PCB design guide and experience sharing
- Jul 28, 2022
Designing a printed circuit board is a very complex problem and it can help you to find the required approach. There should be a specific way to create schematics, how to create library parts, how to place and route parts and finally how to generate manufacturing output files. It's a lot of information to digest all at once, but if you follow a set of well-documented guidelines for layout, you can better understand this complex puzzle and solve it.
PCB design guidelines for CAD libraries
Before you can start PCB design, you must have CAD library parts to work in the design tool. For schematic capture, this would mean symbol and component information as well as simulation models. For layout, the footprint or pad pattern will contain PCB pad and component information. All of this data can be obtained from external sources or developed internally, and the design department will usually provide guidance for both.
For internally developed part data, follow industry standards such as IEEE standard 91 for creating schematic symbols and IPC standard for creating PCB packages. The design department usually has its own internal guidelines as well. These usually specify information such as which CAD layers will be used for what information, and company preferences for part outlines, text and other details. There are also usually guidelines for part inspection and verification.
Schematic Creation Guidelines
Once the library is ready, the PCB designer can start working on the schematic. To ensure that all schematics have the same appearance, most companies will use internal drafting guidelines, which typically include the following.
● Schematic drawing dimensions.
● Worksheet border information such as company logo, name, address, date, part number, and revision number.● The size and appearance of the grid to be used. This is important so all content is drawn to the same scale.
● Symbol size and line width.
● Text height and font size.
For schematic development, the following guidelines are typically used.● Symbol spacing on schematic drawings.
● Component information, such as reference designators, part numbers, values, and pin numbers.
● Net spacing and naming rules.
Finally, guidelines for checking and verifying schematics through design reviews will be provided. After the schematic has successfully passed all these processes, it is ready for PCB layout.
PCB Layout Guide
To begin PCB layout, coordination with the mechanical design of the board is required. Internal guidelines usually exist for exchanging data between mechanical and electrical CAD systems and in design change review systems. There should also be guidelines for working with the contract manufacturer (CM) who will be manufacturing the PCB assembly. the CM can provide a lot of information for the layout, including advice on board stacking configurations, and this communication process needs to be well documented in the company guidelines.
After creating the board outline and layer stack in the PCB layout tool, the designer will begin placing components. In addition to guidelines and documentation, be sure to use Design Rule Check (DRC) and Constraint Manager to eliminate design distractions.
There is a lot to do when designing a printed circuit board, and fortunately we do have different guidelines that can help us get through these difficult processes before we get lost.