Chip adhesive glue against resin overflow and preparation method and application thereof

Abstract

The application provides a chip bonding adhesive capable of preventing resin overflow, a preparation method and application thereof. Raw materials of the chip bonding adhesive include an epoxy resin, a curing agent, an accelerator, a filler, butanediol diglycidyl ether and a ketone solvent with a boiling point lower than 90 DEG C. The filler includes conductive filler or insulating filler. Through reasonable collocation between the components, especially through collocation of the ketone solvent with a boiling point lower than 90 DEG C and butanediol diglycidyl ether, the obtained chip bonding adhesive can effectively inhibit the RBO effect, and can effectively improve the bonding strength of the chip and the substrate, and does not affect the volume resistivity of the chip bonding adhesive itself, and is suitable for bonding of chips in electronic components.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of adhesives, and particularly relates to a chip adhesive with anti-resin bleeding-out, a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the lightening, miniaturization and high integration of packaged components and assemblies, the design is more compact, and the spacing between the chip and the peripheral pad, wire bonding and other interconnection structures is becoming smaller and smaller, which puts forward higher requirements for the chip adhesive.

[0003] After dispensing or scribing on the substrate, the resin or other organic matter such as diluent in the adhesive may sometimes overflow from the adhesive body, spread and diffuse on the surface of the substrate, and form a water stain-like mark, which is called resin bleeding-out (RBO for short). A small amount of RBO will not affect the subsequent wire bonding and circuit function, but when RBO is serious, it will contaminate the pads and wires, resulting in insufficient adhesion strength of the chip to the substrate, or affecting the quality of subsequent wire bonding and EMC molding processes, and if it is a conductive chip adhesive, there is also a risk of short circuit caused by electrochemical migration, resulting in low packaging reliability.

[0004] At present, the product application end often uses process control methods to reduce the influence of RBO, such as controlling the curing conditions, performing plasma cleaning treatment on the substrate, and selecting a substrate with suitable surface roughness, but the above measures cannot fundamentally eliminate RBO. Adding functional additives to the formula to inhibit RBO effect can also effectively reduce RBO. For example, US 4483898 uses a fluorine-substituted alcohol, amide, amine, carboxylic acid, ester with 2-12 carbons as an inhibitor. For example, US20110017400A1 uses a carboxyl-terminated polysiloxane as an inhibitor; but the above methods are all from the perspective of changing the surface energy of the adhesive to improve or inhibit the RBO effect, and the effect is poor and the dependence on the substrate is high.

[0005] Therefore, in view of the above technical problems, it is still a technical problem urgently needed to be solved in the art to develop a chip adhesive that can effectively inhibit the RBO effect and has more excellent adhesion performance. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a chip adhesive with anti-resin bleeding-out, a preparation method and application thereof, which can effectively improve the anti-RBO effect of the adhesive, improve the adhesion strength of the chip to the substrate, and does not affect the volume resistivity of the adhesive itself, and is suitable for application in chip bonding.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a chip adhesive with anti-resin overflow, raw materials of the chip adhesive including an epoxy resin, a curing agent, an accelerator, a filler, butanediol diglycidyl ether, and a ketone solvent with a boiling point lower than 90°C (e.g., 89°C, 88°C, 85°C, 80°C, 75°C, 70°C, 65°C, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C, or 5°C, etc.).

[0009] The filler includes a conductive filler or an insulating filler.

[0010] The raw materials of the chip adhesive provided by the present application include an epoxy resin, a curing agent, an accelerator, a filler, butanediol diglycidyl ether, and a ketone solvent with a boiling point lower than 90°C, and the filler includes a conductive filler or an insulating filler. Through reasonable collocation among the above components, especially through collocation of the ketone solvent with a boiling point lower than 90°C and butanediol diglycidyl ether, the obtained chip adhesive can effectively inhibit the RBO effect, thereby effectively improving the bonding strength of the chip and the substrate, and without affecting the volume resistivity of the adhesive itself. When the filler is a conductive filler, the chip adhesive is a chip conductive adhesive, and the addition of the ketone solvent with a boiling point lower than 90°C can ensure that it has a lower volume resistivity, and can also effectively avoid the risk of short circuit caused by electrochemical migration. When the filler is an insulating filler, the chip adhesive is a chip insulating adhesive, and the addition of the ketone solvent with a boiling point lower than 90°C can ensure that it has a higher volume resistivity.

[0011] Preferably, the raw materials of the chip adhesive include the following components by weight:

[0012]

[0013] The amount of the epoxy resin can be 5 parts by weight, 7 parts by weight, 9 parts by weight, 11 parts by weight, 13 parts by weight, 15 parts by weight, 17 parts by weight, 19 parts by weight, 21 parts by weight, 23 parts by weight, or 25 parts by weight, etc.

[0014] The amount of the curing agent can be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight, etc.

[0015] The amount of the accelerator can be 0.1 part by weight, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight, 0.5 part by weight, 0.6 part by weight, 0.7 part by weight, 0.8 part by weight, 0.9 part by weight, or 1 part by weight, etc.

[0016] The amount of the filler can be 15 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, 50 parts by weight, 55 parts by weight, 60 parts by weight, 65 parts by weight, or 70 parts by weight, etc.

[0017] The amount of the butanediol diglycidyl ether can be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight, etc.

[0018] The amount of the ketone solvent with a boiling point lower than 90℃ can be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight, etc.

[0019] Preferably, the ketone solvent with a boiling point lower than 90℃ includes methyl ethyl ketone and / or acetone.

[0020] Preferably, the curing agent is an amine curing agent or a phenolic curing agent.

[0021] Preferably, the curing agent is a phenolic curing agent, and the raw materials of the chip adhesive further include diethylene glycol dibutyl ether, and further preferably, 2-5 parts by weight (e.g., 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight, etc.) of diethylene glycol dibutyl ether.

[0022] Preferably, the accelerator includes a urea accelerator and / or a triphenylphosphine accelerator.

[0023] Preferably, the conductive filler includes conductive silver powder.

[0024] Preferably, the insulating filler includes insulating silicon powder.

[0025] Preferably, the raw materials of the chip adhesive further include any one or a combination of at least two of a thixotropic agent, a silane coupling agent, or adipic acid.

[0026] When the filler is a conductive filler, the obtained chip adhesive is a chip conductive adhesive, and the addition of the adipic acid helps to further improve the conductivity of the chip conductive adhesive.

[0027] Preferably, the content of the thixotropic agent in the raw materials of the chip adhesive is 0.1-0.5 parts by weight, such as 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, or 0.5 parts by weight, etc.

[0028] Preferably, the silane coupling agent in the raw materials of the die bonding adhesive is 0.1-0.5 parts by weight, for example, 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight or 0.5 parts by weight, etc.

[0029] Preferably, the adipic acid in the raw materials of the die bonding adhesive is 0.1-0.5 parts by weight, for example, 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight or 0.5 parts by weight, etc.

[0030] In a second aspect, the present application provides a preparation method of the die bonding adhesive according to the first aspect, the preparation method comprising: mixing the epoxy resin, the curing agent, the accelerator, the filler, the butanediol diglycidyl ether, the ketone solvent with a boiling point lower than 90℃, the optional diethylene glycol dibutyl ether, the optional thixotropic agent, the optional silane coupling agent and the optional adipic acid to obtain the die bonding adhesive.

[0031] In a third aspect, the present application provides the die bonding adhesive according to the first aspect for use in electronic components.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] The raw materials of the die bonding adhesive provided by the present application include an epoxy resin, a curing agent, an accelerator, a filler, a butanediol diglycidyl ether and a ketone solvent with a boiling point lower than 90℃, and the filler includes a conductive filler or an insulating filler; through the reasonable collocation between the above-mentioned components, especially through the collocation of the ketone solvent with a boiling point lower than 90℃ and the butanediol diglycidyl ether, the obtained die bonding adhesive can effectively inhibit the RBO effect, thereby effectively improving the bonding strength of the chip and the substrate, and does not affect the volume resistivity of the chip adhesive itself, and is suitable for the bonding of chips in electronic components. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 A schematic diagram of the maximum distance L from the farthest position of the RBO after dispensing to the initial peripheral contour of dispensing. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0036] The detailed information of some raw materials involved in the following examples and comparative examples is shown as follows:

[0037] (A) Epoxy resin

[0038] A1: purchased from DIC Corporation, model HP-4710;

[0039] A2: purchased from DIC Corporation, model number HP-7200;

[0040] A3: purchased from DIC Corporation, model number EXA-835LV.

[0041] (B) Curing agent

[0042] Phenolic curing agent: purchased from Shengquan New Material Co., Ltd., Shandong, model number SH5065;

[0043] Amine curing agent: purchased from Chengdu Yuanda Chemical Co., Ltd., specifically 4,4'-diaminodiphenyl sulfone, abbreviated as DDS.

[0044] (C) Accelerator

[0045] Urea accelerator: purchased from Alzchem, model number UR300;

[0046] Triphenylphosphine accelerator: purchased from Aldrich, abbreviated as TPP.

[0047] (D) Filler

[0048] Conductive silver powder: purchased from Metalor (USA), model number EA-0295;

[0049] Insulating silicon powder: purchased from Admatech (Japan), model number SC6200-STE.

[0050] (E) Butanediol diglycidyl ether: purchased from Nagase ChemteX, model number EX-214L.

[0051] (F) Ketone solvent with boiling point less than 90°C

[0052] Methyl ethyl ketone: boiling point 76.9°C, purchased from Wuxi Prospect, model number MEK;

[0053] Acetone: boiling point 56.5°C, purchased from Aldrich.

[0054] (G) Diethylene glycol dibutyl ether: purchased from Aldrich.

[0055] (H) Thixotropic agent: fumed silica, purchased from Cabot, model number TS-720.

[0056] (I) Silane coupling agent: purchased from Jiangsu Chenguang Coupling Agent Co., Ltd., model number KH-560.

[0057] (J) Adipic acid: purchased from Shanghai Mayreal Chemical Technology Co., Ltd.

[0058] The detailed information of the performance test of the following examples and comparative examples is shown as follows:

[0059] (1) Chip thrust: refer to the test method provided in "HG / T 5912-2021 Conductive Adhesive" for testing;

[0060] Silicon wafer size: 2mm x 2mm (500μm thick), substrate: silver-plated copper sheet, copper sheet;

[0061] Curing conditions: place the test piece in an oven, heat from 25℃ to 175℃ at a rate of 5℃ / min, and then keep at 175℃ for 60min;

[0062] Test equipment: DAGE-4000P multifunctional push-pull force machine (Nordson DAGE Precision Industries LTD, USA), with temperature-controlled heating table, shear strength is the thrust size (unit: kgF);

[0063] Take 10 test data for each sample corresponding to the test, and take the arithmetic mean value as the result.

[0064] (2) RBO effect: refer to the test method provided in "HG / T 5912-2021 Conductive Adhesive" for testing;

[0065] Substrate: silver-plated copper sheet, copper sheet;

[0066] Curing conditions: place the test piece in an oven, heat from 25℃ to 175℃ at a rate of 5℃ / min, and then keep at 175℃ for 60min;

[0067] After curing, observe and measure with a metallographic microscope of Shanghai Optical Instrument Factory-6XM-PC, the maximum distance L (see Appendix Figure 1 ) from the farthest position of the glue RBO to the initial peripheral profile of the glue, in μm.

[0068] (3) Volume resistivity / conductive adhesive: refer to the four-probe method in "HG / T 5912-2021 Conductive Adhesive";

[0069] Preparation of conductive film: on a glass substrate, use a thickness control tape to prepare a conductive adhesive film with a thickness of about 25μm, a width of 9mm, and a length of 50mm;

[0070] Curing conditions: place the test piece in an oven, heat from 25℃ to 175℃ at a rate of 5℃ / min, and then keep at 175℃ for 60min;

[0071] Test equipment: TH2516 direct current resistance tester of Changzhou Tonghui Electronics Co., Ltd.

[0072] (4) Volume resistivity / insulating glue: refer to GB / T 1410-2006 Solid Insulating Materials - Determination of Volume Resistivity and Surface Resistivity - Test Methods;

[0073] Preparation of test pieces: circular test pieces with a thickness of 2 mm and a diameter of 80 mm were prepared by filling and platyping with a polytetrafluoroethylene mold;

[0074] Curing conditions: the test pieces were placed in an oven, heated from 25℃ to 175℃ at a rate of 5℃ / min, then kept at 175℃ for 60 min, and demolded after cooling;

[0075] Test equipment: ZC36 high insulation resistance measuring instrument (Shanghai Precision Instruments and Meters Co., Ltd.).

[0076] (5) Other equipment and instruments:

[0077] Heating equipment: GZX-9030MBE (electric heating air drying oven), Shanghai Boxun Industrial Co., Ltd. Medical Equipment Factory;

[0078] Glue preparation equipment: ZYMC-350VS high-speed disperser, Shenzhen Zhongyi Technology Co., Ltd.

[0079] Examples 1-1 to 1-4 and Comparative Example 1-1

[0080] Examples 1-1 to 1-4 and Comparative Example 1-1 each provide a chip conductive adhesive resistant to resin overflow, and the preparation method comprises the following steps:

[0081] (1) Mix epoxy resin A2 and butanediol diglycidyl ether in container A, heat to 90℃ and stir until fully dissolved, cool to room temperature, then add a ketone solvent with a boiling point lower than 90℃ (or not add) and mix to obtain composition A;

[0082] Mix diethylene glycol dibutyl ether and phenolic curing agent in container B, heat to 90℃ and stir until fully dissolved, cool to room temperature to obtain composition B;

[0083] (2) Mix composition A, composition B, accelerator and silane coupling agent, stir until transparent, add conductive filler, disperse at 1000 rpm for 10 min, disperse at 1800 rpm for 10 min, turn on vacuum, degas at 1800 rpm for 10 min under a vacuum degree of <-0.098 MPa, and discharge under normal pressure to obtain the chip conductive adhesive resistant to resin overflow.

[0084] The chip conductive adhesive provided by the above Examples 1-1 to 1-4 and Comparative Example 1-1 contains various components and amounts as shown in Table 1, and in Table 1, the amount of each component is in "parts by weight";

[0085] Meanwhile, the performance test results of the chip conductive adhesive provided in the above-mentioned embodiments 1-1 to 1-4 and comparative example 1-1 are also described in Table 1.

[0086] Table 1

[0087]

[0088]

[0089] According to the data in Table 1, it can be seen that:

[0090] (1) Compared with comparative example 1-1, the RBO effect of the chip conductive adhesive provided in embodiments 1-1 and 1-2 is lower, both being 0 μm, and the volume resistivity is lower, and the chip thrust is higher.

[0091] (2) Compared with embodiment 1-1, the RBO effect of embodiment 1-3 is obvious due to too little MEK added, while the RBO effect of embodiment 1-4 is very low due to too much MEK added, but the chip thrust is significantly reduced due to the existence of holes in the adhesive layer.

[0092] Embodiments 2 and comparative example 2

[0093] Embodiments 2 and comparative example 2 respectively provide a chip conductive adhesive resistant to resin overflow, and the preparation method comprises the following steps:

[0094] (1) Mix epoxy resin A1 and 1 / 2 epoxy resin A3 in container A, heat to 90°C and stir until fully dissolved, cool to room temperature, then add methyl ethyl ketone (or not) and mix to obtain composition A;

[0095] Mix the remaining 1 / 2 epoxy resin A3, butanediol diglycidyl ether, amine curing agent, urea accelerator and adipic acid in container B, heat to 90°C and stir until fully dissolved, cool to room temperature to obtain composition B;

[0096] (2) Mix composition A, composition B and silane coupling agent, disperse at 800 rpm for 5 min, add conductive silver powder, disperse at 1000 rpm for 10 min, disperse at 1800 rpm for 10 min, open the vacuum, degas at a vacuum degree of <-0.098 MPa, 1800 rpm for 10 min, and discharge at normal pressure to obtain the chip conductive adhesive resistant to resin overflow.

[0097] The chip conductive adhesive provided in the above-mentioned embodiments 2 and comparative example 2 comprises various components and amounts as shown in Table 2, wherein the amount of each component in Table 2 is "parts by weight";

[0098] Meanwhile, the performance test of the chip conductive adhesive provided by the above-mentioned embodiment 2 and comparative example 2 is also described in table 2.

[0099] Table 2

[0100]

[0101] According to the data in table 2, it can be seen that:

[0102] Compared with comparative example 2, the RBO effect of the chip conductive adhesive provided by embodiment 2 is 0 μm, and the chip thrust is higher and the volume resistivity is lower.

[0103] Embodiment 3 and comparative example 3

[0104] Embodiment 3 and comparative example 3 respectively provide a chip insulating adhesive resistant to resin overflow, and the preparation method comprises the following steps:

[0105] (1) mixing epoxy resin A2 and butanediol diglycidyl ether in container A, heating to 90℃ and stirring until fully dissolved, cooling to room temperature, then adding methyl ethyl ketone (or not adding) for mixing to obtain composition A;

[0106] Mixing diethylene glycol dibutyl ether and phenolic curing agent in container B, heating to 90℃ and stirring until fully dissolved, cooling to room temperature to obtain composition B;

[0107] (2) mixing composition A, composition B, triphenylphosphine promoter and silane coupling agent, fully stirring until transparent, adding insulating silicon powder and thixotropic agent, dispersing at 1000 rpm for 10 min, dispersing at 1800 rpm for 10 min, opening the vacuum, degassing at 1800 rpm for 10 min under a vacuum degree of <-0.098 MPa, and discharging under normal pressure to obtain the chip insulating adhesive resistant to resin overflow.

[0108] The components and amounts of each component contained in the chip insulating adhesive provided by the above-mentioned embodiment 3 and comparative example 3 are shown in table 3, and in table 3, the amount of each component is in "parts by weight";

[0109] Meanwhile, the performance test of the chip insulating adhesive provided by the above-mentioned embodiment 3 and comparative example 3 is also described in table 3;

[0110] Table 3

[0111]

[0112] According to the data in table 3, it can be seen that:

[0113] Compared with comparative example 3, the RBO effect of the chip insulating adhesive provided by embodiment 3 is 0 μm, and the chip thrust is higher, and the volume resistivity is higher.

[0114] Examples 4-5 and Comparative Example 4

[0115] Examples 4-5 and Comparative Example 4 each provide a resin-overflow-resistant chip insulation adhesive, and a preparation method thereof includes the following steps:

[0116] (1) Mix epoxy resin A1 and 1 / 2 epoxy resin A3 in container A, heat to 90°C and stir until fully dissolved, cool to room temperature, then add a ketone solvent with a boiling point lower than 90°C (or do not add) and mix to obtain composition A;

[0117] Mix the remaining 1 / 2 epoxy resin A3, butanediol diglycidyl ether, amine curing agent, and urea accelerator in container B, heat to 90°C and stir until fully dissolved, cool to room temperature to obtain composition B;

[0118] (2) Mix composition A, composition B, and silane coupling agent, disperse at 800 rpm for 5 min, add insulating silicon powder and fumed silica, disperse at 1000 rpm for 10 min, disperse at 1800 rpm for 10 min, turn on vacuum, degas at a vacuum degree of <-0.098 MPa, 1800 rpm for 10 min, and discharge at normal pressure to obtain the resin-overflow-resistant chip insulation adhesive.

[0119] The chip insulation adhesive provided by Examples 4-5 and Comparative Example 4 above contains each component and the amount of each component is shown in Table 4, wherein the amount of each component is in "parts by weight";

[0120] Meanwhile, the performance test of the chip insulation adhesive provided by Examples 4-5 and Comparative Example 4 above is also recorded in Table 4;

[0121] Table 4

[0122]

[0123]

[0124] According to the data in Table 4, it can be seen that:

[0125] Compared with Comparative Example 4, the chip insulation adhesive provided by Examples 4-5 has an RBO effect of 0 μm, higher chip thrust between silver-plated copper sheets and copper sheets, and higher volume resistivity.

[0126] Applicant states that the present application illustrates a chip bonding adhesive against resin overflow, its preparation method and application by the above-mentioned examples, but the present application is not limited to the above-mentioned examples, that is, it does not mean that the present application must rely on the above-mentioned examples to be implemented. The skilled in the art should understand that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific mode, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A chip adhesive that prevents resin overflow, characterized in that, The raw materials for the chip adhesive are epoxy resin, curing agent, accelerator, filler, butylene glycol diglycidyl ether, methyl ethyl ketone and other excipients; The filler includes conductive filler or insulating filler; When the filler is a conductive filler, the other excipients are any one or a combination of at least two of diethylene glycol dibutyl ether, silane coupling agent or adipic acid; When the filler is an insulating filler, the other auxiliary materials are any one or a combination of at least two of diethylene glycol dibutyl ether, thixotropic agent, silane coupling agent or adipic acid; The epoxy resin comprises 5-25 parts by weight, the curing agent comprises 1-5 parts by weight, the accelerator comprises 0.1-1 parts by weight, the filler comprises 15-70 parts by weight, the butanediol diglycidyl ether comprises 1-5 parts by weight, and the methyl ethyl ketone comprises 1-5 parts by weight.

2. The chip adhesive according to claim 1, characterized in that, The curing agent is an amine curing agent or a phenolic curing agent.

3. The chip adhesive according to claim 1, characterized in that, The curing agent is a phenolic curing agent.

4. The chip adhesive according to claim 1, characterized in that, The raw materials for the chip adhesive also include 2 to 5 parts by weight of diethylene glycol dibutyl ether.

5. The chip adhesive according to claim 1, characterized in that, The accelerators include urea accelerators and / or triphenylphosphine accelerators.

6. The chip adhesive according to claim 1, characterized in that, The conductive filler includes conductive silver powder.

7. The chip adhesive according to claim 1, characterized in that, The insulating filler includes insulating silicon powder.

8. The chip adhesive according to claim 1, characterized in that, The thixotropic agent content in the raw materials of the chip adhesive is 0.1~0.5 parts by weight.

9. The chip adhesive according to claim 1, characterized in that, The raw material of the chip adhesive contains 0.1 to 0.5 parts by weight of silane coupling agent.

10. The chip adhesive according to claim 1, characterized in that, The adipic acid content in the raw materials of the chip adhesive is 0.1~0.5 parts by weight.

11. A method for preparing the chip adhesive as described in any one of claims 1 to 10, characterized in that, The preparation method includes mixing epoxy resin, curing agent, accelerator, filler, butylene glycol diglycidyl ether, methyl ethyl ketone, diethylene glycol dibutyl ether, thixotropic agent, silane coupling agent and adipic acid, or a combination of any one or at least two of these to obtain the chip adhesive.

12. The application of a chip adhesive as described in any one of claims 1 to 10 in electronic components.

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