Four-layer flexible circuit board applied to VCM

Abstract

The utility model discloses a four -layer flexible circuit board for VCM, including four layer base material layer each base material layer is established with circuit slot respectively, is equipped with a circuit layer in each circuit slot, is together through pure glue and is adhered respectively between adjacent base material layer and circuit layer, is equipped with the through -hole of mutual correspondence on each base material layer, and the through -hole is filled with conductive layer, and each circuit layer is conducted through the conductive layer, and the top surface of the uppermost layer base material layer and the bottom surface of the bottommost layer base material layer are equipped with the covering film respectively, and the covering film is connected first base material layer and fourth base material layer through pure glue. The utility model can adapt to VCM miniaturization demand, through setting up circuit slot on each layer PI base material layer, directly setting each layer circuit layer in the circuit slot, thereby optimizing multilayer circuit design, while satisfying each performance requirement of VCM, effectively reduce own thickness and volume, can better adapt to the development trend of electronic equipment miniaturization, light and thin, provide the convenience for the compact layout of camera module.

Description

Technical Field

[0001] This utility model relates to the technical field of flexible circuit boards, and in particular to a four-layer flexible circuit board for use in VCM. Background Technology

[0002] In electronic products, the AF (autofocus) and OIS (optical image stabilization) functions of cameras both rely on a voice coil motor (VCM) to move the lens or the image sensor. The voice coil motors that control this movement are mainly divided into open-loop motors and closed-loop motors. Closed-loop motors can achieve higher precision and faster response speeds through position feedback mechanisms. Therefore, closed-loop motors are commonly used in the camera modules of mid-to-high-end mobile phones.

[0003] Flexible circuit boards used in VCMs are primarily used to connect the VCM to other electronic components, enabling electrical signal transmission and mechanical connections to precisely control functions such as camera focusing and image stabilization. Because the VCM requires high-precision position control, its circuit layout and parameter design need to be more precise to ensure the stability and accuracy of signal transmission, thereby achieving fast and accurate camera focusing.

[0004] To match the structure of the VCM, the flexible circuit board used in the VCM is not only small but also has a special shape and size, requiring design based on the specific VCM model and installation location to ensure tight fit with the VCM and other related components. Therefore, the performance of the FPC directly affects the stability and reliability of the voice coil motor. The circuit layout of traditional FPCs is not ideal, making signal transmission susceptible to interference, affecting the accurate execution of focusing and image stabilization commands by the voice coil motor, thus reducing image quality. Furthermore, during the frequent movement of the voice coil motor, problems such as wire breakage and poor contact are prone to occur, significantly shortening the lifespan of the voice coil motor and the entire camera module. In addition, as electronic devices move towards miniaturization and thinner designs, higher demands are placed on the space utilization and heat dissipation performance of FPCs, which traditional FPCs struggle to meet.

[0005] In view of this, this utility model is developed by deeply exploring the many shortcomings and inconveniences caused by the imperfections of existing flexible circuit boards used in VCM, and actively researching, improving and testing them. Utility Model Content

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a four-layer flexible circuit board for use in VCM that can meet the requirements of VCM.

[0007] To achieve the above objectives, the solution of this utility model is:

[0008] A four-layer flexible circuit board for VCM includes a first PI substrate layer, a second PI substrate layer, a third PI substrate layer, and a fourth PI substrate layer. The first PI substrate layer has a first wiring groove, the second PI substrate layer has a second wiring groove, the third PI substrate layer has a third wiring groove, and the fourth PI substrate layer has a fourth wiring groove. A first wiring layer is disposed within the first wiring groove, a second wiring layer within the second wiring groove, a third wiring layer within the third wiring groove, and a fourth wiring layer within the fourth wiring groove. The first substrate layer is bonded to the second substrate layer with adhesive, the second substrate layer is bonded to the third substrate layer with adhesive, and the third substrate layer is bonded to the fourth substrate layer with adhesive. Corresponding through-holes are provided on the first, second, third, and fourth PI substrate layers, and the through-holes are filled with a conductive layer, which conducts the wiring of the first, second, third, and fourth wiring layers. A cover film is respectively provided on the top surface of the first PI substrate layer and the bottom surface of the fourth PI substrate layer, and the cover films are connected to the first and fourth substrate layers with adhesive.

[0009] Furthermore, the first PI substrate layer, the second PI substrate layer, the third PI substrate layer, and the fourth PI substrate layer are formed into the first circuit groove, the second circuit groove, the third circuit groove, and the fourth circuit groove by laser drilling.

[0010] Furthermore, the thickness of the first PI substrate layer, the second PI substrate layer, the third PI substrate layer, and the fourth PI substrate layer is 50 μm, the depth of the first circuit groove, the second circuit groove, the third circuit groove, and the fourth circuit groove is 50 μm, and the thickness of the first circuit layer, the second circuit layer, the third circuit layer, and the fourth circuit layer is 35 μm. The first circuit layer is disposed on the upper part of the first circuit groove, the second circuit layer is disposed on the upper part of the second circuit groove, the third circuit layer is disposed on the lower part of the third circuit groove, and the fourth circuit layer is disposed on the lower part of the fourth circuit groove. Pure adhesive is disposed in the lower part of the first circuit groove, the lower part of the second circuit groove, the upper part of the third circuit groove, and the upper part of the fourth circuit groove.

[0011] Furthermore, the first circuit layer is a coil layer with a thermal pad at the end of the coil, the second circuit layer is a power layer, the third circuit layer is a signal and sensing layer, and the fourth circuit layer is a thermal management and structural reinforcement layer.

[0012] Furthermore, the coil end of the first circuit layer is provided with a thermal pad, the third circuit layer has Hall signal lines with differential pair routing, and the third circuit layer adopts a dual-path signal line redundancy design; the fourth circuit layer has a temperature compensation circuit and a dendritic copper foil with a serpentine flow channel.

[0013] Furthermore, the first circuit layer, the second circuit layer, the third circuit layer, the fourth circuit layer, and the conductive layer are all copper-plated layers.

[0014] By adopting the above solution, the four-layer flexible circuit board of this invention applied to VCM can meet the miniaturization requirements of VCM. By opening circuit grooves on each PI substrate layer and directly placing each circuit layer in the circuit grooves, the multi-layer circuit design is optimized. While meeting the various performance requirements of VCM, it effectively reduces its thickness and volume, better adapting to the development trend of miniaturization and thinning of electronic devices, and providing convenience for the compact layout of camera modules. Improved heat dissipation performance: The rational design of the first, second, third, and fourth circuit layers enables the circuit layers to work together, allowing the FPC to quickly and effectively dissipate the heat generated by the VCM, avoiding the problem of reduced performance and shortened lifespan of the voice coil motor caused by heat accumulation, and improving the stability of the voice coil motor in high-temperature environments. Through the rational four-layer wiring design and signal shielding measures, this invention effectively reduces signal interference and transmission loss, ensuring that the VCM can accurately receive focus and image stabilization commands, thereby significantly improving the imaging quality of the camera and making the captured images clearer and more stable. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the stacked structure of a four-layer flexible circuit board of the present invention applied to VCM.

[0016] Figure 2 This is a schematic diagram of the manufacturing process of the four-layer flexible circuit board of this utility model applied to VCM. Detailed Implementation

[0017] To further explain the technical solution of this utility model, the following detailed description is provided through specific embodiments.

[0018] like Figure 1As shown, this utility model discloses a multilayer flexible circuit board using VCM, which includes a first PI substrate layer 1, a second PI substrate layer 2, a third PI substrate layer 3, and a fourth PI substrate layer 4. The first PI substrate layer 1 has a first wiring groove 11, the second PI substrate layer 2 has a second wiring groove 21, the third PI substrate layer 3 has a third wiring groove 31, and the fourth PI substrate layer 4 has a fourth wiring groove 41. A first wiring layer 5 is disposed within the first wiring groove 11, a second wiring layer 6 is disposed within the second wiring groove 21, a third wiring layer 7 is disposed within the third wiring groove 31, and a fourth wiring layer 8 is disposed within the fourth wiring groove 41. The first substrate layer 1 and the second substrate layer 2... The first PI substrate layer 1, the second PI substrate layer 2, the third PI substrate layer 3, and the fourth PI substrate layer 4 are bonded together with pure adhesive 9. The first PI substrate layer 1, the second PI substrate layer 2, the third PI substrate layer 3, and the fourth PI substrate layer 4 have corresponding through holes 12. The through holes 12 are filled with a conductive layer 10, which conducts the circuits of the first circuit layer 5, the second circuit layer 6, the third circuit layer 7, and the fourth circuit layer 8 through the conductive layer 10. The top surface of the first PI substrate layer 1 and the bottom surface of the fourth PI substrate layer 4 are respectively provided with a cover film, and the cover film is connected to the first substrate layer 1 and the fourth substrate layer 4 with pure adhesive 9.

[0019] Design the circuits for the first circuit layer 5, the second circuit layer 6, the third circuit layer 7, and the fourth circuit layer 8 according to the functional requirements of VCM, and perform reasonable routing on the FPC board. Convert the design file after layout and routing into a Gerber file. The Gerber file contains graphic information of the four layers of FPC (including the shape and position information of circuits, pads, and holes).

[0020] The first line groove 11, the second line groove 21, the third line groove 31, and the fourth line groove 41 are formed by laser drilling through the first PI substrate layer 1, the second PI substrate layer 2, the third PI substrate layer 3, and the fourth PI substrate layer 4 according to Gerber files. In this embodiment, the thickness of the first PI substrate layer 1, the second PI substrate layer 2, the third PI substrate layer 3, and the fourth PI substrate layer 4 is 50 μm, and the depth of the first line groove 11, the second line groove 21, the third line groove 31, and the fourth line groove 41 is 50 μm. (i.e., penetrating the PI substrate layer from top to bottom), the thickness of the first circuit layer 5, the second circuit layer 6, the third circuit layer 7 and the fourth circuit layer 8 is 35um. The first circuit layer 5 is disposed in the upper part of the first circuit groove 11, the second circuit layer 6 is disposed in the upper part of the second circuit groove 21, the third circuit layer 7 is disposed in the lower part of the third circuit groove 31, and the fourth circuit layer 8 is disposed in the lower part of the fourth circuit groove 41. Pure adhesive 9 is provided in the lower part of the first circuit groove 11, the lower part of the second circuit groove 21, the upper part of the third circuit groove 31 and the upper part of the fourth circuit groove 41.

[0021] In a preferred embodiment of this utility model, the first circuit layer 5 is a coil layer, which is the electromagnetic power core used to generate Lorentz force to drive the VCM movement. A thermistor pad is provided at the end of the coil, and it is directly connected to the temperature monitoring circuit of the fourth circuit layer 8 through the conductive layer 10. The second circuit layer 6 is a power layer used for high-efficiency power distribution and electromagnetic interference suppression. The third circuit layer 7 is a signal and sensing layer used for closed-loop control signal transmission and status feedback. The third circuit layer 7 has Hall signal lines with differential pair routing. The third circuit layer 7 adopts a dual-path signal line redundancy design, and the signal attenuation is <3dB after a single path breakage. The fourth circuit layer 8 is a thermal management and structural reinforcement layer used for heat dissipation and mechanical support. The fourth circuit layer 8 has a temperature compensation circuit and a serpentine flow channel with dendritic copper foil to improve the overall thermal conductivity and heat dissipation of the FPC, while also providing mechanical support. In this embodiment, the four circuit layers work together: power supply layer → coil layer → signal layer → thermal management dissipation, forming a closed loop. This invention effectively reduces signal interference and transmission loss through a reasonable four-layer wiring design and signal shielding measures, ensuring that the VCM can accurately receive focus and image stabilization commands, thereby significantly improving the imaging quality of the camera and making the captured images clearer and more stable.

[0022] When this invention is applied to the fabrication of flexible circuit boards for VCMs, four layers of circuitry are designed according to the functional requirements of the VCM. The designed circuit components are laid out on the FPC board using software, and wiring is designed. The design file after the layout and wiring are completed is converted into a Gerber file. The Gerber file contains graphic information of the four layers of the FPC (including the shape and position information of lines, pads, and holes). During the layout, stress relief grooves or notches are designed in areas prone to stress, including the edges of the circuit board and interfaces, so that the stress of the flexible circuit board is dispersed and released when subjected to external forces, protecting the lines from damage.

[0023] like Figure 2As shown, the next step is to fabricate the circuit layers. A PI substrate with a copper layer is selected, where the copper layer mainly serves as a support, providing support for subsequent grooving. According to the Gerber file, laser drilling is used to drill circuit grooves corresponding to the circuit pattern into the PI substrate. The PI substrate after grooving is treated with plasma equipment to remove resin residue, oil, and other contaminants present in the PI grooves. Then, a blackening process is performed, immersing the plasma-treated PI substrate in a blackening agent to form a graphene conductive layer on the wall of the circuit groove. Graphene is deposited on the surface of the circuit groove through physical adsorption, forming a dense conductive layer of 0.5~1μm, which serves as the base for subsequent copper electroplating. For electroplating filling the circuit grooves, the blackened PI substrate is placed in an electroplating tank containing electroplating solution, ensuring that the electroplating solution completely covers the circuit grooves. Electroplating parameters, including current density, electroplating time, and temperature, are adjusted according to factors such as the size and depth of the circuit grooves and the material of the PI substrate. During the electroplating process, maintaining uniform stirring of the electroplating solution ensures that copper ions are evenly deposited within the plating tank. Stirring also promotes the rising and expulsion of air bubbles, resulting in a more uniform distribution of copper ions and improved coating uniformity. To further prevent air bubbles from getting trapped in the plating tank, this invention incorporates an ultrasonic device within the electroplating tank. The vibration of the ultrasonic waves effectively breaks up and disperses air bubbles, preventing them from adhering to the surface or interior of the plating tank. Simultaneously, the ultrasonic waves enhance the mass transfer process of the electroplating solution, improving electroplating efficiency and coating quality. Furthermore, multiple filling processes are employed during electroplating, allowing gas to escape after each filling before proceeding to the next, until the plating thickness in the plating tank reaches the preset thickness. In this embodiment, the plating thickness is 35µm, leaving sufficient space for adhesive bonding within the PI substrate plating tank, thus improving the bonding strength during subsequent lamination. All four circuit layers are fabricated using the above method.

[0024] After each circuit layer is fabricated, the four-layer flexible circuit board used in VCM is fabricated. Single-sided boards with the second and third circuit layers plated are selected for pure adhesive pressing. The pure adhesive is located on the PI side of the two single-sided boards, with a thickness of 25mm, thus pressing the two single-sided boards into a double-sided board. The intermediate layer circuitry is then fabricated, and the outer copper layer at both ends of the double-sided board is etched. Two single-sided boards with the first and fourth circuit layers plated are then pressed with the double-sided board with etched outer copper layer using pure adhesive. The single-sided boards with the first circuit layer plated are then pressed through pure adhesive... Adhesive is pressed onto the top surface of the double-sided board, and a single-sided board with a first circuit layer electroplated is pressed onto the bottom surface of the double-sided board with pure adhesive to form a four-layer flexible circuit board. Then, through holes are drilled. In this embodiment, the diameter of the through holes is 0.2 mm. After drilling, copper is plated into the through holes, and a layer of copper is plated on the top and bottom surfaces of the four-layer flexible circuit board to form the conductive layer 10. In this embodiment, the thickness of the electroplated copper is >10 μm. Then, etching is performed to remove the surface copper to form a four-layer flexible circuit board with conductive lines. After that, it is processed according to the conventional flexible circuit board process.

[0025] The above embodiments and figures are not intended to limit the product form and style of this utility model. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of this utility model.

Claims

1. A four-layer flexible circuit board for use in VCM, characterized in that, include: The system comprises a first PI substrate layer, a second PI substrate layer, a third PI substrate layer, and a fourth PI substrate layer. The first PI substrate layer has a first wiring groove, the second PI substrate layer has a second wiring groove, the third PI substrate layer has a third wiring groove, and the fourth PI substrate layer has a fourth wiring groove. A first wiring layer, a second wiring layer, a third wiring layer, and a fourth wiring layer are disposed within each of the four wiring grooves. The first substrate layer, the second substrate layer, the second substrate layer, the third substrate layer, and the fourth PI substrate layer are bonded together with pure adhesive. Corresponding through-holes are provided on each of the four PI substrate layers, and these through-holes are filled with a conductive layer, which connects the wiring of the first, second, third, and fourth wiring layers. A cover film is provided on the top surface of the first PI substrate layer and the bottom surface of the fourth PI substrate layer, and the cover films are connected to the first and fourth substrate layers with pure adhesive.

2. The four-layer flexible circuit board for VCM as described in claim 1, characterized in that: The first PI substrate layer, the second PI substrate layer, the third PI substrate layer and the fourth PI substrate layer are formed by laser drilling to form the first circuit groove, the second circuit groove, the third circuit groove and the fourth circuit groove.

3. The four-layer flexible circuit board for VCM as described in claim 1, characterized in that: The thickness of the first PI substrate layer, the second PI substrate layer, the third PI substrate layer, and the fourth PI substrate layer is 50 μm. The depth of the first circuit groove, the second circuit groove, the third circuit groove, and the fourth circuit groove is 50 μm. The thickness of the first circuit layer, the second circuit layer, the third circuit layer, and the fourth circuit layer is 35 μm. The first circuit layer is disposed on the upper part of the first circuit groove, the second circuit layer is disposed on the upper part of the second circuit groove, the third circuit layer is disposed on the lower part of the third circuit groove, and the fourth circuit layer is disposed on the lower part of the fourth circuit groove. Pure adhesive is disposed in the lower part of the first circuit groove, the lower part of the second circuit groove, the upper part of the third circuit groove, and the upper part of the fourth circuit groove.

4. A four-layer flexible circuit board for VCM as described in claim 1, characterized in that: The first circuit layer is a coil layer with a thermal pad at the end of the coil. The second circuit layer is a power layer. The third circuit layer is a signal and sensing layer. The fourth circuit layer is a thermal management and structural reinforcement layer.

5. A four-layer flexible circuit board for VCM as described in claim 1, characterized in that: The first circuit layer has a thermal pad at the end of the coil; the third circuit layer has Hall signal lines with differential pair routing; the third circuit layer adopts a dual-path signal line redundancy design; the fourth circuit layer has a temperature compensation circuit and a dendritic copper foil with a serpentine flow channel.

6. A four-layer flexible circuit board for VCM as described in claim 1, characterized in that: The first circuit layer, the second circuit layer, the third circuit layer, the fourth circuit layer, and the conductive layer are all copper plating layers.

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