Exploring the Fundamentals of Printed Circuit Board Design
In the world of electronics, the design of a Printed Circuit Board (PCB) is a crucial step that requires careful consideration and adherence to best practices. This article outlines the key aspects of PCB design, from the initial stages of conceptualisation to the final delivery of production documents.
The process begins with pre-layout, a phase that involves verifying the Bill of Materials (BOM) for long lead time components and obsolete components, validating manufacturer part numbers (MPNs) and vendor part numbers (VPNs), and creating the stack-up design. The stack-up design is an essential attribute in the basics of PCB design, defining the structure of a multilayer circuit board in a sequential manner.
The next step is the creation of a conceptual block diagram, which serves as the foundation for the PCB design. A schematic design is then created using Computer-Aided Design (CAD) software, representing component symbols and net connections between them. The Stack-up Planner, a vital tool, factors in the copper thickness (1/2 or 1 or 2 ounces) during this phase.
Best practices for selecting appropriate components and package sizes focus on balancing system requirements, manufacturing feasibility, and reliability. For compact devices, surface-mount technology (SMT) components are preferred due to space savings, while through-hole parts may be used for mechanical strength or easier prototyping. Components should be chosen to fit the power needs and connectivity of the design without oversizing, and their electrical ratings must be matched carefully.
Consideration must also be given to thermal and mechanical durability. Use datasheet thermal resistance values (e.g., RθJA) to ensure components can dissipate heat or withstand environmental stresses. Allow spacing between components for heat dissipation and consider industrial-grade parts for harsher conditions.
Proper component placement on a PCB leads to better performance and signal quality. Align SMT components in the same orientation to ease soldering, leave adequate clearance between parts, and group related components to minimise noise and signal interference.
The PCB layout stage involves setting up the board parameters, determining its outline, routing the components, and generating the production documents by adhering to a suitable design checklist. Design for testing requires adding test points for all important signals to facilitate electrical tests and in-circuit tests.
The final set of deliverables should include all the gerber files, including the fabrication and assembly drawings, drill files, IPC-356, ODB, and X-Y placement files for assembly. A PCB assembly drawing contains all the information that is required to assemble the board.
The choice of PCB material (FR4, I-Speed, Rogers, etc.) is based on frequency requirements and environment. Footprints must be checked for top and bottom views, pin pitch, and height for accuracy. It is crucial to decide the appropriate size of the package during the PCB design phase, choosing smaller packages only when necessary.
When designing a new PCB, it is necessary to adhere to circuit design basics, such as choosing appropriate components and package sizes, avoiding long lead-time components, and performing schematic checks. The fabrication drawing contains information about the fabrication and mechanics of the circuit board.
By following these guidelines, designers can create PCBs that are not only functional but also manufacturable, reliable, and cost-efficient. Tools like the Sierra Circuits better DFM tool can further verify the design's manufacturability, ensuring a smooth transition from design to production.
The Stack-up Planner, instrumental in the PCB design process, takes into account the copper thickness during the schematic design stage, which is a crucial aspect of controlled impedance technology.
Effective education-and-self-development for PCB designers involves learning about the appropriate selection of components and package sizes, as well as understanding the basics of controlled impedance technology.
