“Give me six hours to cut down a tree, and I’ll spend the first hour sharpening the axe.”—Abraham Lincoln
These words credited to Abraham Lincoln are an apt introduction to our discussion on the importance of PCB assembly guidelines for trouble-free circuit board production.
Printed circuit boards almost always have mass production as the end goal. PCB design and manufacturing are challenging processes, closely linked to one another. Designing a circuit board is like piecing together a puzzle! Electronic components fit together and work seamlessly only when accurately placed according to solid design principles. The cost of PCB design and assembly and the time taken for manufacturing is vital to deliver a successful end-product.
The feasibility of PCB production depends on developing a design that meets the standards necessary for efficient manufacturing. The same also applies to prototypes, as the prototype will also eventually transition to mass production. If the prototype design is not optimized, it will require redesign at the production stage, which is a costly affair. It is better to follow best practices for design and assembly right from the beginning of the design process.
To design a PCB that will not pose any problems at the manufacturing stage, the PCB designer must understand the assembly process and work hand-in-glove with the manufacturer from the beginning of the PCB development process.
Design for Manufacturability (DFM) is a critical part of the PCB development process. It focuses on selecting the most economical and durable raw materials and manufacturing processes.
It is vital to remember that the larger part (nearly 70%) of costs for PCB raw material and assembly depend on the decisions taken at the design stage. That makes PCB assembly guidelines critical documents—they are not merely items on a checklist to be ticked off!
DFM best practices must guide decisions at the design stage to avoid costly rework at the manufacturing stage.
The three main factors that affect PCB manufacturability are:
- Component selection and procurement
- Component placement
- Circuit board layout
Let’s look at PCB assembly guidelines for each of these in detail:
Before electronic components are placed or routed, the PCB designer considers the following aspects.
Bill of Materials: check for issues such as:
- Unique or difficult-to-acquire parts: These will cost more and increase procurement lead times. Replace them or design them out to avoid delays and cost overruns.
- Parts that are approaching End-of-Life (EOL): Are you using any components that are not available or are likely to be discontinued soon? Identify these and replace them in your Bill of Materials.
Incorrect placement of PCB components cause problems during assembly.
Here are some component placement guidelines to streamline the PCB assembly process:
- Avoid placing components too close to the edge of the board as it causes damage while breaking the boards from the panels.
- Components placed too close together cause problems for automated pick-and-place machines during mass production.
- Components must be oriented correctly for good solder flow during wave soldering.
- Do not place smaller SMT components next to unusually sized or tall components as it creates issues with soldering.
- Try and place all SMT (surface mount technology) components on a single side of the PCB to reduce costs. SMT parts on both sides of the board increase costs and pose more challenges in assembly.
- When placing PCB connectors, provide enough space for plugging or unplugging wires.
- If the footprint design is incorrect or does not match the actual component to be mounted, problems crop up. If one end of a component disconnects from the pad during the soldering process, it creates an open circuit—an unwanted effect called tombstoning.
The schema of components—or layout—lies at the heart of the PCB design process. The design must account for possible connections or interfaces with other PCBs.
Here are a few guidelines to follow for circuit board layout:
- Place connectors, switches, and other mechanical components for convenient access.
- Align components correctly so they do not cause poor solder joints.
- Consider thermal issues and accommodate hot parts in the layout so they receive sufficient airflow.
- Keep traces as short as possible for high-speed signal paths.
- Accommodate test points and provide adequate clearance for test fixtures.
- Silkscreens, reference numbers, or identifiers must be placed clear of pins and also be readable.
PCB assembly guidelines are essential for the success of the end-product. It is critical to partner with your PCB manufacturer from the very start of the design process.
Ask your PCB manufacturer to review your designs, make the best possible component selection, and work with you on component placement and layout.
MIS Electronics provides high-quality components, advanced electronics assembly solutions, and superior customer service, with fully supported turnkey solutions. We partner with you from day one of design to maximize the benefits of DFM for product development. We assist you in making the right components selection and PCB layout decisions, and we adhere strictly to PCB Assembly guidelines.
Get in touch with us today for a free quote for our PCB assembly services.