PCB Design Limitations beyond Borders

The design of printed circuit boards is a complex and detailed process that must meet certain requirements to ensure optimal performance. One of the most important considerations when designing a Printed Circuit Board is edge clearance or the distance between a trace and the edge of the board. Unfortunately, in many cases, edge clearance may be too small to meet certain safety and performance standards. This can lead to problems with electromagnetic interference and other issues.

With the right edge clearance, you can ensure that components do not touch each other and cause short circuits. However, there may be times when you need to extend beyond the standard edge clearance limits to accommodate certain components. So, we want to explore different methods of extending past edge clearance, so that you can create a more functional and aesthetically pleasing design.

The Importance of Edge Clearance

Edge clearance is an important aspect of design. It is the distance between two traces on a circuit board and helps to ensure that the signals are isolated from each other, avoiding interference and crosstalk. Proper edge clearance also prevents shorts from occurring due to accidental contact between two components. Without proper edge clearance, the circuit board may not function correctly, or at all

Edge clearance plays an especially important role in high-speed and high-frequency designs, as it ensures that the traces are far enough apart that they don’t interfere with each other’s signals. Edge clearance also affects the signal integrity and the overall performance of the PC Board. Poorly designed edge clearance can cause signal degradation, data loss, and even the destruction of components.

In general, PCB designers should aim to have at least 6 mils or 0.006 inches of clearance between traces to avoid any potential issues. However, depending on the complexity of the design and the components, this value can be higher. It is also important to remember that edge clearance varies depending on the size of the trace, voltage levels, and other factors. Designers need to consider all of these factors when designing their PCBs to ensure that the edge clearance is adequate for the design.

Factors That Affect Edge Clearance

When it comes to designing a printed circuit board, different parameters can affect the edge clearance of the design. Some of the most important factors include:

1. PCB Size: Edge clearance is directly proportional to the size of the PCB; the larger the PCB, the more distance between components and the edge of the board will be required. This is why it is important to carefully consider the size of the PCB before beginning the design process.
2. Track Width: The width of any tracks on the PCB will also have an impact on the edge clearance. Tracks with larger widths will require more clearance space around them, so designers need to be mindful when choosing track widths in their designs.
3. Components: The size and shape of the components can also have an impact on edge clearance. Larger components require more space around them, as well as additional spacing for any pins or connections that may protrude from the component body.
4. Electrical Clearance: You must also consider the electrical clearance requirements. Adjacent components can affect the electrical signals, so designers must ensure that they maintain adequate spacing between components and the edge of the board.

Understanding and taking into account these factors is crucial when designing a PCB with proper edge clearance. By being aware of these considerations, engineers can make sure that their designs are safe and reliable, while also allowing them to extend past clearance if needed. Other than understanding the factors that affect edge clearance, there are several techniques and strategies that designers can use to increase their margins of safety. One such strategy is implementing guard rails along the edges of the PCB which prevent components from getting too close to the edges.

It’s also possible to use vias instead of traces when routing along the edges of the board since vias have greater electrical clearance than traces. Moreover, using smaller components and smaller track widths wherever possible can help free up some much-needed extra space along the edges.

Another way to increase the margins of safety is by making use of breakout boards whenever necessary. This will allow you to route complex circuits away from the main board, reducing clutter and giving you more room for edge clearance. With careful planning and attention to detail, you can easily extend the past edge clearance without compromising safety or reliability in your PCB design.

Some Important Design Rules

There are certain rules and regulations for designing printed circuit boards. There are many parameters in this regard that you have to follow. Hence, the clearance between different components has to be according to the design rules, such as:

• The edge clearance in the case of resistors should be at least 05”.
• The edge clearance in the case of connectors is possible through tab routing. Sometimes you can combine tab and scored routing. However, try to avoid edge connectors if the design allows you.
• The edge clearance for capacitors should be less than 119”.

Placement of Drill Holes

• You should also try to keep drill holes far from PCB edges. The drill holes near the edges can result in cracks in the board. The appropriate distance of drilled holes from the PCB edge can be 0.010”. This clearance applies to both un-plated and plated holes.
• Moreover, the planes and copper traces’ distance from the board edge should be a minimum of 0.010”.
• The distance of the traces from the mouse bite’s deepest edge should be at least 0.025”.
• The distance of the components from the mouse bite’s deepest edge should be at least 0.075”.

The right distance between the edge and PCB elements helps manufacturers have flawless production.

Tips for Successfully Extending Past Edge Clearance

When designing a printed circuit board, it is important to ensure that there is enough clearance between components and the board edge. When extending past edge clearance, it is important to know how many extensions you need for the components to fit properly.

The amount of extension will depend on the size of the components, their placement relative to the edge, and any other constraints on the board. When possible, use larger pads and add a solder mask to the extended area to increase the chances of having enough clearance. Moreover, the length of any tracks and vias should be as short as possible to reduce their impact on the edge clearance.

To ensure the best results, use professional CAD software and its DRC tool to simulate the layout of your board before fabricating. This will help you to verify that all components have adequate clearance and that there are no overlapping traces. It is also important to measure the actual size of the components before laying them out to make sure they will fit properly.

When designing the board with extended clearance, the first step is to determine how much clearance is necessary. You can evaluate it by measuring the height and width of the components that will be on the board. The clearance should also take into account any extra space that assembly and rework may require.

After determining the clearance, it’s time to design the board. When laying out the board, you must ensure that any exposed edges have a minimum amount of clearance. To extend the edge clearance beyond the recommended minimum, use extended tracks. This will provide an additional amount of space between the edge of the board and the components.

When laying out the tracks, keep in mind that they must remain connected to each other. To ensure that all of the tracks are connected, you can use vias or micro vias. You can use Vias to connect different layers of a PCB, while micro vias can connect the same layer.

In the end, make sure to add a solder mask to any areas with an extended clearance. Solder mask is a protective coating that helps to prevent solder bridging and shorts between components. It also helps to protect against corrosion and improve electrical performance.

Wrap Up

Designing a printed circuit board is a complex process, as it requires precision and accuracy to create a successful product. When it comes to design, certain limitations should be considered. One of these is edge clearance, which limits how close components can be placed to the edges of the board. Fortunately, there are ways to extend past edge clearance, allowing for even more flexibility in PCB design.

Edge clearance plays an especially important role in high-speed and high-frequency designs, as it ensures that the traces are far enough apart that they don’t interfere with each other’s signals. Edge clearance also affects the signal integrity and the overall performance of the PCB. Poorly designed edge clearance can cause signal degradation, data loss, and even the destruction of the components.

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Written by Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.