Understanding LED electronic screens starts with reading the LED unit …
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1. General
(1) When the design rules of the led electronic display unit board are satisfied, the production cost should be reduced as much as possible, such as: use the 2-layer board as much as possible if the 2-layer board can be used; when the cost conflicts with the design rules, the design rules should be guaranteed.
(2) Components are arranged neatly, and the same chips are arranged in rows and columns according to certain rules; the spacing between components should consider the production process and should not affect the welding.
(3) For PCB design, automatic routing cannot be used for design.
2. Rules
(1) Use of wiring layers
When designing a circuit board with more than 2 layers, it is forbidden to use the internal electrical layer. Use the inner layer definition like a normal layer.
For LED unit boards that require blind and buried hole design, for four-layer boards, 1-2, 3-4, 1-4 drilling; for six-layer boards, 1-2, 2-5, 5-6 drilling; The specific process must be confirmed with the PCB manufacturer.
(2) Separate power supply for digital devices and drive devices
To adopt the method of separate wiring of digital ground and analog ground, the power supply of the digital part is only connected to the power supply of the drive part through a jumper at the entrance of the power base.
In the case of space on the board, it is recommended to separate the power supply of the column drive and the power supply of the row drive.
(3) Power line and row line:
The power rail width of the digital part is >=50mil.
The width of the power line and row line should comprehensively consider the current, width, and distance of the power branch. Ensure that the line voltage drop from the power inlet to the module is not greater than 0.01V.
It is recommended that the power base be placed in the middle of the board. When the power socket is placed on one side, reserve the power socket or pad on the symmetrical side to facilitate the flying wire during production.
When wiring is difficult, reserve power pads on the board to facilitate flying wires during production.
There must be a separate power socket or pad on the circuit board where the row driver is located.
The circuit board where the column driver is located must have a separate power socket or pad.
When using non-soldering methods (pin row, hole row and cable row) to connect the power supply and row line, the current of each pin should not exceed 1A, and each connection should have at least two pins.
For users who already have light boards, we will discuss it separately.
It is recommended that the row pipe be placed in the middle of the row line within 1/3 of the entire unit board ground.
For outdoor screens, if the driver board of the lamp board is separated, the row pipe should be placed near the lead-in pin of the row line.
(4) Requirements for ground wire
The width of the ground line in the digital part is >=50mil.
The ground line of the column drive part should be wider than the power line of the row drive, and it is recommended to be more than 1.5 times the width of the power line.
The ground wires of the LED unit board should be arranged in a checkerboard shape, and the branches are connected.
The driving part is covered with copper skin, and the digital part is covered with grid ground. The distance between the ground and other parts is set to 20mil or more. The line width of the grid ground is 25mil, and the center spacing is 40mil.
When laying the ground, avoid dead corners without loops. After the paving is completed, each part of the divided ground will be connected by manual paving.
Put the test ground pin at the power inlet for the analog ground.
Digitally place the test ground pin between the input pin header, output pin header and 9702.
(5) Capacitance requirements
Put a 100u electrolytic capacitor and a 104 capacitor at the power inlet of the drive part and the digital part.
Put a 100u electrolytic capacitor at the entrance and end of the branch of the power line.
It is recommended to leave a 100u electrolytic capacitor near the row driver chip.
There is a 104 capacitor between the power supply pin and the ground of the serial conversion and driving chip.
(6) Chip power pin outlet
For serial-to-parallel chips, the power pin outlet of the row driver chip should be at least as wide as the pin pad.
(7) Column lines and signal lines:
The width of the light board, column line and signal line of the outdoor LED screen is >=12mil. When the PCB size is large, the signal line width is recommended to be 15mil.
In other occasions, it is recommended that the width of column lines and signal lines be 12mil, at least 10mil.
Line spacing is not less than the minimum line width.
(8) Vias:
The light board of the outdoor LED screen, the via parameter is 50 mil, 28 mil.
In other occasions, the via parameters are recommended to be 50 mil and 28 mil. At least 40mil, 24mil.
The spacing between vias and lines is not less than the minimum line width.
The outer diameter of the via hole of the power supply line =the width of the power supply line*1/3. Recommended inner diameter of via: 28mil, 40mil.
Large power and ground traces can increase the via count.
In order to ensure soldering, the vias should not be placed on the pads. At least 5mil away from the pad.
(9) Socket welding device pad:
The via holes for inserting and welding the device pads must ensure that there is no problem with the insertion of the device.
The inner diameter of the ordinary pin row hole is 40mil, and the pad hole of the power socket is 60mil.
(10) Mounting holes:
For the unit board using the LED module, the installation hole should not be located at the junction of the two modules, and there should be no copper foil around the hole to prevent the installation hole from being connected to the DC ground of the unit board. signature).
General components should be placed 3.5mm away from the center of the fixing hole, and relatively high components (such as capacitors, plug-in chips) should be placed more than 5mm away from the center of the fixing hole.
When the user does not have a clear demand, the cascade pin header and power socket should be placed 2cm away from the horizontal and vertical connections of the fixing holes.
When designing a PCB for a specific customer, it is necessary to clarify the customer's fixing hole position and fixing structure to determine the placement of pin headers, power sockets and other components.
(11) module
Components that are plugged in cannot be placed on the border of the module.
Modules are suggested to be placed in "queue placement" or grid to avoid mistakes.
The PCB edge should be at least 20mil smaller than the module.
The module is built according to the front view, and it is positioned on the back side when placed, so as to prevent the front pads of other devices from being covered by the silkscreen on the module boundary.
The module placement center distance should be dot spacing*8. When the accuracy of the module is too low to guarantee the data, the center distance of the module placement should be confirmed with the customer.
(12) Optimization:
After the layout design is completed, it should be reviewed to optimize the routing.
The width of the power line should be increased, and the ground line should be arranged in a checkerboard shape as much as possible.
(13) Board layout sequence: Pre-wiring is required before board layout, and the alignment of the column lines can be adjusted. You can return to modify the schematic diagram and network table to make the alignment of the column lines the most convenient. When laying out the board, first route the wiring, power and ground wires, cascade signal wires, and then other wires.
(14) After the PCB design is completed, there should be a description of the PCB processing process requirements for the led unit board, including: PCB board thickness requirements, PCB board copper foil thickness requirements, PCB board minimum line width, PCB board minimum spacing, PCB minimum via hole parameters . It is convenient to choose the casting manufacturer during the casting process.
(15) After the PCB design is completed, a component list should be made, and various component packages should be clearly marked. If there is a reserved position and components that do not need to be soldered during production, it must be specially indicated. The component list should also include a brief note on soldering precautions.
(16) silk screen layer
After the design of the led unit board is completed, mark the unit board information on the TOP layer of the unit board, including the board number, the basic parameters of the unit board, and the completion date.
The LED unit board should have an obvious cascade connection direction mark at the prominent position of the cascade connection inlet and cascade connection outlet; there should be an obvious mark indication at the 1 pin position of the cascade connection pin header and other pin headers; for the positive and negative poles of the power socket There should be an easy-to-observe +- sign next to the pin, and there should be an obvious indication of the welding direction; for the empty pad designed for the jumper, an obvious network name logo should be placed; for the best led display board and the driver board separated For the unit board, there should be an obvious indication of the direction of insertion on both the light board and the driver board, or it should be asymmetrical in design.
For components with positive and negative poles, the direction of the positive and negative poles should be reflected on the layout. Such as diodes, Zener tubes, electrolytic capacitors, power sockets, etc., and the direction of placement indicates that they cannot be covered after welding;
For the unit board of the virtual pixel, in addition to the welding direction of the LED, there must be an obvious R/G/B mark. For the unit board of the surface-mounted LED lamp that cannot be silk-screened at the bottom, it must be explained in detail in the production instructions. arrangement.
In order not to affect the soldering, the characters on the silk screen layer cannot overlap with the pads.
After the drawing is completed, place the name of the IC under the IC; for 62706 or 595, place the logo of its control color next to the IC;
After the PCB design is completed, place optical positioning points on the diagonal of the PCB.
(17) Detection
After the design is completed, DRC testing is required. When converting to PROTEL2.8 after drawing with PROTEL99 and POWERPCB, DRC detection should also be done.
After using the PowerPCB software to draw a picture, when importing it to the Protel2.8 format, it should be noted that sometimes the size of the via hole on the board will change. After using the Protel99 software to draw the picture, when it is imported into the Protel2.8 format, the vertically placed FILL may be changed to a horizontally placed one. These are the things to look out for in a drawing.
When drawing a PCB, for components with positive and negative poles, it is necessary to be able to reflect the direction of the positive and negative poles on the layout. Such as diodes, Zener tubes, electrolytic capacitors, power sockets, etc.
For two-pin components, you must not use the common 2-pin component library of SIP2 or IDC2, and you must use a dedicated component library.
For power sockets or power pads, be sure to mark the network name (or positive and negative signs) on the silk screen layer.
For single-row needles and double-row needles, there should be obvious marks at the position of one foot.
For other components, there must be an obvious 1-pin mark or a welding direction mark.
For unconventional usage, it must be explained in the production instructions.
For the unit board of virtual pixels, in addition to the welding direction of the LED, there must be an obvious R/G/B mark. For the surface-mounted LED unit board, which cannot be silk-screened at the bottom, it must be explained in detail in the production instructions.
(1) When the design rules of the led electronic display unit board are satisfied, the production cost should be reduced as much as possible, such as: use the 2-layer board as much as possible if the 2-layer board can be used; when the cost conflicts with the design rules, the design rules should be guaranteed.
(2) Components are arranged neatly, and the same chips are arranged in rows and columns according to certain rules; the spacing between components should consider the production process and should not affect the welding.
(3) For PCB design, automatic routing cannot be used for design.
2. Rules
(1) Use of wiring layers
When designing a circuit board with more than 2 layers, it is forbidden to use the internal electrical layer. Use the inner layer definition like a normal layer.
For LED unit boards that require blind and buried hole design, for four-layer boards, 1-2, 3-4, 1-4 drilling; for six-layer boards, 1-2, 2-5, 5-6 drilling; The specific process must be confirmed with the PCB manufacturer.
(2) Separate power supply for digital devices and drive devices
To adopt the method of separate wiring of digital ground and analog ground, the power supply of the digital part is only connected to the power supply of the drive part through a jumper at the entrance of the power base.
In the case of space on the board, it is recommended to separate the power supply of the column drive and the power supply of the row drive.
(3) Power line and row line:
The power rail width of the digital part is >=50mil.
The width of the power line and row line should comprehensively consider the current, width, and distance of the power branch. Ensure that the line voltage drop from the power inlet to the module is not greater than 0.01V.
It is recommended that the power base be placed in the middle of the board. When the power socket is placed on one side, reserve the power socket or pad on the symmetrical side to facilitate the flying wire during production.
When wiring is difficult, reserve power pads on the board to facilitate flying wires during production.
There must be a separate power socket or pad on the circuit board where the row driver is located.
The circuit board where the column driver is located must have a separate power socket or pad.
When using non-soldering methods (pin row, hole row and cable row) to connect the power supply and row line, the current of each pin should not exceed 1A, and each connection should have at least two pins.
For users who already have light boards, we will discuss it separately.
It is recommended that the row pipe be placed in the middle of the row line within 1/3 of the entire unit board ground.
For outdoor screens, if the driver board of the lamp board is separated, the row pipe should be placed near the lead-in pin of the row line.
(4) Requirements for ground wire
The width of the ground line in the digital part is >=50mil.
The ground line of the column drive part should be wider than the power line of the row drive, and it is recommended to be more than 1.5 times the width of the power line.
The ground wires of the LED unit board should be arranged in a checkerboard shape, and the branches are connected.
The driving part is covered with copper skin, and the digital part is covered with grid ground. The distance between the ground and other parts is set to 20mil or more. The line width of the grid ground is 25mil, and the center spacing is 40mil.
When laying the ground, avoid dead corners without loops. After the paving is completed, each part of the divided ground will be connected by manual paving.
Put the test ground pin at the power inlet for the analog ground.
Digitally place the test ground pin between the input pin header, output pin header and 9702.
(5) Capacitance requirements
Put a 100u electrolytic capacitor and a 104 capacitor at the power inlet of the drive part and the digital part.
Put a 100u electrolytic capacitor at the entrance and end of the branch of the power line.
It is recommended to leave a 100u electrolytic capacitor near the row driver chip.
There is a 104 capacitor between the power supply pin and the ground of the serial conversion and driving chip.
(6) Chip power pin outlet
For serial-to-parallel chips, the power pin outlet of the row driver chip should be at least as wide as the pin pad.
(7) Column lines and signal lines:
The width of the light board, column line and signal line of the outdoor LED screen is >=12mil. When the PCB size is large, the signal line width is recommended to be 15mil.
In other occasions, it is recommended that the width of column lines and signal lines be 12mil, at least 10mil.
Line spacing is not less than the minimum line width.
(8) Vias:
The light board of the outdoor LED screen, the via parameter is 50 mil, 28 mil.
In other occasions, the via parameters are recommended to be 50 mil and 28 mil. At least 40mil, 24mil.
The spacing between vias and lines is not less than the minimum line width.
The outer diameter of the via hole of the power supply line =the width of the power supply line*1/3. Recommended inner diameter of via: 28mil, 40mil.
Large power and ground traces can increase the via count.
In order to ensure soldering, the vias should not be placed on the pads. At least 5mil away from the pad.
(9) Socket welding device pad:
The via holes for inserting and welding the device pads must ensure that there is no problem with the insertion of the device.
The inner diameter of the ordinary pin row hole is 40mil, and the pad hole of the power socket is 60mil.
(10) Mounting holes:
For the unit board using the LED module, the installation hole should not be located at the junction of the two modules, and there should be no copper foil around the hole to prevent the installation hole from being connected to the DC ground of the unit board. signature).
General components should be placed 3.5mm away from the center of the fixing hole, and relatively high components (such as capacitors, plug-in chips) should be placed more than 5mm away from the center of the fixing hole.
When the user does not have a clear demand, the cascade pin header and power socket should be placed 2cm away from the horizontal and vertical connections of the fixing holes.
When designing a PCB for a specific customer, it is necessary to clarify the customer's fixing hole position and fixing structure to determine the placement of pin headers, power sockets and other components.
(11) module
Components that are plugged in cannot be placed on the border of the module.
Modules are suggested to be placed in "queue placement" or grid to avoid mistakes.
The PCB edge should be at least 20mil smaller than the module.
The module is built according to the front view, and it is positioned on the back side when placed, so as to prevent the front pads of other devices from being covered by the silkscreen on the module boundary.
The module placement center distance should be dot spacing*8. When the accuracy of the module is too low to guarantee the data, the center distance of the module placement should be confirmed with the customer.
(12) Optimization:
After the layout design is completed, it should be reviewed to optimize the routing.
The width of the power line should be increased, and the ground line should be arranged in a checkerboard shape as much as possible.
(13) Board layout sequence: Pre-wiring is required before board layout, and the alignment of the column lines can be adjusted. You can return to modify the schematic diagram and network table to make the alignment of the column lines the most convenient. When laying out the board, first route the wiring, power and ground wires, cascade signal wires, and then other wires.
(14) After the PCB design is completed, there should be a description of the PCB processing process requirements for the led unit board, including: PCB board thickness requirements, PCB board copper foil thickness requirements, PCB board minimum line width, PCB board minimum spacing, PCB minimum via hole parameters . It is convenient to choose the casting manufacturer during the casting process.
(15) After the PCB design is completed, a component list should be made, and various component packages should be clearly marked. If there is a reserved position and components that do not need to be soldered during production, it must be specially indicated. The component list should also include a brief note on soldering precautions.
(16) silk screen layer
After the design of the led unit board is completed, mark the unit board information on the TOP layer of the unit board, including the board number, the basic parameters of the unit board, and the completion date.
The LED unit board should have an obvious cascade connection direction mark at the prominent position of the cascade connection inlet and cascade connection outlet; there should be an obvious mark indication at the 1 pin position of the cascade connection pin header and other pin headers; for the positive and negative poles of the power socket There should be an easy-to-observe +- sign next to the pin, and there should be an obvious indication of the welding direction; for the empty pad designed for the jumper, an obvious network name logo should be placed; for the best led display board and the driver board separated For the unit board, there should be an obvious indication of the direction of insertion on both the light board and the driver board, or it should be asymmetrical in design.
For components with positive and negative poles, the direction of the positive and negative poles should be reflected on the layout. Such as diodes, Zener tubes, electrolytic capacitors, power sockets, etc., and the direction of placement indicates that they cannot be covered after welding;
For the unit board of the virtual pixel, in addition to the welding direction of the LED, there must be an obvious R/G/B mark. For the unit board of the surface-mounted LED lamp that cannot be silk-screened at the bottom, it must be explained in detail in the production instructions. arrangement.
In order not to affect the soldering, the characters on the silk screen layer cannot overlap with the pads.
After the drawing is completed, place the name of the IC under the IC; for 62706 or 595, place the logo of its control color next to the IC;
After the PCB design is completed, place optical positioning points on the diagonal of the PCB.
(17) Detection
After the design is completed, DRC testing is required. When converting to PROTEL2.8 after drawing with PROTEL99 and POWERPCB, DRC detection should also be done.
After using the PowerPCB software to draw a picture, when importing it to the Protel2.8 format, it should be noted that sometimes the size of the via hole on the board will change. After using the Protel99 software to draw the picture, when it is imported into the Protel2.8 format, the vertically placed FILL may be changed to a horizontally placed one. These are the things to look out for in a drawing.
When drawing a PCB, for components with positive and negative poles, it is necessary to be able to reflect the direction of the positive and negative poles on the layout. Such as diodes, Zener tubes, electrolytic capacitors, power sockets, etc.
For two-pin components, you must not use the common 2-pin component library of SIP2 or IDC2, and you must use a dedicated component library.
For power sockets or power pads, be sure to mark the network name (or positive and negative signs) on the silk screen layer.
For single-row needles and double-row needles, there should be obvious marks at the position of one foot.
For other components, there must be an obvious 1-pin mark or a welding direction mark.
For unconventional usage, it must be explained in the production instructions.
For the unit board of virtual pixels, in addition to the welding direction of the LED, there must be an obvious R/G/B mark. For the surface-mounted LED unit board, which cannot be silk-screened at the bottom, it must be explained in detail in the production instructions.
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