PCB News - The meaning of single panel and the design process of single panel proofing

The meaning of single panel and the design process of single panel proofing

Features of PCB single-sided board:
The so-called single-sided board is the most basic PCB, all the parts are concentrated on one side, and the wires are all concentrated on the other side. Because the wires only appear on one side, we call this kind of PCB a single-sided (Single-sided). Because single-sided boards have many strict restrictions on the design of the circuit (because there is only one side, the wiring cannot cross and must be around a separate path), it has not been used now, and generally only the early circuit boards will be used;
Single-panel wiring diagrams are mainly network printing, that is, a resist is printed on the copper surface, and after etching, the mark is printed with a solder mask, and finally the part's guide hole and shape are completed by punching. In addition, some products that are produced in small quantities and diversified use photoresist to form patterns.

The design process of PCB single-sided proofing

1. Preparation part:
   At the beginning of the PCB layout, you should first complete the schematic design and get a correct schematic. This is the basis of the single-sided proofing design. Through the schematic diagram, we can get a network table of the connection attributes 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 the components. In addition, the structural part is required to provide the size of the board frame, each installation position, and the position of the function excuse.
   2. Specific operation part:
   First, you need to import all the package files and netlists into the PCB file with the frame. Some component packaging errors may be prompted during the import process. Please troubleshoot the errors according to the error prompts.
   3. Related devices of fixed structure:
   You have to fix devices such as LEDs, buttons, decks, liquid crystals, infrared transmitters, etc. Move these devices to the corresponding installation position, and select lock in the properties to prevent misoperation.
   4. Carry out a rough layout:
   The purpose of the general layout is to determine the location of each functional module. In PCB design, the general default is: except for the devices that need to be mounted on the surface, all SMD devices are placed on the side of the plug-in device, generally the bottom layer;

The metering unit is placed in the lower left corner for easy wire entry;
Place the MCU on the back of the LCD, and make the leads short enough;
The interface part is placed in the lower right corner of the PCB for easy wire out;
Keep the transformer away from transformers and manganin shunts that are sensitive to magnetic leakage;
Keep enough creepage distance between the circuits that need to be isolated;
5. Carry out partial layout:
Complete the placement of the corresponding devices for each functional module. The factors that need to be considered in the local layout are: the crystal oscillator should be as close as possible to the crystal oscillator pin, and the trace should be as short as possible;
The decoupling capacitor should be as close as possible to the power input pin of the IC;
Devices with high-speed connections between ICs should be as close as possible;
It is necessary to consider the convenience of maintenance and optimize the placement of some components to avoid production difficulties;
Leave a certain board margin, and the margin should be 4mm or more, otherwise it is easy to cause accidental damage to the pick-up head during placement in the SMT workshop, causing the device to collide with the chain during wave soldering, and it cannot be used for one-time wave soldering. To complete the plug-in welding, more stations need to be arranged for repair welding;
Varistors, polyester capacitors, transient suppression diodes and voltage regulator tubes, and filter capacitors should be placed in the front end of the device that needs to be protected;
Pay attention to the distance between high-voltage and low-voltage signals.
6. Wiring of components
The wiring of components is also a very important process, you need to pay attention to the following aspects when wiring:

Knowing the magnitude of the current that each device may flow and the magnitude of the maximum inrush current can roughly understand the possible impact of the signal carried on the trace on other signals. In order to set the wire thickness
The wiring of the high-voltage signal to the varistor and the 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 prevent the line from being burned by the instantaneous high current;
The main circuit of low-voltage power supply signals is 36 mils to reduce the wire resistance. The width of 24 mils and below can be used near the chip.
The small signal connection can be 10mil or 12mil, too thin will cause the scrap rate to be too high, too thick is meaningless.
Do not route wires near high-frequency signals, such as the bottom of a crystal oscillator;
Minimize the connection of vias. The quality of the wiring directly affects the performance of the PCB board. In the actual wiring, it may be necessary to overthrow it, or even go back to the schematic diagram to modify the IO port definition. This is the most time-consuming part.
7. Carry out the wiring of the power cord:
The wiring of the power cord should be of sufficient width to avoid sudden changes in line width and right-angle corners. In addition, the power cord cannot be formed into a loop.
8. Floor treatment:
A large ground plane is formed, which is equivalent to completing the wiring of the ground wire at the same time.
9. Adjustment of device layout:
When adjusting, it is necessary to prevent a large piece of ground from being connected to the main ground only through a few vias. Pay attention to the integrity of the floor under the chip. In addition, you can better observe the appearance 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. Check the drawing specifications of all PCB boards:
At the same time point out the error and highlight the error.
11. Export the PCB board:
The export format is Protel PCB 2.8 ASCII File.
12. Send out proofing.

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