Mirco LED circuit board and manufacturing method thereof

Abstract

The invention relates to a Mirco LED circuit board and a manufacturing method thereof. The method comprises the following steps: providing an auxiliary film; laser is adopted for melting copper slurry, the molten copper slurry is made to drop on a predefined bonding pad area on the first face of the auxiliary film one by one to be solidified to form a bonding pad, after the copper slurry drops on the bonding pad area, a magnetic field perpendicular to the auxiliary film is applied to one side of the auxiliary film, and the direction of the magnetic field is opposite to the dropping direction of the copper slurry; forming a circuit pattern connected with the bonding pad on the auxiliary film; removing the auxiliary film to obtain a circuit substrate; and connecting the Mirco LED chip to the bonding pad on the circuit substrate to obtain the Mirco LED circuit board. The auxiliary film is used for determining the position where the copper slurry is formed into the bonding pad on the auxiliary film, and the magnetic field perpendicular to the direction of the auxiliary film is used for restraining the outward diffusion range of the copper slurry dripping on the auxiliary film, so that the curing and forming size of the copper slurry can be accurately controlled, the position and size of the bonding pad are more accurate, and the production efficiency is improved. And the yield of the Mirco LED circuit board can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of Micro LED circuit board manufacturing, and particularly to a Micro LED circuit board and a manufacturing method thereof. Background Art

[0002] With the progress of LCD (Liquid Crystal Display) screen backlight technology, the display effect brought by traditional LED (Light Emitting Diode) backlight can no longer meet the needs of consumers for higher display effects. For this reason, Micro-LED (Micro - Light Emitting Diode) technology has emerged.

[0003] Micro-LED display technology refers to a display technology that uses self-luminous micron-scale LEDs as light-emitting pixel units and assembles them onto a driving panel to form a high-density LED array. Due to the characteristics of small size, high integration, and self-luminance of Micro-LED chips, it has greater advantages in terms of brightness, resolution, contrast, energy consumption, service life, response speed, and thermal stability compared with LCD and OLED (Organic Light-Emitting Diode).

[0004] Micro-LED products are to thin-film, miniaturize, and array the LED structure, reduce the size to about 1 - 10 μm, transfer them to a substrate in a batch manner, and then perform encapsulation to complete the display of micro diodes. With the miniaturization and multi-functionality of Micro-LED electronic products, the integration of the PCB (Printed Circuit Board) inside the electronic products is required to be further improved, and the circuit patterns on the PCB will become more and more complex, and more circuits need to be processed on a PCB of a certain area. With the densification and complication of the circuits, higher requirements are put forward for the accuracy of the pads and circuits on the circuit board.

[0005] Therefore, how to accurately form the circuits on the circuit board is an urgent problem to be solved. Summary of the Invention

[0006] Based on this, it is necessary to provide a Micro LED circuit board and a manufacturing method thereof.

[0007] A manufacturing method of a Micro LED circuit board includes:

[0008] Providing an auxiliary film;

[0009] Using a laser to melt copper paste, the molten copper paste is dropped drop by drop on a predefined pad area on the first surface of the auxiliary film to solidify and form pads. Among them, after the copper paste is dropped on the pad area, a magnetic field perpendicular to the auxiliary film is applied on one side of the auxiliary film, and the direction of the magnetic field is opposite to the dropping direction of the copper paste;

[0010] Form a circuit pattern connected to the pads on the auxiliary film;

[0011] Remove the auxiliary film to obtain a circuit substrate;

[0012] Connect the Mirco LED chip to the pads on the circuit substrate to obtain a Mirco LED circuit board.

[0013] In one embodiment, the step of providing the auxiliary film includes:

[0014] Provide the auxiliary film and place the auxiliary film horizontally;

[0015] The step of applying a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film after the copper paste is dropped on the pad area includes:

[0016] After a first preset time after the copper paste is dropped on the pad area, apply a vertically upward magnetic field below the auxiliary film until the copper paste solidifies in the pad area to form the pads.

[0017] In one embodiment, the first preset time is 20 ms to 60 ms.

[0018] In one embodiment, in the step of applying a vertically upward magnetic field below the auxiliary film, the duration of the applied magnetic field is 100 ms to 300 ms.

[0019] In one embodiment, the step of applying a vertically upward magnetic field below the auxiliary film includes:

[0020] After a second preset time of applying a vertically upward magnetic field below the auxiliary film, use multi-source ultrasonic waves to emit ultrasonic waves along a direction perpendicular to the auxiliary film to perform multi-source oscillation on the auxiliary film, and the duration of the ultrasonic waves is 50 ms to 150 ms.

[0021] In one embodiment, the second preset time is 10 ms to 50 ms.

[0022] In one embodiment, the step of forming a circuit pattern connected to the pads on the auxiliary film includes:

[0023] Apply hot melt adhesive on the first side of the auxiliary film, and remove the hot melt adhesive on the pad;

[0024] Deposit an initial copper layer on the hot melt adhesive;

[0025] Attach a dry film on the initial copper layer, expose and develop the dry film;

[0026] Perform horizontal electroplating on the area outside the dry film covered area to form a circuit pattern;

[0027] Strip and flash etch, strip to remove the dry film, and flash etch to remove the initial copper layer covered by the dry film;

[0028] Remove the auxiliary film, and apply hot melt adhesive on the surfaces of the pad and the circuit pattern;

[0029] Laser clean the hot melt adhesive on the surface of the pad to expose the pad on the side where the circuit pattern is located.

[0030] In one embodiment, laser polish the pad formed by curing and stacking copper paste to form a cylindrical pad polish.

[0031] In one embodiment, before the step of providing the auxiliary film, it further includes:

[0032] Place the auxiliary film horizontally, and determine the coordinates on the auxiliary film by combining machine vision positioning;

[0033] Determine the predefined pad area according to the coordinates on the auxiliary film;

[0034] Use laser ablation technology to ablate a burr surface in the pad area.

[0035] A Mirco LED circuit board is manufactured by using the Mirco LED circuit board manufacturing method described in any of the above embodiments.

[0036] The above Mirco LED circuit board and its manufacturing method use an auxiliary film to determine the position where copper paste forms a pad on the auxiliary film, and use a magnetic field perpendicular to the direction of the auxiliary film to constrain the diffusion range of the copper paste dropped on the auxiliary film, so as to be able to accurately control the size of the copper paste curing and forming, and further make the position and size of the pad more accurate, which is beneficial to improving the yield of the Mirco LED circuit board. Description of the Drawings

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 It is a schematic flow chart of a manufacturing method of a Mirco LED circuit board for an embodiment. Detailed implementation manners

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0040] It is worth mentioning that in a Micro-LED circuit board, the pad is used to connect with the Micro-LED chip. The size of the Micro-LED chip is usually between 1 and 100 μm. Since the Micro-LED chip is extremely small, in order to align the clicks on the Micro-LED chip, the position of the pad needs to be very precise. In addition, the position of the pad will also affect the distance, shape and position of the circuit. If there are errors in the position and size of the pad, it will affect the connection of the electrodes of the Micro-LED chip, and through cumulative amplification, it will affect the accuracy of the circuit, resulting in a decrease in the yield of the circuit board. In the prior art, CN116895726A forms pads by means of an auxiliary film and uses a laser 3D forming method to form pads on the auxiliary film, which can ensure the accuracy of the position, shape and size of the pads. However, since the copper paste is in a liquid state and dripped on the auxiliary film, the copper paste will freely diffuse until it solidifies before solidification. Therefore, although the auxiliary film can help position the formed pads, it still cannot very accurately constrain the size and shape of the copper paste on the auxiliary film. For this reason, the present application provides a manufacturing method of a Mirco LED circuit board that can constrain the diffusion of the copper paste on the auxiliary film to make the size and shape of the formed pads more precise.

[0041] As Figure 1 shown, it is a manufacturing method of a Mirco LED circuit board according to an embodiment of the present invention, including:

[0042] Step 110, providing an auxiliary film.

[0043] In this embodiment, the auxiliary film is used to assist in pad positioning and forming circuit patterns. The auxiliary film can be a PET (Polyethylene terephthalate) film or a ceramic film, such as an alumina ceramic film or a silicon nitride ceramic film.

[0044] Step 120: Use a laser to melt the copper paste so that the molten copper paste drops drop by drop on the pad area predefined on the first surface of the auxiliary film. Apply a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film until the copper paste solidifies to form a pad, where the direction of the magnetic field is opposite to the dropping direction of the copper paste.

[0045] In this embodiment, the copper material is heated by a laser so that the copper material located above the auxiliary film melts to form copper paste. The copper paste drops on the pad area of the auxiliary film, and the diffusion of the copper paste on the auxiliary film is restricted by the magnetic field.

[0046] Specifically, when the copper paste drops on the auxiliary film, its shape can be approximately regarded as a disc. Subsequently, the copper paste flows and diffuses outward under the action of gravity. The molten copper paste is still a good conductor and moves in the magnetic field. For force analysis, the outward diffusion movement of the copper paste can be regarded as multiple individual copper conductor movements along the diameter direction of the disc. At this time, according to the right-hand rule, the induced current generated is along the tangent direction of the disc, and according to the left-hand rule, the Lorentz magnetic force received by the copper conductor is perpendicular to the tangent direction and towards the center of the disc, that is, the direction of the Lorentz magnetic force is opposite to the movement direction. Therefore, the movement of the copper conductor can be blocked, and in this way, the diffusion of the copper paste on the auxiliary film can be effectively restricted.

[0047] In this embodiment, by setting a magnetic field with a reasonable magnetic induction intensity, the force on the copper paste can be effectively and accurately controlled, the diffusion range can be restricted, and thus the size of the pad forming can be accurately controlled.

[0048] Step 130: Form a circuit pattern connected to the pad on the auxiliary film.

[0049] Step 140: Remove the auxiliary film to obtain a circuit substrate.

[0050] Step 150: Connect the Mirco LED chip to the pad on the circuit substrate to obtain a MircoLED circuit board.

[0051] In this embodiment, an auxiliary film is used to determine the position where the copper paste forms a pad, and a magnetic field perpendicular to the direction of the auxiliary film is used to restrict the spreading range of the copper paste dropped on the auxiliary film, so that the size of the solidified and formed copper paste can be accurately controlled, and further the position and size of the pad are more accurate, which is beneficial to improving the yield of the MircoLED circuit board.

[0052] In order to accurately restrict the spreading range of the copper paste on the auxiliary film, in one embodiment, the step of applying a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film includes: after the copper paste is dropped on the pad area, a magnetic field perpendicular to the auxiliary film is applied on one side of the auxiliary film.

[0053] In this embodiment, after the copper paste is dropped on the pad area and before the copper paste is solidified, the magnetic field source is turned on to form a magnetic field in the direction perpendicular to the auxiliary film. It is worth mentioning that when the copper paste is dropped, it is in a droplet state and its diameter is smaller than the pad area. In this embodiment, the magnetic field is applied after the copper paste is dropped on the pad area, aiming to allow the copper paste to spread slightly when it is just dropped on the auxiliary film to cover the pad area, and then the magnetic field is applied to restrict the spread of the copper paste, so as to ensure that the size of the pad can accurately cover the pad area and form a pad.

[0054] In one embodiment, the step of providing the auxiliary film includes:

[0055] Provide the auxiliary film and place the auxiliary film horizontally;

[0056] The step of applying a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film after the copper paste is dropped on the pad area includes:

[0057] After a first preset time after the copper paste is dropped on the pad area, a magnetic field with a vertically upward direction is applied below the auxiliary film until the copper paste is solidified in the pad area to form the pad.

[0058] In this embodiment, the copper paste is dropped above the auxiliary film and the auxiliary film is placed horizontally, which is beneficial for the copper paste to accurately drop on the pad area of the auxiliary film. Moreover, placing the auxiliary film horizontally can prevent the copper paste from sliding and spreading to one side due to inclination, so that the formed copper paste can be circular and the shape of the formed pad is more accurate.

[0059] In this embodiment, the magnetic field source is located below the auxiliary film, the magnetic field direction is vertically upward, and the magnetic field passes through the auxiliary film and acts on the copper paste dropped on the auxiliary film. In this way, a Lorentz magnetic force in the direction towards the center of the circle can be formed on the copper paste to effectively restrict the diffusion movement of the copper paste.

[0060] In addition, in this embodiment, the magnetic field source is not activated at the moment when the copper paste drops onto the auxiliary film, but a magnetic field is applied after a first preset time after the copper paste has dropped, aiming to reserve an initial diffusion time for the copper paste so that the copper paste can fully cover the pad area.

[0061] In one embodiment, the first preset time is 20 ms to 60 ms. In this embodiment, the magnetic field source is activated 20 ms to 60 ms after the copper paste drops onto the pad area of the auxiliary film to apply a magnetic field to the copper paste, aiming to allow the copper paste to diffuse from a droplet to a disc shape and reserve a diffusion time for the copper paste to spread from the droplet form to cover the pad area. It is worth mentioning that if the magnetic field is activated immediately when the copper paste drops onto the pad area, the droplet-shaped copper paste will be restricted and unable to spread fully. On the other hand, if the first preset time is too long, the copper paste will diffuse excessively and the copper paste is close to curing or has already cured. Therefore, in this embodiment, activating the magnetic field source 20 ms to 60 ms after the copper paste drops onto the pad area of the auxiliary film can enable the copper paste to spread fully and effectively avoid excessive diffusion of the copper paste. In one embodiment, the first preset time is 50 ms. In this embodiment, activating the magnetic field source 50 ms after the copper paste drops onto the pad area of the auxiliary film can enable the copper paste to spread fully and effectively avoid excessive diffusion of the copper paste, thereby forming a copper paste that fully covers the pad area and making the curing and forming effect of the copper paste better.

[0062] In one embodiment, in the step of applying a vertically upward magnetic field below the auxiliary film, the duration of the applied magnetic field is 100 ms to 300 ms. In this embodiment, applying the magnetic field for 100 ms to 300 ms can effectively restrict the excessive diffusion of the copper paste and, moreover, can avoid keeping the magnetic field on for a long time, effectively saving energy consumption.

[0063] In one embodiment, the step of using a laser to melt the copper paste so that the molten copper paste drops onto the pad area predefined on the first surface of the auxiliary film and applying a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film until the copper paste cures to form a pad includes:

[0064] Using a laser to melt the copper paste so that the molten copper paste drops one by one. During the dropping process, a vertically upward magnetic field is applied below the auxiliary film. When the copper paste drops onto the pad area predefined on the first surface of the auxiliary film, the application of the magnetic field is stopped. 20 ms to 60 ms after the copper paste drops onto the pad area of the auxiliary film, a vertically upward magnetic field is applied below the auxiliary film again until the copper paste cures to form a pad.

[0065] In this embodiment, a magnetic field is applied during the dripping process of the copper paste. The purpose is to prevent the copper paste in the form of droplets from shifting. It is worth mentioning that when the copper paste falls vertically, the velocity direction is parallel to the magnetic field direction. At this time, the Lorentz force acting on the copper paste is 0. However, if the copper paste deviates during the vertical falling process, it will cut the magnetic induction lines and thus be subjected to the Lorentz force. Therefore, the magnetic field can effectively restrain the deviation of the copper paste, enabling the copper paste to be accurately dripped onto the pad area. After the copper paste contacts the pad area, the magnetic field is stopped, allowing the copper paste to undergo preliminary diffusion to cover the pad area. After 20 ms to 60 ms, the magnetic field is applied again to restrain the copper paste and prevent excessive diffusion of the copper paste, thereby forming a copper paste that fully covers the pad area and achieving a better curing and forming effect. Through the above process, the position and size of the formed pad are more accurate.

[0066] The specific process of applying the magnetic field is as follows:

[0067] When a molten copper droplet (a conductive fluid) moves in a magnetic field, the internal free electrons move to generate a current density J, which in turn induces a Lorentz force. Therefore, we have: F L = J × B, where F L is the Lorentz force, J is the current density, and B is the magnetic induction intensity.

[0068] When the copper droplet falls vertically, the velocity direction v is parallel to the magnetic field B direction. At this time, the vector value of v × B is 0, and the Lorentz force is 0.

[0069] After the copper droplet contacts the auxiliary film, it begins to flow and diffuse horizontally. The velocity v direction turns horizontal and is perpendicular to the magnetic field B direction, θ = 90°. At this time, the direction of F L is perpendicular to the velocity v direction and the magnetic field B direction, forming a radial contraction force to prevent the copper paste from diffusing.

[0070] Specifically, when the copper droplet flows horizontally, a circular eddy current is formed inside. The interaction between the eddy current density J and the magnetic field B generates a centripetal force:

[0071] F 约束 ∝ σvB 2 r 2

[0072] where σ is the electrical conductivity of the copper liquid, v is the flow velocity, and r is the droplet radius.

[0073] For example: for a droplet with a diameter d = 5 μm (r = 2.5 μm), a magnetic field B = 1 T, and a flow velocity v = 0.5 m / s, the restraining force is:

[0074] F 约束 ≈ 1.2×10 -6 N

[0075] This binding force is sufficient to counteract the surface tension-driven diffusion.

[0076] Through high-speed imaging observation, after the magnetic field is turned on, when B≥1.2T, the diffusion speed of the copper paste decreases from 1.2m / s to 0.3m / s, and the final diameter shrinks to 60% of that without the magnetic field, and the diffusion diameter can be reduced by more than 40%. The vertical upward magnetic field can effectively constrain the diffusion range of the molten copper droplet on the auxiliary film through the radial contraction effect generated by the Lorentz force, so that the copper paste can accurately form a pad in the pad area.

[0077] In one embodiment, in the step of applying a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film, the magnetic induction intensity of the applied magnetic field is greater than or equal to 1.2T and less than or equal to 1.8T. In this way, the copper paste can be effectively constrained within the required pad area. In one embodiment, the magnetic induction intensity of the applied magnetic field is 1.5T. Compared with the case without the magnetic field, the diffusion diameter of the copper droplet on the auxiliary film is reduced by about 40%. Since no magnetic field is applied when the copper droplet initially contacts the auxiliary film, the copper droplet can diffuse at the initial contact. Therefore, when the magnetic induction intensity of 1.5T is applied after the first preset time, the diffusion diameter on the auxiliary film can be reduced by about 25% compared with the case without the magnetic field, so as to accurately control the diffusion of the copper droplet and avoid diffusion outside the pad area, making the size of the pad more accurate.

[0078] It is worth mentioning that in order to accurately detect the dripping of the copper paste onto the pad area, in some embodiments, a CCD (charge coupled device) can be used to collect the image of the auxiliary film, and image analysis is used to detect the copper paste dripping on the pad, so as to detect the dripping of the copper paste onto the pad area and accurately determine the moment when the copper paste contacts the pad area. In order to further accurately determine the moment when the copper paste drips onto the pad area, in some embodiments, an infrared detection probe can also be used to detect the dripping of the copper paste onto the auxiliary film. The infrared detection probe can identify the temperature of an object and can detect a moving object. Therefore, it can detect the movement of the copper paste in real time and accurately determine the moment when the copper paste drips onto the pad area, and then realize the precise control of the turning on and off of the magnetic field.

[0079] In one embodiment, the step of applying a vertically upward magnetic field below the auxiliary film includes:

[0080] After a second preset time of applying a vertically upward magnetic field below the auxiliary film, multi-source ultrasonic waves are emitted along the direction perpendicular to the auxiliary film to oscillate the auxiliary film multi-source, where the duration of the ultrasonic wave is 50ms to 150ms.

[0081] In this embodiment, ultrasonic waves are used to cause local multi-source high-frequency vibrations of the auxiliary film, aiming to enable the copper paste located in the pad area to be evenly spread while being constrained by the magnetic field. In this embodiment, the multi-source ultrasonic waves are used to ensure that the vibrations are evenly distributed, so that uniform vibrations can be generated in each pad area on the auxiliary film.

[0082] Specifically, the droplet shape of the copper paste is characterized by a larger length in the vertical direction and a smaller length in the horizontal direction. When dropped on the auxiliary film, the copper paste flows and diffuses along the horizontal direction, and the copper paste at the top will also slide down accordingly. Under the constraint of the magnetic field, the diffusion speed of the edge of the copper paste will be reduced or the diffusion will stop, and at the same time, the copper paste at the top will also stop sliding and diffusing. It is worth mentioning that although the sliding diffusion mainly moves in the vertical direction, it will also produce horizontal diffusion and will also be constrained by the magnetic field. Therefore, it will cause the thickness of the copper paste formed on the pad area to be too large and uneven. In this embodiment, multi-source ultrasonic waves are added to enable the ultrasonic waves to act evenly on the auxiliary film, so that the auxiliary film can vibrate evenly at different positions, especially generating vibrations in the pad area. The purpose of the vibration is to drive the copper paste at the top to slide down, making the thickness of the copper paste uniform. It should be understood that the copper paste at the edge has a smaller thickness and lower gravitational potential energy, and can be constrained by the magnetic field to prevent further outward diffusion. However, the copper paste at the top has a larger gravitational potential energy. By using ultrasonic vibrations, the copper paste at the top can overcome the constraint of the magnetic field and slide down under the combined action of gravitational potential energy, so that the copper paste can be evenly distributed, spread out fully, and have a more regular and precise shape, forming a disc-shaped pad. It is worth mentioning that after the pad is formed, although the shape of the pad can be polished and corrected by laser polishing, this polishing can only polish the excess burrs and protrusions and perform local shape adjustment, and cannot change the overall shape of the pad. Therefore, through the combined action of ultrasonic vibration and magnetic field constraint, the copper paste can be evenly distributed while being constrained, thus forming a pad with a more precise shape.

[0083] In one embodiment, the second preset time is 10 ms to 50 ms. In this embodiment, 10 ms to 50 ms after applying a magnetic field to the copper paste, the ultrasonic source is started to perform ultrasonic oscillation on the copper paste, so that the copper paste that has not slid down and diffused in time at the top can slide down during the vibration. It is worth mentioning that, on the one hand, if the ultrasonic wave is turned on too early, the copper paste at the edge will diffuse excessively due to its large thickness and the diffusion is irregular. On the other hand, if the ultrasonic wave is turned on too late, the copper paste has tended to solidify, and the oscillation at this time cannot make the copper paste spread evenly. Therefore, in this embodiment, 10 ms to 50 ms after applying a magnetic field to the copper paste, the ultrasonic source is started to perform ultrasonic oscillation on the copper paste, which can avoid excessive diffusion of the copper paste, make the copper paste that has not slid down and diffused in time at the top slide down during the vibration, make the copper paste in the pad area evenly distributed, and the thickness of each part is uniform, so that the shape of the formed pad is more accurate.

[0084] In order to form a circuit pattern, in one embodiment, the step of forming a circuit pattern connected to the pad on the auxiliary film includes:

[0085] Coat hot melt adhesive on the first side of the auxiliary film and remove the hot melt adhesive on the pad;

[0086] Deposit an initial copper layer on the hot melt adhesive;

[0087] Attach a dry film on the initial copper layer, expose and develop the dry film;

[0088] Perform horizontal electroplating in the area outside the dry film coverage area to form a circuit pattern;

[0089] Strip and flash etch, strip to remove the dry film, and flash etch to remove the initial copper layer covered by the dry film;

[0090] Remove the auxiliary film and coat hot melt adhesive on the surfaces of the pad and the circuit pattern;

[0091] Laser clean the hot melt adhesive on the surface of the pad to expose the pad on the side where the circuit pattern is located.

[0092] In this embodiment, the circuit pattern is a circuit connecting each pad, which is used to undertake the power transmission and control of the Mirco LED. First, coat hot melt adhesive on the side of the auxiliary film where the pad is set. Subsequently, remove the hot melt adhesive on the top surface of the pad so that the surface of the pad is exposed. The process of removing the hot melt adhesive is as follows: First, use a ceramic brush to grind the plate starting from the top of the hot melt adhesive to roughly grind the hot melt adhesive on the surface of the pad and remove the excess hot melt adhesive. Subsequently, use a laser cleaning method to remove the remaining hot melt adhesive on the pad so that the top surface of the exposed pad is flush with the surface of the hot melt adhesive.

[0093] Subsequently, an initial copper layer is deposited on the surface of the hot melt adhesive, and the initial copper layer connects the pads. The thickness of the initial copper layer is less than 1 micron, and a relatively thin initial copper layer is deposited on the pads and the hot melt adhesive by chemical sputtering or other electroless copper plating methods.

[0094] Subsequently, a dry film is globally attached on the initial copper layer, and then the dry film outside the circuit pattern area is removed through exposure and development. At this time, the pattern outside the dry film coverage area is the subsequent circuit pattern. Horizontal electroplating is performed in the area outside the dry film coverage area to form a circuit pattern with a thickness of 7 - 8 microns. The circuit pattern is connected to the pads.

[0095] Subsequently, the film is removed and flash etched. The film removal removes the dry film, and the flash etching removes the initial copper layer covered by the dry film, so that only the circuit pattern remains on the hot melt adhesive. Subsequently, the auxiliary film is removed, and the pads are subjected to double - sided immersion gold. Finally, the auxiliary film is removed.

[0096] Subsequently, the pads are cleaned using plasma technology; after removing the auxiliary film, in order to avoid residual auxiliary film at the bottom of the pads, the bottom of the pads, that is, the end where the pads are in contact with the auxiliary film, is etched using plasma gas to ensure that there is no residual auxiliary film material on the pads. Subsequently, AOI (Automated Optical Inspection) inspection is performed on the circuit pattern and the pads. AOI inspection is performed on the pads and the circuit pattern formed on their top to detect the appearance and status of the circuit pattern.

[0097] Subsequently, hot melt adhesive is coated on the surface of the pads and the circuit pattern again. The hot melt adhesive in this step is used as a solder mask layer and an insulating layer. At this time, the hot melt adhesive covers the circuit pattern and the pads on one side of the circuit pattern.

[0098] Subsequently, laser cleaning is performed again to expose the pads close to the circuit pattern. The end of the pads far from the circuit pattern has already been exposed. At this time, the laser cleaning refers to cleaning one end of the pads close to the circuit pattern, so that both ends of the pads are exposed and other areas are wrapped by the hot melt adhesive.

[0099] Double - sided immersion gold treatment is performed on the pads. Immersion gold is performed on both exposed ends of the pads simultaneously to increase their conductive connectivity and at the same time increase the thickness of the pads. During the immersion gold process, a very thin oxide layer can be formed on the metal surface, and this oxide layer can effectively prevent metal corrosion, thereby improving the corrosion resistance of the pads and the circuit pattern.

[0100] In one embodiment, the pads formed by curing and stacking copper paste are polished using a laser to form cylindrical pad polishing.

[0101] In this embodiment, after the copper paste is cured and formed, the pads are polished using a laser to make the shape of the pads more precise.

[0102] In one embodiment, before the step of providing the auxiliary film, the following steps are further included:

[0103] Place the auxiliary film horizontally, and determine the coordinates on the auxiliary film by combining machine vision positioning;

[0104] Determine the pre-defined pad area according to the coordinates on the auxiliary film;

[0105] Use laser ablation technology to ablate a burr surface in the pad area.

[0106] In this embodiment, first, the coordinates on the auxiliary film are accurately determined by using machine vision positioning, and based on this, the position and size of the pad area are accurately determined. Subsequently, based on the determined position and size of the pad area, a burr surface is ablated in the pad area by using laser ablation technology. The range of the burr surface coincides with the range of the pad area, and there are multiple burrs on the burr surface. In this embodiment, the function of the burr surface is that, on the one hand, it can play a role in positioning and marking the pad area, so that the copper paste can be accurately aligned with the pad area, and the burr surface increases the friction of the pad area, which can play a certain role in blocking the diffusion of the copper paste and prevent the copper paste from diffusing excessively. On the other hand, during the ultrasonic oscillation process, the burrs on the burr surface vibrate under the action of ultrasonic oscillation, which can make the pad areas at different positions generate the same or similar vibration amplitudes, and the vibration of the burrs can also strengthen the vibration amplitude of the top of the copper paste, so that the copper paste at the top can slide down, so that the copper paste can not only fully cover the pad area, but also be evenly distributed, making the shape of the formed pad more accurate.

[0107] In one embodiment, a Mirco LED circuit board is provided, which is manufactured by using the Mirco LED circuit board manufacturing method described in any one of the above embodiments.

[0108] In this embodiment, the position where the copper paste forms a pad on the auxiliary film is determined by using the auxiliary film, and the range of the outward diffusion of the copper paste dropped on the auxiliary film is restricted by using a magnetic field perpendicular to the direction of the auxiliary film, so that the size of the copper paste cured and formed can be accurately controlled, and further the position and size of the pad are more accurate, which is beneficial to improving the yield of the Mirco LED circuit board.

[0109] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0110] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several variations and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A manufacturing method of a Mirco LED circuit board, characterized in that, Including: Providing an auxiliary film; Using laser-melted copper paste, such that the melted copper paste is dropped drop by drop onto a predefined pad area on the first surface of the auxiliary film and solidifies to form pads. Among them, after the copper paste is dropped onto the pad area, a magnetic field perpendicular to the auxiliary film is applied on one side of the auxiliary film, where the direction of the magnetic field is opposite to the dropping direction of the copper paste; Forming a circuit pattern connected to the pads on the auxiliary film; Removing the auxiliary film to obtain a circuit substrate; Connecting the Mirco LED chips to the pads on the circuit substrate to obtain a Mirco LED circuit board.

2. The Mirco LED circuit board according to claim 1, characterized in that, The step of providing the auxiliary film includes: Providing the auxiliary film and placing the auxiliary film horizontally; The step of, after the copper paste is dropped onto the pad area, applying a magnetic field perpendicular to the auxiliary film on one side of the auxiliary film, includes: After a first preset time after the copper paste is dropped onto the pad area, applying a vertically upward magnetic field below the auxiliary film until the copper paste solidifies in the pad area to form the pads.

3. The Mirco LED circuit board according to claim 2, characterized in that, The first preset time is 20 ms to 60 ms.

4. The Mirco LED circuit board according to claim 2, characterized in that, In the step of applying a vertically upward magnetic field below the auxiliary film, the duration of the applied magnetic field is 100 ms to 300 ms.

5. The Mirco LED circuit board according to claim 2, wherein, The step of applying a vertically upward magnetic field below the auxiliary film includes: After a second preset time of applying a vertically upward magnetic field below the auxiliary film, using multi-source ultrasonic waves to emit ultrasonic waves along a direction perpendicular to the auxiliary film to perform multi-source oscillation on the auxiliary film, where the duration of the ultrasonic waves is 50 ms to 150 ms.

6. The Mirco LED circuit board according to claim 5, wherein, The second preset time is 10 ms to 50 ms.

7. The Mirco LED circuit board according to any one of claims 1-6, characterized in that, The step of forming a circuit pattern connected to the pads on the auxiliary film includes: Coating a hot melt adhesive on the first surface of the auxiliary film and removing the hot melt adhesive on the pads; Depositing an initial copper layer on the hot melt adhesive; Sticking a dry film on the initial copper layer, exposing and developing the dry film; Performing horizontal electroplating on areas outside the dry film covering area to form a circuit pattern; Removing the film and flash etching, removing the dry film during film removal and flash etching to remove the initial copper layer covered by the dry film; Removing the auxiliary film, and coating a hot melt adhesive on the surfaces of the pads and the circuit pattern; Laser cleaning the hot melt adhesive on the surface of the pads to expose the pads on the side where the circuit pattern is located.

8. The Mirco LED circuit board according to any one of claims 1-6, characterized in that Performing laser polishing on the pads formed by solidifying and piling up the copper paste to form cylindrically polished pads.

9. The Mirco LED circuit board according to any one of claims 1-6, characterized in that, Before the step of providing the auxiliary film, it further includes: Placing the auxiliary film horizontally, and determining the coordinates on the auxiliary film by combining machine vision positioning; Determining the predefined pad area according to the coordinates on the auxiliary film; Using laser ablation technology to ablate a burr surface in the pad area.

10. A Mirco LED circuit board, characterized in that, Manufactured by using the Mirco LED circuit board manufacturing method described in any one of claims 1-9.

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