Electronic Design - PCB board design with the popularity of computers

Electronic CAD technology is not only a special tool for senior professionals to design large-scale integrated circuits, especially the emergence of Protel software, so that ordinary engineers can also use it to deal with circuit design problems in daily work and improve work efficiency. Protel is currently the most convenient, efficient and user-friendly interface in the circuit-aided design (EDA) industry, and it is also the most commonly used EDA tool in China.

In this article, Protel99 SE is used as a design tool to analyze and discuss the basic principles and empirical techniques in PCB design.

1: Quickly determine the shape of the PCB. The design of the PCB board must first determine the shape of the circuit board, usually in the forbidden wiring layer to draw the electrical wiring range.

Unless there are special requirements, the shape of the general circuit board is rectangular, and the aspect ratio is generally 3:2 or 4:3, which is more ideal. Before drawing, you can draw any two horizontal lines and two vertical lines, and then use the "Set Origin" tool in the "Place Toolbar" to set the end point of the line segment as the origin, that is, the coordinates (0,0) and then double-click each The line segment is correspondingly changed with the coordinate values of its start and end point, so that the 4 line segments end to form a closed rectangular frame, and the appearance of the circuit board is determined to be completed. If you need to adjust the size of the board during the drawing process, you only need to modify the corresponding coordinate value of each line segment. From the cost, the length of the copper wire, the ability to resist noise, the smaller the size of the circuit board, but the size of the board is too small, the heat dissipation is poor, and adjacent wires are easy to cause interference. However, when the size of the circuit board is larger than 200mmx150mm, the mechanical strength of the circuit board should be considered, and the fixing holes should be properly installed to play a supporting role.

2: Component layout Before starting the layout, first load the components through the network table. The network table often encounters errors that the network table cannot be fully loaded. These errors can be divided into two categories: one is that the component cannot be found, and the solution is to confirm that the component has been It is packaged in the schematic, and the corresponding PCB component library has been added. If you still can’t find the component, you need to build a component package; the other is pin loss, the most common is diode, transistor pin loss, this is because the schematic diagram of the pin is generally the letters a, K, E, B The PCB components of, C and pins are all numbers 1, 2, and 3. The solution is to change the definition of the schematic or change the definition of the PCB component to make it consistent. Experienced designers usually build their own PCB component library based on the package shape of the actual component, which is easy to use and error-prone.