One of the best times I can remember having with my daughter was taking her to the circus for the first time. She was fascinated with the huge snakes they had and so I had to let her go down and touch them. This fit her persona, as she always had an affinity for animals. I, on the other hand, was more interested in the impressive acts by people that didn’t seem impossible for me to duplicate. Juggling is one example of an act I have pursued but have yet to master. As I learned, it is not easy to stay focused on multiple objects simultaneously. However, being able to do so is a mandate for being a successful juggler.
Juggling multiple objectives is also required for good PCB layout. This includes not only following rules and guidelines for board layout but ensuring that your PCB design process incorporates all the issues that may impact the process and quality of your board’s manufacturing. For example, knowing when and how to design for testability (DFT) can significantly affect the turnaround time, quality and reliability of your design. The right balance can be achieved by first defining all of the design objectives. With these in place, the best PCB layout for your design can be derived.
What are PCB Layout Design Objectives?
It is typical to view the PCB layout design as a discrete part of the design stage of board development. The layout may be created in this manner. However, doing so will usually lead to errors at some point further along in the development process that may require you to redesign the layout. This unnecessary waste of valuable resources like time and money can be minimized, if not eliminated altogether, by adopting a more comprehensive view of PCB layout design.
There are specific good practices or tips that should be employed for PCB layout design to ensure that your board can be built. However, they should be performed with the overarching goal of fulfilling the overall objectives of your product’s design intent. These include promoting efficiency for board fabrication and PCB assembly as well as ensuring that your board meets or surpasses all applicable regulatory requirements and operates reliably over its lifecycle.
PCB Layout Design for Objectives
Support Smooth Board Fabrication
Building your board according to the specifications of your design is indeed the job of your contract manufacturer (CM). However, ensuring that your design file(s) includes all the pertinent information for your board’s fabrication and assembly is the designer’s responsibility. That information must contain PCB layout values and tolerances for trace widths, copper weights or thicknesses, board clearances and drill holes that are tailored to your CM’s capabilities; otherwise, you will experience delays for clarifications and possible redesign. Additionally, you need to make good choices for your board’s stackup, including choosing the best materials, selecting the best via option(s), including the right number of layers and balancing their arrangement based on board type. Making good choices for the construction of your board depends on your following design for manufacturing (DFM) guidelines based on your CM’s equipment capabilities and processes.
Support Efficient PCB Assembly
The best DFM guidelines will include several suggestions, tips, and requirements to facilitate the efficient assembly of your PCB. Known as design for assembly (DFA) guidelines, these are meant to enable you to make choices that will not only prevent a stall of your board’s assembly but also assist your CM in the process. Essentials for good DFA include: making sure that your footprint pads match the components listed in your electronics component list or BOM; using adequate spacing and clearances between board elements; choosing sufficient solder mask dams and expansion; utilizing the silkscreen for markings and identifiers; and applying good thermal relief. PCB assembly (PCBA) starts with having the necessary components for your design available. Time spent waiting on back ordered components is time wasted and time added to your product delivery date. To avoid this, you should optimize your component selection by understanding your component’s lifecycle and being aware of shortages. Another way you can assist your CM and PCBA is to include a panelization scheme as part of your design. As boards are usually processed in sheets instead of individually, the process includes depanelization or breaking the sheets down into boards. By determining the panelization layout, you eliminate a task for the CM and can determine which method of depanelization is used. Designing with this objective in mind will greatly aid your CM and promote efficient PCBA.
Smooth the Process of Regulatory Approval
The best design and manufactured product in the world will never get used unless it can pass all regulatory standards and requirements for the board itself and the components it utilizes. There are a number of standards that may apply based on your board’s classification, flexibility and usage. Typically, some type of design testing will be necessary and design for testability (DFT), which includes steps to prepare your board for testing by your CM, may be required. An essential objective is being aware of the standards that apply to your design and how you can demonstrate your compliance.
Reliable Operation Once Deployed
Another consideration that should be addressed throughout your development process is whether your board will be able to perform as designed for its projected lifecycle. Operation and performance are obviously the major driving forces behind your component selection and schematic creation. However, for your PCB layout design, meeting this objective takes on broader implications, specifically the manufacturability of your board along with its quality and reliability. The ability of your board to be manufactured as designed depends on your choice of CM services. For example, should you opt for a turnkey service provider or try to manage the multiple companies involved for the different stages of manufacturing yourself? If you choose turnkey, then you need to consider whether your CM should be primarily a fabricator or assembler. Subsequently, your board’s quality will depend on your CM’s commitment and methods used to implement a quality service. This is even more important if you are developing a critical system for the aerospace, medical devices, or automotive industries as there are strict requirements for quality management. Just as important as your product’s ability to perform its intended function is whether it will do so for its projected operational lifecycle. It is a mistake to assume that board materials are the only factor of concern for reliability. You should also consider your board’s retention of its mechanical properties during manufacture. Therefore, you should apply good thermal design principles and not overlook the importance of the surface finish for your board, which provides protection against the environment.
|Tempo‘s Custom PCB Manufacturing Service|
Creating the best PCB layout for your design does involve the application of a good layout paradigm; however, this should be done from the perspective of meeting your overall design objectives. Your CM can be a great asset to you in meeting this goal. At Tempo Automation, we will work with you from day one of design to ensure your PCB manufacturing process is optimized to meet your quality and reliability needs.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.