Design Rules Check (DRC) setup in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This table shows the setup parameters for Design Rules Check (DRC) in a PCB design. It includes minimum clearance between elements, allowed trace widths, and via sizes.

Cell	Value
A1	Rule Name
B1	Minimum Clearance (mm)
C1	Maximum Trace Width (mm)
D1	Minimum Trace Width (mm)
E1	Via Size (mm)
A2	Clearance
B2	0.2
C2
D2
E2
A3	Trace Width
B3
C3	1.0
D3	0.15
E3
A4	Via
B4
C4
D4
E4	0.6

Formula Trace

IF(AND(Clearance >= B2, TraceWidth <= C3, TraceWidth >= D3, ViaSize = E4), "Pass", "Fail")

Step 1: Clearance >= B2

Step 2: TraceWidth <= C3

Step 3: TraceWidth >= D3

Step 4: ViaSize = E4

Step 5: AND(TRUE, TRUE, TRUE, TRUE)

Step 6: IF(TRUE, "Pass", "Fail")

Cell Reference Map

    A       B       C       D       E
1 |Rule Name|MinClr |MaxTrW |MinTrW |ViaSz |
2 |Clearance| 0.2   |       |       |      |
3 |Trace W. |       | 1.0   | 0.15  |      |
4 |Via      |       |       |       | 0.6  |

References used:
- B2 for minimum clearance
- C3 for max trace width
- D3 for min trace width
- E4 for via size

This map shows the cells referenced in the DRC formula for clearance, trace width, and via size rules.

Result

    A       B       C       D       E       F
1 |Rule Name|MinClr |MaxTrW |MinTrW |ViaSz |Result|
2 |Clearance| 0.2   |       |       |      |      |
3 |Trace W. |       | 1.0   | 0.15  |      |      |
4 |Via      |       |       |       | 0.6  |      |
5 |Test Val | 0.25  | 0.5   |       | 0.6  |Pass  |

The 'Result' cell shows 'Pass' because all DRC conditions are met.

The final result cell shows 'Pass' indicating the design meets all the specified rules.

Sheet Trace Quiz - 3 Questions

What does the formula check first in the DRC setup?

A If clearance is at least the minimum required

B If trace width is less than maximum

C If via size matches the required size

D If trace width is greater than minimum

Key Result

IF(AND(condition1, condition2, ..., conditionN), "Pass", "Fail") checks all rules and returns Pass only if all are true.

Practice

1. What is the main purpose of setting up Design Rules Check (DRC) in PCB design?

easy

A. To ensure the PCB layout meets manufacturing and electrical requirements

B. To create the schematic diagram of the circuit

C. To program the microcontroller on the PCB

D. To generate the bill of materials automatically

Solution

1. Step 1: Understand DRC role in PCB design

   DRC is used to check if the PCB layout follows specific rules for spacing, sizes, and electrical constraints.

2. Step 2: Identify the main goal of DRC setup

   The goal is to catch errors early to ensure the PCB can be manufactured and works correctly.

3. Final Answer:

   To ensure the PCB layout meets manufacturing and electrical requirements -> Option A

4. Quick Check:

   DRC purpose = ensure design rules met [OK]

Hint: DRC checks design rules before manufacturing [OK]

Common Mistakes:

• Confusing DRC with schematic creation
• Thinking DRC programs components
• Assuming DRC generates parts list

2. Which of the following is the correct way to set a minimum clearance rule in a DRC setup?

easy

A. Clearance == 0.15mm

B. Clearance >= 0.15mm

C. Clearance < 0.15mm

D. Clearance = 0.15mm

Solution

1. Step 1: Understand clearance rule syntax

   In DRC setup, you define the minimum clearance as a fixed value, e.g., Clearance = 0.15mm.

2. Step 2: Identify correct syntax for minimum clearance

   Using an equality assignment sets the rule; inequalities are not used in this context.

3. Final Answer:

   Clearance = 0.15mm -> Option D

4. Quick Check:

   Minimum clearance set by assignment = value [OK]

Hint: Use assignment (=) to set DRC clearance values [OK]

Common Mistakes:

• Using inequality signs instead of assignment
• Confusing comparison operators with rule definitions
• Writing clearance as a condition instead of a value

3. Given the following DRC rules:
MinTrackWidth = 0.2mm
MinClearance = 0.15mm
If a track is 0.18mm wide and the clearance between two tracks is 0.14mm, what will the DRC report?

medium

A. Errors: Track width and clearance below minimum

B. Error: Track width below minimum

C. Error: Clearance below minimum

D. No errors, all rules met

Solution

1. Step 1: Check track width against minimum

   The track width is 0.18mm, which is less than the minimum 0.2mm, so this violates the rule.

2. Step 2: Check clearance against minimum

   The clearance is 0.14mm, less than the minimum 0.15mm, so this also violates the rule.

3. Final Answer:

   Errors: Track width and clearance below minimum -> Option A

4. Quick Check:

   Width < 0.2mm and Clearance < 0.15mm = Errors [OK]

Hint: Compare values directly to minimum rules [OK]

Common Mistakes:

• Ignoring one of the two rule violations
• Assuming no error if only one rule fails
• Mixing up width and clearance values

4. You set a DRC rule for minimum hole size as MinHoleSize = 0.3mm. After running DRC, you still see errors for holes sized 0.35mm. What is the most likely cause?

medium

A. The holes are actually smaller than 0.3mm

B. The hole size units are mismatched (e.g., inches vs mm)

C. The DRC rule syntax is incorrect

D. The DRC tool does not check hole sizes

Solution

1. Step 1: Verify units used in hole size and DRC rule

   If the holes are 0.35mm but errors appear, units might be mismatched, e.g., holes measured in inches but rule in mm.

2. Step 2: Confirm DRC rule syntax and tool capability

   The syntax MinHoleSize = 0.3mm is correct and DRC tools do check hole sizes, so these are unlikely causes.

3. Final Answer:

   The hole size units are mismatched (e.g., inches vs mm) -> Option B

4. Quick Check:

   Unit mismatch causes false errors [OK]

Hint: Always check units match between design and rules [OK]

Common Mistakes:

• Assuming syntax error without checking units
• Ignoring unit differences between design and rules
• Thinking DRC ignores hole sizes

5. You want to set up a DRC rule that enforces a minimum spacing of 0.2mm between copper traces but allows a smaller spacing of 0.1mm between traces on different layers. How should you configure the DRC rules?

hard

A. Set MinClearance = 0.1mm for all layers without exceptions

B. Set MinClearance = 0.2mm and ignore layer differences

C. Set MinClearance = 0.2mm and enable LayerSpecificClearance = true with InterLayerClearance = 0.1mm

D. Set MinClearance = 0.3mm to cover all cases

Solution

1. Step 1: Understand clearance rules for same and different layers

   Minimum spacing between traces on the same layer is 0.2mm, but between layers it can be smaller (0.1mm).

2. Step 2: Configure DRC to handle layer-specific clearances

   Enable a setting like LayerSpecificClearance = true and set InterLayerClearance = 0.1mm to allow smaller spacing between layers.

3. Final Answer:

   Set MinClearance = 0.2mm and enable LayerSpecificClearance = true with InterLayerClearance = 0.1mm -> Option C

4. Quick Check:

   Layer-specific clearance rules = Set MinClearance = 0.2mm and enable LayerSpecificClearance = true with InterLayerClearance = 0.1mm [OK]

Hint: Use layer-specific clearance settings for different spacing [OK]

Common Mistakes:

• Applying one clearance value for all layers
• Ignoring inter-layer spacing rules
• Setting clearance too large and restricting design