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Designing the layout of your printed circuit board is crucial to creating a reliable, cost-effective board. While circuit design and component selection are also essential, you should always make sure you leave enough time for PCB layout. A lot goes into determining the optimal PCB layout design, especially since today&#;s boards are becoming more complex, compact and lightweight. The growing popularity of flexible PCBs complicates the process, too.

If you don&#;t account for important PCB layout considerations, you may end up with a design that doesn&#;t translate well to the real world. An inadequate layout can result in several problems such as electromagnetic interference, conflicts from components on either side of the board, limited board functionality and even total board failure. Plus, if you don&#;t get the layout right the first time around, you will need to rework it, which can cause manufacturing delays and added costs.

So, what are the PCB layout design rules and considerations you need to keep in mind? Let&#;s look at the steps of PCB layout design and identify some of the core considerations for each phase. Of course, there are other considerations you may want to keep in mind, too, but these are some of the most critical aspects of PCB layout design you should be aware of.

 

Basic PCB Design Steps

PCB design plays a role in every step of the printed circuit board production process from the moment you know you need a PCB to final production. The basic design process includes six steps.

 

1. Concept

After identifying the need for a PCB, the next step is determining the board&#;s final concept. This initial phase involves defining the functions the PCB will have and perform, its features, its interconnection with other circuits, its placement in the final product and its approximate dimensions. Also, consider the approximate temperature range the board will operate in and any other environmental concerns.

2. Schematic

The next phase is to draw the circuit schematic based on the final concept. This diagram includes all the information needed for the electrical components of the board to function appropriately, as well as details such as component names, value, rating and manufacturer part numbers.

While you&#;re creating your schematic, you&#;ll be creating your bill of materials. This BOM contains information on all of the components you need for your PCB. Always keep these two documents up to date.

 

3. Board-Level Block Diagram

Next, you will complete a board-level block diagram, a drawing describing the final dimensions of the PCB. Mark areas designated for each block, sections of components that are connected for electrical reasons or because of constraints. Keeping related components together will enable you to keep your traces short.

 

4. Component Placement

The next step is component placement, which determines where you will place each element on the board. Often, you may go through several rounds of refining component placement.

5. First-Pass Routing

Next, determine the routing and the routing priority for the circuit.

 

6. Testing

After you&#;ve completed the design, you should conduct a series of tests to ensure it meets all your needs. If it does, the design is complete. If not, you will go back to the phases where you need to make adjustments.

Design Documentation

As you go about creating your PCB, you&#;ll develop numerous documents. These documents include:

• The Hardware Dimensional Drawings: Describes the size of the bare board
• The Schematic: Maps out the electrical features of the board
• The Bill of Materials: Describes the components needed for the project
• The Layout File: Describes the basic layout of the PCB
• The Component Placement File: Describes the location of the individual components.
• The Assembly Drawings and Instructions: Explains how to assemble the board
• The User Guides: While not required, they&#;re useful for providing additional information to the user
• The Gerber File Set: The collection of output files of the layout that the PCB manufacturer will use to create the PCB

 

PCB Layout Best Practices

There&#;s a lot to consider regarding PCB layout and design. Some considerations apply to the entire process, while some are specific to particular steps. Here are seven relevant factors to keep in mind.

 

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1. Board Constraints

The first constraints you should look at are those associated with the bare board. Some of these basic constraints include the size and the shape of the board.

You will need to ensure you have adequate board area for the circuit. The size of the end product, the functionality the board must provide and other factors determine how large the board should be. Electronic products and the circuit boards they incorporate are becoming increasingly smaller. Before you start the design process, estimate the size of the board. If you do not have enough space for all the functionality required with a more straightforward design, you may need to use a multilayer or high-density interconnect (HDI) design.

The standard PCB is rectangular. This remains, overwhelmingly, the most common shape for PCBs. It is possible to create boards in other forms, however. PCB designers most often do this because of size constraints or use in irregularly shaped products.

Another critical consideration is the number of layers you&#;ll need, which power levels and design complexity will help decide. It&#;s best to figure out how many you need early in the layout design process. Adding more layers may increase production costs but enable you to include more tracks. This may be necessary for more complex boards with advanced functionality.

Use at least two vias to make layer transitions for all high-current paths. Using multiple vias at layer transitions increases reliability, improves thermal conductivity and reduces inductive and resistive losses.

 

2. Manufacturing Processes

You should also consider the manufacturing processes you&#;d like to employ to produce the board. Different methods have different limitations and constraints. You&#;ll need to use reference holes or points that work with the manufacturing process on the board. Always ensure holes are clear of components.

Also, keep the board mounting method in mind. Different approaches may require you to leave different areas of the board open. Using multiple technology types, such as both through-hole and surface mount components, can increase the cost of your boards but may be necessary in some cases.

Always check with your fabricator to make sure they have the capabilities to produce the type of board you need. Some might not, for instance, be able to manufacture boards with many layers &#; or those that use a flexible design.

 

3. Materials and Components

Consider during the layout phase the materials and components you plan to use for your board. You&#;ll first need to make sure the desired items are accessible. Some materials and parts are hard to find, while others are so expensive they&#;re cost-prohibitive. Different components and materials may also come with different designs needs.

Take time to ensure you&#;ve chosen the optimal materials and components for your board, and also that you&#;ve designed a board that plays to those items&#; strengths.

 

4. Component Placement Order

One of the most fundamental PCB design guidelines involves the order in which you place components on the board. The recommended order is connectors, then power circuits, then precision circuits, then critical circuits and then the rest of the elements. Power levels, noise susceptibility, generation and routing capability also influence routing priority for a circuit.

5. Orientation

When placing components, try to orient those that are similar to one another in the same direction. This will make the soldering process more efficient and help prevent mistakes from occurring during it.

 

6. Placement

Try not to place parts on the solder side of the PCB that will sit behind plated through-hole parts.

 

7. Organization

Logically organizing your components can reduce the number of required assembly steps, increasing efficiency and reducing costs. Aim to put all your surface mount components on one side of the board and all your through-hole components on the top side.

Power, Ground and Signal Trace Considerations

The above tips focused on PCB component placement. For those components to work as desired, you also need to route the power, ground and signal traces. Completing this step efficiently will help ensure your signals have a reliable path to travel to keep your board functioning properly. Here are five factors to keep in mind.

 

1. Power and Ground Planes

One fundamental PCB layout design rule is to keep your power and ground planes internally within your board. They should also be centered and symmetrical to prevent bowing and twisting of your board. Bowing can cause components to move out of position and potentially damage the board. Other recommendations include using common rails for each supply, making sure you have reliable, extensive traces and avoiding creating daisy chains to connect components.

High voltage in power circuits can interfere with low-voltage and current control circuits. You can use the placement of your power ground and control ground to help minimize this interference. Try to keep your grounds for each power supply stage separated. If you need to place some together, make sure they&#;re toward the end of your supply path. If your ground plane is in the middle layer of your board, include a small impedance path to prevent power circuit interference.

You should also keep your digital and analog grounds separate in a similar fashion. Try only to have analog lines cross your analog ground to reduce capacitive coupling.

 

2. Track Design

This step also involves connecting signal traces according to your schematic. You always want your traces to be as short and direct as possible. If you have horizontal trace routing on one side of the PCB, place vertical traces on the other side.

Your board may require multiple nets with different currents, which will determine the net width you need. Using a trace width calculator can help with this step. Thin tracks can only carry so much current. Tracks that are 0.010&#; inches or 10 mils thick can only take a current of around one amp, while a track that is 250 mils thick can carry as much 15 amps with a 30 degree Celsius temperature rise.

 

3. Pad and Hole Dimension

You&#;ll also need to determine pad and hole dimensions early in the PCB design process. As the size of the pads and holes decreases, getting the right pad-to-hole size ratio becomes more crucial. It&#;s especially critical when working with via holes. The bare PCB manufacturer may be able to provide guidelines on the standards and aspect ratio they require.

Another important consideration is the shape of the PCB pads. PCB footprints can vary according to the manufacturing process. Wave soldering typically requires larger footprints than infra-red reflow soldering does, for instance.

 

4. Signal Integrity and RF Issues

PCB layout design plays a crucial role in ensuring signal integrity and preventing electrical problems such as interference, often referred to as radio-frequency interference or electromagnetic interference.

Avoiding these problems has a lot to do with how you route your traces. To prevent signal issues, avoid running tracks parallel to each other. Parallel tracks will have more crosstalk, which can cause various problems that are difficult to fix once you&#;ve built the PCB. If tracks need to cross over each other, make sure they do so at right angles. This will reduce capacitance and mutual inductance between the lines, decreasing crosstalk in turn.

Using semiconductor components that generate low electromagnetic radiation can also help with signal integrity. Sometimes, other needs may require parts that have higher electromagnetic generation, though.

When designing a PCB, eliminate antennas, which can radiate electromagnetic energy, as well as large loops of signal and ground-return lines that carry high frequencies. You must position integrated circuits carefully to achieve short interconnect lines.

Placing a close ground grid over the PCB is another essential RF PCB layout design guideline that helps to ensure that return lines are close to the signal lines. This keeps the effective antenna area relatively small. In a multilayer board, you can achieve this with a ground plane.

Additional reading:
What is 2.54 mm pitch connector?
IDC Connectors - Wiring Supplies

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5. Thermal Issues

Thermal issues can impact many different parts of the design process. Larger boards and those with higher component density and higher processing speeds tend to have more heat-related problems. For smaller boards, they might not be a concern, but for more advanced ones, they can be a significant challenge.

To prevent heat-related problems, you need to allow heat to dissipate. First, identify components that generate a lot of heat. You should be able to find each component&#;s thermal resistance ratings in its datasheet. Then, you can follow the recommended guidelines for diverting heat from that component.

Ensure you leave sufficient space around all components that may get hot. The more heat they create, the more area they will need to cool off. It&#;s also vital not to place critical components near heat sources.

Ideally, the entire board will have the same operating temperature. Use thermally conductive planes to dissipate heat across a wide area, which speeds the rate at which temperature decreases by increasing the surface area used for heat transfer.

If thermal issues are substantial for your board, you may need to include cooling fans, heat sinks and thermal reliefs, which are critical for wave soldering on multilayer boards and assemblies with high copper content. You can create heat sinks using a heat sink paste, a polymer filled with finely dispersed solid particles. You can apply this paste using screen or stencil printing. After a drying or baking process, it becomes fixed and acts as a heat sink.

It&#;s always advisable to use thermal reliefs on through-hole components, which slows the rate at which heat sinks through the component plates. As a general rule, use a thermal relief pattern any time a via or hole connects to a ground or power plane. You may also want to use teardrops where traces and pads meet to provide additional support and reduce thermal stress.

 

The Importance of Testing

Throughout the PCB design process, as well as the rest of the PCB manufacturing process, you should continuously check your work. Catching problems early on will help minimize their impact and reduce the costs of fixing them.

Two common tests you should perform are the electrical rules check and the design rules check. These tests will help you solve many of the more significant problems you may encounter.

Once you can pass your ERC and DRC tests without any problems, you should check the routing of every signal and compare your board to your schematic in detail.

 

Solving PCB Layout Design Problems With CAD

Today, most PCB designers use advanced computer-aided design (CAD) software systems to create their PCBs. Similarly, manufacturers use computer-aided manufacturing software. Using these systems can help you solve many of the layout problems you may encounter. Some of the advantages of using these software systems include:

• Simple, Semi-Automated Design Processes: CAD programs allow you to drag and drop components where you need them to go on your design. Many systems will even create the traces for you, and then you can move, add or remove components or reroute them as needed. This approach can increase the efficiency and accuracy of your design process.
• Design Validation: Before you send your design to the manufacturing stage, you can test it using a CAD system to verify your tolerances, compatibility, component placement and other aspects. Many systems can even catch basic errors in real time, minimizing or eliminating their impact.
• Manufacturing File Generation: You can generate Gerber files and other files formats you may need to send to the manufacturer with a CAD system. Creating these files directly from the design software can help increase their accuracy and ensure a smooth transition to the manufacturing stage.
• Documentation: You can also use these systems to generate and save detailed documentation related to component use, error reports, design status, version control and more, which can assist with future projects.
• Rule Creation: Some of these programs allow you to create and store custom rule sets, which you can share with designers to improve the functionality of the software.
• Template Creation: You can even create templates for use in future projects. Once you create a design, you can save it and reuse it as a template for other projects.
• Increased Efficiency and Reduced Costs: Incorporating computer-aided design into your operations can improve the efficiency and accuracy of your design process, which reduces overall costs.

 

Choosing a PCB Supplier

Need printed circuit boards? Millennium Circuits Limited is your go-to source. We have a range of PCB capabilities that will surely meet the needs of your project, and we pride ourselves on providing outstanding customer service. We offer both domestic and offshore PCB capabilities, so we can provide multiple financing options and quick turnaround times. No matter which solution you choose, you can rest assured you&#;ll receive only the highest quality PCB products.

To learn more about our PCB services and how they can help your business, request a quote by detailing your project information, including a Gerber file. We also offer a free design check through our website so you can be sure your design is ready for manufacturing. To learn more about MCL and our many capabilities, contact us, request a quote or continue exploring our website today.

 

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Whether you are moving at a high speed or you're designing a high-speed printed circuit board, good board design practices help ensure your design will work as intended and can be manufactured at volume. In this guide, we've compiled some of the essential PCB board design and layout guidelines that apply to most modern circuit boards. Specialty designs may need to follow additional board layout guidelines, but the PCB layout guidelines shown here are a good place to start for most board designs.

The guidelines shown here are focused on a few key areas that will help you with routing, manufacturability, basic signal integrity, and assembly:

When starting a new printed circuit board design, it&#;s sometimes easy to forget about the important design rules that will govern your project. There are some simple clearances that, if determined early in the design, will eliminate a lot of component shifting and re-routing later. So where can you get this information?

The first place to start is to talk to your PCB design rules fabrication house. A good fabricator will usually post their capabilities online or will supply this information in a document. If it's not in an obvious location on their website, send them an and ask for their capabilities. It's best to do this first before you start placing components. While you're at it, make sure to submit your proposed stack-up for review, or look for their standard stack-up data and use that.

Once you've found their list of capabilities, you should compare these to whatever industry reliability standard you'll work with (Class 2 vs. Class 3, or a specialty standard). Once these points are determined, you should select the more conservative design layout limits needed to ensure manufacturability and reliability, and you can encode these into your board design rules.

As you proceed through the layout process, your board design rules will help you eliminate most design errors that will lead to fabrication and assembly problems. After setting the board design rules, you can start the placement process.

The component placement stage of your PCB layout design process is both an art and a science, requiring a strategic consideration of the prime real estate available on your board. The goal in component placement is to create a board that can easily be routed, ideally with as few-layer transitions as possible. In addition, the design has to comply with the design rules and satisfy must-have component placements. These points can be difficult to balance, but a simple process can help a board designer place components that meet these requirements:

1. Place must-have components first. There are often components that must be placed in specific locations, sometimes due to mechanical enclosure constraints or due to their size. It's best to place these components first and lock in their position before proceeding to the rest of the layout.
2. Place large processors and ICs. Components like high pin count ICs or processors generally need to make connections to multiple components in the design. Locating these components centrally makes trace routing easier in the PCB layout.
3. Try to avoid crossing nets. When components are placed in the PCB layout, the unrouted nets are normally visible. It's best to try and minimize the number of crossing nets. Each net intersection will require a layer transition through vias. If you can eliminate net crossings with creative component placement, it will be easier to implement the best routing guidelines for a PCB layout.
4. SMD PCB board design rules. It&#;s recommended to place all surface mount device (SMD) components on the same side of the board. The main reason for this arises during assembly; each side of the board will require its own pass down the SMD soldering line, so placing all SMDs on one side will help you avoid some extra assembly costs. 
5. Experiment with orientation. It's okay to rotate components to try and eliminate net intersections. Try to orient connected pads so that they face each other as this can help simplify routing.

If you follow points #1 and #2, it's much easier to lay out the rest of your board without too much crossover between routes. In addition, your board will have that modern look and feel to the layout, where a central processor supplies data to all the other components around the perimeter of a board.

The main processor in this PCB layout design is centrally located with traces routed out from the edges. This is the ideal placement of larger ICs and peripherals.

With components placed, it&#;s now time to route power, ground, and signal traces to ensure signals have a clean and trouble-free path of travel. Here are some guidelines to keep in mind for this stage of your layout process:

It&#;s generally the case that power and ground are placed on two internal layers. For a 2-layer board, this might not be so easy, so you would want to place a large ground plane on one layer, and then route signals and power traces on the other layer. With 4-layer circuit board stack-ups and higher layer counts, you should use ground planes instead of trying to route ground traces. For components that need direct power connections, it&#;s recommended to use common rails for each supply if a power plane is not used; ensure you have wide enough traces (100 mils is fine for 5 to 10 A) and don't daisy chain power lines from part to part.

Some recommendations state that plane layer placement must be symmetrical, but this is not strictly required for manufacturing. In large boards, this might be needed to reduce the chances of warping, but this is not a concern in smaller boards. Focus on access to power and ground, as well as ensuring all traces have strong return path coupling to the nearest ground plane first, then worry about perfect symmetry in the PCB design stack-up.

Next up, connect your signal traces to match the nets in your schematic. PCB layout best practices recommend that you always place short, direct traces between components when possible, although this may not always be practical on larger boards. If your component placement forces horizontal trace routing on one side of the board, then always route traces vertically on the opposite side. This is one of many important 2-layer PCB board design rules.

Printed circuit board design rules and PCB layout guidelines become more complex as the number of layers in your stack-up increases. Your routing strategy will require alternating horizontal and vertical traces in alternating layers unless you separate each signal layer with a reference plane. In very complex boards for specialized applications, many of the commonly-touted PCB best practices may no longer apply, and you'll need to follow PCB board design guidelines that are particular to your application.

PCB layout designs use traces to connect components, but how wide should these traces be? The required trace width for different nets depends on three possible factors:

1. Manufacturability. Traces cannot be too thin, otherwise, they can't be reliably manufactured. In the majority of cases, you'll be working with trace widths that are much larger than the minimum value your fabricator can produce.
2. Current. The current carried in a trace will determine the minimum required width to prevent the trace from overheating. When the current is higher, the trace will need to be wider.
3. Impedance. High-speed digital signals or RF signals will need to have a specific trace width to hit a required impedance value. This doesn't apply to all signals or nets, so you don't need to enforce impedance control on every net in your board design rules.

For traces that don't need specific impedance or high current, a 10 mil trace width is fine for the vast majority of low-current analog and digital signals. Printed circuit board traces that carry more than 0.3 A may need to be wider. To check this, you can use the IPC- nomograph to determine your PCB design trace width for a required current capacity and temperature rise limit.

Preferred routing (arrows indicate component shifting direction)

 

Non-preferred routing (arrows indicate component shifting direction)

The ground plane can act as a large heat sink that then transports heat evenly throughout the board. Therefore, if a particular via is connected to a ground plane, omitting the thermal relief pads on that via will allow heat to conduct to the ground plane. This is preferable to keeping heat trapped near the surface. However, this can create a problem if through-hole components are assembled on the board using wave soldering as you need to keep heat trapped near the surface.

Thermal reliefs are one PCB layout design feature that might be needed to ensure a board will be manufacturable in a wave soldering process, or in other words, for through-hole components connected directly to planes. Because it can be difficult to maintain process temperatures when a through-hole is a solder point directly to a plane, it&#;s recommended thermal reliefs be used to ensure the soldering temperature can be maintained. The idea behind thermal relief is simple: it slows the rate at which heat is dissipated into the plane during soldering, which will help prevent cold joints.

 

The typical thermal relief pattern

Some designers will tell you to use a thermal relief pattern for any via or hole that is connected to an internal ground or power plane, even if it is just a small polygon. This advice is often overgeneralized. The need for a thermal via on any through-hole component will depend on the size of the copper plane or polygon that will make a connection on the internal layer, and it is something you should request your fabricator review before you place your board into production.

Through-hole pads on copper pour could require the same thermal pad application as planes. When the pour is very large, it starts to look a lot like a plane, and so a thermal pad should naturally be applied if a through-hole pin will be soldered into that connection.

For SMD parts, this is not always the case. Whether the thermal gets applied to the pour region depends on how the PCB will be assembled. A reflow soldering process will heat up the board uniformly as the device passes through the reflow oven, so the potential form tombstoning is much lower for those SMD pads, regardless of the presence of a thermal connection.

If the design will be assembled by hand, such as with solder paste and a heat gun, then the PCB layout might need thermals to trap enough heat near the pad and prevent tombstoning. When soldering by hand, it can be difficult to maintain consistent heating across the component leads, and a thermal connection can help prevent a tombstoning defect.

Thermal connection on a polygon in Altium Designer.

By default, Altium Designer will maintain thermal connections onto polygons when you create a new project. This is configured using the Polygon Connect rule in the PCB design rules editor. You can change this setting to apply based on specific footprints, layers, component classes, nets/net classes, or any other conditions using the query language in Altium Designer.

There are some routing guidelines for PCB design rules about how to group and separate components and traces so that you ensure easy routing while preventing electrical interference. These grouping guidelines can also help with thermal management as you might need to separate high-power components.

Some components are best placed in the PCB layout design by grouping them in one area. The reason is that they might be part of a circuit and they may only connect to each other, so there would be no need to place the components on different sides or areas of the board. PCB layout then becomes an exercise in designing and laying out individual groups of circuitry so that they can be easily connected together with traces.

In many layouts, you'll have some analog and some digital components, and you should prevent the digital components from interfering with the analog components. The way this was done decades ago was to split up ground and power planes into different regions, but this is not a valid design choice in modern board designs. Unfortunately, this is still communicated in many board layout guidelines and it leads to many bad routing practices that create EMI.

Instead, use a complete ground plane below your components, and do not physically break the ground plane up into sections. Keep the analog components with other analog components operating at the same frequency. Also, keep the digital components with other digital components. You can visualize this as having each type of component occupying a different region above the ground plane in the PCB layout design, but the ground plane should stay uniform in the majority of board designs.

Example of digital & analog sections in a PCB.

It is also appropriate to separate components that will dissipate a lot of heat on the board into different areas. The idea behind separating these high-power components is to equalize the temperature around the PCB layout, rather than to create large hotspots in the layout where high-temperature components are grouped. This can be accomplished by first finding the &#;thermal resistance&#; ratings in your component&#;s datasheet and calculating the temperature rise from the estimated heat dissipation. Heatsinks and cooling fans can be added to keep component temperatures down. You may have to carefully balance the placement of these components against keeping trace lengths short as you devise a routing strategy, which can be challenging.

It&#;s easy to get overwhelmed toward the end of your design project as you scramble to fit your remaining pieces together for manufacturing. Double and triple-checking your work for any errors at this stage can mean the difference between a manufacturing success or failure.

To help with this quality control process, it&#;s always recommended to start with your Electrical Rules Check (ERC) and Design Rules Check (DRC) to verify you&#;ve met all of your established constraints. With these two systems, you can easily define gap widths, trace widths, common manufacturing requirements, high-speed electrical requirements, and other physical requirements for your particular application. This automates PCB design layout review guidelines for validating your layout.

Note that many design processes state that you should run design rule checks at the end of the board design phase while preparing for manufacturing. If you use the right design software, you can run checks throughout the design process, which allows you to identify design potential problems early and correct them quickly. When your final ERC and DRC have produced error-free results, it&#;s then recommended to check the routing of every signal and confirm that you haven&#;t missed anything by running through your schematic one wire at a time.

There you have it - our top PCB layout guidelines that apply to most circuit board designs! Although the list of recommendations is short, this guideline can help you get well on your way toward designing a functional, manufacturable board in no time. These PCB board design guidelines only scratch the surface, but they form a foundation for building upon and solidifying a practice of continual improvement in all your design practices.

If you want to get started with the best PCB board design software with a built-in rules-driven design engine that helps you stay accurate, use the advanced design tools in Altium Designer®. When a design is finished and ready to be released to manufacturing, the Altium 365&#; platform makes it easy to collaborate and share your projects.

We have only scratched the surface of what&#;s possible with Altium Designer on Altium 365. Start your free trial of Altium Designer + Altium 365 today.

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