A guide to PCB design and assembly
The performance of your circuit will depend greatly on your PCB configuration. It’s your PCB structure that holds everything together – it connects your circuits and provides the functional reliability your customer expects in purpose-driven smart devices each time it’s used.
Part 1: Design your PCB
Poor circuit-board design can cause function and reliability problems. To save your team needless hassles, surprises and costs, designing your PCB layout starts before the actual act of designing: ideation, definition and validation.
This will show you if you can improve the overall product with your PCB. It will also allow you to ensure compatibility among the project’s PCB design components. This stage – pre-emptive knowledge sharing – reveals who’s a team player and who’s not. You should be collaborating. Perhaps you have suggestions of your own on the overall product. You should also firm-up budgets and timelines.
Our guide takes you through:
PCB design basics: Pay especial attention to these areas
Before we get to the different points of PCB design practices, it’s worth noting the three main areas you need to pay attention to in order to keep costs down:
- Components: Use components that are easily available. If you go for niche parts, you’ll pay more, along with possible delays in lead times, which further drive up costs.
- Placement: As we’ll go into more detail below, think in terms of simplicity, right down to how a component is rotated, which can affect solderability.
- PCB Layout: Try to avoid a complex PCB assembly. A simple PCB layout is best but take every possibility into account to keep costs down. Will your design connect to other boards or interfaces? Don’t wait until you’re well underway to discover that the answer is “yes.”
You’ll also need to think about materials. You can learn more in our guide Your PCB substrate: a guide to materials.
How to design a circuit board
Now you can think about your PCB layout design and prototyping your PCB requirements. The PCB design process involves the following steps:
1. Start with a good PCB design software solution.
It should allow you to draw both schematics and printed circuit boards. Some of the most popular ones include Cadsoft Eage, KiCad and gEDA-project. CAD libraries can also be extremely helpful.
2. Consider the fabrication and avoid concentrating parts too close together.
Think about your PCB assembly and soldering vs. using a pick. What will your budget allow? Don’t make the design too complex. Avoid blind and buried vias. Simple is best and will save money.
3. Use a PCB trace width calculator to determine how thick and wide your traces should be.
Aim for a 41°F (5°C) temperature rise. If you have extra space on the board, use bigger traces. They don’t cost anything extra.
4. Surface Mount Technology (SMT) or through holes?
SMT costs less in terms of time and money. However, if your application involves mechanical and environmental stress and high heat, through holes are more reliable. You can also use a combination of both.
5. Errors in circuit-board patterns are the easiest mistakes to make.
If your pad-to-pad spacing is off by just a hair, the pins won’t align properly, making soldering difficult or downright impossible. Your PCB design software should have a library of electronic components. The library should include the schematic symbol and PCB landing pattern for each component. Stick to these components in your design and you should be fine. If you’re not using software, you must manually draw the schematic symbol and the PCB landing pattern. Pay close attention to what you’re doing.
6. Make sure your components fit on your board.
Print your design to a 1:1 scale so that you have a realistic view of your printed circuit board design.
7. Place decoupling capacitors as close as possible to the power and ground pins of integrated circuits.
This will maximize your decoupling efficiency. Placing capacitors farther away introduces unwanted inductance.
8. Design PCBs to optimize layout of switching regulators.
You have two types of electronic voltage regulators to choose from: linear regulators and switching regulators. Linear regulators are inexpensive, simple to lay out, but the downside is, they can waste a lot of power. While switching regulators are more complex, they’re also more efficient for applications that need a lot of power without a lot of noise.
9. Avoid blind and buried vias if possible.
A blind via connects an external layer to an internal layer and a buried via connects two internal layers. No matter what, a via passes through all layers of the PC board to connect traces from one layer to the next. Both types of vias can result in the size of the PCB increasing as well as the cost. Each via has limitations based on how layers stack on the board and should be avoided.
Circuit board components explained
Here’s a quick look at the components you’ll need to consider. You can learn more in our Ultimate guide to PCB hardware.
PCB standoffs and spacers
For maintaining space and positioning components within your PCB. Both are also available in round shapes. The difference between standoffs and spacers is simple: spacers are unthreaded, with a through hole. Standoffs are threaded on both ends and come in either male or female designs.
Used for mounting printed circuit boards and small panels at right angles within equipment.
Card guides and ejectors
Card guides mount circuit boards in tight spaces, such as a PCB rack. Card ejectors relieve stress to the PCB and its circuitry by helping to remove the card from restricted spaces. Ejectors are also known as pullers.
Provides electrical insulation of components on the PCB and chassis to prevent electrical shock. Ideal for high-voltage and high-temperature applications in which PCB assembly methods such as wave soldering and potting are used.
Fan guards, filters, gaskets, mounts and rivets are examples of components you’ll need for your PCB’s heat management. These will help your fan run efficiently and safely.
The lens holder transmits light at a 10˚ angle. You’ll also need LED mounting hardware for mounting, positioning and restricting movement of your LED lights.
PCB grommets fasten PCBs. The example shown here is particularly ideal for securing heavy PCB components.
Part 2: Printed circuit board assembly
PCB manufacturing and assembly are two different disciplines. They each require their own set of processes and equipment.
For the record, printed circuit board manufacturing is the fabrication of the bare printed circuit board itself. PCB components assembly is about the placement of components on the bare printed circuit board. Often, PCB assembly and manufacturing are undertaken by different companies, but not always.
Take these steps to ensure a quality, cost-effective result.
Is your assembler IPC certified?
IPC (Institute for Printed Circuits) is a global organization responsible for setting international quality standards for PCB design, manufacturing and assembly. The general assembly standards are:
- IPC-A-610 – Acceptability of Electronic Assemblies: the industry accepted workmanship criteria for PCB Assembly
- J-STD-001 -Requirements for Soldered Electrical and Electronic Assemblies: recognized worldwide as the sole industry-consensus standard covering soldering materials and processes
- IPC-7711/7721 – Rework of Electronic Assemblies/Repair and Modification of Printed Boards and Electronic Assemblies: essential during the prototype stage to ensure changes to specification can be implemented effectively
IPC certification ensures you’ll get Best Practice from your assembler, so include this on your search checklist.
PCB components assembly process: Think twice before offshoring
Consider the total cost of your PCB assembly. It’s tempting to go for low-cost overseas assembly, but what are the risks you might encounter? How can you be sure they won’t cut corners with substandard or even imitation parts? Board malfunctions or failures will eat up your initial cost savings. There’s also the issue of potential shipping problems from an overseas assembler. There’s something to be said for being able to sit down face-to-face with your assembler to talk about your needs while getting their advice.
Involve your PCB assembler from the start
You’ve determined your PCB design parameters and decided on your PCB assembler. Don’t wait until after the manufacturing process to involve them. They can act as a valuable resource, offering suggestions on effective circuit board designs. They can also let you know about any new or improved materials or techniques. The more you know, the better your final product.
Your labels should be consistent and make sense
You’ve double-checked all the markings on your design documents, right? Do the same for the markings on the components you’re including with your PCB layout design.
Make sure all the parts are numbered, labelled, and match your documentation – and make them easy to read. Leave nothing to guesswork. For example, if it’s a Z, not an O, then make that clear.
Use all the tools from the beginning to get the most effective results at the end
Ask your assembler if they have any tools that can help you with your design and schematic creation, along with Design-for-Manufacturing (DFM) reviews. DFM analysis during the design flow eliminates costly and time-consuming problems from PCB assembly and test.
Prioritize your features
Doubtlessly, you’re pressured to pack more and more features into a small board size. That’s just not always possible. Take the time to list the capabilities you want. Don’t just list them, rank them. For instance, which is most important, higher power output or stronger signal transmission? Enlist the help of your PCB manufacturer. They’re in the perfect position to show you how to improve your design to get the outputs you want, or at least, the most important ones.
Plan your lead time, from design to assembly
Don’t assume your standard lead times apply to every design. If you’re developing a circuit board design different from what you usually design, you could be in for longer lead times all the way around. Take every step into consideration when doing your time estimates.
File formats
Lastly, ensure that the manufacturer you’re using is experienced with the file formats you’ll be submitting. Not doing so can add unnecessary time to your project.
Download free CADs and try before you buy
Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen exactly what you need. If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.
Whatever your requirements, you can depend on fast despatch. Request your free samples or download free CADs now.
Questions?
Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.