Basic Process And Skills of PCB Processing (1)

1. Preliminary Work of Circuit Board Design

1.1 Use the schematic design tool to draw the schematic diagram and generate the corresponding network table. While in some special cases, such as the circuit board is relatively simple, and the network table is already available, it is not necessary to design the schematic diagram and directly enter the PCB design system and generate a netlist.

1.2 Manually Change The Network Table
Define the pads that are not on the schematic diagram, such as the fixed pins of some components, to the network connected to it, and those without any physical connection can be defined to the ground or protection ground. Change some device pin names that are inconsistent with those in the PCB package library to those in the PCB package library, especially for diodes and transistors.

2. Draw The Package Library of Your Own Defined Non-Standard Device

It is recommended to put all the components drawn by yourself into a dedicated design file for the PCB library created by yourself.

3. Set up the PCB design environment and draw the frame of the printed circuit, including the hollow in the middle, etc.

3.1 The first step after entering the PCB system is to set up the PCB design environment, including setting the grid size and type, cursor type, layout parameters, wiring parameters, etc. Most parameters can use the system default values, and after these parameters are set, they conform to personal habits and do not need to be modified in the future.

3.2 Planning the circuit board, mainly to determine the border of the circuit board, including the size of the circuit board and so on. Place appropriately sized pads where you need to place the mounting holes. For 3mm screws, 6.5~8mm outer diameter and 3.2~3.5mm inner diameter pads can be used for standard boards, which can be transferred from other boards or PCB izard.

Note: Before drawing the border of the circuit board, be sure to set the current layer to the Keep Out layer, that is, prohibit the wiring layer.

4. After opening all the required PCB library files, load the netlist file and modify the part package.

This step is a very important part. The netlist is the soul of PCB automatic routing, and it is also the interface between the schematic design and the impression circuit board design. Only after the netlist is loaded, the circuit board can be wired.

In the process of schematic design, ERC inspection does not involve the packaging of parts. Therefore, when the schematic diagram is designed, the package of the part may be forgotten, and the package of the part can be modified or supplemented according to the design situation when the netlist is introduced.Of course, netlists can be manually generated directly within the PCB, and part packaging can be specified.

5. Arrange the position of the part package, also known as the part layout

Protel99 can perform automatic layout or manual layout. For automatic layout, run “Auto Place” under “Tools”, you need to be patient enough to use this command. The key to routing is layout, and most designers use manual layout. Select a component with the mouse, hold down the left mouse button, drag the component to the destination, release the left button, and fix the component. Protel99 adds some new tricks in layout. New interactive layout options include automatic selection and automatic alignment. Similar packaged components can be quickly collected using automatic selection, then rotated, unfolded, and organized into groups that can be moved to the desired location on the board. When a simple layout is complete, use automatic alignment to neatly expand or shrink a group of similarly packaged components.

Tip: During automatic selection, use Shift+X or Y and Ctrl+X or Y to expand and contract the X and Y directions of the selected components.​​

Note: The layout of parts should be comprehensively considered in terms of mechanical structure heat dissipation, electromagnetic interference, and the convenience of future wiring. Devices related to mechanical size are laid out and locked first, followed by large space-consuming devices and core components of the circuit, and then small peripheral components.

6. Make appropriate adjustments according to the situation and then lock all devices

If the board space allows, you can put some wiring areas similar to the experimental board on the board. For large boards, more fixing screw holes should be added in the middle. Fixing screw holes should also be added on the sides of stressed components such as heavy components or large connectors on the board. If necessary, some test pads can be placed in appropriate positions. It is best to add them in the schematic diagram. Increase the size of the via hole of the pad that is too small, and define the net of all the fixed screw hole pads to ground or protective ground, etc.

After putting it away, use the VIEW3D function to check the actual effect and save it to disk.