PCB Tech - What is the whole process of PCB design in SMT production?

PCB was born in 1936, and the United States made extensive use of this technology in military radios in 1943. Since the mid-1950s, PCB technology has been widely adopted.

At present, PCB has become the "mother of electronic products", and its use has almost penetrated into various terminal categories of electronic industry, including computers, communications, consumer electronics, industrial control, medical equipment, defense ordnance, aerospace and many other fields. .

PCB has grown from single-layer to double-sided, multi-layer and flexible, and continues to maintain their respective growth trends. Because of the inexhaustible growth towards high precision, high density and high reliability, the continuous reduction of volume, cost reduction, and improvement of functions have enabled printed boards to continue to grow vitality in the future growth projects of electronic equipment.

So how is the PCB conceived? After reading the following seven steps, you will understand: 1. Preliminary preparations, including preparatory component libraries and rationale diagrams. Before stopping the PCB design, we should first prepare the logic diagram SCH component library and PCB component packaging library.

The PCB component packaging library is best established by the engineer according to the dimensions and materials of the selected device. In principle, the PC component package library is established first, and then the SCH component library is established.

PCB component packaging library requirements are high, which indirectly affects the installation of PCB; the reason is that the requirements of SCH component library are relatively loose, but we must pay attention to the definition of pin attributes and the corresponding relationship with PCB component packaging library.

2. The PCB layout design is based on the previously affirmed circuit board size and various machine positioning, draw the PCB board frame under the PCB design, and arrange the required connectors, buttons/switches, screw holes, assembly holes, etc. according to the positioning requirements .

Fully consider and confirm the wiring area and non-wiring area (such as how large the area around the screw hole belongs to the non-wiring area). 3. PCB structure design The structure design is to place the components in the PCB frame according to the design requirements.

Create a collection list (Design-Create Netlist) in the Daoli map tool, and then import the collection list (Design-Import Netlist) in the PCB software.

After the collection table is imported successfully, it will exist in the software background. Through the Placement operation, all devices can be called out, and there is a flying line reminding connection between the pins. At this time, the device structure can be imagined.

The PCB structure design is the first major process in the entire design process of the PCB. The larger the PCB board, the more black and white the structure can indirectly affect the difficulty level of the previous wiring.

SMT chip processing

The structural design relies on the circuit board designer's basic circuit skills and the richness of the design experience, which is a relatively junior requirement for the circuit board designer. Low-level circuit board designers have a shallow experience, suitable for small module structure design, or PCB structure design missions with low overall board difficulty.

4. PCB wiring design PCB wiring design is the most intensive process in all PCB design, which indirectly affects the function of the PCB board.

In the process of PCB design, wiring generally has three situations: First, it is distribution, which is the most basic entry requirement for PCB design; second is the contentment of electrical functions, which is a measure of whether a PCB board is qualified or not. After the wiring is laid out, adjust the wiring to make it reach the best electrical function;

Thirdly, it is neat and beautiful. The chaotic and disorderly wiring, even if the electrical functions are passed, will bring great inconvenience to the early revision and optimization, testing and maintenance. The wiring requirements are neat and tidy, and it cannot be intertwined and unorganized.

5. Wiring optimization and silk screen placement "PCB design is not the best, as long as it is better", "PCB design is an art with shortcomings". This is mainly due to the fact that PCB design wants to achieve the design requirements of all aspects of hardware, and individual needs There are often conflicts, and it is impossible to have both fish and bear paws.

PCB patch production workshop

For example: a PCB design project must be designed as a 6-layer board by the circuit board designer’s evaluation, but the product hardware must be designed as a 4-layer board due to cost considerations and requirements. The signal crosstalk between adjacent wiring layers increases and the signal quality decreases.

The experience of the common assumption is that the time to optimize the wiring is twice that of the initial wiring. After the PCB wiring optimization is completed, the need to stop and dispose of, the important thing is the silk screen logo on the PCB board. It is envisaged that the bottom silk screen characters need to be mirrored to avoid mixing with the top silk screen.

6. Collect DRC inspection and layout inspection. Quality control is the main component of the PCB design process. Common quality control measures include: design self-inspection, design mutual inspection, expert review meetings, special inspections, etc.

Principle diagram and layout element diagram are the most basic design requirements. Collecting DRC inspection and layout examination is to confirm that the PCB design meets the two input prerequisites of the principle diagram netlist and layout element diagram.

Ordinary circuit board designers have their own checklist for the quality of their designs. The items in the checklist come from the company or part of the standard, and the other department comes from its own experience summary.

Special inspections include Valor inspections and DFM inspections. The content of these two departments focuses on the PCB design and output back-end processing light drawing files.

7. PCB manufacturing. Before the PCB is formally processed and manufactured, the circuit board designer needs the same as the PE of the PCB supplier. Answer the manufacturer’s question about PCB processing.

This includes, but is not limited to: PCB board model selection, circuit layer line width adjustment, impedance control adjustment, PCB stack thickness adjustment, overview processing technology, aperture control and commission standards, etc.