Nowadays, PCB design is a highly complex procedure for there are thousands of connections and electrical components involved in PCB fabrications of a multilayer PCB.
No matter how careful or skilled you are, your design will undoubtedly have some mistakes when working with so many components. The errors may include misplaced pins, misaligned visas, and others.
Often you will realize these errors during the production phase, forcing you to make corrections that will take time and are costly.
Fortunately, you can take steps to prevent such errors early on. Top on the list is undertaking a design rule check (DRC).
A faulty IC chip on a PCB
Source: Wikipedia
Contents
What is a Design Rule Check?
DRC complete name design rule check refers to a group of rules that a circuit designer can employ in a schematic design.
These DRCs ensure the schematic meets all the manufacturing tolerances and dimensional tolerances the designer set for the board.
During any production process, either small scale or large scale, there are bound to be variations in the design.
PCB processing on a CNC machine
A manufacturer's ability to manage these variations directly affects the quality of their final product.
Hence, it would be best to consider the variations that may occur by providing an adequate margin of error in your design. Doing so increases the chances of you getting well-functioning parts.
A design rule check enables you to ascertain that your schematic falls within the design margins you had factored in.
Therefore, when there is a design rule violation on one of the design margins, your DRC will alert you by indicating an error on the schematic.
Such errors include; incorrect via size or lacking PIN, a faulty component designator, etc.
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Types of DRCs
There are many types of design rule checks:
- Shorts Violation
- Minimum area
- Notch spacing
- Over maximum stack level
- Wide metal jog
- End line spacing requirement
- Minimum via spacing width
- Ground wire and power supply coupling
- Minimum metal spacing width
- Keep Via wire out the enclosure
- Minimum edge length
- Improperly aligned via wire
- Below minimum edge length
Design Rule Check: Easy EDA Tutorial
Below you will learn steps on how you can use a DRC. There are three steps to follow:
- Design rule setting
- Set Rule for a Net
- Check the DRC Error
Let us have a closer look at each of these steps.
Design Rule Setting
Tap tools, then scroll to the design rule dialog box to set your design rule.
Design rule dialog box
Once you open the design rule dialog box, you will have to set it according to your required PCB specifications.
You can navigate to the additional options section and change all the design rule types.
For instance;
Rule
The rule box will be at default. You are free to add a new rule or rename it, then set new parameters for each Net.
Track width
The printed circuit board's track width should not be lower than the set value.
Clearance
Clearance of various objects on the PCB that have varying Net can't be below allocated value.
Electronic components on a PCB
Via Diameter
The PCBs printed should not go below the value you set.
Via Drill Diameter
Refers to the current rules via drill diameter; Thus, the printed circuit boards via drill diameter can't go lower than the set value.
Track length
The length of tracks in a similar net, including arc length, ought not surpass your set value. Please note we include the arc length because it may go unlimited once the input box empties.
Real-time DRC (design rule setting)
Once you enable this feature, the DRC will be active through the routing process. Thus when an error occurs, you will notice an X mark on the canvas.
Asses object to the copper area.
This feature compares the object to the copper area. You should thus ensure you activate it. If you don't, you will have to generate a Gerber then reconstruct the copper area.
Confirm object to board Outline
Once activated, you can set an amount to determine object clearance to the board outline.
Employ design rule when via placing and routing
The system will follow the set DRC width when installing a via and routing.
A typical circuit design process
Source: Wikipedia
Indicate DRC boundary during routing
After activation, there will be an outline on all sides of the track. Moreover, the outline's diameter will vary regarding the DRC settings.
Set Rule for a Net
You can either work with the default rule or make another one by clicking on the new Icon.
Pick a network from the right side; hold down the CTRL-key if you want to pick multiple networks.
In addition, the CTRL key can aid you in either keyword filtering or rule classification filtering.
A control key on a keyboard
Afterward, you can choose the rule you want to change from the set rule area. Then tap on the apply button for the Net to apply the law.
Finally, tap on the settings icon to apply all the rules you have set.
Check the DRC Error
Tap on the top menu bar, scroll to design and click on Check DRC. You will then have to tap refresh for the DRC to work.
Check a design rule can run.
Note that if you have a large PCB, it will take longer to check the DRC than a smaller PCB.
Once the check is complete, you can view the design violations in the DRC messages panel and make the required changes on the offending object.
DRC and DFM
DFM refers to optimizing electrical components or a schematic design to produce them quickly and at a lower cost. (DFM means to design for manufacturing).
Design for manufacturing mainly occurs during the design stage of the schematic, as it is easy, therefore reducing the cost of manufacture.
In contrast, the primary purpose of a DRC is to check whether there is a problem or not.
In addition, DRCs do not encompass all the guidelines needed to make or assemble a PCB.
For example, a batch mode design rule check will define the minimum spacing between electrical components on a digital circuit board.
On the other hand, DFM will determine the circuit board design process.
Thus, when you compare the two, you will realize that DRC will occur after DFM, meaning that DRC is a DFM subset in some cases.
How DRCs Minimize Board Respins
Constantly taking a PCB design through re-spins will incur additional costs.
A DRC increases the chances of a schematic design meeting performance needs and lowers time to market costs by reducing potential respins.
DRC checks are so comprehensive that they can capture many mistakes that a manual inspection couldn't spot.
PCB inspection
They include;
- Signal integrity (SI)
- Power integrity (PI)
- Electromagnetic interference (EMI)
- Safety checks
It is mainly for safety purposes that circuit designers recommend performing a mode design rule check on all products.
Beyond DRC
Since DRC only checks your schematics' validity and correctness, process engineers developed systems that can aid them in layout and schematic stages.
One such process is ERC, full name Electrical rule check that works to confirm the device meets all the rules regarding;
- Power domain crossing
- Floating devices
- Highest allowed series pass gates
Note that the ERC will only be effective when implemented in the design space.
Conclusion
This post has taught you what a design rule is, its functions, the types of DRCs, and its importance.
We also hope you can clearly state the differences between DFM and DRC. As we conclude, please get in touch with us for more information about DRC.
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