U43A0069

1. Lack of planning

With PCB layouts, preparation is the most important part of the job.  The amount of time spent preparing will affect the success of the design.  Selecting the right PCB design software is the most important; each having advantages, disadvantages and limitations.

Each PCB is unique it it’s own way.

Some areas of the design are more important than the rest, for example power supplies, impedance signals, DDR, address and data bus.  If these areas are not completed before the rest of design, precious time is lost and considerable effort is then spent reworking the layout.

Setting up rules and constraints are there to guide from the placement stage till the gerbers are completed.  When a PCB is planned correctly, the rest of the design will become a much simpler process.

 

2. Constraint rules

There isn’t anything more powerful than the human mind, unfortunately it is not perfect!

There are lots of things to think about with a PCB design, and it is easy to get lost with all of the information.  By using the tools available from PCB software, constraints can be implemented; spacing, keepouts, length matching, propagation delays.

Once these rules have been implemented, the designer can focus on other areas of the layout.

 

3. Poor Communication

As PCBs become more complex, the communication between engineer and PCB designer is essential.  By eliminating any placement or routing issues early on can save on costly reworks.

It is very important for the engineer to review the circuit board as often as possible.  Using on-line meeting tools can allow the engineer to inspect the board in real time and discuss potential issues.

By setting out clear objectives and agreeing on them from the start of the layout can give the designer a better understanding of what you want to achieve and can shorten time-to-market.

 

4. Using ineffective layout techniques

PCB layouts are becoming more complex thanks to advancements in electronic technology.  Problems such as electrical noise, crosstalk, impedance mismatch, timing issues, ESD – all need careful consideration.
Practical PCB design rules, board stackup, PWR & GND planes, decoupling capacitors, faraday shields – these are valuable when used correctly.
Reference designs provides the optimum solution to meet requirements for complex layouts.  Some of their suggestion may be difficult to achieve, but they do give some insight on how the PCB should be designed correctly.

 

5. Forgetting to backup data

Backup completed designs, no brainer.  Hundreds of hours are invested in most designs, eventually all designs will have to be modified.

Obsolete components and new technology will demand the board is updated.

If the original files have been lost, the whole project will have to start again or be scrapped.  The use of a cloud is a cheap and easy solution to backing up data.

 

6. Becoming a One man island

Any experienced PCB designer may look on a completed design and see perfection.  It is easy to get “tunnel vision”; concentrating on one area of the board and missing a detail on another.  A colleague not as involved in the project can be more impartial and provide an objective and invaluable insight.

Regular design reviews can help detect future errors and allow individuals to share experiences and knowledge.

Despite increasing levels of semiconductor integration and readily available systems-on-chips for many applications.

In addition to the increasing availability of highly-featured development boards, electronics often still require a custom PCB.

Even for “one-off” developments, the humble PCB still performs an important role.

It’s a physical platform for a design, and the most flexible for pulling an electronics system together.

In this article, we outline ten best practices of PCB design, most of which have stayed consistent for 25 years.

These rules are in no particular order and applied to any PCB design project. This should prove as a useful guide both to veteran design engineers as well as makers alike…

Use the right grid

Find a grid spacing that suits as many of your components as possible and use it throughout.

Although multiple grids may seem appealing. A little additional thought at the early stages of the layout can avoid spacing difficulties and maximize board use.

Many devices are available in different package sizes, so use that to your advantage.

Furthermore, as the polygon is an important shape when adding copper to your board. Boards with multiple grids will often produce polygon-fill discrepancies, not standardizing on one grid can make your life difficult.

Keep trace lengths as short and direct as possible

This rule applies even if it means going back over parts of the layout again to optimize track lengths.

This applies particularly in analogue and high-speed digital circuitry where impedance and parasitic effects will always play a part in limiting your system performance.

Whenever possible, use a power plane to manage the distribution of power lines and ground.

Using pours on the power plane is a quick and easy option in most PCB design software. It applies plenty of copper to common connections and helps ensure power flows as effectively as possible with minimal impedance or voltage drop. That ground return paths are adequate. If possible, run multiple supply lines in the same area of the board and remember that if the ground plane runs over a large section of one layer.

It can have a positive impact on cross-talk between lines running above it on an adjacent layer.

Group related components and test points together

Place the discrete components needed for an opamp close to that device so the bypass capacitors and resistors are co-located with it.

This helps with the track lengths in Rule #2, and it also makes testing and fault-finding easier.

Panelise your PCB by replicating the board you need several times on a larger board

Using a size which best suits the equipment used by your manufacturer will improve the cost of prototypes and manufacturing.

Start by laying out the board as one panel. Ask your board house what size panel they prefer. After correcting the design rules, do your best to step and repeat your design multiple times within the preferred panel size.

Consolidate your component values

As a designer, you will have picked some discrete components that could be a higher or lower value and work just the same.

Consolidating on a smaller range of standard values makes the BOM simpler and probably less expensive.

It also makes stock decisions easier in the long run if you have a range of PCBs based on your preferred device values.

Design rule check (DRC) as often as you can

The DRC function on PCB software takes a little time, but checking as you go can save hours on more complex designs.

Every layout decision is important, but the DRC keeps the most important ones top-of-mind.

Use the silkscreen wisely

The silkscreen can be used to portray a wealth of useful information to the board builder. As well as the service or test engineer, installer, or device operator.

Clear labels depicting functions and test points are obvious, but orientation of components and connectors should also be considered wherever possible.

Even if annotation ends up under your components following board assembly, it’s still a good practice. Full use of silk screening on both sides of the board streamlines production and can reduce re-work.

Decoupling caps are not optional

Do not try and optimize your design by avoiding decoupling power lines and trusting the absolute limits of component data sheets. Capacitors are inexpensive and robust; take the time to fit them in wherever possible and remember Rule #6 – use a range of standard values to keep the inventory neat.

Generate your own PCB manufacturing data and verify it before sending it out to be fabricated

Most board houses will be happy to do this for you. If you output your own Gerber files first and use a free viewer to verify it looks as you envisioned, then you can avoid misunderstanding.

You may even catch an error inadvertently included before it’s set forever in fiberglass, resin, and copper.

As circuit designs are more widely shared, and reference designs are relied upon more and more by in-house teams, we believe it’s important that basic rules like these remain in printed circuit design.

Keeping sight of the basics means developers retain the flexibility to add value to their products and extract the most from every board they make. Finally, anyone new to board design will accelerate their learning-curve and confidence when the basics are “designed in.”

Click here to see our guide on designing a good PCB Layout

Check out our video on high speed design

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