The Importance of PCB Layout Preparation

Electronic devices are regularly shrinking due to consumer demands for portability and light-weight products such as big-screen televisions, tablet computers and powerful smartphones, drone devices and recently, even wearable technology. The shrinking of all these devices means the printed circuit boards (PCBs) integrated in their production must be fabricated on smaller footprints while providing ever-more-complex functionality and smaller components.

PCB designers are continuously challenged to meet the needs of electronic products through engineering boards with the most effective placement of components that will accommodate the required functionality while meeting the specifications of the product to contain the board. Components that are smaller in size must, therefore, be placed closer together while avoiding potential negative impact from placement issues.

The truth is that preparation plays an important role in PCB layout results. Beginning with the most important requirements can help streamline the design process by determining the constraints on the design. Sizing and placement of critical elements, including minimum and maximum tolerances, required components, electrical demands including impedance factors and power needs all combine to generate an initial set of constraints for the PCB design. It’s also a good practice to create and save sets of like constraints and templates for subsequent designs or projects. Having time-proven templates available can streamline the design of new boards or upgrades to existing PCBs. Once constraints are set and understood, it makes the details much less error-prone, saving time and money.

Board layout techniques can include such strategies as devices embedded on inner layers of PCBs to reduce board size. This must be evaluated with manufacturers to verify that these capabilities can be met in actual fabrication.

Errors or lack of planning in the layout specification of PCB design can cause multiple problems:

• Manufactured products that don’t perform as specified or designed
• Quality or functional issues may surface due to components and circuit paths that conflict with other board elements from factors such as electromagnetic interference, current flow, track width, component size, and physical board limitations.
• Boards may not be able to be manufactured exactly as specified, resulting in back-and-forth decisions between the designer and manufacturer. This extends lead time and increases cost.
• Worst case – the engineer goes back to the “drawing board” to rework the design for manufacturability.

In practice, most PCBs are designed with CAD or other PCB design tools that the technician is most familiar and comfortable with. In truth, once the design has been completed the fabricator will manufacture the board from files or documentation generated from the design tools using their own automation tools and sophisticated Computer Aided Manufacturing (CAM) manufacturing techniques. The two processes may not be totally synchronized in their processing, resulting in boards that may not produce the desired results, or may not be easily manufactured, causing delays and increasing costs.

How Should PCB Designers Meet the Demands of Effective PCB Layout?

Designers are therefore incentivized to produce a design that will not only produce the desired functionality consistently, but will generate a layout that allows efficient manufacturing at the desired cost point. Engineers need to understand the manufacturing process to some level in order to comprehend how fabrication methodology will react to their designs. Multi-layer boards and double-sided laminates or double-sided component placement designs can make the layout all the more critical in designing for manufacturing (DFM).

Placement of components may vary during manufacturing as determined by automation tools with results that are not precisely what the designer intended. In many cases, the end product is acceptable and functions properly, but failures could also be an unintended consequence.

Routing of circuit paths can be altered during manufacturing that will still produce a workable PCB, but may also result in boards that are more difficult to install or repair than the original design had intended.

An effective tool available to PCB designers prior to prototype creation is DFM software. Such tools analyze the designer’s files and evaluate them for any issues or omissions related to fabrication. Combining the use of PCB design tools and DFM applications is the best solution to designing PCBs of the highest quality that will be functional and cost-effective to manufacture.

It’s also important to work with a fabricator who provides 24/7 support of all technical aspects of PCB orders, including a detailed review of submitted designs with CAM tools.