Designing the layout of a printed circuit board is crucial for creating a reliable and cost-effective board. While circuit design and component selection are also important, you should always ensure that sufficient time is allocated for PCB layout. Determining the optimal PCB layout design requires considering many factors, especially as today's circuit boards are becoming increasingly complex, compact, and lightweight. The growing popularity of flexible PCBs also complicates the process.

　　If you don't consider important PCB layout factors, you may end up with a design that doesn't work well in the real world. Poor layout can lead to a variety of problems, such as electromagnetic interference, component clashes on both sides of the board, limited board functionality, or even complete board failure.

　　So, what PCB layout design rules and considerations do you need to keep in mind? Let's look at the steps in PCB layout design and identify some core considerations for each stage. Of course, you may need to remember other considerations, but these are some key aspects of PCB layout design that you should be aware of.

　　 Basic PCB Design Steps

　　From the point you know you need a PCB to final production, PCB design plays a significant role in every step of the printed circuit board production process. The basic design process includes six steps.

　 　1. Concept

　　After determining the need for a PCB, the next step is to determine the final concept of the board. This initial stage involves defining the functions the PCB will have and perform, its characteristics, its interconnection with other circuits, its location in the final product, and its approximate dimensions. In addition, consider the approximate temperature range in which the board will operate and any other environmental concerns.

　 　2. Schematic

　　The next stage is to draw a circuit schematic based on the final concept. This diagram includes all the information needed for the electrical components of the board to function properly, as well as details such as component names, values, ratings, and manufacturer part numbers.

　　When creating the schematic, you will create a bill of materials. This BOM contains information on all the components required for the PCB. Always keep both documents up-to-date.

　 　3. Board-Level Block Diagram

　　Next, you will complete a board-level block diagram, which is a drawing that describes the final dimensions of the PCB. Mark the areas designated for each block, as well as the component parts that are connected due to electrical reasons or due to constraints. Placing related components together will keep your traces shorter.

　 　4. Component Placement

　　The next step is component placement, which determines where you will place each component on the board. Typically, you may need to go through several rounds of refining component placement.

　 　5. First-Pass Routing

　　Next, determine the routing of the circuit and the routing priorities.

　　6. Testing

　　Once the design is complete, you should perform a series of tests to ensure that it meets all your requirements. If it does, the design is complete. If not, you will return to the stage that needs adjustment.

　　 Design Documents

　　When creating a PCB, you will develop a large amount of documentation. These documents include:

　　Hardware dimensional drawing: Describes the dimensions of the bare board

　　Schematic: Draws the electrical characteristics of the board

　　Bill of Materials: Describes the components required for the project

　　Layout file: Describes the basic layout of the PCB

　　Component placement file: Describes the location of individual components.

　　Assembly drawings and instructions: Explain how to assemble the board

　　User guides: While not required, they are useful for providing users with more information

　　Gerber file set: A collection of layout output files that the PCB manufacturer will use to create the PCB

　 　PCB Layout Best Practices

　　There are many factors to consider regarding PCB layout and design. Some considerations apply to the entire process, while others are specific to particular steps. Here are seven relevant factors to keep in mind.

　　 1. Bare Board Related Constraints

　　The first thing you need to consider is the constraints related to the bare board. These basic constraints include the size and shape of the board.

　　You need to ensure that there is sufficient board area to place the circuit. The size of the final product, the functionality the board must provide, and other factors determine the size of the board. Electronics and the circuit boards they contain are getting smaller and smaller. Estimate the size of the board before starting the design process. If a simpler design doesn't have enough space to accommodate all the required functionality, it may be necessary to use a multilayer or high-density interconnect (HDI) design.

　　Standard PCBs are rectangular. This remains the common shape for PCBs. However, boards of other shapes can also be created. PCB designers often do this because of size limitations or for products with irregular shapes.

　　Another key consideration is the number of layers you need, power levels and design complexity will help determine this. Determine how many layers you need early in the layout design process. Adding more layers may increase production costs, but it allows you to include more tracks. This may be necessary for more complex boards with advanced functionality.

　　Use at least two vias for layer transitions for all high-current paths. Using multiple vias at layer transitions improves reliability, improves thermal conductivity, and reduces inductive and resistive losses.

　 　2. Manufacturing Process

　　You should also consider the manufacturing process you will use to produce the board. Different methods have different limitations and constraints. You need to use reference holes or points that match the manufacturing process on the board. Always ensure that there are no components in the holes.

　　In addition, keep in mind the mounting method of the board. Different methods may require you to leave different areas of the board empty. Using multiple technology types (e.g., through-hole and surface mount components) may increase the cost of the board, but may be necessary in some cases.

　　 3. Materials and Components

　　Consider the materials and components you plan to use for the board during the layout phase. First, you need to ensure that the required items are available. Some materials and parts are difficult to find, while others are very expensive and too costly. Different components and materials may also have different design requirements.

　　Take the time to ensure that you have selected the optimal materials and components for your board, and ensure that your designed board is able to leverage the strengths of these components.

　 　4. Component Placement Order

　　One of the more basic PCB design guidelines involves the order in which components are placed on the board. The suggested order is connectors, then power circuitry, then precision circuitry, then critical circuitry, then the remaining components. Power levels, noise sensitivity, generation, and routing capabilities will also affect the routing priority of the circuit.

　 　5. Orientation

　　When placing components, try to orient similar components in the same direction. This will make the soldering process more efficient and help prevent errors during soldering.

　 　6. Placement

　　Try not to place parts on the PCB solder surface located behind plated-through-hole parts.

　 　7. Organization

　　Reasonably organizing components can reduce the number of assembly steps required, improve efficiency, and lower costs. Try to place all surface mount components on one side of the board and all through-hole components on the top of the board.

　 　Power, Ground, and Signal Routing Considerations

　　The above tips mainly focus on the placement of PCB components. In order for these components to work as expected, you also need to arrange the power, ground, and signal lines. Efficiently completing this step will help ensure your signals have a reliable transmission path, thus ensuring your board functions correctly.