Printed circuit boards, also known as PCBs, form the core of every electronic piece today. These small green components are essential for everyday appliances and industrial machines alike. PCB design and layout is an important component of any product’s function before ypu make PCBA - this is what determines the success or failure of a piece of equipment. With the constant evolution of technology, these designs have continued to advance. Today, the complexity and expectations of these designs have reached new heights, thanks to the innovation of electrical engineers.
The recent advances in PCB design systems and technology have had sweeping effects across the industry. As a result, PCB design rules and production processes have evolved to achieve new layouts and capabilities. Today, smaller tracks and multilayer boards are commonplace in mass-produced PCBs - such designs would have been unheard of years ago. PCB design software has also helped with this progression. These programs provide tools with which electronic engineers can design better PCBs from the ground up.
Even with these improved capabilities, PCB board layouts are difficult to design. Even the most experienced electronic engineer may struggle with creating a circuit on a PCB or how to design a PCB board according to best practices in the industry. Even more difficult is creating a quality board to meet customers’ needs. With customer designs, balancing the functionality of the PCB with best design practices is an involved process. This is why we’ve outlined the process of designing PCBs, including some essential PCB design rules.
Determining the Need
The first of the major PCB design steps is a need. For most electronic engineers, these requirements are dictated by the customer, who will list all the requirements the PCB must meet. The electronic engineer must then convert the needs listed by the client into electronic form. Essentially, this means translating them into a language of electronic logic, which is what the engineer will use when designing the PCB.
The needs of the project determine several aspects of the design of the PCB. This includes everything from the materials to the final appearance of the PCB itself. The application of the PCB, such as medical or automotive, will often determine the materials in the PCB. For example, many medical PCBs for electronic implants are made with flexible bases. This allows them to fit in small spaces while also withstanding an internal organic environment. The final appearance of the PCB is determined mostly by its circuits and functionality - for instance, many more complex PCBs are made with multiple layers.
The electronic engineer will determine and list these needs, then use this list of requirements to design the initial schematic of the PCB, as well as the BOM.
Schematics
The schematic design is essentially the blueprint manufacturers and other engineers use during the development and production processes. The schematic determines the function of the PCB, the characteristics of the design and the placement of components. The hardware of the PCB is also listed in this schematic. This equipment includes the material of the PCB, the components involved in the design and any other materials the manufacturer will need during the production process.
All this information is contained in the schematic during the initial design stage. After finishing the first schematic, the designer does a preliminary analysis, checking for potential problems and editing them as necessary. The schematic is then uploaded to a special tool for use in PCB design software, which can run simulations to ensure functionality. These simulations enable engineers to catch any design errors they may have missed during initial schematic check. After that, the electronic design of the circuit can be converted into a “netlist,” which lists information about the interconnectivity of components.
While considering the design of their schematic, electronic engineers should keep in mind a few crucial circuit board design basics from the start. A few of these considerations to implement during the schematic development stage include the following:
• Selecting Appropriate PCB Panel Size: Selecting the board size most compatible with the equipment to be used is a basic, yet often forgotten, best practice. This way, extra space isn’t wasted, traces are kept to a minimum length, and overall material costs are kept somewhat low. It is important, however, to ensure that the design specs are optimized for mass production. Going too small with a board design may not be feasible for mass-production setups that produce enough variation between pieces to disrupt smaller designs.
• Select the Correct Grid: Grid spacing is always set and applied to suit most components. Sticking to this grid is one of the most beneficial things an engineer can do to avoid spacing issues, so selecting the best one for the job is crucial. If some parts don’t work as well with the grid, the designer should try to find alternatives, or, better yet, use self-designed products.
• Implement DRC as Much as Possible: Many PCB assembly companies make the mistake of running design rule checks (DRC) software only at the end of the design process. This lets small mistakes and questionable design choices build up, resulting in more remedial work at the end of the design process. Instead, designers should check their work with a DRC as often as is workable. This allows them to address problems identified by the DRC as quickly as possible and minimizes the number of massive changes at the end of the design process. This ends up saving time and smoothing out the editing process, so it isn’t as back-heavy.
Bill of Materials
While the schematic is being generated, the electronic engineer also develops a fine Bill of Materials, or BOM. This is the list of components used in the PCB board schematic. Once both the BOM and the schematic are completed, the electronic engineer passes on both to a layout engineer and component engineer. These engineers check the specifics and obtain the necessary components for the project. Specifically, the component engineer is responsible for choosing components that fit the schematic in terms of maximum operating voltage and current. They’re also responsible for selecting equipment that falls within reasonable cost and size parameters.
The five most important aspects BOM components must meet include the following:
• Quantity: The number of components purchased must meet, at a minimum, the number of components listed in the BOM.
• Reference Designators: Each component must be identified according to its place within the circuit on the PCB.
• Value: Each component should fall within a specific range of values, including ohms, farads, etc. Cost is a factor if it is of concern to the client.
• Footprint: The location of each component must be listed.
• Manufacturer Part Number: Track the part number in case of malfunction, both for the assemblers’ sake and for the reference of the manufacturer.
In addition to these basic BOM guidelines, it’s a good idea to keep a few considerations in mind while formulating both the BOM and the schematic in general. These include the following PCB design tips:
• Integrate Components: Choosing components is one of the most important jobs as a designer. To help with the process, you have the option to pick up discrete components with high or low component values and similar effects. By integrating these components and producing a small standard value category, you can effectively simplify the bill of materials and decrease the cost of the product.
• Apply a Decoupling Capacitor: Never try to optimize your design by getting rid of decoupling power lines. Many designers avoid these capacitors in a misguided attempt to reduce costs. Capacitors are low in price and are very durable, adding longevity to your design. Capacitors will also help maintain the orderliness of your circuit board while keeping costs low. Focus on the tips above if you’re concerned about your BOM.