What are some best guidelines for designing a PCB?

A good PCB design is crucial for circuit performance and fabrication ease. The main areas of board design are the layout and routing. These give immense flexibility to the designer.

To be a better designer, there are some practices you should follow, these are some of the techniques you must implement in your design.

Technique #1: Strategic Component Placement

One of the first steps on the path to a good design is, understanding the importance of component placement.

Technique #2: Deciding Ideal Trace Sizes

The standard for measuring trace thickness is copper ounces. One oz. of copper is the trace thickness when 1 oz. Cu is spread uniformly over an area of 1 sq. foot. Commonly used values of thickness are 1oz. or 2oz., however, most manufacturers can provide up to 6oz.

For designers working on multi-layer boards, another important thing to consider is that traces you make on outward layers or external layers are better vented and exposed to the surroundings for easier radiation of heat. Hence, they will be cooler than traces on the internal layers.

Technique #3: Efficient Routing

Routing is one of the most important steps in PCB design. To route a PCB basically means connecting signal traces according to the schematic. It is usually best to place traces as directly between components as possible and use short trace lengths.

Technique #4: Power Plane Setting

It’s an easy option to use pours on the power plane. It is a good method to ensure even power flow and reduce impedance and voltage drop; and it also helps in checking if the ground return paths are sufficient.

Technique #5: Ground Plane Setting

A commonly known and followed design practice is to have a common ground plane. This provides a uniform reference point where you can measure voltage at.

Technique #6: Avoiding 90 Degree Corners

This is a common practice even in mechanical design. Sharp edges and corners such as 90 degree corners should try to be avoided as they are points of stress concentration. Similarly in PCB design as well, you should try and avoid 90 degree corners.

It’s better to use 45 degree angles, and angles up to 80-85 degrees on the higher side.

Technique #7: Understanding Thermal Resistance

Heat distribution across the board affects performance a lot. To start with, you can identify which components are dissipating the maximum heat on the PCB. This can be done by referring to the Thermal Resistance ratings in the datasheets of your components, followed by adhering to guidelines on heat dissipation and distribution.

Technique #8: Thermal Relief

Once you have understood the heat signature of the board, the next step to ensuring optimal thermal performance is thermal relief. This is the process of connecting a trace or a fill to a component pin, and thus making it easier to solder. This connection is short to help in reducing the effect of electrical resistance.

Technique #9: Auto-Routing and When To Use It

The auto-routing feature might appeal to beginners, and they may feel it’s going to save them the cumbersome task of routing. However, the auto-router is not a substitute for manual routing. You may use it on certain occasions and for certain reasons.

Technique #10: Bypass Capacitor Placement

The purpose of using Bypass capacitors is to have a filtering process for AC components and DC components. Additionally, they help in reducing noise, garbage signals, ripples and other such unwanted AC signals.

Technique #11: Working With Mixed Signal Circuits

To ensure a good PCB design for those of you working with mixed signal circuits, try to ensure that you keep digital and analog ground planes separate.

While working with mixed signal circuits, another rule to remember is that you should shield analog grounds from interference and noise.

Technique #12: Optimal Silkscreen Utilization

The Silkscreen is a widely used, standard layer in PCBs globally. This is extremely useful for labeling and displaying important information, such as: component labeling, application of the board, details about the author, revision number and so on.

Make sure you label clearly the test points, functions, and try to include orientation of parts and connectors wherever you can. This is a good design practice.

A judicious usage of the silkscreen on both sides of the PCB improves the workflow during fabrication and production, and can also help you reduce reworking.

Some guidelines for annotations that you can refer to are: If you have line resolutions of 0.008” and font heights of 0.040”, you will have to develop and provide exposure additionally. It is usually a good idea to have the minimum line resolution at 0.010” and font heights at 0.060”.

Technique #13: Quality Control and Design Verification

Rushing through the final steps in the design process can ruin all the work you have put in. And a little bit of extra effort at this stage can really help make your project fabrication a success.

You can initiate the quality control process by applying the DRC and ERC systems.

Not only will this help you avoid unexpected errors before manufacturing, but also save the effort of changing blocks of design built upon some incorrect component.

So now we have looked at 13 of the PCB Design Best Practices, which will help you become a better designer along with improving your technique and skills.

Of course, there are more specific tips and guidelines for your particular design tasks, but the guidelines and techniques mentioned here will always be useful to you.

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