End face processing method of optoelectronic chip

Abstract

The invention relates to an end face processing method of a photoelectron chip, which comprises the following steps: a plurality of grooves are manufactured on the surface of the photoelectron chip with salient points, the grooves are distributed in an axial symmetry manner along any central axis of the photoelectron chip, one groove is manufactured on the central axis of the photoelectron chip every 300-1000 microns, and the grooves are distributed in an axial symmetry manner along any central axis of the photoelectron chip; at least four grooves are formed in the preset clamping area, and at least four grooves are formed in the non-clamping area; covering the surface of the photoelectron chip, which is provided with the convex points, with a protection sheet with a convex structure on the surface, fixing by embedding the convex structure and the groove, filling an adhesive to form a composite structure, clamping by adopting a clamp, grinding and polishing the end surface of the photoelectron chip, and removing the protection sheet and the adhesive to obtain the photoelectron chip. And obtaining the processed photoelectron chip. According to the method, the salient points of the photoelectron chip can be protected, meanwhile, the stress of the single point position can be reduced by controlling the distribution of the grooves, and the photoelectron chip is prevented from being damaged.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic integration technology, and particularly to an end face processing method for optoelectronic chips. Background Art

[0002] An optoelectronic chip is an integrated chip that combines photonics and electronics technologies, and has characteristics such as ultra-high speed, low power consumption, high bandwidth, and anti-electromagnetic interference. It realizes ultra-high speed data transmission and signal processing through photon integration, and its energy consumption is significantly lower than that of a pure electronic solution. It is mainly applied in fields such as optical interconnection in data centers, 5G / 6G communication base stations, fiber optic sensor networks, medical imaging devices, and autonomous driving lidar, promoting energy efficiency and performance breakthroughs in the next generation of computing, communication, and sensing systems.

[0003] The surface of an optoelectronic chip usually contains a series of bumps for subsequent electrical packaging. However, the fabrication of bumps will seriously deteriorate the performance of the ports, making the grinding and polishing process of the end face of the optoelectronic chip a necessary process. However, when grinding and polishing the end face of the optoelectronic chip, it is necessary to clamp the surface of the optoelectronic chip. When the fixture is in direct contact with the surface of the optoelectronic chip, the bumps on it tend to be damaged, seriously affecting the subsequent packaging process. To solve this problem, traditional methods usually directly cover a protective sheet on the surface of the optoelectronic chip. However, in this way, the protective sheet and the chip are prone to relative displacement during the processing, and the reliability is not high. Summary of the Invention

[0004] Based on this, it is necessary to provide an end face processing method for an optoelectronic chip in view of the above problems, which can protect both the bumps and the optoelectronic chip itself from damage.

[0005] An end face processing method for an optoelectronic chip includes the following steps:

[0006] Making a plurality of grooves on the surface of the optoelectronic chip with bumps, wherein the grooves are axially symmetrically distributed along any central axis of the optoelectronic chip, and on the central axis of the optoelectronic chip, 1 groove is made every 300 μm - 1000 μm, at least 4 grooves are made in the preset clamping area, and at least 4 grooves are made in the non-clamping area;

[0007] Covering a protective sheet on the surface of the optoelectronic chip with bumps, wherein the surface of the protective sheet has a raised structure that can be matched with the grooves in the optoelectronic chip, and the height of the raised structure is greater than the sum of the depth of the groove and the height of the bump. The raised structure is used to embed into the groove to fix the optoelectronic chip and the protective sheet, and an adhesive is filled between the optoelectronic chip and the protective sheet to form a composite structure;

[0008] Clamp the composite structure with a fixture, and the clamping position of the fixture corresponds to the preset clamping area of the optoelectronic chip, and then grind and polish the end face of the optoelectronic chip;

[0009] After the grinding and polishing process, remove the protective sheet and the adhesive to obtain the processed optoelectronic chip.

[0010] In one embodiment, on the central axis of the optoelectronic chip, one groove is made every 600 μm - 800 μm;

[0011] And / or, make 4 - 6 grooves in the preset clamping area;

[0012] And / or, make 8 - 10 grooves in the non - clamping area.

[0013] In one embodiment, the vertical distance between the groove in the preset clamping area and the edge of the optoelectronic chip is greater than or equal to 400 μm;

[0014] And / or, the vertical distance between the groove in the non - clamping area and the edge of the optoelectronic chip is greater than or equal to 400 μm;

[0015] And / or, the vertical distance between the groove in the preset clamping area and the central axis is greater than or equal to 300 μm;

[0016] And / or, the vertical distance between the groove in the non - clamping area and the central axis is greater than or equal to 300 μm.

[0017] In one embodiment, within the preset clamping area, the distance between the grooves is greater than or equal to 400 μm;

[0018] And / or, within the non - clamping area, the distance between the grooves is greater than or equal to 400 μm;

[0019] And / or, the distance between the grooves in the preset clamping area and the grooves in the non - clamping area is greater than or equal to 400 μm.

[0020] In one embodiment, the optoelectronic chip has two non - clamping areas, and the grooves are made in each non - clamping area.

[0021] In one embodiment, the depth of the groove is 80 μm - 300 μm;

[0022] And / or, the maximum material size of the groove is greater than or equal to 100 μm.

[0023] In one embodiment, the sum of the depth of the groove and the height of the bump differs from the height of the protruding structure by 50 μm - 100 μm.

[0024] In one embodiment, the adhesive completely fills the gap between the optoelectronic chip and the protection sheet.

[0025] In one embodiment, the Young's modulus of the protection sheet is greater than or equal to 70 GPa;

[0026] and / or, the thickness of the protection sheet is greater than or equal to 1 mm;

[0027] and / or, the adhesive does not react with acidic substances and alkaline substances.

[0028] In one embodiment, the protection sheet is selected from a silicon oxide sheet, a silicon sheet, a silicon nitride sheet, or a glass sheet;

[0029] and / or, the adhesive is selected from one or more of paraffin, epoxy resin, ultraviolet glue, or photoresist.

[0030] In the present invention, the composite structure composed of the protection sheet, the adhesive, and the optoelectronic chip can avoid the direct contact between the bumps of the optoelectronic chip and the fixture or the protection sheet during the grinding and polishing process, fully protecting the bumps of the optoelectronic chip from being damaged. At the same time, by making grooves on the surface of the optoelectronic chip and controlling the distribution of the grooves in the present invention, after the protection sheet is embedded in the optoelectronic chip, not only will there be no relative displacement during the grinding and polishing process, but also the reliability is high, and the stress at a single point position can be reduced to prevent damage to the optoelectronic chip. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a schematic flow chart of the processing process of the end face processing method of the optoelectronic chip;

[0033] Figure 2 It is a top view of the optoelectronic chip;

[0034] Figure 3 It is a top view of the protection sheet.

[0035] In the figure, 1 is the optoelectronic chip; 11 are the bumps; 12 are the grooves; 2 is the protection sheet; 21 is the raised structure; 3 is the adhesive; 4 is the processed optoelectronic chip; 5 is the preset clamping area. Detailed Embodiments

[0036] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, these embodiments or examples are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention.

[0038] To prevent relative displacement between the protective sheet and the optoelectronic chip during the end face treatment, grooves can be formed on the surface of the optoelectronic chip, and a convex structure corresponding to each of the grooves can be provided on the protective sheet. Then, the convex structure on the protective sheet is embedded into the groove on the surface of the optoelectronic chip to mechanically engage the protective sheet with the optoelectronic chip, which can prevent displacement. However, in this way, the optoelectronic chip often gets damaged during the treatment process.

[0039] Through further research, it is found that the reason for the damage of the optoelectronic chip during the treatment process is the relatively high stress at a single point position. For this reason, as shown in Figure 1 、 Figure 2 and Figure 3 The end face treatment method of the optoelectronic chip provided by the present invention includes the following steps:

[0040] S1, making a plurality of grooves 12 on the surface of the optoelectronic chip 1 with bumps 11, wherein the grooves 12 are axially symmetrically distributed along any central axis of the optoelectronic chip 1, and on the central axis of the optoelectronic chip 1, 1 groove 12 is made every 300 μm - 1000 μm, at least 4 grooves 12 are made within the preset clamping area 5, and at least 4 grooves 12 are made in the non-clamping area;

[0041] S2, covering a protective sheet 2 on the surface of the optoelectronic chip 1 with bumps 11, wherein the surface of the protective sheet 2 has a convex structure 21 that can be matched with the groove 12 in the optoelectronic chip 1, and the height of the convex structure 21 is greater than the sum of the depth of the groove 12 and the height of the bump 11. The convex structure 21 is used to embed into the groove 12 to fix the optoelectronic chip 1 and the protective sheet 2, and an adhesive 3 is filled between the optoelectronic chip 1 and the protective sheet 2 to form a composite structure;

[0042] S3, clamping the composite structure with a fixture, and the clamping position of the fixture corresponds to the preset clamping area 5 of the optoelectronic chip 1, and then polishing the end face of the optoelectronic chip 1;

[0043] S4. After the grinding and polishing process is completed, the protective sheet 2 and the adhesive 3 are removed to obtain the processed optoelectronic chip 4.

[0044] Thus, when the groove 12 is fabricated on the surface of the optoelectronic chip 1 having the bump 11, by controlling the distribution of the groove 12, the stress at the single point position can be reduced to prevent damage to the optoelectronic chip 1.

[0045] It can be understood that the shape of the optoelectronic chip 1 is not limited, such as circular, square, rectangular, etc., and can be customized according to needs. As Figure 2 shown, when the optoelectronic chip 1 is rectangular, it has two central axes, the transverse and the longitudinal. The groove 12 can be axially symmetrically distributed along the transverse central axis of the optoelectronic chip 1 or axially symmetrically distributed along the longitudinal central axis of the optoelectronic chip 1.

[0046] Optionally, when fabricating the groove 12 on the central axis of the optoelectronic chip 1, one groove 12 is fabricated every 300 μm - 1000 μm. The distance between two adjacent grooves 12 can be the same or different. When different, it can be incremented successively, decremented successively, or changed irregularly, as long as it is controlled between 300 μm - 1000 μm. Further, it is preferably to fabricate one groove 12 every 600 μm - 800 μm.

[0047] It should be noted that the preset clamping area 5 and the non-clamping area include the central axis. The number of grooves 12 fabricated within the preset clamping area 5 and the non-clamping area in the present invention does not include the grooves 12 on the central axis, that is, the number of grooves 12 off the central axis is at least more than 8.

[0048] Optionally, when fabricating the groove 12 within the preset clamping area 5, the number of grooves 12 can be 4, 6, 8, 10, etc., and further preferably 4 - 6. At the same time, further control the vertical distance between the groove 12 within the preset clamping area 5 and the edge of the optoelectronic chip 1 to be greater than or equal to 400 μm, and the vertical distance from the central axis to be greater than or equal to 300 μm. This can not only further reduce the stress at the single point position to prevent damage to the optoelectronic chip 1, but also ensure more reliable fixation of the protective sheet 2 and the optoelectronic chip 1.

[0049] Similarly, when making the grooves 12 in the non-clamping area, the number of the grooves 12 can be 4, 8, 10, 12, etc., and is further preferably 8 - 10. At the same time, further control the vertical distance between the grooves 12 in the non-clamping area and the edge of the optoelectronic chip 1 to be greater than or equal to 400 μm, and the vertical distance from the central axis to be greater than or equal to 300 μm, which can not only further reduce the stress at a single point to prevent damage to the optoelectronic chip 1, but also ensure more reliable fixation of the protection sheet 2 and the optoelectronic chip 1.

[0050] It can be understood that within the preset clamping area 5, the vertical distances of multiple grooves 12 on the same side of the central axis from the central axis can be the same or different, and the vertical distances from the edge of the optoelectronic chip 1 can be the same or different; similarly, within the non-clamping area, the vertical distances of multiple grooves 12 on the same side of the central axis from the central axis can be the same or different, and the vertical distances from the edge of the optoelectronic chip 1 can be the same or different.

[0051] To further reduce the stress at a single point to prevent damage to the optoelectronic chip 1, and at the same time further improve the fixing effect between the protection sheet 2 and the optoelectronic chip 1, within the preset clamping area 5, the distance between the grooves 12 is greater than or equal to 400 μm, and / or within the non-clamping area, the distance between the grooves 12 is greater than or equal to 400 μm, and / or the distance between the grooves in the preset clamping area and the grooves in the non-clamping area is greater than or equal to 400 μm. Further, the distances between the grooves 12 not on the central axis are all greater than or equal to 400 μm, and the distances between different grooves 12 can be the same or different.

[0052] It can be understood that in order to make the grinding and polishing process more stable, the preset clamping area 5 is generally located in the central area of the optoelectronic chip 1. At this time, the areas on both sides of the preset clamping area 5 in the optoelectronic chip 1 are non-clamping areas, and it is preferred that grooves 12 are made in both non-clamping areas.

[0053] When making the grooves 12 on the surface of the optoelectronic chip 1, the shape of the grooves 12 can be a cylinder, a triangular prism, a quadrangular prism, etc. To reduce the manufacturing difficulty of the grooves 12 and the assembly difficulty between the grooves 12 and the convex structures 21, the shape of the grooves 12 is preferably a cylinder. Correspondingly, the shape of the convex structures 21 is also a cylinder, and the size of the convex structures 21 is not greater than the size of the grooves 12.

[0054] Further, to make the convex structure 21 on the protective sheet 2 more easily embedded in the groove 12 of the optoelectronic chip 1 and ensure that the optoelectronic chip 1 and the protective sheet 2 after fitting are more stable and do not undergo relative displacement, the depth of the groove 12 is preferably 80 μm - 300 μm. At the same time, the maximum material size (MMS) of the groove 12 is controlled to be greater than or equal to 100 μm, and more preferably 120 μm - 200 μm. For example, when the groove 12 is a cylinder, the diameter of the groove 12 is greater than or equal to 100 μm. With such a setting, the contact area between the convex structure 21 and the groove 12 can be increased, and the single-point stress can be further reduced.

[0055] Optionally, the sum of the depth of the groove 12 and the height of the bump 11 differs from the height of the convex structure 21 by 50 μm - 100 μm. In this way, the adhesive 3 filled between the optoelectronic chip 1 and the protective sheet 2 can effectively buffer the pressure during clamping by the fixture or during polishing, thereby avoiding damage to the bump 11 and also avoiding waste caused by excessive use of the adhesive 3.

[0056] It should be noted that when filling the adhesive 3, the adhesive 3 can cover the bump 11 but not completely fill the gap between the optoelectronic chip 1 and the protective sheet 2, or it can completely fill the gap between the optoelectronic chip 1 and the protective sheet 2. In the present invention, it is preferred that the adhesive 3 completely fills the gap between the optoelectronic chip 1 and the protective sheet 2.

[0057] At the same time, when filling the adhesive 3 between the optoelectronic chip 1 and the protective sheet 2, the filling method and sequence are not limited. The adhesive 3 can be first coated on the non-groove 12 area of the surface of the optoelectronic chip 1 with the bump 11, and then the convex structure 21 of the protective sheet 2 is embedded in the groove 12 of the optoelectronic chip 1 to form the composite structure; or the adhesive 3 can be coated on the surface of the protective sheet 2 with the convex structure 21, and then the convex structure 21 of the protective sheet 2 is embedded in the groove 12 of the optoelectronic chip 1 to form the composite structure; or the convex structure 21 of the protective sheet 2 can be embedded in the groove 12 of the optoelectronic chip 1, and then the adhesive 3 is injected between the optoelectronic chip 1 and the protective sheet 2 to form the composite structure.

[0058] To avoid the penetration and contamination of the relevant solvents or impurities during the polishing process to the bump 11, the adhesive 3 selected in the present invention does not react with acidic substances or alkaline substances. Further, to facilitate the removal of the adhesive 3 and the protective sheet 2 after the polishing process, the adhesive 3 is selected from substances that can be erased by conventional cleaning agents, including one or several of paraffin, epoxy resin, ultraviolet glue, or photoresist.

[0059] To ensure that the protection sheet 2 does not deform when clamped by a fixture, it is preferred that the Young's modulus of the protection sheet 2 is greater than or equal to 70 GPa, and the thickness of the protection sheet 2 is greater than or equal to 1 mm. Further, the protection sheet 2 is selected from a silicon oxide sheet, a silicon sheet, a silicon nitride sheet, or a glass sheet.

[0060] It can be understood that the size of the protection sheet 2 can be larger than, smaller than, or equal to the size of the optoelectronic chip 1, but it is required to completely cover the bumps 11 on the optoelectronic chip 1 to protect the bumps 11. Preferably, the size of the protection sheet 2 is the same as the size of the optoelectronic chip 1.

[0061] In addition, the protection sheet 2 and the raised structure 21 can be an integral structure or a non-integral structure. In the case of a non-integral structure, the material of the raised structure 21 can be the same as or different from that of the protection sheet 2, and is selected from one or more of silicon oxide, silicon, silicon nitride, metal, or glass.

[0062] It can be understood that when the composite structure is clamped by a fixture in the present invention, the clamping position of the fixture corresponding to the preset clamping area 5 of the optoelectronic chip 1 means that the fixture does not directly contact the preset clamping area 5 of the optoelectronic chip 1, but is clamped on the protection sheet 2 corresponding to the preset clamping area 5 and on the optoelectronic chip 1.

[0063] It should be noted that when the end face of the optoelectronic chip 1 is ground and polished, the grinding and polishing methods are grinding or polishing, etc., and the present invention will not elaborate too much here.

[0064] After the grinding and polishing treatment, the type of cleaning agent for removing the adhesive 3 can be selected according to the composition of the adhesive 3. For example, when the adhesive 3 is paraffin, alcohol can be used for wiping to obtain the processed optoelectronic chip 4.

[0065] Therefore, in the end face treatment method of the present invention, the protection sheet 2, the adhesive 3, and the optoelectronic chip 1 form the composite structure, which can avoid the direct contact between the bumps 11 of the optoelectronic chip 1 and the fixture or the protection sheet 2 during the grinding and polishing treatment, fully protecting the bumps 11 of the optoelectronic chip 1 from damage. At the same time, by making the groove 12 on the surface of the optoelectronic chip 1 and controlling the distribution of the groove 12, after the protection sheet 2 is embedded in the optoelectronic chip 1, not only will there be no relative displacement during the grinding and polishing treatment, but the reliability is high, and the stress at a single point position can be reduced to prevent damage to the optoelectronic chip 1.

[0066] After testing, when the groove 12 is made in the manner of the present invention, after the optoelectronic chip 1 is ground and polished, the optoelectronic chip 1 is not damaged. However, when the distribution method of the groove 12 is slightly changed, for example:

[0067] (1) When no groove 12 is made on the central axis, or one groove 12 is made every 1200 μm on the central axis, or one groove 12 is made every 1500 μm on the central axis, or one groove 12 is made every 200 μm on the central axis, after the optoelectronic chip 1 is ground and polished, the optoelectronic chip 1 is damaged;

[0068] (2) The grooves 12 in the preset clamping area are symmetric along the central axis, but the number is only 2, or the number of grooves 12 in the preset clamping area is 5, resulting in asymmetry along the central axis, or when the number of grooves 12 in the preset clamping area is 4, and there are 2 grooves 12 on both sides of the central axis, but the distances of the grooves 12 on both sides of the central axis from the central axis are different, resulting in asymmetry along the central axis, after the optoelectronic chip 1 is ground and polished, the optoelectronic chip 1 is damaged;

[0069] (3) The grooves 12 in the non-clamping area are symmetric along the central axis, but the number is only 2, or the number of grooves 12 in the non-clamping area is 5, resulting in asymmetry along the central axis, or when the number of grooves 12 in the non-clamping area is 4, and there are 2 grooves 12 on both sides of the central axis, but the distances of the grooves 12 on both sides of the central axis from the central axis are different, resulting in asymmetry along the central axis, after the optoelectronic chip 1 is ground and polished, the optoelectronic chip 1 is damaged.

[0070] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0071] The above-described embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for end face treatment of an optoelectronic chip, characterized in that, It includes the following steps: Fabricate a plurality of grooves on the surface of the optoelectronic chip with bumps, wherein the grooves are axially symmetrically distributed along any central axis of the optoelectronic chip, and on the central axis of the optoelectronic chip, 1 groove is fabricated every 300μm - 1000μm, at least 4 grooves are fabricated in the preset clamping area, and at least 4 grooves are fabricated in the non-clamping area; Cover a protective sheet on the surface of the optoelectronic chip with bumps, wherein the surface of the protective sheet has a raised structure that can be matched with the grooves in the optoelectronic chip, and the height of the raised structure is greater than the sum of the depth of the grooves and the height of the bumps. Use the raised structure to embed into the grooves to fix the optoelectronic chip and the protective sheet, and fill an adhesive between the optoelectronic chip and the protective sheet to form a composite structure; Clamp the composite structure with a fixture, and the clamping position of the fixture corresponds to the preset clamping area of the optoelectronic chip, and then grind and polish the end face of the optoelectronic chip; After the grinding and polishing process is completed, remove the protective sheet and the adhesive to obtain the processed optoelectronic chip.

2. The end face processing method of the optoelectronic chip according to claim 1, wherein On the central axis of the optoelectronic chip, 1 groove is fabricated every 600μm - 800μm; And / or, fabricate 4 - 6 grooves in the preset clamping area; And / or, fabricate 8 - 10 grooves in the non-clamping area.

3. The end face processing method of the optoelectronic chip according to claim 1, wherein, The vertical distance between the grooves in the preset clamping area and the edge of the optoelectronic chip is greater than or equal to 400μm; And / or, the vertical distance between the grooves in the non-clamping area and the edge of the optoelectronic chip is greater than or equal to 400μm; And / or, the vertical distance between the grooves in the preset clamping area and the central axis is greater than or equal to 300μm; And / or, the vertical distance between the grooves in the non-clamping area and the central axis is greater than or equal to 300μm.

4. The end face processing method of the optoelectronic chip according to claim 1, wherein, In the preset clamping area, the distance between the grooves is greater than or equal to 400μm; And / or, in the non-clamping area, the distance between the grooves is greater than or equal to 400μm; And / or, the distance between the grooves in the preset clamping area and the grooves in the non-clamping area is greater than or equal to 400μm.

5. The end face processing method of the optoelectronic chip according to claim 1, characterized in that The optoelectronic chip has two non-clamping areas, and the grooves are fabricated in each non-clamping area.

6. The end face processing method of the optoelectronic chip according to claim 1, wherein, The depth of the grooves is 80μm - 300μm; And / or, the maximum material size of the grooves is greater than or equal to 100μm.

7. The end face processing method of the optoelectronic chip according to claim 1, characterized in that, The difference between the sum of the depth of the grooves and the height of the bumps and the height of the raised structure is 50μm - 100μm.

8. The end face processing method of the optoelectronic chip according to claim 1, characterized in that, The adhesive completely fills the gap between the optoelectronic chip and the protective sheet.

9. The end face processing method of the optoelectronic chip according to claim 1, wherein The Young's modulus of the protective sheet is greater than or equal to 70GPa; And / or, the thickness of the protective sheet is greater than or equal to 1mm; And / or, the adhesive does not react with acidic substances and alkaline substances.

10. The end face treatment method of the optoelectronic chip according to claim 9, characterized in that, The protective sheet is selected from silicon oxide sheets, silicon sheets, silicon nitride sheets or glass sheets; And / or, the adhesive is selected from one or more of paraffin, epoxy resin, ultraviolet glue or photoresist.

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