Direct display LED printed board manufacturing process

Abstract

A direct display LED printed board manufacturing process specifically comprises the following steps that S1, raw materials are prepared, specifically, an original circuit board, lamp beads and a bonding pad are prepared, the original circuit board is divided into four layers and is numbered as L1, L2, L3 and L4 from top to bottom, L2 and L3 are daughter boards, and L1 and L4 are mother boards; according to the manufacturing process of the direct-display LED printed board, stress is released to the maximum extent by baking the daughter board for 4 hours at 180 DEG C when the daughter board is cut, so that warping of the daughter board is improved, the distance between bonding pads on a circuit board and the sizes of the bonding pads are changed, the positions of the bonding pads are kept, the distance between the bonding pads is guaranteed, and meanwhile, the direct-display LED printed board is manufactured through the butterfly PAD. AOI (automatic optical inspection) equipment analysis is facilitated, and the direct display LED yield is improved through the improved solder mask process.

Description

Technical Field

[0001] The invention relates to the technical field of direct display LED printed boards, and in particular to a direct display LED printed board manufacturing process. Background Art

[0002] The LED display market has entered a period of rapid growth. Major companies have continuously increased their research and development of small-pitch technology and market layout. The dot pitch of LED displays has continued to achieve breakthroughs, pixel density has increased, and resolution has also been greatly improved. Small-pitch LEDs are accelerating their penetration into the large-screen display field. At present, the Chinese market is far ahead, followed by markets such as North America and Europe.

[0003] At present, LED direct display in the industry has become the current trend of large-screen commercial use due to its advantages in brightness, color gamut, resolution, etc. At the same time, the difficulty of its printed circuit board is also increasing, mainly in the characteristics of high pad accuracy, small spacing, strict dimensional accuracy and ink color consistency. Therefore, the present invention provides a direct display LED printed circuit board manufacturing process, which can realize the processing of direct display LED printed circuit boards, solve the problems of warping, dimensional pad accuracy, etc. of direct display LED printed circuit boards, thereby improving the direct display LED yield. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a direct display LED printed circuit board manufacturing process.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A direct display LED printed circuit board manufacturing process specifically includes the following steps: S1, preparing raw materials: preparing an original circuit board, lamp beads and pads, and the original circuit board is divided into 4 layers, and they are numbered from top to bottom as L1, L2, L3, L4, where L2 and L3 are sub-boards, L1 and L4 are motherboards;

[0007] S2. Daughter board cutting and baking: The model of the daughter board is TG-FR-4. Two daughter boards are placed in a baking oven for baking. The baking temperature is 180℃ and the baking time is 4 hours. Drilling and copper plating of daughter boards: Drill holes at the planned positions on the two daughter boards, and use chemical methods to deposit a thin layer of copper on the insulating hole wall as the basis for subsequent electroplating. Dry film on the inner layer of the daughter board: A special photosensitive film is attached to the surface of the copper plate, and the board with the film is exposed. The light-transmitting part is solidified, and the non-light-transmitting part is still a dry film. Then after development, the unsolidified dry film is removed. Etching of the inner layer of the daughter board: The required graphics are transferred to the copper foil through a dry film or a wet film to protect the required copper foil from being etched away. Under acidic conditions, an acidic etching solution (such as an acidic cupric chloride solution) is used to etch the copper foil not covered by the protective film to remove the unnecessary copper foil. AOI on the inner layer of the daughter board: Data collection, data processing, and graphic analysis are performed on the graphics on the daughter board, and finally the defective areas are marked. Browning and pressing of the daughter board;

[0008] S3, motherboard pressing and browning copper reduction: browning copper reduction to 7-9μm, reduce copper thickness, and pave the way for small pitch production in advance; motherboard laser drilling plasma degumming; motherboard PTH electroplating hole filling: chemical copper plating is carried out on the motherboard to deposit a layer of chemical copper on the board surface or hole wall. During this process, the bath liquid should maintain normal air stirring to convert more soluble divalent copper, and first perform mechanical or laser drilling, and use a drilling machine or other tools to process and clean the holes to ensure that the hole surface is smooth, and use laser filling potion to fill the 4mil laser hole, and the depression is controlled below 15μm; motherboard copper reduction: first scrap the board for batch production to improve activity, and confirm the copper reduction rate for the first piece, and reduce the copper to 15±3μm; motherboard ceramic grinding plate: use cloth woven cloth for polishing to grind off the copper particles and roughness caused by copper reduction; motherboard dry film outer layer etching: use 25μ m thin dry film, exposure energy 16mJ, development speed 3.2m / min, exposure level 7-9 grids, outer layer etching is made with inner layer etching line, and after completion, it is sent to AOI scanning and detection; motherboard solder mask: made with Yanmo special ink DMK25, ink viscosity is 120±20dpa.s, wet film thickness fixed parameter thickness is 15-25um, the first side is printed with circuit surface, the second side is printed with lamp bead surface, DI special machine is selected for exposure and marked, and the lamp bead surface is exposed first, then the circuit surface, exposure energy 40~80mJ / cm2, after development, full color difference is checked and pad is fully checked with a magnifying glass, and ink color consistency is monitored after baking △E≤1.0; motherboard text gold; motherboard controlled depth drilling: confirm expansion and contraction, re-drill belt according to expansion and contraction to prevent drilling deviation, and confirm hole depth after first piece slicing; motherboard electrical measurement and general inspection: adopt special large-point measuring machine for electrical measurement.

[0009] In one of the embodiments, the lamp beads prepared in the raw materials in step S1 are 32400 groups, the spacing of the pads is 2.16mil±0.02, the pad size is 5.22mil*4.72mil with a tolerance of ±0.02mm, the spacing of the pads is guaranteed to be 1.3mil, and butterfly PADs are added on the four edges of the circuit board. The diameter of the central butterfly PAD is designed to be 1mm-2mm, and the surrounding frame is 2.5mm*2.5mm, with a width of 1mm. The butterfly PAD spacing is 20mm, covering the entire edge of the board for AOI equipment to analyze data. Before drilling and copper plating of the sub-board in step S1, the surface of the workpiece needs to be cleaned to remove impurities such as oil, oxide scale and rust to ensure the quality of the coating. During electroplating, the workpiece is hung on a hook, and the metal ions are reduced to the surface of the workpiece by current to form the required coating. Different hanging plating methods are used according to different workpieces. Hanging plating is suitable for small and complex-shaped workpieces, while wire-wound plating is suitable for large and flat-shaped workpieces. Before etching the inside of step S1, the surface of the circuit board needs to be cleaned and processed to ensure the etching effect. At the same time, a layer of anti-etching mold needs to be pressed on the sub-board to ensure the exposure effect. When the sub-board is browned and pressed in step S1, the activated copper surface is immersed in a browning solution to form a uniform organic metal coating. This process is usually carried out under high temperature and pressure to form mechanical and chemical dual bonding characteristics with the semi-cured sheet, and the core board, PP and copper foil are stacked and pressed in the designed order with fully automatic equipment, and then cooled and solidified after heating.

[0010] In one of the embodiments, when etching the outer layer in step S2, because the copper thickness is 10μm, the inner layer etching line is used, the etching amount is small, the first piece is made, the pad size and spacing are measured, and the AOI is sent for scanning. After passing the test, batch production is carried out. When laser drilling and plasma debonding of the motherboard in step S2, the expansion and contraction are specified in advance, the drilling is carried out at 1:1, and plasma is used to remove the laser residual glue to reduce the risk of ICD.

[0011] Compared with the prior art, the present invention has at least the following advantages:

[0012] A direct-display LED printed circuit board manufacturing process of the present invention bakes the sub-board at 180°C for up to 4 hours when cutting the material to release stress to the greatest extent, thereby improving its warping, and by changing the spacing and pad size of the pads on the circuit board and maintaining their positions, thereby ensuring their spacing, and by setting up a butterfly PAD, it is convenient for AOI equipment analysis, and when solder masking, in order to ensure consistency, the special ink DMK25 of Yanmo is used. At the same time, for the same batch of centralized production, the same material number of silk screen printing is produced by a dedicated person and a dedicated machine, and after the machine is adjusted OK, it should be avoided to adjust the machine again (pay special attention to remind the shift or overtime printing when handing over). The oil and water are added in a unified standard, and the ink viscosity (120±20dpa.s) & wet film thickness are fixed parameter thickness (thickness 15-25um). It is made of 51 mesh and ink is applied from the circuit surface. The circuit surface is printed on the first side, and the lamp bead surface is printed on the second side to ensure the flatness of the lamp bead surface. It is preferred to use a new knife. If the silk screen is poor, it cannot be printed again directly. The surface ink can be removed with white paper before printing or developing, washing and exposure. Select a DI special machine and mark it. Expose the lamp bead surface first, then the circuit surface. The exposure energy is 40-80mJ / cm2. After development, check the color difference and use a magnifying glass to check the pad. After baking, monitor the ink color consistency (△E≤1.0), so as to improve the yield of its direct display LED.

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the embodiments will be briefly introduced below. It should be understood that they should not be regarded as limiting the scope. DETAILED DESCRIPTION

[0014] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0015] In the description of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientation or positional relationships, are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0016] Unless otherwise clearly stipulated and limited, terms such as "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0018] A direct display LED printed circuit board manufacturing process specifically includes the following steps:

[0019] S1. Prepare raw materials: prepare the original circuit board, lamp beads and solder pads. The original circuit board is divided into 4 layers, and they are numbered from top to bottom as L1, L2, L3, and L4, of which L2 and L3 are sub-boards, L1 and L4 are motherboards;

[0020] S2. Daughter board cutting and baking: The model of the daughter board is TG-FR-4. Two daughter boards are placed in a baking oven for baking. The baking temperature is 180℃ and the baking time is 4 hours. Drilling and copper plating of daughter boards: Drill holes at the planned positions on the two daughter boards, and use chemical methods to deposit a thin layer of copper on the insulating hole wall as the basis for subsequent electroplating. Dry film on the inner layer of the daughter board: A special photosensitive film is attached to the surface of the copper plate, and the board with the film is exposed. The light-transmitting part is solidified, and the non-light-transmitting part is still a dry film. Then after development, the unsolidified dry film is removed. Etching of the inner layer of the daughter board: The required graphics are transferred to the copper foil through a dry film or a wet film to protect the required copper foil from being etched away. Under acidic conditions, an acidic etching solution (such as an acidic cupric chloride solution) is used to etch the copper foil not covered by the protective film to remove the unnecessary copper foil. AOI on the inner layer of the daughter board: Data collection, data processing, and graphic analysis are performed on the graphics on the daughter board, and finally the defective areas are marked. Browning and pressing of the daughter board;

[0021] S3, motherboard pressing and browning copper reduction: browning copper reduction to 7-9μm, reduce copper thickness, and pave the way for small pitch production in advance; motherboard laser drilling plasma degumming; motherboard PTH electroplating hole filling: chemical copper plating is carried out on the motherboard to deposit a layer of chemical copper on the board surface or hole wall. During this process, the bath liquid should maintain normal air stirring to convert more soluble divalent copper, and first perform mechanical or laser drilling, and use a drilling machine or other tools to process and clean the holes to ensure that the hole surface is smooth, and use laser filling potion to fill the 4mil laser hole, and the depression is controlled below 15μm; motherboard copper reduction: first scrap the board for batch production to improve activity, and confirm the copper reduction rate for the first piece, and reduce the copper to 15±3μm; motherboard ceramic grinding plate: use cloth woven cloth for polishing to grind off the copper particles and roughness caused by copper reduction; motherboard dry film outer layer etching: use 25μ m thin dry film, exposure energy 16mJ, development speed 3.2m / min, exposure level 7-9 grids, outer layer etching is made with inner layer etching line, and after completion, it is sent to AOI scanning and detection; motherboard solder mask: made with Yanmo special ink DMK25, ink viscosity is 120±20dpa.s, wet film thickness fixed parameter thickness is 15-25um, the first side is printed with circuit surface, the second side is printed with lamp bead surface, DI special machine is selected for exposure and marked, and the lamp bead surface is exposed first, then the circuit surface, exposure energy 40~80mJ / cm2, after development, full color difference is checked and pad is fully checked with a magnifying glass, and ink color consistency is monitored after baking △E≤1.0; motherboard text gold; motherboard controlled depth drilling: confirm expansion and contraction, re-drill belt according to expansion and contraction to prevent drilling deviation, and confirm hole depth after first piece slicing; motherboard electrical measurement and general inspection: adopt special large-point measuring machine for electrical measurement.

[0022] In one of the embodiments, the lamp beads prepared in the raw materials in step S1 are 32400 groups, the spacing between the pads is 2.16mil±0.02, the pad size is 5.22mil*4.72mil with a tolerance of ±0.02mm, the spacing between the pads is guaranteed to be 1.3mil, and butterfly PADs are added to the four edges of the circuit board. The diameter of the central butterfly PAD is designed to be 1mm-2mm, the surrounding borders are 2.5mm*2.5mm, the width is 1mm, and the butterfly PAD spacing is 20mm, covering the entire edge of the board for AOI equipment to analyze the data.

[0023] In one of the embodiments, before drilling and copper plating on the daughter board in step S1, the surface of the workpiece needs to be cleaned to remove impurities such as oil, scale and rust to ensure the quality of the coating. During electroplating, the workpiece is hung on a hook and the metal ions are reduced to the surface of the workpiece by electric current to form the desired coating. Different workpieces are plated in different ways. Hanging plating is suitable for small and complex-shaped workpieces, while wire-wound plating is suitable for large and flat workpieces.

[0024] In one of the embodiments, before etching the inside of step S1, the circuit board surface needs to be cleaned and processed to ensure the etching effect, and a layer of anti-etching mold needs to be pressed on the daughter board to ensure the exposure effect.

[0025] In one embodiment, during the browning and laminating of the sub-board in step S1, the activated copper surface is immersed in a browning solution to form a uniform organic metal coating. This process is usually carried out under high temperature and pressure to form a mechanical and chemical dual bonding property with the prepreg, and the core board, PP and copper foil are stacked and laminated in the designed order by fully automatic equipment, and then cooled and solidified after heating.

[0026] In one of the embodiments, when etching the outer layer in step S2, because the copper thickness is 10 μm, the inner layer etching line is used, the etching amount is small, the first piece is made, the pad size and spacing are measured, and it is sent to AOI scanning. After passing the test, batch production will be carried out.

[0027] In one of the embodiments, during the laser drilling and plasma debonding of the motherboard in step S2, the expansion and contraction are specified in advance, the drill is performed at a 1:1 ratio, and plasma is used to remove the laser residual glue to reduce the ICD risk.

[0028] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A direct display LED printed circuit board manufacturing process, characterized in that: The specific steps include: S1. Prepare raw materials: prepare the original circuit board, lamp beads and solder pads. The original circuit board is divided into 4 layers, and they are numbered from top to bottom as L1, L2, L3, and L4, of which L2 and L3 are sub-boards, L1 and L4 are motherboards; S2. Daughter board cutting and baking: The model of the daughter board is TG-FR-4. Two daughter boards are placed in a baking oven for baking at a temperature of 180°C for 4 hours. Sub-board drilling and copper plating: Drill holes at the planned locations on the two sub-boards, and use chemical methods to deposit a thin layer of copper on the insulating hole wall as the basis for subsequent electroplating; Dry film in the inner layer of the sub-board: a special photosensitive film is pasted on the surface of the copper board, and the board with the film is exposed. The transparent part is cured, and the non-transparent part is still a dry film. Then it is developed to remove the uncured dry film; Etching of the inner layer of the daughter board: transfer the required pattern to the copper foil through dry film or wet film to protect the required copper foil from being etched away. Under acidic conditions, use acidic etching solution (such as acidic cupric chloride solution) to etch the copper foil not covered by the protective film to remove the unnecessary copper foil; AOI of the inner layer of the daughter board: collect data, process data, analyze graphics on the daughter board, and finally mark the defective areas; Browning and lamination of sub-boards; S3, motherboard pressing and browning copper reduction: Browning copper reduction to 7-9μm, reducing copper thickness, paving the way for fine pitch production in advance; Motherboard laser drilling and plasma degumming; Motherboard PTH electroplating hole filling: Chemical copper plating is performed on the motherboard to deposit a layer of chemical copper on the board surface or hole wall. During this process, the bath liquid should maintain normal air stirring to convert more soluble divalent copper, and first perform mechanical or laser drilling, and use a drill press or other tools to process and clean the holes to ensure that the hole surface is smooth, and use laser hole filling solution to fill the 4mil laser hole, and the depression is controlled below 15μm; Copper reduction on motherboard: firstly scrap the board and make batches to improve the activity, confirm the copper reduction rate of the first piece, and reduce the copper to 15±3μm; Motherboard ceramic grinding plate: Use cloth to polish and remove the copper particles and roughness caused by copper reduction; Motherboard dry film outer layer etching: use 25μm thin dry film, exposure energy 16mJ, development speed 3.2m / min, exposure level 7-9 grids, outer layer etching is made using inner layer etching line, and after completion, it is sent to AOI scanning inspection; Motherboard solder mask: Made of Yanmo special ink DMK25, the ink viscosity is 120±20dpa.s, the wet film thickness is fixed parameter thickness of 15-25um, the first side is printed with circuit surface, the second side is printed with lamp bead surface, the exposure is selected on a DI dedicated machine and marked, and the lamp bead surface is exposed first, then the circuit surface, the exposure energy is 40~80mJ / cm2, the color difference is fully inspected after development and the pad is fully inspected with a magnifying glass, and the ink color consistency is monitored after baking △E≤1.0; Motherboard literalized gold; Controlled depth drilling of motherboard: confirm the expansion and contraction, re-drill the drill belt according to the expansion and contraction to prevent drilling deviation, and confirm the hole depth by slicing the first piece; Motherboard electrical test: Use a dedicated large-point measuring machine for electrical testing.

2. A direct display LED printed circuit board manufacturing process according to claim 1, characterized in that: The raw materials prepared in step S1 include 32400 sets of lamp beads, the pad spacing is 2.16mil±0.02, the pad size is 5.22mil*4.72mil with a tolerance of ±0.02mm, the pad spacing is guaranteed to be 1.3mil, and butterfly PADs are added on the four edges of the circuit board. The center butterfly PAD has a diameter of 1mm-2mm, and the surrounding borders are 2.5mm*2.5mm and 1mm wide. The butterfly PAD spacing is 20mm, covering the entire edge of the board for AOI equipment to analyze the data.

3. A direct display LED printed circuit board manufacturing process according to claim 1, characterized in that: S1 step Before drilling and copper plating on the daughter board, the surface of the workpiece needs to be cleaned to remove impurities such as oil, oxide scale and rust to ensure the quality of the coating. During electroplating, the workpiece is hung on a hook and the metal ions are reduced to the surface of the workpiece by electric current to form the required coating. Different workpieces are plated in different ways. Hanging plating is suitable for small and complex workpieces, while wire-wound plating is suitable for large and flat workpieces.

4. The direct display LED printed circuit board manufacturing process according to claim 1, characterized in that: Before etching the inside of step S1, the circuit board surface needs to be cleaned and processed to ensure the etching effect. At the same time, a layer of anti-etching mold needs to be pressed on the daughter board to ensure the exposure effect.

5. The direct display LED printed circuit board manufacturing process according to claim 1, characterized in that: During the S1 step of browning and pressing the sub-board, the activated copper surface is immersed in the browning solution to form a uniform organic metal coating. This process is usually carried out under high temperature and pressure to form a mechanical and chemical dual bonding property with the semi-cured sheet, and the core board, PP and copper foil are stacked and pressed in the designed order by fully automatic equipment, and then cooled and solidified after heating.

6. A direct display LED printed circuit board manufacturing process according to claim 1, characterized in that: When etching the outer layer in step S2, because the copper thickness is 10μm, the inner layer etching line is used, the etching amount is small, the first piece is made, the pad size and spacing are measured, and it is sent to AOI scanning. After passing the test, batch production will be carried out.

7. A direct display LED printed circuit board manufacturing process according to claim 1, characterized in that: In step S2, when laser drilling and plasma debonding the motherboard, specify the expansion and contraction in advance, drill at a 1:1 ratio, and use plasma to remove laser residual glue to reduce ICD risks.