Method for manufacturing FPC (Flexible Printed Circuit) antenna through integrated injection molding and antenna

Abstract

The invention relates to the technical field of wireless communication equipment manufacturing, in particular to a method for manufacturing an FPC flexible antenna through integrated injection molding and the antenna, and the method comprises the following steps: preparing a copper foil layer on the surface of a double-layer polyimide substrate flexible circuit, and chemically plating a nickel-gold layer on the surface of the copper foil layer; a receding groove is formed in a golden finger area of the FPC flexible circuit board, and a positioning hole is formed in the edge of the FPC flexible circuit board; a Teflon coating is sprayed on the inner wall of the mold cavity, and a positioning column is mounted in the mold cavity; the method comprises the following steps: firstly, fixing a preprocessed FPC flexible circuit board in a mold cavity through a positioning column; and injecting a thermoplastic high polymer material heated to a molten state into a mold cavity, applying a dwell pressure to the injected molten material, so that the FPC flexible circuit board is completely coated with the molten material, cooling, and demolding to obtain the FPC flexible antenna. According to the invention, seamless integration of the antenna and the shell can be realized, so that the coupling problem of line damage and impedance mismatch in a traditional injection molding antenna is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless communication device manufacturing, and particularly relates to a method for manufacturing an FPC flexible antenna by integrated injection molding and the antenna. BACKGROUND

[0002] The existing assembly method of a walkie-talkie antenna mainly has the following technical defects: 1. Structural problem: the current commonly used external antenna is fixed by welding or screwing, the fixing method needs to separately perform antenna installation and feed point welding, the assembly is complex, and the assembly efficiency is reduced; 2. Insufficient reliability: in a vibration environment, the welding point is prone to cracking, and the screwing fixing method also has the risk of thread slippage; 3. Electromagnetic performance defect: there is a lack of effective electromagnetic isolation between the metal shell and the antenna, and significant electromagnetic coupling occurs in the 400-470 MHz operating frequency band, so that the voltage standing wave ratio (VSWR) is increased to more than 1.5 (the ideal value should be less than or equal to 1.3), and signal attenuation is greater than or equal to 3 dB.

[0003] The above defects have restricted the development of the industry, and a new type of FPC flexible antenna capable of simultaneously optimizing assembly efficiency, electromagnetic compatibility and mechanical reliability is urgently needed. SUMMARY

[0004] The present application aims to provide a method for manufacturing an FPC flexible antenna by integrated injection molding and the antenna to solve the problems in the background art.

[0005] To solve the above technical problems, the technical solution adopted by the present application is: a method for manufacturing an FPC flexible antenna by integrated injection molding, comprising the following steps: S1, FPC pretreatment: a copper foil layer is prepared on the surface of a double-layer polyimide substrate flexible circuit, and a nickel-gold layer is chemically plated on the surface of the copper foil layer to form an FPC flexible circuit board; in this process, an empty slot is arranged in the gold finger area of the FPC flexible circuit board, and a positioning hole is formed at the edge of the FPC flexible circuit board; S2, mold pretreatment: a Teflon coating is sprayed on the inner wall of the mold cavity, and a positioning column matched with the positioning hole is installed in the mold cavity; S3, injection integration: first, the pretreated FPC flexible circuit board is fixed in the mold cavity through the positioning column, at this time, the empty slot in the gold finger area faces the melt flow direction; then, the thermoplastic high polymer material heated to a molten state is injected into the mold cavity, a holding pressure is applied to the injected molten material, so that the molten material completely covers the FPC flexible circuit board, and then cooling is performed, and the FPC flexible antenna is obtained after demolding.

[0006] Preferably, the S3 injection integration further comprises: S4, preparation of the impedance matching layer: coating BaTiO3-PTFE composite material layer by layer in the FPC feed point area to form a coating layer structure of three-layer stepped dielectric constant gradient layer, and heat pressing and curing to make the interface porosity of each layer ≤1%, and the coating thickness of each coating layer is 1 / 8 of the electromagnetic wave wavelength λ; wherein the heat pressing and curing temperature is 150-170℃, and the pressure is 5-8MPa.

[0007] Preferably, after the S3 injection molding integration, it further comprises: the coating layer structure comprises a coating bottom layer, a coating middle layer and a coating top layer arranged from bottom to top, wherein the coating bottom layer comprises a mixture of 80-90wt% PTFE powder and 10-20wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating bottom layer is 2.8±0.2 at 1MHz frequency; the coating middle layer comprises a mixture of 60-80wt% PTFE powder and 20-40wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating middle layer is 3.5±0.2 at 1MHz frequency; the coating top layer comprises a mixture of 50-60wt% PTFE powder and 40-50wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating top layer is 4.2±0.2 at 1MHz frequency.

[0008] Preferably, the coating bottom layer comprises a mixture of 85wt% PTFE powder and 15wt% BaTiO3 nanoparticles; the coating middle layer comprises a mixture of 70wt% PTFE powder and 30wt% BaTiO3 nanoparticles; the coating top layer comprises a mixture of 55wt% PTFE powder and 45wt% BaTiO3 nanoparticles; the particle size of BaTiO3 is 1-3μm, and surface modification by silane coupling agent is required before coating.

[0009] Preferably, in the S1 step, the width of the avoidance groove is 0.3±0.05mm; and the thickness of the double-layer polyimide substrate flexible circuit is 0.08-0.12mm.

[0010] Preferably, in the S1 step, the material of the nickel-gold layer is Ni or Au, and the thickness of the nickel-gold layer is 1-3μm.

[0011] Preferably, in the S2 step, the thickness of the Teflon coating layer is 3-7μm; and the positional tolerance of the positioning column and the positioning hole is ±0.05mm.

[0012] Preferably, in the S3 step, the melting temperature of the thermoplastic polymer is 180-220℃, the holding pressure is 70-90MPa, and the cooling rate is ≤3℃ / s.

[0013] Preferably, in the S3 step, the thermoplastic polymer is PC or ABS.

[0014] The application further provides an integrally injection-molded FPC flexible antenna produced by the method.

[0015] As can be seen from the above description of the structure of the application, compared with the prior art, the application has the following advantages: 1. The FPC flexible circuit board is pre-embedded in the mold cavity, and is covered by PC / ABS material injection molding, so that the antenna and the shell are seamlessly integrated, the manufacturing process of the FPC flexible antenna is simple, the production efficiency is improved, the production cost is reduced, and the stability of the structure is ensured.

[0016] 2. The application forms a coating layer structure of three-layer stepped dielectric constant gradient layers by coating BaTiO3-PTFE composite materials layer by layer in the FPC feed point area, that is, by adjusting the proportion of fillers to realize the gradient change of dielectric constant ε from 2.8 to 4.2, so that the antenna impedance is stabilized at 50Ω±5%.

[0017] 3. The application solves the coupling problem of line damage and impedance mismatch in the traditional injection-molded antenna by strictly following the order of avoiding groove processing→Teflon spraying→gradient dielectric layer hot pressing. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0019] The application will be described in detail below with reference to the embodiments.

[0020] Embodiment 1

[0021] The method for integrally injection-molding an FPC flexible antenna comprises the following steps: S1, FPC pretreatment: preparing a copper foil layer on the surface of a double-layer polyimide substrate flexible circuit with a thickness of 0.08 mm, and chemically plating Ni with a thickness of 1 μm on the surface of the copper foil layer to form an FPC flexible circuit board; in this process, the gold finger area of the FPC flexible circuit board is provided with an avoiding groove with a width of 0.3±0.05 mm, and the edge of the FPC flexible circuit board is shaped with a positioning hole; S2, mold pretreatment: spraying a Teflon coating with a thickness of 3 μm on the inner wall of the mold cavity, and installing a positioning column matched with the positioning hole in the mold cavity, wherein the positional tolerance of the positioning column and the positioning hole is ±0.05 mm; S3, injection molding integration: the pretreated FPC flexible circuit board is fixed in the mold cavity through the positioning column at this time, and the clearance groove in the gold finger area faces the melt flow direction; then, the PC heated to a molten state and at a temperature of 180℃ is injected into the mold cavity, a holding pressure of 70MPa is applied to the injected molten material, so that the molten material completely covers the FPC flexible circuit board, and then cooling at a cooling rate of ≤3℃ / s is carried out, and the FPC flexible antenna is obtained after demolding; S4, preparation of impedance matching layer: BaTiO3-PTFE composite material is coated layer by layer in the FPC feed point area to form a three-layer step dielectric constant gradient layer coating layer structure, and the interface porosity of each layer is ≤1% through heat pressing and curing; the coating thickness of each coating layer is 1 / 8 of the electromagnetic wave wavelength λ; the heat pressing and curing temperature is 150℃, and the pressure is 5MPa; the coating layer structure includes a coating bottom layer, a coating middle layer and a coating top layer arranged from bottom to top, the coating bottom layer includes a mixture of 80wt% PTFE powder and 20wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating bottom layer is 2.8±0.2 at 1MHz frequency; the coating middle layer includes a mixture of 60wt% PTFE powder and 40wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating middle layer is 3.5±0.2 at 1MHz frequency; the coating top layer includes a mixture of 50wt% PTFE powder and 50wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating top layer is 4.2±0.2 at 1MHz frequency; the particle size of BaTiO3 is 1-3μm, and surface modification is required before coating with silane coupling agent.

[0022] Example 2

[0023] The method for integrally injection molding FPC flexible antenna includes the following steps: S1, FPC pretreatment: a copper foil layer is prepared on the surface of a double-layer polyimide substrate flexible circuit with a thickness of 0.10mm, and a chemical plating of Au with a thickness of 2μm is performed on the surface of the copper foil layer to form an FPC flexible circuit board; in this process, the gold finger area of the FPC flexible circuit board is provided with a clearance groove with a width of 0.3±0.05mm, and the edge of the FPC flexible circuit board is shaped with a positioning hole; S2, mold pretreatment: a Teflon coating with a thickness of 5μm is sprayed on the inner wall of the mold cavity, and a positioning column matched with the positioning hole is installed in the mold cavity, wherein the positional tolerance of the positioning column and the positioning hole is ±0.05mm; S3, injection molding integration: the pretreated FPC flexible circuit board is fixed in the mold cavity through the positioning column at this time, and the avoidance slot of the gold finger area faces the melt flow direction; then, the ABS heated to a molten state and with a temperature of 200℃ is injected into the mold cavity, and a holding pressure of 80MPa is applied to the injected molten material, so that the molten material completely covers the FPC flexible circuit board, and then cooling at a cooling rate of ≤3℃ / s is carried out, and the FPC flexible antenna is obtained after demolding; S4, preparation of impedance matching layer: BaTiO3-PTFE composite material is coated layer by layer in the FPC feed point area to form a three-layer step dielectric constant gradient layer coating layer structure, and the interface porosity of each layer is ≤1% through heat pressing and curing, and the coating thickness of each coating layer is 1 / 8 of the electromagnetic wave wavelength λ; wherein the heat pressing and curing temperature is 160℃, and the pressure is 7MPa; wherein: the coating layer structure includes a coating bottom layer, a coating middle layer and a coating top layer arranged from bottom to top, the coating bottom layer includes a mixture of 85wt% PTFE powder and 15wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating bottom layer is 2.8±0.2 at 1MHz frequency; the coating middle layer includes a mixture of 70wt% PTFE powder and 30wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating middle layer is 3.5±0.2 at 1MHz frequency; the coating top layer includes a mixture of 55wt% PTFE powder and 45wt% BaTiO3 nanoparticles, and the dielectric constant ε of the coating top layer is 4.2±0.2 at 1MHz frequency; the particle size of BaTiO3 is 1-3μm, and surface modification is required before coating with silane coupling agent.

[0024] Example 3

[0025] The method for integrally injection molding the FPC flexible antenna comprises the following steps: S1, FPC pretreatment: a copper foil layer is prepared on the surface of a double-layer polyimide substrate flexible circuit with a thickness of 0.12mm, and a thickness of 3μm Ni is electroless plated on the surface of the copper foil layer to form an FPC flexible circuit board; in this process, the gold finger area of the FPC flexible circuit board is provided with an avoidance slot with a width of 0.3±0.05mm, and the edge of the FPC flexible circuit board is shaped with a positioning hole; S2, S2, mold pretreatment: a Teflon coating with a thickness of 7μm is sprayed on the inner wall of the mold cavity, and a positioning column matched with the positioning hole is installed in the mold cavity, wherein the positional tolerance of the positioning column and the positioning hole is ±0.05mm; S3, injection molding integration: the pretreated FPC flexible circuit board is fixed in the mold cavity through the positioning column at this time, and the clearance groove of the gold finger area faces the melt flow direction; then, the PC heated to a molten state and having a temperature of 220 DEG C is injected into the mold cavity, a holding pressure of 90 MPa is applied to the injected molten material, the molten material completely covers the FPC flexible circuit board, and then cooling at a cooling rate of ≤3 DEG C / s is performed, and the FPC flexible antenna is obtained after demolding; S4, preparation of impedance matching layer: BaTiO3-PTFE composite material is coated layer by layer in the FPC feed point area to form a coating layer structure of three-layer stepped dielectric constant gradient layer, and the interface porosity of each layer is ≤1% through heat pressing and curing, and the coating thickness of each coating layer is 1 / 8 of the electromagnetic wave wavelength λ; wherein the heat pressing and curing treatment temperature is 170 DEG C, and the pressure is 8 MPa; wherein: the coating layer structure includes a coating bottom layer, a coating middle layer and a coating top layer arranged from bottom to top, the coating bottom layer includes a mixture of 90wt% PTFE powder and 10wt% BaTiO3 nanoparticles, the dielectric constant ε of the coating bottom layer is 2.8±0.2 at a frequency of 1 MHz; the coating middle layer includes a mixture of 80wt% PTFE powder and 20wt% BaTiO3 nanoparticles, the dielectric constant ε of the coating middle layer is 3.5±0.2 at a frequency of 1 MHz; the coating top layer includes a mixture of 60wt% PTFE powder and 40wt% BaTiO3 nanoparticles, the dielectric constant ε of the coating top layer is 4.2±0.2 at a frequency of 1 MHz; the particle size of BaTiO3 is 1-3 μm, and surface modification is required before coating with silane coupling agent.

[0026] Table 1 - The following table is the VSWR and return loss, in terms of the angle of the transmitting antenna, characterizes how much of the active system output energy is reflected back due to the antenna not being perfectly matched. The closer the antenna impedance and the characteristic impedance of the feedline, the smaller the reflection coefficient, the smaller the VSWR (VSWR≥1, best match when 1), the greater the return loss (RL≥0dB, best match when ∞), the better the match.

[0027] Table 1 is the relationship table of antenna return loss and VSWR

[0028] r (reflection coefficient) RL (return loss) VSWR (voltage standing wave ratio) 1.00 0.00 ∞ 0.90 0.92 19.00 0.80 0.94 9.00 0.70 3.10 5.67 0.60 4.44 4.00 0.50 6.02 3.00 0.40 7.96 2.33 0.30 10.46 1.86 0.20 13.98 1.50 0.10 20.00 1.22 0.09 20.92 1.20 0.08 21.94 1.17 0.07 23.10 1.15 0.06 24.44 1.13 0.05 26.02 1.11 0.04 27.96 1.08 0.03 30.46 1.06 0.02 33.98 1.04 0.01 40.00 1.02 0.00 ∞ 1.00 As can be seen from Table 1, the closer the antenna impedance and the characteristic impedance of the feedline, the smaller the reflection coefficient, the smaller the VSWR (VSWR≥1, best match when 1), the greater the return loss (RL≥0dB, best match when ∞), the better the match. The impedance of the FPC flexible antenna prepared by the method of the application is stable at 50Ω±5%, thereby solving the coupling problem of line damage and impedance mismatch in traditional injection molded antennas.

[0029] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for integrally injection molding a flexible FPC antenna, characterized in that, Includes the following steps: S1, FPC pretreatment: A copper foil layer is prepared on the surface of the double-layer polyimide substrate flexible circuit, and a nickel-gold layer is chemically plated on the surface of the copper foil layer to form an FPC flexible circuit board; during this process, the gold finger area of ​​the FPC flexible circuit board is provided with clearance grooves, and the edge of the FPC flexible circuit board is formed with positioning holes. S2. Mold pretreatment: Teflon coating is sprayed on the inner wall of the mold cavity, and positioning pins that match the positioning holes are installed in the mold cavity; S3. Injection Molding Integration: First, the pre-treated FPC flexible circuit board is fixed in the mold cavity by positioning pins. At this time, the clearance groove in the gold finger area faces the direction of melt flow. Then, the thermoplastic polymer material heated to the molten state is injected into the mold cavity. Holding pressure is applied to the injected molten material to completely cover the FPC flexible circuit board. After cooling, the FPC flexible antenna is obtained after demolding.

2. The method for integral injection molding of an FPC flexible antenna according to claim 1, characterized in that: The S3 injection molding integration also includes: S4. Preparation of impedance matching layer: BaTiO3-PTFE composite material is coated layer by layer in the feed point region of FPC to form a three-layer stepped dielectric constant gradient coating layer structure, and the porosity of each layer interface is ≤1% by hot pressing curing. The coating thickness of each coating layer is 1 / 8 of the electromagnetic wave wavelength λ. The temperature of the hot pressing curing treatment is 150~170℃ and the pressure is 5~8MPa.

3. The method for integrally injection molding an FPC flexible antenna according to claim 2, characterized in that: In step S4, the coating layer structure includes a bottom coating layer, an intermediate coating layer, and a top coating layer arranged from bottom to top. The bottom coating layer comprises a mixture of 80-90 wt% PTFE powder and 10-20 wt% BaTiO3 nanoparticles, and the dielectric constant ε of the bottom coating layer is 2.8 ± 0.2 at a frequency of 1 MHz. The intermediate coating layer comprises a mixture of 60-80 wt% PTFE powder and 20-40 wt% BaTiO3 nanoparticles, and the dielectric constant ε of the intermediate coating layer is 3.5 ± 0.2 at a frequency of 1 MHz. The top coating layer comprises a mixture of 50-60 wt% PTFE powder and 40-50 wt% BaTiO3 nanoparticles, and the dielectric constant ε of the top coating layer is 4.2 ± 0.2 at a frequency of 1 MHz.

4. The method for integral injection molding of an FPC flexible antenna according to claim 3, characterized in that: The coating base layer comprises a mixture of 85 wt% PTFE powder and 15 wt% BaTiO3 nanoparticles; the coating intermediate layer comprises a mixture of 70 wt% PTFE powder and 30 wt% BaTiO3 nanoparticles; the coating top layer comprises a mixture of 55 wt% PTFE powder and 45 wt% BaTiO3 nanoparticles; the BaTiO3 has a particle size of 1~3 μm and needs to be surface modified with a silane coupling agent before coating.

5. The method for integral injection molding of an FPC flexible antenna according to claim 1, characterized in that: In step S1, the width of the clearance groove is 0.3±0.05mm; the thickness of the double-layer polyimide substrate flexible circuit is 0.08~0.12mm.

6. The method for integral injection molding of an FPC flexible antenna according to claim 1, characterized in that: In step S1, the nickel-gold layer is made of Ni or Au, and its thickness is 1~3μm.

7. The method for integral injection molding of an FPC flexible antenna according to claim 1, characterized in that: In step S2, the thickness of the Teflon coating is 3~7μm; the positional tolerance between the positioning post and the positioning hole is ±0.05mm.

8. The method for integral injection molding of an FPC flexible antenna according to claim 1, characterized in that: In step S3, the melting temperature of the thermoplastic polymer is 180~220℃, the holding pressure is 70~90MPa, and the cooling rate is ≤3℃ / s.

9. The method for integral injection molding of an FPC flexible antenna according to claim 1, characterized in that: In step S3, the thermoplastic polymer is PC or ABS.

10. A flexible FPC antenna manufactured by integral injection molding, characterized in that: The FPC flexible antenna is manufactured using the method of integral injection molding as described in any one of claims 1 to 9.