CN118591084A

CN118591084A - Printed circuit board of LED display module and preparation method thereof

Info

Publication number: CN118591084A
Application number: CN202411072213.5A
Authority: CN
Inventors: 李志吉; 朱雪君
Original assignee: Shenzhen City Xinguang Core System Device Co ltd
Current assignee: Shenzhen City Xinguang Core System Device Co ltd
Priority date: 2024-08-06
Filing date: 2024-08-06
Publication date: 2024-09-03

Abstract

The invention provides a printed circuit board of an LED display module and a preparation method thereof, wherein the printed circuit board of the LED display module comprises a board body and a plurality of bonding pad groups, each bonding pad group comprises four LED bonding pads, each LED bonding pad is arranged on the surface of the board body, the four LED bonding pads of the same bonding pad group are arrayed around a central area, the edge part of each LED bonding pad, which faces the central area, is recessed away from the central area, a unfilled corner for enlarging the area of the central area is formed, the geometric center of each LED bonding pad is positioned outside the area where the unfilled corner is positioned, the minimum inscribed circle diameter of a space defined by all unfilled corner boundaries of the same bonding pad group is not less than 0.2mm, and the board body is provided with a via hole under each central area. The printed circuit board of the LED display module can reserve space for the through hole under the condition of not changing the original LED bonding pad and circuit layout, and can also use common drilling equipment to prepare the through hole on the board body.

Description

Printed circuit board of LED display module and preparation method thereof

Technical Field

The invention relates to the technical field of printed circuit boards, in particular to a printed circuit board of an LED display module and a preparation method thereof.

Background

Along with the development of the electronic products in the directions of light weight, thin weight and miniaturization, the LED display module is also advanced in the directions of high density and high difficulty. The P1.25 pitch LED display module (the center distance between adjacent LED pixels is 1.25 mm) represents a high-end level of the current LED display technology, and can provide higher resolution and better image quality.

On the printed circuit board of the P1.25 pitch LED display module, the arrangement of LED pads and associated wiring occupies almost all of the available space on the board surface. This highly integrated design makes it extremely difficult to provide functional vias (e.g., GND, VCC, signal vias, etc.) on the board without changing the original layout. At present, a solution for reserving space for functional via holes on a circuit board without changing the original LED bonding pads and circuit layout on the circuit board and preparing the functional via holes on the circuit board of the P1.25-interval LED display module by using common drilling equipment is not found in the industry.

Disclosure of Invention

The invention mainly aims to solve the technical problems that the prior art cannot reserve space for functional via holes under the condition of not changing the original LED bonding pads and circuit layout, and the common drilling equipment can be used for preparing the functional via holes on the P1.25-interval LED display module.

The invention provides a printed circuit board of an LED display module, which comprises a board body and a plurality of bonding pad groups, wherein each bonding pad group comprises four LED bonding pads, each LED bonding pad is arranged on the surface of the board body, the four LED bonding pads of the same bonding pad group are arranged in an array mode around a central area, the edge part of each LED bonding pad, which faces the central area, is recessed away from the central area, a unfilled corner for expanding the area of the central area is formed, the geometric center of each LED bonding pad is positioned outside the area where the unfilled corner is located, the minimum inscribed circle diameter of a space defined by all unfilled corner boundaries of the same bonding pad group is not less than 0.2mm, and a through hole is formed under each central area of the board body.

In some embodiments, the LED pads include a long lateral side, a long vertical side, a short lateral side, a short vertical side, and a beveled edge, the long lateral side being disposed parallel to the short lateral side, the long vertical side being disposed parallel to the short vertical side;

The long transverse edge, the short vertical edge, the inclined edge, the short transverse edge and the long vertical edge are sequentially connected end to form the outer contour of the LED bonding pad;

the bevel edge forms the boundary of the unfilled corner;

The length of the short transverse edge is 65 to 85 percent of the length of the long transverse edge;

The length of the short vertical edge is 65% to 85% of the length of the long vertical edge.

The second aspect of the present invention provides a method for manufacturing a printed circuit board, comprising:

acquiring the size of an LED bonding pad, the distance between a plurality of LED bonding pads of the same bonding pad group, the diameter of a via hole, the depth of the via hole and the preset distance, wherein the preset distance is the minimum distance between the outer contour of the LED bonding pad and the periphery of the via hole;

Forming via holes at a plurality of first preset positions on the plate body according to the via hole diameter and the via hole depth;

Determining four LED bonding pad positions on the periphery of the via hole according to the LED bonding pad size and the spacing between the plurality of LED bonding pads of the same bonding pad group;

And forming LED bonding pads with unfilled corners at each LED bonding pad position according to the LED bonding pad size and the preset spacing.

In some embodiments, the forming an LED pad with a unfilled corner at each of the LED pad locations according to the LED pad size and the predetermined pitch includes:

Determining the unfilled corner shape, position and size of each LED bonding pad according to the LED bonding pad size and the preset distance;

designing an LED bonding pad graph with unfilled corners based on the unfilled corner shape, the position and the size;

and forming an LED bonding pad at each LED bonding pad position according to the corresponding LED bonding pad pattern with unfilled corners.

In some embodiments, forming the LED pads according to the corresponding LED pad pattern with unfilled corners at each LED pad position includes:

Generating a corresponding photoetching mask pattern according to the LED bonding pad pattern with the unfilled corner;

coating photoresist on the surface of the plate;

exposing the photoresist-coated plate body using the photolithography mask pattern;

Developing the exposed plate body, removing the unexposed photoresist, and forming an expected pattern corresponding to the LED bonding pad pattern with the unfilled corner;

electroplating on the expected pattern to form an LED bonding pad with unfilled corners;

And removing the residual photoresist.

In some embodiments, the determining the unfilled corner shape, position and size of each LED pad according to the LED pad size and the predetermined pitch includes:

calculating an initial unfilled corner depth according to the preset distance;

determining the opening width of the unfilled corner according to the size of the LED bonding pad, wherein the opening width of the unfilled corner is the distance between two unfilled corner endpoints on the edge of one side of the LED bonding pad, which is close to the via hole;

establishing a thermodynamic model, wherein the thermodynamic model comprises an LED chip, an LED bonding pad and surrounding structures thereof;

simulating heat distribution conditions of the LED chips under different unfilled corner shapes during working based on the thermodynamic model by utilizing finite element analysis software;

according to the heat distribution simulation result, adopting an iterative optimization algorithm to adjust shape parameters of the unfilled corner, including curvature, depth and opening width of the unfilled corner, so as to minimize the hot spot temperature;

Stress analysis is carried out on the optimized unfilled corner shape, and stress distribution of the LED bonding pad under different working conditions is calculated;

And fine-tuning the unfilled corner shape based on the stress analysis result so that the maximum stress value does not exceed a preset threshold value, and determining the final unfilled corner shape, position and size.

carrying out metallization treatment on the inner wall of the via hole to form a conductive layer;

filling the via hole subjected to metallization treatment with an insulating material, so that the insulating material fills the via hole and does not overflow from the periphery of the via hole;

forming a complete LED bonding pad at the position of the LED bonding pad according to the size of the LED bonding pad;

And removing part of the structure of the complete LED bonding pad according to the preset distance by adopting a selective removing process to form the LED bonding pad with unfilled corners.

In some embodiments, the forming the LED pad with unfilled corners at each of the LED pad locations includes:

filling the metallized via hole with an insulating material, and overflowing part of the insulating material from the periphery of the via hole to cover part of the LED bonding pad position;

Depositing conductive material on the area, which is not covered by the insulating material, of the LED bonding pad to form an LED bonding pad with unfilled corners;

And removing the insulating material at the positions covering the LED bonding pads.

The third aspect of the present invention provides a method for manufacturing a printed circuit board, comprising:

Manufacturing LED bonding pads with unfilled corners at a plurality of second preset positions on a board body according to the sizes of the LED bonding pads and the intervals among a plurality of LED bonding pads of the same bonding pad group;

And determining the positions of the through holes in the central areas of the four LED bonding pads with the unfilled corners according to the preset spacing, and forming the through holes in the determined positions according to the diameters of the through holes and the depths of the through holes.

The technical scheme provided by the embodiment of the application has at least the following advantages:

According to the technical scheme, the edge part of each LED bonding pad facing the central area is outwards recessed to form a special unfilled corner structure, the available area of the central area of the bonding pad group is effectively enlarged, sufficient space is provided for the arrangement of functional via holes, and the space defined by four unfilled corner boundaries of the same bonding pad group can accommodate an area with the minimum inscribed circle diameter not smaller than 0.2mm, so that the requirement of the size of a conventional functional via hole is met.

Secondly, by keeping the geometric center of the LED pads outside the unfilled corner region, it is ensured that the effective mounting area of the LED chip is not affected. This is because the LED chip is generally rectangular or square, and its effective mounting area is mainly concentrated at the central portion of the pad. Since the unfilled corner is located at the edge of the bonding pad and does not extend to the center of the bonding pad, the main mounting area of the chip is not affected. The design ensures the effective contact area between the LED chip and the bonding pad, thereby maintaining good electrical connection and heat dissipation performance, and further ensuring the high density characteristic and excellent display effect of the LED display module.

Furthermore, this design makes it possible to provide vias directly under the central region of each pad group without changing the overall arrangement of the LED pads. This greatly increases the design flexibility of the printed circuit board so that various functional connections (e.g., GND, VCC, signal transmission, etc.) can be more conveniently implemented.

Finally, because the space left aside is large enough, the processing can be performed by using common PCB drilling equipment without adopting expensive laser drilling technology. Conventional PCB drilling equipment is generally capable of reliably machining holes having diameters above 0.2 mm. In the invention, the minimum inscribed circle diameter of the space created by the unfilled corner design is not less than 0.2mm, and the requirement is just met. This means that standard PCB manufacturing equipment and processes can be used to produce circuit boards of this design without the need to invest in special laser drilling equipment. This not only greatly reduces the production cost, but also significantly shortens the production cycle. Because laser drilling is generally a relatively time consuming process, while mechanical drilling can be accomplished more quickly. In addition, more PCB manufacturers can accept orders for such designs, which increases production flexibility, further improving overall production efficiency.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a printed circuit board of a prior art LED display module;

FIG. 2 is a schematic diagram of a printed circuit board of an LED display module according to the present invention;

FIG. 3 is a schematic flow chart of an embodiment of a method for manufacturing a printed circuit board according to the present invention;

fig. 4 is a flow chart of another embodiment of the method for manufacturing a printed circuit board according to the present invention.

Reference numerals illustrate:

1. A plate body; 11. a via hole; 2. a pad group; 21. an LED bonding pad; 211. unfilled corners; 212. a long transverse edge; 213. long vertical edges; 214. short transverse edges; 215. short vertical edges; 216. a beveled edge; 22. a central region.

The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It should be noted that, if directional indications (such as up, down, left, right, front, and rear … …) are included in the embodiments of the present invention, the directional indications are merely used to explain the relative positional relationship, movement conditions, etc. between the components in a specific posture (as shown in the drawings), and if the specific posture is changed, the directional indications are correspondingly changed.

Furthermore, the description of "first," "second," etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, "and/or" throughout this document includes three schemes, taking a and/or B as an example, including a technical scheme, a technical scheme B, and a technical scheme that both a and B satisfy; in addition, the technical solutions of the embodiments may be combined with each other, and it is necessary to base that the technical solutions can be implemented by those skilled in the art, and when the technical solutions are contradictory or cannot be implemented, it should be considered that the combination of the technical solutions does not exist and is not within the scope of protection claimed by the present invention.

FIG. 1 is a schematic diagram of a printed circuit board of a prior art LED display module; FIG. 2 is a schematic diagram of a printed circuit board of an LED display module according to the present invention; it should be noted that, in fig. 1 and fig. 2, only a partial structure of the printed circuit board is shown, not a complete structure of the printed circuit board, and both the two diagrams are schematic diagrams in a top view, in fig. 1, the upper four LED pads 21 form one pad group 2, and the lower four LED pads 21 form another pad group 2, which is also the case in fig. 2.

Referring to fig. 2, an embodiment of the present application provides a printed circuit board of an LED display module. The printed circuit board of the LED display module comprises a board body 1 and a plurality of bonding pad groups 2, each bonding pad group 2 comprises four LED bonding pads 21, each LED bonding pad 21 is arranged on the surface of the board body 1, the four LED bonding pads 21 of the same bonding pad group 2 are arrayed around a central area 22, the edge part of each LED bonding pad 21, which faces the central area 22, is recessed away from the central area 22, a unfilled corner 211 for enlarging the area of the central area 22 is formed, the geometric center of each LED bonding pad 21 is positioned outside the area where the unfilled corner 211 is located, the minimum inscribed circle diameter of a space defined by the boundaries of all unfilled corners 211 of the same bonding pad group 2 is not less than 0.2mm (millimeter), and a through hole 11 is formed under each central area 22 of the board body 1.

Specifically, the board body 1 is a basic structure of an LED display module printed circuit board. In the exemplary embodiment, the plate body 1 is not a simple support plane, but a complex multilayer structure. Specifically, the board body 1 generally includes a plurality of layers, of which the Top layer and the Bottom layer (Bottom layer) are the most critical.

The top layer is the layer where the LED pads 21 are located. On this layer, the specially designed LED pads 21 described in the above embodiments can be seen. The LED pads 21 are preferably 0.3mm by 0.3mm, which is an optimized size that meets the mounting requirements of the LED chips without taking up excessive board space. The Bottom layer (Bottom layer) is then mainly used for arranging the column lines of LEDs. This is a conventional solution in LED display module design, and by routing on the bottom layer, the wiring complexity of the top layer can be effectively reduced, leaving more space for the LED pads 21.

It should be noted that, in the LED display module, four LED pads 21 of the same pad group 2 are typically used to mount one complete RGB (red, green and blue) pixel. Specifically, the four pads are used for mounting a red LED chip, a green LED chip, a blue LED chip, and one common anode (or common cathode) connection point, respectively. The arrangement mode can realize full-color display in the minimum space, and is the basis of a high-resolution LED display screen.

In the P1.25-pitch LED display module, the center distance of adjacent pixel points is 1.25mm. This means that the four LED pads 21 of each pad group 2 must be closely arranged in an area of not more than 1.25mm x 1.25mm, the actual size possibly being slightly smaller than this value, to leave the necessary gap. The size of each LED pad 21 is typically about 0.3mm x 0.3mm in consideration of the size of the LED chip itself and soldering requirements. In this compact arrangement, the spacing between the four LED pads 21 may be only around 0.1 mm.

In such a compact layout, it becomes extremely difficult to place one via 11 having a diameter of 0.2mm in the central region 22 of the pad group 2. In conventional designs, there is not enough space to accommodate the via 11, it being understood that the via 11 plays a critical role in the printed circuit board, the via 11 may connect different layers of the printed circuit board, current and signals may be transferred between the layers through conductive coatings on the peripheral walls of the via 11, the via 11 may also help dissipate heat generated during operation of the LED, improve stability and lifetime of the display module, and in addition, the via 11 may provide additional grounding points or be used to distribute power among different layers, etc.

In the present invention, in order to solve the above-described problems, each LED pad 21 adopts an innovative design. Specifically, the edge portion of each LED pad 21 facing the central region 22 of the pad group 2 is recessed away from the central region 22, forming a special unfilled corner 211 structure. The main purpose of this unfilled corner 211 is to enlarge the available area of the central region 22 of the padset 2, providing sufficient space for the placement of the functional vias 11.

Notably, although the LED pad 21 has this unfilled corner 211, the geometric center of the LED pad 21 is still located outside the area of the unfilled corner 211. This design ensures that the main mounting area of the LED chip is not affected. The LED chip is generally rectangular or square, and its effective mounting area is mainly concentrated in the central portion of the bonding pad. By limiting the unfilled corner 211 to the edge of the bond pad and not extending to the center of the bond pad, the present invention ensures an effective contact area between the LED chip and the bond pad, thereby maintaining good electrical connection and heat dissipation.

In addition, in the PCB manufacturing industry, common drilling apparatuses generally include a mechanical drilling machine, a numerical control drilling machine, a multi-axis drilling machine, a high-speed drilling machine, and the like. A common feature of these devices is that they are capable of handling holes of diameters around 0.2mm and above. For example, mechanical drills may typically handle holes between 0.2mm and 6.35 mm. And even the numerical control drilling machine can process holes with the diameter of 0.1mm, and the multi-shaft drilling machine and the high-speed drilling machine can easily handle holes with the diameter of 0.2 mm.

The use of these conventional PCB drilling equipment for the fabrication of the vias 11 provides several advantages. First, it significantly reduces production costs. The purchase and maintenance cost of the common PCB drilling equipment is far lower than that of the special laser drilling equipment, which directly reduces the equipment investment of manufacturers. Secondly, the production efficiency is improved. The operation of the common drilling equipment is simpler, the equipment debugging time is shorter, the production flow is smoother, and the whole production efficiency is improved. In addition, since the common drilling equipment is widely used in the industry, operators are generally familiar with the drilling equipment, and the drilling equipment is also helpful for reducing operation errors and improving the stability of product quality.

More importantly, the use of conventional drilling equipment increases the flexibility of production. Most PCB manufacturers are equipped with these conventional devices, which means that printed circuit boards employing LED display modules designed according to the present application can be produced by more manufacturers. This not only facilitates rapid expansion of capacity, but also provides more supplier options for customers, helping to control procurement costs and ensure stability of the supply chain.

In some embodiments, the LED pad 21 includes a long lateral side 212, a long vertical side 213, a short lateral side 214, a short vertical side 215, and a beveled edge 216, the long lateral side 212 being disposed parallel to the short lateral side 214, the long vertical side 213 being disposed parallel to the short vertical side 215;

the long transverse edge 212, the short vertical edge 215, the oblique edge 216, the short transverse edge 214 and the long vertical edge 213 are connected end to end in sequence to form the outer contour of the LED bonding pad 21;

the beveled edges 216 form the boundary of the unfilled corner 211;

the length of the short lateral edge 214 is 65% to 85% of the length of the long lateral edge 212;

the length of the short vertical edge 215 is 65% to 85% of the length of the long vertical edge 213.

In this embodiment, long lateral edge 212 is disposed parallel to short lateral edge 214 and long vertical edge 213 is disposed parallel to short vertical edge 215. This parallel arrangement ensures that the LED pads 21 remain rectangular in overall basic shape, facilitating accurate positioning and soldering of the LED chips. The five sides are connected end to end in the order of long lateral side 212, short vertical side 215, beveled side 216, short lateral side 214, long vertical side 213.

The bevel 216 may take a straight shape or may be curved (e.g., circular arc) as long as the function of the unfilled corner 211 is achieved. Secondly, the specific ratio of the short side to the long side can be adjusted within a given range according to actual requirements.

This design not only provides sufficient space for the via 11, but also ensures a sufficient mounting area for the LED chip. At the same time, this design is also easy to manufacture, since it essentially retains the rectangular body shape, modified only at one corner. This design allows for manufacturing feasibility and cost control while meeting functional requirements.

In another embodiment of the present application, a method for manufacturing a printed circuit board is further provided, which is used for manufacturing the printed circuit board of the LED display module provided in the foregoing embodiment, and the method for manufacturing the printed circuit board provided in the other embodiment of the present application will be described in detail with reference to the accompanying drawings.

Fig. 3 is a flow chart of a method of manufacturing a printed circuit board.

Referring to fig. 3, the LED pad size, the pitch between the plurality of LED pads of the same pad group, the via diameter, the via depth, and the predetermined pitch, which is the minimum pitch between the outer contour of the LED pad and the periphery of the via, are obtained;

accurate acquisition of these parameters is the basis for the overall manufacturing process and they determine the specific implementation details of the subsequent steps. The parameters may be obtained from the results of product specification requirements, process limitations, or design optimizations. For example, LED pad size is typically determined by the size of the LED chip, while pad pitch is required to take into account display resolution requirements. The diameter and depth of the vias depend on the electrical performance and the requirements of the fabrication process.

The formation of the via hole may be performed using a mechanical drilling machine, a numerical control drilling machine, a multi-axis drilling machine, a high-speed drilling machine, etc., and the via hole may be precisely positioned and drilled according to a pre-designed drawing.

This step is accomplished using PCB design software that automatically calculates the optimum pad layout based on the parameters entered. In this process, an appropriate tolerance space needs to be reserved for each pad in consideration of the tolerance of PCB manufacturing. At the same time, the isolation requirement between the bonding pads is also considered, so that the sufficient insulation distance between the different bonding pads is ensured.

This step can be accomplished in a number of ways, such as photolithography using a specially designed photolithographic mask, followed by selective etching or plating. In the photolithography process, precise control of exposure time and development time is required to ensure that the shape and size of the unfilled corners meet design requirements. If the electroplating method is adopted, the current density and the electroplating time need to be controlled to ensure the uniformity of the thickness of the bonding pad. In this step, the flatness and roughness of the pad surface also need to be taken into account to ensure good soldering of the subsequent LED chips.

It will be appreciated that if the LED pads are fabricated and then the vias are formed, then the drilling process of the vias may cause mechanical stress to the formed LED pads, resulting in deformation or microcracking of the LED pads. The preparation method of this example avoids this problem. For ease of understanding, the following example assumes a pad microcrack rate of 1% due to drilling stress in the conventional method, and the method of the present invention can reduce this rate to nearly 0%. This means that in mass production, every 10000 bonding pads are produced, the method can reduce about 100 potential failure points, and the reliability and yield of the product are improved remarkably.

Further, the forming of the LED pads with unfilled corners at each of the LED pad positions according to the LED pad size and the predetermined pitch includes:

This step may be performed by PCB design software, such as Altium Designer, cadence Allegro or Mentror GRAPHICS PADS, and the like. The factors such as the size of the LED chip, the welding requirement, the heat dissipation requirement, the distance between the LED chip and the through hole and the like need to be comprehensively considered. For example, if the LED chip size is 0.2mm×0.2mm, the pad size is 0.3mm×0.3mm, and the predetermined pitch is 0.05mm, a right triangle unfilled corner may be selected, whose right-angle side lengths are 0.05mm and 0.05mm, respectively. The method has the significance of providing accurate design parameters for the subsequent manufacturing process, ensuring that the design of the unfilled corner is Kong Liuchu enough space and not excessively influencing the welding area of the LED chip.

In this step, the previously determined parameters are converted into specific patterns. For example, a standard rectangular pad may be created and then a software shape editing tool, such as a polygon tool or a cutting tool, may be used to precisely define the unfilled corner. The importance of this step is to translate the abstract parameters into specific manufacturing instructions, providing direct guidance for the subsequent manufacturing process. At the same time, this step also allows the designer to make final visual inspections and optimizations to ensure that the design meets expectations.

This step can be used to transfer the pad pattern to the copper-clad plate using a precision lithography machine, and then remove the unwanted copper foil by selective etching, leaving the precise pad shape. Or copper may be deposited directly at predetermined locations to form pads using high precision selective electroplating techniques. The significance of this step is that it converts the design into an actual physical structure, which is the core of the overall manufacturing process.

It will be appreciated that the above steps provide design flexibility, allowing for fine tuning of the unfilled corners of each pad according to specific requirements, accommodating different LED chip and via requirements. Furthermore, this stepwise optimization approach helps to improve manufacturing yields, as each step can be inspected and adjusted. Finally, this approach provides the potential for mass production because once the design is determined, it can be quickly replicated onto a large number of pads.

this step requires the LED pad pattern data of the previous design to be imported into the mask making system, which will convert the pattern into a high precision photolithographic mask.

Coating photoresist on the surface of the plate;

This step may be accomplished using a glue application device, such as a spin coater or spray application device.

this step is performed in a lithographic machine, requiring precise control of exposure time and intensity. The significance of this step is that the pattern on the mask is accurately transferred to the photoresist layer, which lays the foundation for the subsequent development and etching process.

And removing the residual photoresist.

It can be appreciated that by combining photolithography and electroplating, a bonding pad with a flat surface and sharp edges can be obtained, which is beneficial to the accurate positioning and reliable welding of subsequent LED chips. Finally, the method is compatible with the existing PCB manufacturing process, special equipment is not needed, and the production cost is reduced.

Further, the determining the unfilled corner shape, position and size of each LED pad according to the LED pad size and the predetermined pitch includes:

calculating an initial unfilled corner depth according to the preset distance;

In the practical implementation process, if the preset distance is 0.05mm, the initial unfilled corner depth can be set to be 0.07mm, so that a room for subsequent optimization can be reserved.

The surrounding structure includes a board material, a copper foil layer, and the like. This model can be constructed using software such as Ansys or COMSOL, in which the geometry, material properties and thermal properties of the individual components are precisely described.

in this process, various unfilled corner shapes, such as straight, curved or compound curves, can be tried and simulated at different operating powers. For example, the operating state of the LED at 0.1W, 0.2W, and 0.3W power was simulated, observing how heat was distributed in the pads and PCB.

In this process, the unfilled corner curvature, depth and opening width are gradually changed with the goal of minimizing the hot spot temperature. For example, in the above example, the maximum hot spot temperature can be changed by increasing the unfilled corner depth to 0.08mm and adjusting the opening width to 0.12 mm.

this step uses structural mechanics analysis software to calculate the stress distribution of the LED pads under different operating conditions. The stress state of the LED display module under different conditions such as normal operation, thermal circulation, mechanical vibration and the like is simulated.

This preset threshold is set based on the fatigue limit of the material used. For example, if the copper alloy pad material is used with a fatigue limit of 200MPa, the maximum allowable stress may be set to 150MPa, leaving a safety margin of 50 MPa. By repeatedly adjusting the shape of the unfilled corner, the edge of the unfilled corner can be gradually rounded slightly in the process, so that the stress concentration is effectively reduced, and the maximum stress is reduced from 180MPa to 140MPa.

Through this series of calculation, simulation and optimization steps, the shape, position and size of the unfilled corner are finally determined. This process may require multiple iterations, each of which may trade-off thermal and mechanical properties. For example, the final unfilled corner design may be an arcuate unfilled corner with a depth of 0.075mm and an opening width of 0.11mm, which provides adequate heat dissipation while also ensuring mechanical strength of the bond pad. The optimized unfilled corner design not only reserves enough space for the through hole, but also obtains good balance between heat radiation performance and structural reliability, and lays a foundation for realizing the high-performance LED display module.

In the above embodiment, the via hole is formed on the board body, and then the LED pad with the unfilled corner is formed around the via hole, but the preparation method of the present application is not limited to prediction, and in other embodiments, the forming the LED pad with the unfilled corner at each LED pad position according to the LED pad size and the predetermined pitch includes:

This step is accomplished using an electroplating process. First, the inner walls of the via may be cleaned using a chemical cleaner to remove any impurities and oxides that may affect the quality of the metallization. The inner walls of the via are then treated with an activator to enhance their conductivity. Next, the plate is immersed in a plating solution, and a thin, uniform metal layer, typically copper, is deposited on the inside walls of the vias by an electrolytic process.

The conductive layer ensures reliable transmission of electrical signals between the different layers of the board body.

The insulating material may be selected from epoxy resins because it has good insulation and mechanical strength. The filling process adopts a vacuum filling technology, and the technology can ensure that the insulating material is uniformly filled into each corner of the via hole, so that bubbles or gaps are avoided. During the filling process, the amount of insulating material injected can be precisely controlled, for example, for a via with a volume of 0.00628mm (assuming a diameter of 0.2mm and a depth of 0.2 mm), 0.00630mm of epoxy can be injected, and a further 0.00002mm is used to compensate for possible shrinkage. After filling is complete, a curing process is performed, typically at a temperature of 150 ℃ for 2 hours, to ensure complete hardening of the insulating material.

The completely filled vias not only prevent the penetration of chemicals during subsequent processing, but also improve the board's resistance to thermal cycling and mechanical vibration.

This step would first apply a layer of photoresist to the surface of the plate and expose the LED pads using a precisely aligned photolithographic mask. After exposure, developing treatment is carried out to remove the unexposed photoresist, and the patterns of the LED bonding pads are exposed. Then, electroplating is performed, copper is deposited on the exposed area, and a complete LED bonding pad is formed. And after the electroplating is completed, removing the residual photoresist to obtain the complete LED bonding pad.

This step may employ laser etching techniques. A portion of the LED pads is precisely removed using a precision laser etching apparatus.

The method is beneficial to improving the manufacturing consistency and yield. Since the formation of the complete pads is a relatively simple and controllable process, consistency in mass production can be more easily achieved. The subsequent selective removal process may be performed by a precisely controlled device, such as a laser etch, to ensure accuracy and repeatability of each unfilled corner.

In addition, in other embodiments, the forming the LED pad with the unfilled corner at each LED pad position includes:

In this step, it is necessary to precisely calculate and control the amount of insulating material injected. This calculation takes into account the volume of the via, the amount of flash required, and the possible shrinkage of the material during curing. Second, it is also necessary to design the viscosity and flow characteristics of the insulation material. The material needs to be fluid enough to fill the via and overflow, but not too fluid to be controlled. This can be achieved by adjusting the material formulation or adding specific rheology modifiers. For example, an epoxy resin that exhibits a moderate viscosity (e.g., 10,000-15,000 cP) at room temperature may be used, which allows the material to flow slowly and controllably.

The injection process can use a precision dispensing device to precisely control the injection volume in very small increments (e.g., 0.0001 mL). The injection rate also needs to be precisely controlled, and a slow and uniform injection rate, such as 0.01mL/s, is typically used to ensure that the material has sufficient time to evenly distribute.

The body was heated slightly (40-50 ℃) during injection to allow more even flow and distribution of material. But the temperature should not be too high, otherwise the viscosity of the material would be reduced, resulting in excessive flow.

The surface of the plate body and the edge of the via hole are specially treated to create subtle surface tension differences. For example, the surrounding of the via may be treated to be more hydrophilic, while a bit further away may be more hydrophobic. Such differences in surface characteristics can help control the flow range of the material.

Finally, the overflow process is monitored in real time using an optical detection system. The system can measure the overflow range through image analysis and fine-tune injection parameters according to feedback, so as to realize closed-loop control.

And removing the insulating material at the positions covering the LED bonding pads. The specific choice may be determined by techniques such as chemical etching, laser lift-off or mechanical grinding, depending on the insulating material used and the requirements for the quality of the solder surface.

This embodiment provides a natural and accurate way to form the unfilled corners without requiring complex mask designs or sophisticated etch controls. The overflow of insulating material effectively acts as a perfect mask, ensuring that the shape and size of the unfilled corner corresponds exactly to the via position. Second, this approach simplifies the manufacturing process. Other embodiments may require multi-step photolithography and etching processes to form complex pad shapes, which combine corner-void formation with via filling, reducing manufacturing steps and time.

In addition to the preparation of forming the via and then forming the LED pad, in other embodiments, the LED pad may be formed first and then the via may be prepared.

Specifically, a further embodiment of the present application further provides a method for manufacturing a printed circuit board, which is used for manufacturing the printed circuit board of the LED display module provided in the foregoing embodiment, and the method for manufacturing the printed circuit board provided in another embodiment of the present application will be described in detail with reference to the accompanying drawings.

Fig. 4 is a flow chart of a method of manufacturing a printed circuit board.

Referring to fig. 4, the LED pad size, the pitch between the plurality of LED pads of the same pad group, the via diameter, the via depth, and the predetermined pitch, which is the minimum pitch between the outer contour of the LED pad and the periphery of the via, are obtained;

In this embodiment, the LED pads can be fabricated on an ideal flat surface, which is advantageous for obtaining a higher quality pad surface. A flat, uniform pad surface is critical for accurate positioning and reliable soldering of subsequent LED chips.

The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A printed circuit board of an LED display module, comprising:

A plate body (1);

Each bonding pad group (2) comprises four LED bonding pads (21), each LED bonding pad (21) is arranged on the surface of the plate body (1), the four LED bonding pads (21) of the same bonding pad group (2) are arrayed around a central area (22), the edge part of each LED bonding pad (21) facing the central area (22) is recessed away from the central area (22), a unfilled corner (211) for enlarging the area of the central area (22) is formed, the geometric center of each LED bonding pad (21) is positioned outside the area where the unfilled corner (211) is located, the minimum inscribed circle diameter of a space defined by the boundaries of all unfilled corners (211) of the same bonding pad group (2) is not less than 0.2mm, and the plate body (1) is provided with a via hole (11) under each central area (22).

2. The printed circuit board of an LED display module according to claim 1, wherein the LED bonding pad (21) comprises a long lateral side (212), a long vertical side (213), a short lateral side (214), a short vertical side (215) and a sloping side (216), the long lateral side (212) being arranged in parallel with the short lateral side (214), the long vertical side (213) being arranged in parallel with the short vertical side (215);

The long transverse edge (212), the short vertical edge (215), the inclined edge (216), the short transverse edge (214) and the long vertical edge (213) are connected end to end in sequence to form the outer contour of the LED bonding pad (21);

-said sloping edge (216) forms a boundary of said unfilled corner (211);

the short lateral edge (214) has a length of 65% to 85% of the length of the long lateral edge (212);

the short vertical edge (215) has a length of 65% to 85% of the length of the long vertical edge (213).

3. A method for manufacturing a printed circuit board for manufacturing the LED display module set according to any one of claims 1 to 2, comprising:

4. The method of manufacturing a printed circuit board according to claim 3, wherein forming LED pads with unfilled corners at each of the LED pad positions according to the LED pad size and the predetermined pitch comprises:

5. The method of manufacturing a printed circuit board of claim 4, wherein forming LED pads at each of the LED pad positions according to the corresponding LED pad pattern having unfilled corners comprises:

coating photoresist on the surface of the plate;

And removing the residual photoresist.

6. The method of manufacturing a printed circuit board of claim 4, wherein said determining the unfilled corner shape, position and size of each of said LED pads according to said LED pad size and said predetermined pitch comprises:

calculating an initial unfilled corner depth according to the preset distance;

7. The method of manufacturing a printed circuit board according to claim 3, wherein forming LED pads with unfilled corners at each of the LED pad positions according to the LED pad size and the predetermined pitch comprises:

8. A method of manufacturing a printed circuit board according to claim 3, wherein said forming LED pads with unfilled corners at each of said LED pad locations comprises:

Filling the via hole subjected to metallization treatment with an insulating material, and overflowing part of the insulating material from the periphery of the via hole to cover part of the LED bonding pad position;

9. A method for manufacturing a printed circuit board for manufacturing the LED display module set according to any one of claims 1 to 2, comprising: