welding area 201 may also include an adhesive layer disposed on the surface of the wafer and a barrier layer located between the welding layer and the adhesive layer. In some embodiments, the barrier layer is metal platinum, which can be used to prevent the reaction between the welding layer and the solder from extending to one side of the wafer and causing adverse effects on the wafer. The adhesive layer can be a metal material or non-metal material such as metal titanium or chromium that can adhere well to the wafer.

[0078] In some embodiments, the wafer 200 is a window wafer, but may also be other wafers, such as a substrate wafer for welding with a window wafer.

[0079] It is understandable that the window wafer mentioned here can be used to form a sealed accommodating cavity by welding with the base wafer through the solder 300, and the sealed accommodating cavity can be provided with a MEMS unit, a getter, etc. to form a MEMS device, such as a MEMS infrared detector. Accordingly, the window wafer can be a wafer for external light (such as infrared light) to pass through and irradiate the MEMS device. The base wafer can be a wafer for setting MEMS.

[0080] The present application further provides a pre-welding method, which can use the above-mentioned pre-welding device 100. The pre-welding method may include the following steps S101 to S107:

[0081] In step S101, a wafer is placed on a carrying table surface S3 of a carrying table;

[0082] In step S103, a screen is disposed on a side of the wafer facing away from the carrier, and at least a portion of the positioning structure is supported between the screen and the carrier surface S3, so that there is a gap between the screen and the carrier surface S3;

[0083] In step S105, solder is provided, wherein the solder is located in the hollow limiting structure and correspondingly located on the welding area;

[0084] In step S107, the wafer and the solder are heated for pre-welding, so that the solder is melted during the heating and pre-welding process and welded to the welding area of ​​the wafer to form a welding ring, and the welding ring is separated from the wire mesh.

[0085] In the above pre-welding method, at least part of the positioning structure is supported between the wire mesh and the carrier table surface, so that there is a preset distance between the wafer on the carrier table surface and the wire mesh. Under the action of the heating device, the solder melts during the heating pre-welding process and can be laid on the welding area of the wafer, and the solder is separated from the wire mesh after melting, that is, the initial limit of the solder is realized through the hollow limiting structure of the wire mesh. When heated, the solder melts and is welded to the welding area, and the solder is separated from the wire mesh when heated and melted, without sticking to the wire mesh, forming a welding ring separated from the wire mesh. This pre-welding device can complete the pre-welding process of the wafer and the solder in a short time, which is beneficial to improving the production efficiency of products.

[0086] Please refer to the following Figure 6 and, if necessary, in combination with Figures 7 to 12 shown below to illustrate the above pre-welding method.

[0087] Please combine Figure 7 and Figure 8 In step S101, place the wafer 200 on the carrier table surface S3 of the carrier table 10.

[0088] Please combine Figure 9 and Figure 10 In step S103, place the wire mesh 20 on the side of the wafer 200 away from the carrier table 10, and support at least part of the positioning structure 30 between the wire mesh 20 and the carrier table surface S3, so that there is a gap between the wire mesh 20 and the carrier table surface S3.

[0089] Please combine Figure 11 shown below. In step S105, set the solder 300. The solder 300 is located in the hollow limiting structure 210 and corresponds to being above the welding area 201.

[0090] Please combine Figure 12 and Figure 13 shown below. In step S107, perform heating pre-welding on the wafer 200 and the solder 300, so that the solder melts during the heating pre-welding process and is welded to the welding area 201 of the wafer 200 to form a welding ring 301, and the welding ring 301 is separated from the wire mesh 20.

[0091] In this application, when the structural embodiment and the method embodiment do not conflict, they can complement each other.

[0092] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of a preferred embodiment, and the modules or processes in the accompanying drawings are not necessarily essential for implementing the present invention. The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A pre-welding device for pre-welding solder on a wafer, wherein the wafer has a welding area for pre-welding with the solder, It is characterized in that include: A carrying platform, having a carrying platform surface for carrying a wafer; A wire mesh, wherein the wire mesh has a first surface and a second surface which are opposite to each other, and a preset area on the wire mesh opposite to the welding area is provided with one or more hollow limiting structures which penetrate the first surface and the second surface, and the hollow limiting structures are used for laying solder and limiting the solder; A positioning structure, at least partially supported between the screen and the carrying table, so that a wafer on the carrying table is spaced a preset distance from the screen; The heating device is used to heat and pre-weld the solder, so that the solder melts during the heating and pre-welding process and is welded to the welding area of ​​the wafer to form a welding ring, and the welding ring is separated from the wire mesh.

2. The pre-welding device according to claim 1, It is characterized in that The positioning structure is arranged on the screen, and at least a part of the positioning structure protrudes out of the first surface.

3. The pre-welding device according to claim 1, It is characterized in that The positioning structure includes a positioning pillar.

4. The pre-welding device according to claim 1, It is characterized in that A portion of the carrying table is concave to form a carrying groove for carrying wafers, and the positioning structure is supported on an area of ​​the carrying table outside the carrying groove.

5. The pre-welding device according to claim 4, It is characterized in that The depth of the bearing groove is the same as the thickness of the wafer, and the height of the positioning pillar protruding from the first surface of the screen is equal to the preset distance.

6. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The solder has a first height in the thickness direction of the pre-welding device, the first height is H3, the thickness of the wire mesh is H1, and the preset distance is H2, wherein the first height H3, the thickness H1 of the wire mesh and the preset distance H2 satisfy the following conditions: 0.9(H1+H2)≤H3≤1.1(H1+H2).

7. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The orthographic projection of the positioning structure in the thickness direction of the pre-welding device is located outside the preset area of ​​the wire mesh.

8. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The solder has a first height in the thickness direction of the pre-soldering device, the first height is H3, the welding area is an annular area, and the ring width of the annular area is greater than or equal to 0.5H3.

9. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The solder is in the shape of a ball, a block or a sheet.

10. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The solder is a metal solder, the welding area is provided with a metal welding layer, and the welding ring comprises an intermetallic compound generated by the reaction between the metal welding layer and the metal solder during the heating pre-welding process.

11. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The thickness of the screen is less than or equal to the preset distance.

12. The pre-welding device according to any one of claims 1 to 5, It is characterized in that The wafer is a window wafer.

13. A pre-welding method, using the pre-welding device as described in any one of claims 1 to 12, It is characterized in that include: Placing a wafer on a carrying table of a carrying table; The screen is arranged on a side of the wafer away from the carrier, and at least a part of the positioning structure is supported between the screen and the carrier surface, so that there is a gap between the screen and the carrier surface; Setting solder, wherein the solder is located in the hollow limiting structure and correspondingly located on the welding area; The wafer and the solder are heated for pre-welding, so that the solder is melted during the heating and pre-welding process and welded to the welding area of ​​the wafer to form a welding ring, and the welding ring is separated from the wire mesh.

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