Manufacturing method of a cover film with low dielectric loss

Abstract

The present invention discloses a manufacturing method of a cover film with low dielectric loss, comprising the following steps: Step 1, synthesize a prepolymer - polyamic acid solution of a thermoplastic polyimide resin with low dielectric loss; Step 2, prepare glue: add the polyamic acid solution synthesized in Step 1, epoxy resin YX8100BH30, epoxy resin NC-3000-H, curing agent CUA-4, latent curing agent, flame retardant SPB-100, solvent cyclohexanone, and solvent methyl ethyl ketone into a container, stir and then stand still to defoam; Step 3, take the glue prepared in Step 2 and coat it on a PI film; Step 4, after coating, bake it, and then press the release surface of the release paper with a laminator. After the cover film with low dielectric loss is manufactured, immediately store it in a cold storage. The cover film manufactured by the present invention has a low dielectric loss value, and the test value at 10 GHz is about 0.003; 2. Good heat resistance: the solder heat resistance is 300 °C / 30 s; 3. The peel strength ≥ 1.0 kgf / cm; 4. Excellent chemical resistance performance.

Description

Technical Field

[0001] The present invention relates to the technical field of cover films, and particularly to a manufacturing method of a cover film with low dielectric loss. Background Art

[0002] As one of the materials of flexible copper clad laminates (FCCL), the cover film plays the following roles in flexible printed circuits (FPC): covering and protecting the (FPC) circuit, enhancing the flexural resistance of the FPC; protecting the circuit from damage by temperature, humidity, and corrosive substances; covering for subsequent surface treatment of the FPC; and acting as a solder mask in subsequent SMT of the FPC. With the popularization and application of 5G high-frequency technology, and with the development of high-frequency FPCs, such as the application of high-speed data transmission lines and USB 3.1, the demand for cover films with low dielectric loss is increasing continuously.

[0003] As shown in the attached drawings of the specification Figure 1 The structure of a common cover film mainly consists of a three-layer structure of polyimide film / adhesive / release paper. The adhesive is mainly based on epoxy resin and acrylic acid. The common cover film has the following defects:

[0004] 1. The dielectric loss value is relatively large, and the measured value at 10 GHz is about 0.01;

[0005] 2. Poor solder heat resistance: It can only reach 260 °C for 10 seconds. The peel strength drops sharply due to the deterioration of the adhesive. Generally, when performing SMT soldering on a flexible board, the temperature mostly exceeds 300 °C. In addition, the temperature during the lamination process in the production of rigid-flex boards is also as high as 200 °C, which is not applicable to these applications for common cover films, and the application fields are limited;

[0006] In recent years, in order to reduce the dielectric loss, the following methods have been adopted:

[0007] Replace the components of the epoxy resin, such as replacing rubber and resin.

[0008] Currently, the more serious problems of cover films with low dielectric loss are:

[0009] 1. The dielectric loss value is relatively large;

[0010] 2. The peel strength is relatively low;

[0011] 3. Poor solder heat resistance;

[0012] 4. Poor chemical resistance. Summary of the Invention

[0013] The purpose of the present invention is to provide a manufacturing method of a cover film with low dielectric loss to solve the problems mentioned in the above background art.

[0014] To achieve the above object, the present invention provides the following technical solutions:

[0015] A manufacturing method of a cover film with low dielectric loss, comprising the following steps:

[0016] Step 1, synthesize a prepolymer - polyamic acid solution of a thermoplastic polyimide resin with low dielectric loss;

[0017] Step 2, prepare glue: add the polyamic acid solution synthesized in Step 1, epoxy resin YX8100BH30, epoxy resin NC - 3000 - H, curing agent CUA - 4, latent curing agent, flame retardant SPB - 100, solvent cyclohexanone, and solvent methyl ethyl ketone into a container, stir and then let stand for defoaming;

[0018] Step 3, take the glue prepared in Step 2 and coat it on a PI film;

[0019] Step 4, after coating, perform baking, and then press the release surface of the release paper with a laminator. After the cover film with low dielectric loss is manufactured, immediately store it in a cold storage.

[0020] Preferably, the synthesis method of the polyamic acid solution comprises the following steps:

[0021] S1, in a three - necked container filled with nitrogen, add a cyclohexanone solution, then add Priamine™ 1074, and then mechanically stir until completely dissolved;

[0022] S2, place the product of S1 in an oil bath, add BTDA, and mechanically stir to dissolve to obtain a polyamic acid resin;

[0023] S3, take out the mechanical stirring of S2, put it into magnetic stirring, heat up and then reflux, then stop stirring, and then cool and let stand for defoaming.

[0024] Preferably, the oil bath temperature in S2 is 65 - 75 °C.

[0025] Preferably, in S3, heat up to 155 - 170 °C, and the reflux time is 3 - 5 hours.

[0026] Preferably, the weight - part ratio of the polyamic acid solution, epoxy resin YX8100BH30, epoxy resin NC - 3000 - H, curing agent CUA - 4, latent curing agent, flame retardant SPB - 100, solvent cyclohexanone, and solvent methyl ethyl ketone in Step 2 is: 119:46:121:35:1:10:25:362, and in Step 2, stir at a speed of 1000 RPM for 2 hours.

[0027] Preferably, in the third step, the thickness of the PI film is 12.5 um, and the dry film thickness of the coating is 15 - 17 um or 25 - 27 um.

[0028] Preferably, in the fourth step, the baking temperature is 145 - 155 °C, the baking time is 2 - 4 minutes, and the lamination temperature of the laminator is 95 - 100 °C.

[0029] Preferably, in the fourth step, the temperature of the cold storage is ≤5 °C.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The dielectric loss value is low, and the test value at 10 GHz is about 0.003;

[0032] 2. Good heat resistance: The solder heat resistance is 300 °C / 30 s;

[0033] 3. The peel strength ≥ 1.0 kgf / cm;

[0034] 4. Excellent chemical resistance: After chemical resistance testing, the peel strength reduction rate ≤ 10%:

[0035] The chemical resistance is quite excellent, and the peel strength does not change significantly after long-term immersion in chemical reagents (isopropyl alcohol, 2 mol / L hydrochloric acid, 2 mol / L sodium hydroxide solution). Description of the Drawings

[0036] In the following description of the exemplary embodiments with reference to the drawings, more details, features, and advantages of the present invention are disclosed. In the drawings:

[0037] Figure 1 A schematic diagram showing the prior art according to the present invention is shown; Detailed Embodiments

[0038] The following describes the technical solutions in the embodiments of the present invention clearly and completely with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] The chemical materials used to prepare the intermediate pre-solution are as follows:

[0040] 1. Priamine™ 1074 diamine: Purchased from Croda, UK;

[0041] 2. BTDA (3,3',4,4'-benzophenone tetracarboxylic dianhydride): Purchased from Shanghai Liluo Industry Co., Ltd.;

[0042] 3. Cyclohexanone: Solvent, electronic grade, purity ≥ 99.8%, water content ≤ 0.08%. Purchased from Liaocheng Meisi New Materials Technology Co., Ltd.

[0043] The chemical materials used for preparing the glue are as follows:

[0044] 1. YX8100BH30: Epoxy resin, purchased from Mitsubishi Chemical Corporation, Japan;

[0045] 2. NC-3000-H: Epoxy resin, purchased from Nippon Kayaku Co., Ltd., Japan;

[0046] 3. CUA-4: Curing agent, purchased from IHARA Chemical industry co.,ltd, Japan;

[0047] 4. Boron trifluoride-2-methylimidazole: Latent curing agent, purchased from Dongying Heyi Chemical Co., Ltd.;

[0048] 5. SPB-100: Flame retardant, purchased from Otsuka Chemical Co., Ltd., Japan;

[0049] 6. Methyl ethyl ketone: Solvent, electronic grade, purity ≥ 99.7%, water content ≤ 0.3%, purchased from Dongguan Baibaishun Petrochemical Co., Ltd.;

[0050] The coating materials are as follows:

[0051] 1. PI film: Model is Kapton EN type, manufacturer: DuPont

[0052] 2. Release paper: Model is 130WE2D-TB, manufacturer: Kunshan Taibo Adhesive Materials Co., Ltd.

[0053] Synthesis Example 1

[0054] 1. Preparation of a prepolymer - polyamic acid solution of a thermoplastic polyimide resin with low dielectric loss:

[0055] ① In a three-necked container filled with nitrogen, add 118.08 grams of cyclohexanone solution, and then add 32.4 grams (0.06 mole) of Priamine™ 1074, and stir mechanically at room temperature (25 °C) until completely dissolved;

[0056] ② Place the product of the first step in an oil bath at 70 °C, add 19.34 grams (0.06 mole) of BTDA, and stir mechanically to dissolve to obtain a polyamic acid resin.

[0057] ③ Take out the mechanical stirring of ②, put it into magnetic stirring, heat up to 160 °C, reflux for 4 hours, then stop stirring, cool to room temperature (25 °C), and let it stand for defoaming. The resin solid content is measured to be 31.1% and the viscosity is 587 CPS.

[0058] 2. Preparation of glue:

[0059] Add 118.08 g of the polyamic acid solution synthesized in Step 1, 45.89 g of epoxy resin YX8100BH30, 121.1 g of epoxy resin NC-3000-H, 34.44 g of curing agent (CUA-4), 1.05 g of latent curing agent (boron trifluoride-2-methylimidazole), 10.19 g of flame retardant (SPB-100), 25.2 g of solvent (cyclohexanone), and 362 g of solvent (methyl ethyl ketone) into a 1000-ml PE bottle in sequence, stir at a speed of 1000 RPM for 2 hours, then let it stand for defoaming. The solid content of the resin is measured to be 36.1% and the viscosity is 385 CPS; Example

[0060] Fabrication and Performance Testing of 1215-Type Low Dielectric Loss Covering Film

[0061] ⑴ Take the above glue and coat it on a PI film of DuPont's Kapton EN model with a thickness of 12.5 um. The dry film thickness of the coating is 15 - 17 um. The coating process: cut the width of the PI to 295 mm, use a laboratory automatic coater, set the rotation speed to 425 RPM, and use a 0.16-mm scraper.

[0062] ⑵ After coating, bake it at 150 °C for 3 minutes, then press the release surface of the release paper with a laminator at 100 °C. The model of the release paper is Taibo 130WE2D-TB. After the covering film is fabricated, immediately store it in a cold storage (≤5 °C).

[0063] ⑶ Fabrication of test samples:

[0064] Use the fast press of Shenzhen Bion Electronic Equipment Co., Ltd., model: SZBYD-80T-01A, and set the parameters as follows: temperature: 180 °C, pre-press pressure: 10 kgf / cm 2 , forming pressure 110 kgf / cm 2 , pre-press time: 10 seconds, forming press time: 120 seconds. The substrate for pressing is an LP-type electrolytic copper foil from Shandong Jinbao with a thickness of 35 um. Press it on the shiny surface of the 35-um copper foil. After pressing, bake it at 170 °C for two hours and then test the performance:

[0065] ⑷ Performance testing:

[0066] ① Dielectric constant and dielectric loss:

[0067] Test three groups of test pieces, and the three groups of test values are:

[0068] a. Dielectric constant: 2.91, dielectric loss: 0.0032;

[0069] b. Dielectric constant: 2.90, Dielectric loss: 0.0031;

[0070] c. Dielectric constant: 2.91, Dielectric loss: 0.0030;

[0071] ② Solder heat resistance (tested strictly according to the method of IPC-TM-650 2.4.13) (300 °C / 30 s), twelve pieces were tested and all passed;

[0072] ③ Peel strength (for a line with a width of 3.175 mm): MD direction: 1.45 kgf / cm, TD direction: 1.39 kgf / cm, and the performance is qualified;

[0073] ④ Chemical resistance: Take the test pieces for peel strength and soak them successively in the chemical reagents: isopropyl alcohol, 2 mol / L hydrochloric acid, and 2 mol / L sodium hydroxide solution. Immerse them in each of these three chemical reagents for 210 seconds in sequence, take them out and dry them, and then test the peel strength. The measured values are: MD direction: 1.39 kgf / cm, TD direction: 1.38 kgf / cm, and the peel strength decline rate ≤ 10%, and the performance is qualified; Example

[0074] Manufacture and performance test of the 1225-type low dielectric loss cover film

[0075] ⑴ Take the above glue and coat it on a KANEKA NPI film with a thickness of 12.5 um. The dry film thickness after coating is 25 - 27 um. The coating process: cut the width of the PI to 295 mm, use a laboratory automatic coater, set the rotation speed to 425 RPM, and use a 0.20 mm doctor blade,

[0076] ⑵ After coating, bake it at 150 °C for 3 minutes, and then use a laminator to press the release surface of the release paper at 100 °C. The model of the release paper is Taibo 130WE2D-TB. After the cover film is manufactured, immediately store it in a cold storage (≤ 5 °C).

[0077] ⑶ Manufacture of test samples:

[0078] Use a fast press from Shenzhen Bion Electronic Equipment Co., Ltd., model: SZBYD-80T-01A, and set the parameters as follows: temperature: 180 °C, pressure 110 kgf / cm 2 , pre-pressing time: 10 seconds, forming and pressing time: 120 seconds. The pressing substrate is an LP-type electrolytic copper foil from Shandong Jinbao with a thickness of 35 um, and it is pressed on the shiny surface of the copper foil. After pressing, bake it at 170 °C for two hours and then test the performance:

[0079] ⑷ Performance test:

[0080] ① Dielectric constant and dielectric loss:

[0081] Three groups of test specimens were tested, and three groups of test values are as follows:

[0082] a. Dielectric constant: 2.85, Dielectric loss: 0.0032;

[0083] b. Dielectric constant: 2.87, Dielectric loss: 0.0030;

[0084] c. Dielectric constant: 2.90, Dielectric loss: 0.0031;

[0085] ② Solder heat resistance (tested strictly according to the method of IPC-TM-650 2.4.13) (300°C / 30 s). Twelve specimens were tested and all passed.

[0086] ③ Peel strength (for lines with a line width of 3.175 mm): MD direction: 1.63 kgf / cm, TD direction: 1.55 kgf / cm. All performances passed.

[0087] ④ Chemical resistance: Take the specimens for peel strength test and soak them in the chemical reagents: isopropyl alcohol, 2 mol / L hydrochloric acid, and 2 mol / L sodium hydroxide solution in sequence for 210 seconds each. Take them out and dry them, then test the peel strength. The measured values are: MD direction: 1.58 kgf / cm, TD direction: 1.49 kgf / cm, and the peel strength degradation rate ≤ 10%. All performances passed.

[0088] Testing instruments, testing standards and methods:

[0089] 1. Thickness: Measured by a NIKON MS-4G type altimeter made in Japan, accurate to 0.1 μm.

[0090] 2. Peel strength: Tested by a Shimadzu AG-1 type universal tensile testing machine made in Japan

[0091] According to the standard: IPC-TM-650 2.4.9 Method A

[0092] Tensile speed: 50 mm / min

[0093] Specimen width: 3.175 mm

[0094] Specimen test distance: 70 mm

[0095] 90-degree angle roller test.

[0096] Dielectric constant and dielectric loss

[0097] Tested by using an E5071C ENA type network analyzer and an N9030A type split dielectric resonator (SPDR) from "Keysight Technologies (China) Co., Ltd."

[0098] Constant temperature and humidity machine: KTHA-415TBS model made in Taiwan, China;

[0099] According to the standard: IPC-TM-650 2.5.5.3 test method

[0100] Test method: Place the etched PI film test piece of 81.3mm×81.3mm in a constant temperature and humidity machine at 23ºC and 50% RH for 24 hours, then stack it to a thickness of 0.4mm, adjust the frequency of the high resistance meter to 10GHz and then measure.

[0101] 4. Electronic balance

[0102] Model: LT1002, Manufacturer: Changshu Tianliang Instrument Co., Ltd. Maximum weighing: 1000g, Precision: 0.01g.

[0103] 5. Solder heat resistance

[0104] Test with the YSC type tin furnace of "Yongli Technology Co., Ltd." in Taiwan, China

[0105] According to the standard: IPC-TM-650 2.4.13

[0106] Test conditions: Immerse the test piece in the tin furnace after baking at 135℃ for 1 hour and observe its changes.

[0107] 6. Solid content of the glue:

[0108] Instrument used: METTLER TOLEDO HG53 type moisture analyzer.

[0109] Test conditions: Weigh 2±0.1 grams of resin, at 160℃ or 180℃ or 190℃, and read the value after the mass is constant for 1 minute.

[0110] 7. Viscosity of the glue:

[0111] Instrument used: BROOKFIELD LVDV-I+ type rotational viscometer

[0112] Test conditions: Test after maintaining a constant temperature in a water bath at 25℃ for more than 30 minutes.

[0113] 8. Chemical resistance:

[0114] According to the standard: IPC-TM-650 2.3.2 Method A.

[0115] 9. Automatic coater:

[0116] Use the automatic translation type coater of Huanyang Precision Machinery in Taiwan, China.

[0117] 10. Magnetic stirrer for laboratory use:

[0118] Manufacturer: Gongyi Yuhua Instrument Co., Ltd., Model: DF-101T collector constant temperature heating magnetic stirrer.

[0119] 11. Laboratory high-speed mixer

[0120] Equipment name: Digital display constant speed powerful electric mixer

[0121] Manufacturer: Shanghai Specimen Model Factory, Model: JB300-SH disperser.

[0122] 12. The test samples were made using a fast press machine from Shenzhen Bion Electronic Equipment Co., Ltd. Model: SZBYD-80T-01A. The parameters were set as follows: Temperature: 180°C, Pre-pressing pressure: 10kgf / cm 2 , molding pressure 110kgf / cm 2 , Pre-pressing time: 10 seconds, molding and pressing time: 120 seconds.

[0123] 13. Oven: Manufacturer: Zhisheng, Taiwan, China, Model: SMO-1B, maximum temperature can reach 200℃.

[0124] 14. Laminating machine: Manufacturer: Xiangmeng, Model: HK 330S, the highest temperature can reach 200℃.

[0125] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0126] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A manufacturing method of a cover film with low dielectric loss, characterized in that, It includes the following steps: Step 1: Synthesize a prepolymer - polyamic acid solution of a thermoplastic polyimide resin with low dielectric loss; Step 2: Prepare the glue: Add the polyamic acid solution synthesized in Step 1, epoxy resin YX8100BH30, epoxy resin NC - 3000 - H, curing agent CUA - 4, latent curing agent, flame retardant SPB - 100, solvent cyclohexanone, and solvent methyl ethyl ketone into a container, stir, and then let it stand to defoam; Step 3: Take the glue prepared in Step 2 and coat it on the PI film; Step 4: After coating, bake it, and then use a laminator to press the release surface of the release paper. After the low - dielectric - loss cover film is made, immediately store it in a cold storage; The synthesis method of the polyamic acid solution includes the following steps: S1: In a three - necked container filled with nitrogen, add a cyclohexanone solution, then add Priamine™ 1074, and then mechanically stir until it is completely dissolved; S2: Place the product of S1 in an oil bath, add BTDA, and mechanically stir to dissolve to obtain a polyamic acid resin; S3: Take out the mechanical stirring of S2, put it into magnetic stirring, heat up and reflux, then stop stirring, and then cool and let it stand to defoam; In Step 2, the weight - part ratio of the polyamic acid solution, epoxy resin YX8100BH30, epoxy resin NC - 3000 - H, curing agent CUA - 4, latent curing agent, flame retardant SPB - 100, solvent cyclohexanone, and solvent methyl ethyl ketone is: 119:46:121:35:1:10:25:

362. In Step 2, stir at a speed of 1000 RPM for 2 hours.

2. The manufacturing method of a cover film with low dielectric loss according to claim 1, characterized in that The oil - bath temperature in S2 is 65 - 75°C.

3. The manufacturing method of a cover film with low dielectric loss according to claim 1, characterized in that, In S3, heat up to 155 - 170°C, and the reflux time is 3 - 5 hours.

4. The manufacturing method of a cover film with low dielectric loss according to claim 1, characterized in that In Step 3, the thickness of the PI film is 12.5 μm, and the dry - glue thickness of the coating is 15 - 17 μm or 25 - 27 μm.

5. The manufacturing method of a low dielectric loss cover film according to claim 1, characterized in that In Step 4, the baking temperature is 145 - 155°C, the baking time is 2 - 4 minutes, and the laminating temperature of the laminator is 95 - 100°C.

6. The manufacturing method of a cover film with low dielectric loss according to claim 1, characterized in that, In Step 4, the temperature of the cold storage is ≤5°C.

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