7 Basic Steps of PCB Design and Cost Considerations

PCBA     |      2021-10-15 17:14

Abstract: PCB is widely used in electronic products. The article will tell you how to do PCB design in seven steps from preliminary preparation to structure, layout, wiring and silk screen, network inspection. In the design process, we should consider the cost in advance. The factors to be considered are: number of layers, size, degree of difficulty, plate material, surface treatment, etc.

 

Table of Contents

1. Seven steps of PCB design

    1.1 Preparation

    1.2 PCB structure design

    1.3 PCB Netlist design

    1.4 PCB layout design

    1.5 Wiring optimization and silk screen placement

    1.6 Network DRC inspection and structure inspection

    1.7 PCB manufacturing

2. Factors affecting PCB design cost

    2.1 PCB layers

    2.2 PCB size

    2.3 Difficulty of manufacturing

    2.4 PCB board material

    2.5 PCB surface treatment

 

PCB was born in 1936, and the United States used this technology extensively in military radios in 1943; PCB technology has been widely adopted since the mid-1950s. At present, PCB has become the “mother of electronic products”, and its applications have penetrated almost into various terminal fields in the electronics industry, including computers, communications, consumer electronics, industrial control, medical instruments, national defense, aerospace and many other fields.

PCB has developed from single-layer to double-sided, multi-layer and flexible, and still maintains their own development trends. Due to the continuous development of high precision, high density and high reliability, continuous reduction in size, cost reduction, and performance improvement, the printed circuit board will still maintain a strong vitality in the future development of electronic equipment.

So how is the PCB designed? After reading the following seven steps, you will understand:

 

1. Seven steps of PCB design

1.1 preliminary preparation

Preliminary preparation includes preparing component libraries and schematic diagrams. Before proceeding with PCB design, we must first prepare the schematic SCH component library and PCB component packaging library.

PCB component package library is best established by engineers based on the standard size data of the selected device. In principle, establish the PC component package library first, and then establish the schematic SCH component library.

The PCB component package library has higher requirements, which directly affects the PCB installation; the schematic diagram SCH component library requirements are relatively loose, but attention should be paid to defining the pin attributes and the corresponding relationship with the PCB component package library.

PCB structure design drawing

 

1.2 PCB structure design

According to the determined circuit board size and various mechanical positioning, draw the PCB board frame in the PCB design environment, and place the required connectors, buttons/switches, screw holes, assembly holes, etc. according to the positioning requirements.

Fully consider and determine the wiring area and non-wiring area (such as how much area around the screw hole belongs to the non-wiring area).

 PCB structure design drawing

1.3 PCB layout design

The layout design is to place the components in the PCB frame according to the design requirements. Generate the netlist (Design→Create Netlist) in the schematic tool, and then import the netlist (Design→Import Netlist) in the PCB software. After the netlist is successfully imported, it will exist in the background of the software. Through the Placement operation, all devices can be called out, and there is a flying line prompt connection between the pins. At this time, the layout design of the device can be carried out.

PCB layout design is the first important process in the entire PCB design process. The more complex the PCB board, the better the layout can directly affect the difficulty of later wiring.

Layout design relies on the circuit board designer’s basic circuit knowledge and rich design experience, which is a higher level requirement for the circuit board designer. The junior circuit board designer has little experience and is suitable for small module layout design or PCB layout design tasks with lower difficulty of the whole board.

 pcb layout

 

1.4 PCB wiring design

PCB wiring design is the process with the largest workload in the entire PCB design, which directly affects the performance of the PCB board.

In the process of PCB design, wiring generally has three realms:

First of all, it is the layout, which is the most basic entry requirement for PCB design;

Secondly, it is the satisfaction of electrical performance, which is a standard to measure whether a PCB board is qualified. After the wiring is laid out, carefully adjust the wiring to achieve the best electrical performance;

Once again, it is neat and beautiful, messy wiring, even if the electrical performance is passed, it will bring great inconvenience to the later modification of the board optimization and testing and maintenance. The wiring requirements are neat and uniform, not crisscross and out of order.

 PCB wiring design

 

1.5 wiring optimization and silk screen placement

“PCB design is not the best, only better” “PCB design is an art of defects”, this is mainly because PCB design needs to realize the design requirements of all aspects of hardware, and individual requirements may conflict, fish and bear Do not have both.

For example: a PCB design project needs to be designed as a 6-layer board after evaluation by the circuit board designer, but the product hardware must be designed as a 4-layer board due to cost considerations, so the signal shielding ground layer can only be sacrificed, resulting in adjacent wiring The signal crosstalk between layers increases and the signal quality decreases.

The general design experience is: the time to optimize the wiring is twice the time of the first wiring. After the PCB layout optimization is completed, post-processing is required. The first thing to do is the silk screen logo on the PCB surface. The bottom silk screen characters need to be mirrored during design to avoid confusion with the top silk screen.

pcb silk screen

 

1.6 network DRC inspection and structure inspection

Quality control is an important part of the PCB design process. General quality control methods include: design self-inspection, design mutual inspection, expert review meetings, special inspections, etc.

Schematic and structural element diagrams are the most basic design requirements. Network DRC inspection and structural inspection are to confirm that the PCB design meets the two input conditions of the schematic netlist and structural element diagram.

General circuit board designers will have their own accumulated design quality inspection Checklist, where the entries partly come from the company or department’s specifications, and the other part comes from their own experience summary. Special inspections include Valor inspection and DFM inspection of the design. These two parts focus on the PCB design output back-end processing gerber file.

 network DRC inspection and structure inspection

 

1.7 PCB system board

Before the PCB is officially processed and manufactured, the circuit board designer needs to communicate with the PE of the PCB supplier to answer the manufacturer’s confirmation questions about the PCB board processing.

This includes, but is not limited to: selection of PCB board model, adjustment of circuit layer line width and line spacing, adjustment of impedance control, adjustment of PCB stacking thickness, surface treatment processing technology, aperture tolerance control and delivery standards, etc.

 PCB system board

 

2. Factors affecting PCB design cost

2.1 PCB layers

Generally, under the same area, the more PCB layers, the more expensive. The design engineer should use as few layers as possible to complete the PCB design while ensuring the quality of the design signal.

 PCB layers

2.2 PCB size

With a certain number of layers, the smaller the PCB size, the lower the price. If the design engineer can reduce the size of the PCB without affecting the electrical performance in the PCB design, the size can be reduced reasonably and the cost can be reduced.

 PCB size

 

2.3 Difficulty of manufacturing

The main parameters that affect PCB manufacturing are the minimum line width, minimum line spacing, minimum drilling, etc. If these parameters are set too small or the process capability has reached the minimum limit of the PCB factory, the yield of the PCB will be lower, and the production The cost will increase. Therefore, in the process of designing PCB, try to avoid challenging the limits of the factory, set a reasonable line width and line spacing, and drill holes. In the same way, through holes can complete the design, try not to use HDI’s blind and buried holes, because the processing technology of blind and buried holes is much more difficult than that of through holes, which will increase the production cost of PCB.

 Difficulty of pcb manufacturing

 

2.4 PCB board material

There are many classifications of PCB boards, common paper-based printed circuit boards, epoxy glass fiber cloth printed circuit rice composite substrate printed circuit boards, special substrate printed circuit board metal substrates, etc. There is a big gap in the processing of different materials, and some special materials will have a longer processing cycle, so in the design, try to choose materials that meet the design requirements and are more common and inexpensive, such as FR4 materials.

 

 

2.5 PCB surface treatment

Surface treatments include Immersion gold, Immersion Tin, HAL Lead free,HAL Tin Lead,OSP., and immersion silver. The order of cost is immersion gold> immersion silver> immersion tin> HAL Lead free> HAL Tin Lead> OSP. When designing PCB, you can choose according to your needs, but don’t ask too much to cause wasted cost.

PCB board material