1. When starting the PCB layout, the schematic design should be completed first, and a correct schematic should be obtained, which is the basis of the single-sided PCB board proofing design. Through the schematic diagram, we can get a network list of the connection properties of each device. In addition, according to the parameters of the device, we can find the relevant component information and establish the package of all components. In addition, it is also necessary for the structural part to cooperate to give the size of the board and frame, as well as the positions of each installation and functional excuse.
2. After the PCB board proofing manufacturer completes the preparations, it will enter the specific operation part, but firstly, all package files and netlists need to be imported into the PCB file where the outer frame has been established. Some component packaging errors may be prompted during the import process, please eliminate the errors according to the error prompts.
3. After completing the import file operation, the first step to do is to fix the structure-related components, such as LEDs, buttons, card holders, liquid crystals, infrared transmitters, etc. Move these components to the corresponding installation positions, and select lock in the properties to prevent misoperation.
4. After the priority device is established, we can make a general layout. The purpose of the general layout is to determine the position of each functional module. In PCB design, the default is generally:
A. Except for the devices that need to be installed on the surface, all SMD devices are placed on one side of the plug-in device, which is generally the bottom layer;
B. The metering unit is placed in the lower left corner, which is convenient for entering the line;
C. The MCU is placed on the back of the LCD, and the leads are short enough;
D. The interface part is placed in the lower right corner of the PCB for easy outgoing;
E. The transformer is far away from the devices that are sensitive to magnetic flux leakage such as transformers and manganese-copper shunts;
F. Sufficient creepage distance should be reserved between circuits that need to be isolated;
5. After the general layout is completed, the partial layout can be carried out. Complete the placement of the corresponding devices for each functional module. Factors that need to be considered in the partial layout are:
A. The crystal oscillator should be as close as possible to the crystal oscillator pins, so that the traces should be as short as possible;
B. The decoupling capacitor should rely on the power input pin of the IC as far as possible;
C. Devices with high-speed connections between ICs should be as close as possible;
D. Consider the convenience of maintenance and optimize the placement of some devices to avoid production difficulties;
E. Leave a certain board margin, and the margin is required to be more than 4mm, otherwise it is easy to cause accidental damage to the patch reclaimer during patching in the SMT workshop, and cause the device to collide with the chain during wave soldering, which cannot be used at one time. After wave soldering completes plug-in soldering, more stations need to be arranged for repair welding;
F. Varistors, polyester capacitors, transient suppression diodes and voltage regulators, and filter capacitors should be placed at the front end of the device to be protected;
G. Pay attention to the distance between high-voltage and low-voltage signals.
6. After the local layout is completed, the components can be connected. The connection needs to pay attention to the following aspects:
A. Proofing the pcb board to understand the magnitude of the current that each device may flow and the magnitude of the large inrush current, and to roughly understand the possible influence of the signals carried on the traces on other signals. In order to set the thickness of the trace
B. The wiring from the high-voltage signal to the two ends of the varistor and polyester capacitor should be as wide as possible, so that the protection device can release the overload energy in time, and at the same time, it can also prevent the line from being burned by an instantaneous large current;
C. The main line trace of low-voltage power supply signal adopts 36mil to reduce the wire resistance, and the width of 24mil or less can be used near the chip.
D. The small signal connection can be 10mil or 12mil, too thin will cause high scrap rate, too thick is meaningless.
E. Do not route near high-frequency signals, such as the bottom of the crystal oscillator;
F. Minimize the connection of vias. The quality of the trace directly affects the performance of the PCB board, and it may be necessary to redo the actual wiring, or even go back to the schematic diagram to modify the IO port definition. This is the most time-consuming part.
7. After all signal lines are routed, the power lines can be routed. The power lines should be routed with sufficient width to avoid sudden changes in line width and right-angled corners. Also, the power cords cannot be formed into a loop.
8. After the line connection is completed, the ground can be processed to form a large ground plane, which is equivalent to completing the ground wire wiring.
9. After completing the ground plane, you can use this as a reference to adjust the device layout with the goal of maximizing the ground area. When adjusting, it is necessary to prevent the large ground plane from being connected to the main ground only through a few vias. Pay attention to the integrity of the floor covering under the chip. In addition, it can better observe the aesthetics of wiring and device placement, and whether the return loop of each signal is complete. In this step, complete the adjustment and modification of all device labels, and mark the company Logo and PCB version number.
10. DRC verification is an efficient and reliable inspection tool. It can reliably check the drawing specifications of all PCB boards according to the rules we set, and at the same time point out errors and highlight them.
11. After confirming that all the designs are correct, the PCB board can be exported, and the export format is Protel PCB 2.8 ASCII File.
12. Finally, the document control will issue the proofing.
PCSPCB is a production enterprise specializing in single- and double-sided circuit boards and aluminum-based circuit boards. It has a factory building of more than 50,000 square meters and a complete set of advanced automatic circuit board production equipment. The annual output of circuit boards is more than 100,000 square meters. Enterprises in temperature control instruments, automation instruments, LED lights, car lights, electric vehicle accessories, communication equipment, electrical appliances, electronics and electric power industries produce supporting circuit board products.
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