Flexible substrate, flexible circuit board, preparation method of flexible circuit board and flexible lamp strip

Abstract

The invention discloses a flexible substrate, a flexible circuit board, a preparation method of the flexible circuit board and a flexible lamp strip. The flexible substrate comprises a film, a first copper foil and a second copper foil, the film comprises a first surface and a second surface, and a plurality of conductive holes penetrating through the first surface and the second surface are formed in the film; the first copper foil is attached to the first surface; the second copper foil is attached to the second surface; wherein the first copper foil and the second copper foil are welded at the conductive hole, so that the first copper foil and the second copper foil are electrically connected. According to the flexible circuit board and the substrate thereof provided by the invention, the resistance of the welding spots is small, the solder spreading is uniform, the stability is good, and the preparation process is efficient and environment-friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible circuit board, in particular to a flexible substrate, a flexible circuit board, a preparation method thereof and a flexible lamp strip. BACKGROUND

[0002] The flexible circuit board is a flexible circuit board specially designed for LED lighting and display. It has the characteristics of lightness, thinness and bendable folding, improves the reliability and service life of LED components, and at the same time, the flexible circuit board breaks away from the rectangular restriction of rigid board, has high design freedom and is easy to install, greatly expands the application boundary of LED technology, and is an indispensable electronic component for realizing creative lighting and flexible electronic equipment.

[0003] At present, the traditional process of the flexible circuit board uses high-precision mechanical drilling or laser drilling to punch through holes for interlayer interconnection on the substrate. In order to make the hole wall conductive, chemical copper plating or black hole process is needed to deposit a thin copper layer in the hole, and then full-plate electroplating is performed to thicken the copper layer in the hole to ensure the reliability of the through hole. However, in the actual manufacturing process, due to the involvement of copper plating and electroplating processes, the cost is high, the production cycle is long, and heavy metal pollution of water bodies is involved, which is relatively not friendly to the environment.

[0004] Therefore, there is an urgent need for an alternative process of chemical copper plating or black hole with short production cycle and environment-friendly to realize the conductivity of the hole wall of the through hole on the substrate. SUMMARY

[0005] The purpose of the present application is to provide a flexible substrate, a flexible circuit board, a preparation method thereof and a flexible lamp strip, which aims to solve the problems of high cost, long production cycle and much waste in the preparation of the existing flexible circuit board.

[0006] In a first aspect, the present application provides a flexible substrate, comprising: a film, the film comprising a first surface and a second surface, the film being provided with a plurality of conductive holes penetrating through the first surface and the second surface; a first copper foil, the first copper foil being attached to the first surface; and a second copper foil, the second copper foil being attached to the second surface; wherein the first copper foil and the second copper foil are welded at the conductive holes to electrically connect the first copper foil and the second copper foil.

[0007] In one embodiment, the film is further provided with a plurality of positioning holes penetrating through the first surface and the second surface. The thin film, the first copper foil and the second copper foil all extend along a first direction, the first copper foil has the same width as the thin film along a second direction, and the second copper foil has a width along the second direction smaller than that of the thin film along the second direction, so that the thin film can expose an edge along the second direction relative to the second copper foil, and a plurality of positioning holes are arranged at the edge; The first direction is perpendicular to the second direction.

[0008] In one embodiment, the edge includes a first edge and a second edge arranged opposite on two sides of the thin film, and the first edge and the second edge are both distributed with a plurality of positioning holes.

[0009] In one embodiment, the first copper foil and the second copper foil are laser pulse welded at the conductive holes to electrically connect the first copper foil and the second copper foil.

[0010] In a second aspect, the present application also provides a preparation method of a flexible circuit board, which comprises the following steps: providing a thin film, a first copper foil and a second copper foil; processing a plurality of conductive holes on the thin film; attaching the first copper foil and the second copper foil on two sides of the thin film respectively; applying welding to the first copper foil and the second copper foil at the conductive holes according to a circuit design to electrically connect the first copper foil and the second copper foil to prepare a flexible substrate; preparing a flexible circuit board from the flexible substrate.

[0011] In one embodiment, the welding in the step of applying welding to the first copper foil and the second copper foil at the conductive holes according to a circuit design to electrically connect the first copper foil and the second copper foil is laser pulse welding, the pulse energy of the laser pulse welding is 5-25 MJ, the pulse width is 0.2-1 ms, the pulse frequency is 20-50 Hz, the defocusing amount is -2-0, and the laser pulse welding is protected by inert gas.

[0012] In one embodiment, the step of preparing a flexible circuit board from the flexible substrate specifically comprises: transferring a circuit pattern to the flexible substrate; performing circuit pattern etching on the flexible substrate; attaching a cover film on the flexible substrate; performing surface treatment on the flexible substrate to obtain a flexible circuit board.

[0013] Specifically, transferring the circuit pattern to the flexible substrate comprises: pasting dry photosensitive film on both sides of the flexible substrate respectively, exposing according to the designed circuit pattern, and cleaning the unexposed dry photosensitive film to expose the part of copper foil to be etched. In the process, the unexposed dry photosensitive film is cleaned by 3% sodium carbonate solution.

[0014] Specifically, etching the circuit pattern on the flexible substrate comprises: spraying and etching the exposed part of copper foil on the flexible substrate, and then removing the film to obtain the flexible substrate with etched circuit pattern. In the process, the pressure of the spraying and etching is 1.5 kg for the upper spraying and 2.0 kg for the lower spraying, the spraying time is 2 min, and the film removing process uses 3% sodium hydroxide solution.

[0015] Specifically, after etching the circuit pattern on the flexible substrate, automatic optical detection is performed to detect the qualification of the flexible substrate.

[0016] Specifically, pasting the cover layer on the flexible substrate comprises: pasting the cover film with LED pad and connector position window on the qualified flexible substrate and baking and curing.

[0017] Specifically, the flexible substrate is surface treated to obtain the flexible circuit board, which comprises: printing text, anti-oxidation treatment, and water washing treatment on the flexible substrate, and drying to obtain the flexible circuit board. In the process, the flexible substrate is immersed in OSP medicine after pretreatment, and an anti-oxidation film with a thickness of 0.2 μm to 0.5 μm is formed on the surface of the first copper foil and the second copper foil.

[0018] In one embodiment, in the process of etching the circuit pattern on the flexible substrate, the etching uses 45 ℃ to 50 ℃ and 3% to 5% copper chloride solution.

[0019] In a third aspect, the present application also provides a flexible circuit board, which is a board body prepared by the flexible substrate of any one of the above embodiments or the preparation method of the flexible circuit board of any one of the above embodiments.

[0020] In a fourth aspect, the present application also provides a flexible lamp strip, which comprises the flexible circuit board of any one of the above embodiments.

[0021] The embodiments of the present application have the following beneficial effects: The flexible substrate, the flexible circuit board and the flexible lamp strip adopt the structure that the thin film is provided with a plurality of conductive holes penetrating through the first surface and the second surface, the first copper foil is attached to the first surface, the second copper foil is attached to the second surface, and the first copper foil and the second copper foil are welded at the conductive holes to electrically connect the first copper foil and the second copper foil.

[0022] The preparation method of the flexible circuit board realizes the electrical conductivity between the first copper foil and the second copper foil through welding, has high production efficiency and low cost, does not produce heavy metal wastewater, and has good environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Among them: Figure 1 It is a schematic diagram of the composite mode of the flexible substrate before welding in an embodiment of the present application. Figure 2 It is an AOI automatic optical detection image of the welding point of the flexible substrate in an embodiment of the present application. Figure 3 It is a schematic diagram of the preparation method of the flexible circuit board in an embodiment of the present application.

[0025] Reference signs: 100, thin film; 200, first copper foil; 300, second copper foil; 400, conductive hole; 500, positioning hole. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0028] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" and "second" may explicitly or implicitly include at least one of the stated features. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0029] Please see Figure 1 This invention discloses a flexible substrate, which is a circuit board substrate made of flexible material, providing flexible physical support for flexible circuit boards. One embodiment of the flexible substrate includes a thin film 100, a first copper foil 200, and a second copper foil 300. The thin film 100 includes a first surface and a second surface, and has a plurality of conductive holes 400 penetrating the first surface and the second surface. The first copper foil 200 is bonded to the first surface; the second copper foil 300 is bonded to the second surface. The first copper foil 200 and the second copper foil 300 are soldered at the conductive holes 400 to electrically connect them. The flexible substrate prepared with this structure exhibits uniform solder spread, good stability, no bridging between adjacent solder joints, and low resistance, providing a flexible substrate with superior overall electrical performance and stability.

[0030] Specifically, the material of the film can be either PI (polyimide) or PET (polyester).

[0031] In one embodiment, the film 100 is further provided with a plurality of positioning holes 500 penetrating the first surface and the second surface; the film 100, the first copper foil 200 and the second copper foil 300 all extend along a first direction, the width L2 of the first copper foil 200 is the same as the width L1 of the film 100 along a second direction, and the width L3 of the second copper foil 300 along the second direction is smaller than the width L1 of the film 100 along the second direction, so that the film 100 can expose its edge relative to the second copper foil 300 in the second direction, and the plurality of positioning holes 500 are disposed at the edge; the first direction is perpendicular to the second direction.

[0032] Understandably, the positioning hole 500 allows for the positioning of the composite of the first copper foil 200, the thin film 100, and the second copper foil 300, facilitating subsequent confirmation of the processing reference position. This positioning hole 500 serves two purposes: firstly, it acts as a positioning reference for subsequent laser pulse welding, preventing dimensional deviations during the welding of the conductive hole 400; secondly, it serves as a monitoring reference for the thermal expansion and contraction deformation of the substrate during processing, allowing for correction of subsequent processing positions based on this reference, thus ensuring the processing quality of the flexible substrate.

[0033] Furthermore, in this embodiment, the edge includes a first edge and a second edge disposed opposite to each other on both sides of the film 100, and both the first edge and the second edge are provided with a plurality of positioning holes 500. The positioning holes 500 on both sides facilitate the improvement of positioning accuracy and stability.

[0034] In one embodiment, the first copper foil 200 and the second copper foil 300 are laser pulse welded at the conductive hole 400 to electrically connect the first copper foil 200 and the second copper foil 300.

[0035] Specifically, laser pulse welding uses a high-energy-density laser to form a weld pool at the weld point, which allows the copper foil at the weld point to melt and flow to the copper foil on the other side, ultimately connecting the copper foils on both sides at the conductive hole 400, thus achieving a higher quality weld. Unlike copper plating and film coating, laser pulse welding is highly efficient and produces less waste, making it a green way to achieve conductivity on flexible substrates. In this process, no complex chemical reactions and post-processing are involved, making the overall process green, efficient, and significantly cost-effective.

[0036] Please see Figure 3 This invention also provides a method for preparing a flexible circuit board, the method comprising the following steps: S610, providing a thin film 100, a first copper foil 200, and a second copper foil 300.

[0037] S620, A plurality of conductive holes 400 are formed on the thin film 100.

[0038] S630, the first copper foil 200 and the second copper foil 300 are respectively attached to both sides of the film 100.

[0039] S640. According to the circuit design, the first copper foil 200 and the second copper foil 300 are welded at the conductive hole 400 to electrically connect the first copper foil 200 and the second copper foil 300 to form a flexible substrate.

[0040] S650. The flexible substrate is prepared to form a flexible circuit board.

[0041] It is understood that, through the preparation method of the present invention, the first copper foil 200 and the second copper foil 300 are welded at the conductive hole 400 according to the circuit design, and the first copper foil 200 and the second copper foil 300 are electrically connected to form a flexible substrate. The conductivity between the first copper foil 200 and the second copper foil 300 is achieved by welding. The production efficiency is high and the cost is low. It does not generate heavy metal wastewater and has good environmental friendliness.

[0042] In one embodiment, step S620 specifically includes the following steps: S621. Coat both sides of the film 100 with epoxy adhesive and laminate with a release film. During the adhesive coating process, control the amount of excess adhesive to be 0.08μm~0.1μm.

[0043] S622. Bake the film 100 to set its shape. The baking temperature is 100℃~140℃ and the baking time is 3h~5h.

[0044] Furthermore, the baking temperature can be selected as 100℃, 110℃, 120℃, 130℃ or 140℃, and the baking time can be selected as 3.0h, 3.5h, 4.0h, 4.5h or 5h.

[0045] S623. The positioning hole 500 and the conductive hole 400 are cut out on the film 100 after it has been coated with adhesive and laminated by roll-to-roll punching or circular cutter cutting.

[0046] Step 620 involves pre-cutting positioning holes and conductive holes on the film, which facilitates subsequent positioning and processing and improves processing accuracy. The amount of adhesive overflow controlled during the film-to-release film lamination process provides an allowance for adhesive application to the cut holes, avoiding insufficient adhesive defects.

[0047] In one embodiment, in step S630, specifically, the first copper foil 200 is laminated to one side of the perforated film 100, and the second copper foil 300 is laminated to the other side. The film is then rolled up and pressed together, and baked to obtain a cured substrate.

[0048] Furthermore, the baking temperature in step S630 is between 160℃ and 190℃, and the baking time is between 1.5h and 2.5h. Specifically, the baking temperature can be selected from 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, or 190℃, and the baking time can be selected from 1.5h, 2h, or 2.5h.

[0049] If the baking and curing time is too short or the temperature is too low in step 630, the adhesive will not be able to form a complete chemical bond or cross-linking structure and will not be fully cured, affecting the bonding strength and durability. If the adhesive is over-cured or thermally degraded, its molecular structure will be destroyed, thereby reducing the bonding performance and material life.

[0050] In one embodiment, in step S640, specifically, after the industrial camera optically aligns and identifies the conductive hole 400, the first copper foil 200 and the second copper foil 300 are welded at the location of the conductive hole 400 using a laser to form a weld pool, thereby obtaining the flexible substrate. Using the positioning hole 500 as a reference, the industrial camera, through a high-resolution industrial camera, advanced image processing algorithms, and coordinate mapping relationships, ensures the accuracy of the welding and guarantees the stability of the conductivity of the first copper foil 200 and the second copper foil 300.

[0051] In one embodiment, in step S640, the welding is laser pulse welding, the pulse energy of the laser pulse welding is 5~25MJ, the pulse width is 0.2~1ms, and inert gas protection is used during the laser pulse welding process.

[0052] Specifically, the pulse energy can be selected as 5MJ, 10MJ, 15MJ, 18MJ, 20MJ or 25MJ; the pulse width can be selected as 0.2ms, 0.3ms, 0.4ms, 0.5ms, 0.6ms, 0.7ms, 0.8ms, 0.9ms or 1ms.

[0053] Specifically, the pulse frequency of laser pulse welding is 20~50Hz, selectable from 20Hz, 21Hz, 22Hz, 23Hz, 24Hz, 25Hz, 30Hz, 40Hz, 45Hz or 50Hz; the defocusing amount is -2~0, selectable from -2, -1 or 0; the inert gas can be one of helium, argon or nitrogen. The inert gas can protect the weld pool formed by pulsed laser welding, prevent the weld surface from being oxidized and reduce the conductivity. In addition, the purging shielding gas can make the temperature distribution of the weld pool more uniform, thereby improving the heat transfer and solidification process of the weld pool, avoiding local overheating or undercooling, and reducing cracks in the weld; nitrogen is preferred as the inert gas because it has lower cost.

[0054] In one embodiment, step S650 specifically includes: S651. Transfer the circuit pattern to the flexible substrate.

[0055] S652, Etching circuit patterns on the flexible substrate.

[0056] S653. A cover film is attached to the flexible substrate.

[0057] S654. Perform surface treatment on the flexible substrate to obtain a flexible circuit board.

[0058] In step S650, the circuit pattern is accurately transferred onto the copper foil to form a circuit, providing a pattern template for subsequent etching to form the circuit.

[0059] Specifically, in step S651: photosensitive dry films are attached to both sides of the flexible substrate and exposed according to the designed circuit pattern, and the unexposed photosensitive dry films are cleaned off to expose the copper foil that needs to be etched away.

[0060] The unexposed photosensitive dry film is cleaned using a 3% sodium carbonate solution. The exposure process involves inputting the CAD design data of the circuit board into the computer of the LDI (Laser Direct Imaging) device. The flexible substrate with the photosensitive dry film attached is fixed on the worktable of the LDI device. The LDI system scans the positioning points on the flexible substrate, calculates the actual tensile, compressive, and torsional deformation of the entire board, and corrects the graphic deformation and data in a timely manner. After data correction, the control system drives the laser head to use a focused UV laser beam to perform high-speed and precise scanning on the substrate surface according to the corrected graphic data. An exposure reaction occurs where the laser point passes.

[0061] Specifically, in step S652, the exposed copper foil is etched away by spraying under pressure on the top and bottom of the flexible substrate, and then the film is removed to obtain a flexible substrate with a circuit pattern formed after etching. The pressure of the upper and lower pressurized spraying is 1.5 kg for the upper spray and 2.0 kg for the lower spray, and the spraying time is 2 min; the film removal process uses a 3% sodium hydroxide solution.

[0062] Specifically, after etching circuit patterns on a flexible substrate, an automated optical inspection is performed to check the qualification of the flexible substrate.

[0063] Specifically, in step S653, after opening the LED pad and connector position windows in the cover film, it is attached to the qualified flexible substrate and baked to cure. The cover film is a thin film 100 with adhesive and solder resist white oil, used to protect the circuit. After the cover film is bonded to the flexible substrate, it is pressed together by a hot press at 180°C and 135kg pressure for 80 seconds, and then placed in an oven and baked at 170°C for 1 hour to allow the adhesive to fully cure.

[0064] Specifically, in step S654, the flexible substrate is subjected to text printing, anti-oxidation treatment and water washing treatment and then dried to obtain a flexible circuit board. The text printing process involves printing the required text and graphics on the flexible LED strip circuit board at the corresponding positions using a high-speed automatic screen printing machine, and then baking and curing them. The antioxidant treatment process involves immersing the flexible substrate in OSP solution after pretreatment to form an antioxidant film with a thickness of 0.2~0.5μm on the surface of the first copper foil 200 and the second copper foil 300. The water washing process involves washing away excess chemicals from the surface with water, followed by thorough drying of the flexible circuit board with hot air or infrared rays to prevent water stains from remaining. The pretreatment process involves micro-etching with 3-5% dilute hydrochloric acid.

[0065] In this embodiment, the organic molecules in the OSP solution undergo a complexation reaction with the copper foil surface, forming a dense organic protective film on the copper surface through chemical bonding.

[0066] In one embodiment, during the step of etching the circuit pattern on the flexible substrate, the etching is performed using a 3% to 5% copper chloride solution at 45°C to 50°C.

[0067] Please see Figure 1 This invention provides a flexible circuit board, which is a board body prepared using the flexible substrate of any of the above embodiments or the preparation method of the flexible circuit board of any of the above embodiments. It is understood that the first copper foil 200 and the second copper foil 300 are soldered at the conductive hole 400, electrically connecting the first copper foil 200 and the second copper foil 300. The flexible substrate made with this structure exhibits uniform solder spread, good stability, no bridging between adjacent solder joints, and low resistance, providing a flexible substrate with superior overall electrical performance and stability.

[0068] Please see Figure 1 This invention provides a flexible light strip, which includes the flexible circuit board of any of the above embodiments. It is understood that the first copper foil 200 and the second copper foil 300 are soldered at the conductive hole 400, electrically connecting the first copper foil 200 and the second copper foil 300. The flexible substrate manufactured with this structure exhibits uniform solder spread, good stability, no bridging between adjacent solder joints, and low resistance, providing a flexible substrate with superior overall electrical performance and stability.

[0069] More specific implementation examples will be described in detail below.

[0070] Example 1 This embodiment discloses a method for fabricating a flexible circuit board, specifically including the following steps: Step 1: Fabrication of flexible substrate.

[0071] Positioning holes 500 and conductive holes 400 are cut on the film 100: The 255mm wide and 25μm thick polyimide film 100 is coated with epoxy adhesive on both sides and laminated with a release film, and baked at 120℃ for 4 hours to set the shape, controlling the amount of adhesive overflow to 0.09μm; the positioning holes 500 and conductive holes 400 are punched on the coated and laminated thick polyimide film 100.

[0072] Composite copper foil with film 100: Composite one side of the perforated thick polyimide film 100 with first copper foil 200 and the other side with second copper foil 300 to obtain an uncured substrate. The first copper foil 200 is 255 mm wide and 20 μm thick, and the second copper foil 300 is 250 mm wide and 20 μm thick. Roll-to-roll and press the uncured substrate together, and bake at 175°C for 2 hours to obtain a cured substrate.

[0073] Conductivity of the flexible substrate is achieved by welding conductive holes 400: After the conductive holes 400 are optically aligned and identified by an industrial camera, the first copper foil 200 and the second copper foil 300 are welded at the location of the conductive holes 400 by laser pulse to obtain the flexible substrate. Inert gas protection is used during the laser pulse welding process.

[0074] The pulse energy of laser pulse welding is 15MJ, the pulse width is 0.5ms, the pulse frequency is 40Hz, and the defocusing amount is -1.

[0075] Step 2: Transfer the circuit pattern to the flexible substrate.

[0076] Photosensitive dry films are attached to both sides of the flexible substrate.

[0077] The CAD design data of the circuit pattern is input into the computer of the laser direct imaging device. The flexible substrate with the photosensitive dry film attached is fixed on the worktable of the LDI device. The LDI system calculates the actual tensile, compressive and torsional deformation of the entire board by scanning the positioning points on the flexible substrate and corrects the pattern deformation and data in a timely manner. After the data correction, the control system drives the laser head to use a focused UV laser beam to perform high-speed and precise scanning on the surface of the flexible substrate according to the corrected pattern data. An exposure reaction occurs where the laser point passes.

[0078] Use a 3% sodium carbonate solution to wash away the unexposed dry film, exposing the copper foil that needs to be etched away.

[0079] Step 3: Etch the circuit pattern on the flexible substrate.

[0080] The flexible substrate is mounted onto the roll-to-roll etching machine and introduced into the working plane of the etching tank production line. It is then sprayed with a 45°C, 4% copper chloride solution at an upper spray pressure of 1.5 kg and a lower spray pressure of 2.0 kg for 2 minutes. The copper foil without dry film protection is etched away, leaving the designed circuit pattern. The dry film protecting the circuit pattern is then removed with 3% sodium hydroxide.

[0081] Step 4: Conformity test.

[0082] AOI (Automated Optical Inspection) is performed on flexible substrates to check for circuit defects, breaks, and the integrity of the circuit pattern.

[0083] Step 5: Composite a cover layer onto the flexible substrate.

[0084] Pre-cut windows for LED pads and connector positions, precisely align the cover film with the completed circuit flexible substrate, press it together for 80 seconds at 180℃ and 135kg pressure using a hot press, and then place the pressed flexible substrate in an oven and bake at 170℃ for 1 hour to allow the adhesive to fully cure.

[0085] Step 6: Perform surface treatment on the flexible substrate to obtain a flexible circuit board.

[0086] According to the design requirements, the required text and graphics are printed on the flexible substrate at the corresponding positions using a high-speed automatic screen printing machine and then baked and cured.

[0087] The above-mentioned flexible substrate is acid-washed and then immersed in OSP solution to form a 0.4μm organic protective film. Excess OSP solution on the surface is washed off with water, and the flexible circuit board is thoroughly dried with hot air or infrared light to prevent water stains from remaining.

[0088] Comparative Example 1 The difference from Example 1 is that in step 1, an electroplating copper plating process is used to achieve the electrical connection between the first copper foil 200 and the second copper foil 300.

[0089] The resulting flexible circuit board was subjected to performance testing.

[0090] 1. Conductivity test of flexible circuit boards: The flexible circuit board prepared in Example 1 was subjected to AOI automated optical inspection. The inspection results are shown in [Figure 1]. Figure 2 ,from Figure 2 As can be seen, there were no signs of incomplete welding, false welding, or cold welding. The solder was spread evenly, the weld joints were smooth and bright, and there was no bridging.

[0091] 2. Electrical testing of flexible printed circuit boards: The flexible circuit boards and electroplated copper-clad flexible circuit boards prepared in Example 1 and Comparative Example 1 were subjected to contact resistance tests. The test methods were as follows: Using a micro-ohmmeter and a four-point wire test multimeter, and in accordance with the electrical testing requirements of IPC-9252 PCB printed circuit boards and assemblies, the solder joint resistance of five solder joints and the via resistance of five vias were accurately measured using the four-wire method. The test results are as follows: Table 1 As shown in Table 1, the flexible circuit board obtained in Embodiment 1 of the present invention has low solder joint resistance and small resistance difference between solder joints; while in the copper-plated flexible circuit board, the resistance at the copper plating is high and the resistance difference between holes is large.

[0092] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A flexible substrate, characterized in that, include: A thin film, comprising a first surface and a second surface, wherein the thin film is provided with a plurality of conductive holes penetrating the first surface and the second surface; The first copper foil is bonded to the first surface; as well as The second copper foil is bonded to the second surface; The first copper foil and the second copper foil are soldered at the conductive hole to electrically connect the first copper foil and the second copper foil.

2. The flexible substrate according to claim 1, characterized in that, The film is also provided with a plurality of positioning holes penetrating the first surface and the second surface; The film, the first copper foil, and the second copper foil all extend along a first direction. The width of the first copper foil and the film along a second direction is the same, and the width of the second copper foil along the second direction is less than the width of the film along the second direction, so that the film can expose its edge relative to the second copper foil in the second direction. A plurality of positioning holes are provided at the edge. The first direction is perpendicular to the second direction.

3. The flexible substrate according to claim 2, characterized in that, The edge includes a first edge and a second edge disposed opposite to each other on both sides of the film, and both the first edge and the second edge are provided with a plurality of positioning holes.

4. The flexible substrate according to claim 1, characterized in that, The first copper foil and the second copper foil are laser pulse welded at the conductive hole to electrically connect the first copper foil and the second copper foil.

5. A method for fabricating a flexible circuit board, characterized in that, The preparation method includes the following steps: Provide a thin film, a first copper foil, and a second copper foil; A plurality of conductive holes are formed on the thin film; The first copper foil and the second copper foil are respectively attached to both sides of the film; According to the circuit design, the first copper foil and the second copper foil are soldered at the conductive hole to electrically connect the first copper foil and the second copper foil to prepare a flexible substrate; The flexible substrate is used to fabricate a flexible circuit board.

6. The method for preparing a flexible circuit board according to claim 5, characterized in that, The steps involve welding the first copper foil and the second copper foil at the conductive hole according to the circuit design, electrically connecting the first copper foil and the second copper foil. The welding is laser pulse welding, with a pulse energy of 5~25MJ and a pulse width of 0.2~1ms. Inert gas protection is used during the laser pulse welding process.

7. The method for preparing a flexible circuit board according to claim 5, characterized in that, The step of fabricating the flexible substrate into a flexible circuit board specifically includes: Transfer the circuit pattern to the flexible substrate; Circuit patterns are etched onto the flexible substrate; A cover film is laminated onto the flexible substrate; The flexible substrate is surface treated to obtain a flexible circuit board.

8. The method for preparing a flexible circuit board according to claim 7, characterized in that, In the step of etching the circuit pattern on the flexible substrate, the etching is performed using a 3% to 5% copper chloride solution at 45°C to 50°C.

9. A flexible circuit board, characterized in that, The flexible circuit board is a board body prepared by using the flexible substrate according to any one of claims 1 to 4 or by the preparation method of the flexible circuit board according to any one of claims 5 to 8.

10. A flexible light strip, characterized in that, The flexible light strip includes the flexible circuit board as described in claim 9.

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