Guide

How Design Rule Checking (DRC) Works in PCB Design?

design rule check(DRC) in pcb design
18 Dec
PCB design is a complex process involving enormous components and their interconnection on a multilayer circuit board. For proper functioning, the design layout and connections must be governed by a set of rules - Design Rule Check (DRC).
Design Rule Check (DRC) is a crucial process in electronic design automation (EDA) to ensure that a circuit design adheres to specified manufacturing rules and constraints. It can help PCB designers identify issues early in the design process, improving the reliability and manufacturability of integrated circuits (ICs). By catching violations before PCB fabrication, DRC minimizes costly iterations and enhances overall design efficiency.

What is Design Rule Check?

Design rule checking (DRC) is an automated process used to check the PCB layout design before fabrication to ensure that it complies with design guidelines and constraints. These are based on the design requirements, industrial manufacturing standards, and capabilities of the PCB fabrication process.
what is design rule check in PCB design?

Why Use DRC in PCB Design?

PCB Design Rule Check (DRC) can find anomalies in PCB design layout and generate reports. It ensures that the designed product meets quality standards in terms of performance and manufacturing, thereby preventing design errors and manufacturing anomalies.
DRC is crucial for upholding PCB quality in production. Practically, it acts as a quality assurance check at the design stage. Design rules are generally defined to serve the following key purposes:
  • DRC in terms of design requirements
Many times, PCB applications require a designer to control certain parameters in their layout design. These are very crucial and impact the performance and reliability of the circuit.
  • DRC in terms of manufacturing capability
PCB designers should ask the PCB fabrication and assembling facility regarding the constraints, tolerances, and accuracy measures of tools and machinery used for PCB fabrication. This data dictates the accuracy with which the PCB layout can be manufactured.

Advantages of DRC in PCB Design

DRC check brings the following advantages to the PCB design process:
1
Design rule check violations are captured in time by PCB design software. This helps to improve the PCB layout design before it gets manufactured, hence reducing errors and thereby saving time and money.
2
Manufacturing tolerances and constraints can be made a part of design rules, hence manufacturing becomes compatible with design with fewer defects.
3
This process tends to optimize the board space as some DRC rules dictate avoiding longer paths between interconnects.
4
Ensure signal integrity by ensuring track spacing and clearances to avoid undesirable coupling and crosstalk.
5
DRC brings quality assurance and reliability to the PCB layout during the design phase.
6
DRC check ensures compliance with design requirements and industrial regulations.

Common Design Rules in DRC Check

  1. Minimum Clearance
The minimum tolerable space between two conducting tracks, pads, or vias is known as minimum clearance. This is an important parameter that is crucial not only for fabrication, but also to avoid short circuits, EMI, and unwanted coupling.
  1. Track Width
Track width determines the safe current carrying capacity of the track. The greater the current rating required; the greater the track width. For high current, track width should be worked out using ohms law for determining ohmic losses and hence heat dissipation.
Circuit board components be correctly placed in such a way that these components should not occupy large spaces as well as not be too congested to result in coupling or interference. Congestion may also lead to soldering defects while assembling.
  1. Annular Ring
DRC check looks for the annular ring (the area of copper around a drilled hole) around that it suffices the minimum requirements to prevent breakout.
area of copper around a drilled hole
  1. Spacing between Vias
Sometimes many via are placed on a plane for making either a low inductance path or for heat conduction. Their size, placement, and spacing are also a part of PCB design rule checking.
  1. Solder Mask Clearance
It is the gap between exposed traces and the solder mask. DRC checks that this clearance is enough to avoid solder bridging, avoiding short circuits during assembly.
  1. Boundary Clearance
It means placing the tracks and assembling electronic components at a certain gap from the PCB boundary for physical strength and proper assembling.
  1. Ground Clearance
Sometimes designer wants the ground plane parallel to the signal track, effectively making it a coplanar line. This enhances signal integrity and lesser EMI effects. PCB Design rule checking can check for the clearance from ground plane.
  1. Floating Island
This design rule means the DRC checks to look for patches that are isolated from all other nets.
  1. Via Placement
Via are used to connect layers. These are commonly used to provide power, ground connections, and thermal management of ICs as well as to connect layers in a multi-layer PCB. DRC Checks the aspect ratio of vias to ensure manufacturability and reliability.
vias on pcb
  1. Impedance Control
Ensures tracks have the required impedance for high-speed signals.
  1. Length Matching
This DRC rule signifies that differential pairs in balanced transmission tracks are of equal length to maintain signal integrity.
  1. Thermal Relief Pad Design
This design rule ensures proper thermal relief for pads connected to large copper areas to facilitate heat distribution for soldering.
  1. Silkscreen Violations
Ensures that silkscreen elements do not overlap with pads or vias, which could interfere with soldering and inspection.

How to Implement DRC in PCB Design

To implement design rule checking in PCB, PCB layout designers use specialized tools to automatically examine the layout. The layout is evaluated based on a defined criteria known as design rules. The DRC rules can be edited as per design requirements. The software tool examines and generates the report for anomalies and rule violations. This report highlights the layout design issues thereby allowing the designer to make corrections.
design rule - hole size

How to Run Design Rule Check?

In this section, we will discuss the entire process that involves design rule checks during PCB layout design. Following is the implementation cycle used for analyzing a circuit board through DRC check:
DRC improve PCB quality
  1. Identify Design Rules
Based on the circuit design requirement and manufacturing process. The PCB designer can configure design rules in PCB layout design software.
  1. PCB design
Design your PCB layout, keeping the defined rules in mind. Place components and route traces according to the design requirements.
  1. Run Initial DRC
There are two methods generally available in PCB design software. Both have their own merits. A designer can use any one or both DRC tools for design verification.
  • Real-time DRC. In Real-time DRC, the software application continuously checks the layout design against defined DRC rules chosen, as you develop the PCB layout. The results are almost instantaneously available, and the PCB layout can be worked on to remove errors, if any.
  • Batch DRC. This process involves a thorough check of the entire PCB layout at a specific point in the design process, where the designer wants to look for a detailed report. The tool will highlight any violations of the design rules. Thorough checking enables a detailed review of the design; thus reporting issues that might have been missed in real-time DRC. A batch test is generally considered a benchmark before design finalization.
  1. Review & Correct Errors
The Design rule-checking report is then analyzed to look for the nature and location of each error. The error is then corrected by editing the design at that location.
  1. Re-run DRC
After addressing the errors by making necessary edits and corrections, run the DRC tool again to look for any other anomalies. Keep reviewing and correcting errors until the DRC tool reports no error or violation.
  1. Prepare for Fabrication
At this stage, the PCB layout is good for undergoing fabrication and assembly. Generate the fabrication files i.e. Gerber file for Copper track, drills, Boundary, solder mask, and labelling.
By following these steps, you can ensure that your PCB design complies with all necessary DRC rules and is ready for reliable manufacturing.
PCB Design Rule Check Software & Tools

PCB Design Rule Check Software & Tools

Many PCB design software have an in-built program for DRC monitoring. Remember DRC check is only meant to report errors or violations in design layout. It will not auto-correct them. However, some programs may suggest error correction schemes. Some of the popular PCB layout software with DRC are as follows:

Conclusion

The design rule-checking process is a crucial process for evaluating PCB design, ensuring that layouts adhere to predefined design and manufacturing constraints. By applying the DRC check, the PCB layout designer can identify and correct potential issues during the design phase before getting it fabricated, thereby significantly reducing the risk of costly rework and production delays.
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About Xiaoji Lee

I am a PCBA sales engineer at Fulltronics company. As an outgoing girl, I have enjoyed communicating with people from the very beginning. Since joining the OEM PCB&PCBA field. I have become senior sales, that involves both negotiation and business development.

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