Some PCB Design Guidelines You Need to Know An Advise From a PCB Engineer

Start with a Good Schematic Design

Before even beginning your PCB layout, it’s critical to start with a well-designed schematic. The schematic forms the foundation of your PCB, so any mistakes or oversights here will carry through to the physical board.

Some key things to keep in mind when creating your schematic:

Use consistent naming conventions for components, nets, and pins
Include all necessary components and connections
Double-check pin assignments and power requirements
Add notes about any special requirements or constraints

Taking the time to thoroughly review and refine your schematic before beginning PCB layout can save you a lot of headaches down the line. It’s much easier to make changes and catch errors at the schematic level.

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Choose the Right Number of Layers

One of the first decisions you’ll need to make when starting your PCB layout is how many copper layers to use. This will be dictated by a variety of factors, including:

Complexity of the circuit
Required component density
Signal integrity concerns
Cost considerations

In general, more complex boards will require more layers. For example, a simple circuit might only need 2 layers, while a high-speed digital design could require 8 or more. More layers provide more routing flexibility but also increase manufacturing costs.

Here are some general guidelines for common layer counts:

Layers	Typical Applications
1	Very simple circuits (e.g. LED Flasher)
2	Low-complexity analog and digital
4	General purpose analog/digital
6+	High-speed digital, dense boards

It’s a good idea to start with the minimum number of layers needed to comfortably route all your signals, and only add more if absolutely necessary. Unused layers are just wasted money.

Use a Good Stack-Up

Along with choosing the number of layers, you’ll also need to define the stack-up of your board. The stack-up specifies the ordering and thickness of copper and insulating layers.

A proper stack-up is critical for maintaining good signal integrity, especially for high-speed designs. In general, you’ll want to follow these guidelines:

Use thicker dielectrics between power and ground layers to minimize capacitance
Keep signal layers close to ground for good reference
Route critical signals between ground layers when possible
Be mindful of trace impedance and match to specifications

Here’s an example of a common 4-Layer Stack-Up:

Layer	Type	Thickness (mils)
Top	Signal	1.4
Gnd	Plane	0.7
Pwr	Plane	0.7
Bottom	Signal	1.4

Work with your manufacturer to specify an appropriate stack-up based on the needs of your design. Many fabricators have standard stack-ups that are optimized for good performance.

Follow Good Layout Practices

Creating a clean, well-organized PCB layout is equal parts art and science. While the exact layout will vary depending on the specific circuit requirements, there are some general best practices to keep in mind:

Component Placement

Place components logically based on schematic flow
Group related components together
Minimize distance between connected components
Provide adequate clearance around components for assembly
Consider mechanical constraints and connector placement

Routing

Route signals as directly as possible
Avoid unnecessarily long or meandering traces
Use rounded corners instead of sharp 90° bends
Keep trace widths and spacing consistent
Route power and ground lines first
Avoid crossing split planes with signals

Planes and Pours

Use large area fills for power and ground
Stitch multiple planes together with vias
Provide good grounding for connectors and components
Pour copper on unused areas to improve shielding

Silkscreen and Assembly

Clearly label all components and connectors
Provide polarity indicators and pin 1 markers
Add test points for critical signals
Include fiducials for machine assembly
Ensure adequate clearance for solder mask and paste

Taking the time to create a clean, logical layout can make assembly and debug much easier. It also helps ensure good signal integrity and reliable operation.

Carefully Route High-Speed Signals

Routing high-speed digital signals is one of the trickiest aspects of PCB design. As edge rates continue to increase, even short traces can act like transmission lines. This makes proper high-speed design techniques critical.

Some key things to keep in mind when routing high-speed signals:

Keep lines as short and direct as possible
Maintain consistent trace impedance
Avoid routing over split planes
Minimize vias and layer changes
Use sufficient ground vias for stitching
Carefully match trace lengths for parallel buses
Consider differential pairs for very high-speed signals

Impedance control is especially important for high-speed signals. Work with your manufacturer to establish controlled impedance specifications and use a stack-up that enables easy impedance matching.

Length matching is critical for high-speed parallel buses. Ideally, traces should be matched within a few mils to minimize timing skew. If needed, you can serpentine traces to add delay:

Many PCB tools have length matching features to help automate this.

Make Power Distribution a Priority

A clean, robust power distribution network (PDN) is one of the most important, but often overlooked, aspects of PCB design. Your PDN needs to deliver clean, stable power to all the components on your board.

Some tips for an effective power distribution network:

Use large copper pours and dedicated power planes
Decouple ICs with proper bypass capacitors
Use multiple vias to stitch power planes together
Partition analog and digital supplies to minimize cross-talk
Keep high current traces short and wide
Simulate PDN impedance to check for resonance

Here’s an example PDN impedance curve:

The goal is to keep the impedance across the required frequency range below the target impedance, usually a few 10s of milliohms.

Also pay attention to return paths and grounding. Use a solid ground plane and stitch well with vias. Avoid slots or cuts in the ground plane, as this can impede current flow and cause EMI issues.

Consider Thermal Factors

As electronic components continue to shrink and power densities rise, thermal management is an increasingly important consideration in PCB design. Overheating can significantly impact reliability and lead to premature failure.

Some thermal design tips:

Identify hot components and place them strategically
Provide adequate copper for heat sinking
Use thermal vias and planes to spread heat
Allow for sufficient air flow and ventilation
Consider active cooling (fans, heat pipes) for very high power boards

Thermal simulations and modeling can help predict hotspots and optimize design. Many PCB tools include thermal analysis features.

Here’s an example board thermal profile:

Keeping component temperatures within rated limits is critical for long-term reliability. By considering thermal factors up front, you can avoid power problems down the line.

Plan for EMC

Passing EMC testing is a critical hurdle that all electronic products must clear before going to market. Careful PCB design and layout can help minimize EMI and improve compliance.

Some EMC design best practices:

Partition the board into analog, digital, and power sections
Keep switching power supplies away from sensitive analog
Use solid ground planes and stitch well with vias
Minimize power plane cuts and slots
Route high-speed signals away from board edges
Apply shielding (copper, cans) to sensitive or noisy areas
Use filters on all I/O lines

It’s a good idea to consider EMC factors from the very beginning of the design process. Trying to “band-aid” EMC issues after the fact is often difficult and expensive. Proactive EMC design can save a lot of headaches in compliance testing.

Don’t Neglect DFM

Designing a great PCB is important, but it’s equally critical that your board can be manufactured reliably and cost-effectively. This is where design for manufacturability (DFM) comes in.

Some key DFM considerations:

Use standard materials and components when possible
Adhere to manufacturer’s design rules and guidelines
Provide adequate spacing and clearances for fabrication
Avoid tiny vias, traces, and clearances
Allow for fiducials and tooling holes
Consider panelization and assembly flow
Clearly document any special requirements

Work closely with your fabricator and assembler to identify any potential manufacturing issues up front. They can provide valuable feedback and guidance to optimize your design for production.

Here are some typical manufacturer clearances:

Item	Clearance
Trace width	3-4 mils
Trace spacing	3-4 mils
Via drill	8-10 mils
Via-to-via spacing	8 mils
Silkscreen-to-pad	5 mils
Component-to-component	10 mils

Following good DFM practices from the start can help avoid costly redesigns and production delays down the road.

Conduct Design Reviews

Even the most seasoned PCB designers can make mistakes or overlook things. That’s why it’s so important to get a second (or third) set of eyes on your design before sending it off for fabrication.

A thorough design review should include participation from key stakeholders, including:

Other PCB engineers
Electrical engineers
Mechanical engineers
Manufacturing/assembly representatives
Test and validation personnel

During the review, carefully go through all aspects of the design, including:

Schematic
Component selection
Layout/routing
Stack-up
Manufacturing specs
Bill of Materials (BOM)

Look for any errors, oversights, or areas for improvement. Encourage feedback and constructive criticism from all reviewers. It’s much better to catch and fix issues at this stage than after the boards have been built.

Documenting and sharing review findings is also important. Use a collaborative issue tracking or mark-up tool to record and discuss items.

Prototype and Test

Before committing to a full production run, it’s always a good idea to prototype and thoroughly test your PCB design. Prototyping allows you to:

Verify functionality and performance
Identify any design issues or bugs
Optimize and refine the design
Perform real-world testing (thermal, EMC, shock/vibe, etc.)

There are a few common prototyping options:

In-house rapid prototyping (LPKF, CNC, etc.)
Quick-turn prototype services
Low-volume production run

Based on the results of your prototyping and testing, you may need to make changes or tweaks to the design. Keep careful notes and document any modifications.

Once you’re satisfied that the design meets all requirements and is ready for production, you can confidently release the final files to your manufacturer.

FAQs

What is the most important factor in PCB design?

There’s no single “most important” factor in PCB design, as it really depends on the specific application and requirements. However, some of the key considerations that are critical for most designs include signal integrity, power integrity, manufacturability, and reliability.

How do I choose the right number of layers for my PCB?

The number of layers needed for a PCB design depends on the complexity of the circuit, the required component density, and the signal integrity demands. A simple design might only require 2 layers, while a complex, high-speed digital board could need 8 or more. Work with your manufacturer to determine the optimal layer count for your design.

What are some common PCB design mistakes to avoid?

Some common PCB design mistakes include:

Incorrect component footprints or pinouts
Violating manufacturer’s design rules (e.g. trace spacing, via size)
Improper grounding or power distribution
Poor high-speed signal routing (e.g. impedance mismatch, crosstalk)
Inadequate thermal management
Neglecting DFM considerations

Catching these issues in the design phase can save a lot of time and money.

How important is the PCB stack-up?

The PCB stack-up is a critical design decision, especially for high-speed or mixed-signal designs. The stack-up defines the ordering and spacing of copper and insulating layers, which has a big impact on signal integrity and EMC. Work closely with your manufacturer to choose or design a stack-up that meets your performance needs.

What tools are used for PCB design?

There are many software tools available for PCB design, ranging from simple schematic capture tools to full-featured suites that handle schematic, layout, simulation, and more. Some of the most popular PCB design tools include:

Altium Designer
Cadence Allegro/OrCAD
Mentor Graphics PADS
KiCad (open source)
Eagle

The choice of tool depends on the complexity of your designs, your budget, and your team’s preferences and experience. Many tools offer free trials, so it’s a good idea to test drive a few before committing.

Conclusion

PCB design is a complex field that requires a blend of technical skills, attention to detail, and creative problem solving. By following the guidelines and best practices outlined in this article, you’ll be well on your way to creating reliable, manufacturable PCBs that meet all your design goals.

Remember, the key to successful PCB design is careful planning, attention to detail, and close collaboration with your manufacturing partners. Don’t be afraid to ask for help or guidance when needed. And always, always prototype and test your designs before committing to production.

Happy designing!

Artist 3D

Some PCB Design Guidelines You Need to Know An Advise From a PCB Engineer

Start with a Good Schematic Design

Choose the Right Number of Layers

Use a Good Stack-Up

Follow Good Layout Practices

Component Placement

Routing

Planes and Pours

Silkscreen and Assembly

Carefully Route High-Speed Signals

Make Power Distribution a Priority

Consider Thermal Factors

Plan for EMC

Don’t Neglect DFM

Conduct Design Reviews

Prototype and Test

FAQs

What is the most important factor in PCB design?

How do I choose the right number of layers for my PCB?

What are some common PCB design mistakes to avoid?

How important is the PCB stack-up?

What tools are used for PCB design?

Conclusion

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Some PCB Design Guidelines You Need to Know An Advise From a PCB Engineer

Start with a Good Schematic Design

Choose the Right Number of Layers

Use a Good Stack-Up

Follow Good Layout Practices

Component Placement

Routing

Planes and Pours

Silkscreen and Assembly

Carefully Route High-Speed Signals

Make Power Distribution a Priority

Consider Thermal Factors

Plan for EMC

Don’t Neglect DFM

Conduct Design Reviews

Prototype and Test

FAQs

What is the most important factor in PCB design?

How do I choose the right number of layers for my PCB?

What are some common PCB design mistakes to avoid?

How important is the PCB stack-up?

What tools are used for PCB design?

Conclusion

Related posts:

Recent Posts

Categories

Tag Cloud