Electrical Rules Check (ERC) in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This data represents a simplified Electrical Rules Check (ERC) table for a PCB design. Each row shows a net with two pins, their types, connection status, and the ERC result indicating if the connection passes or fails electrical rules.

Cell	Value
A1	Net Name
B1	Pin 1 Type
C1	Pin 2 Type
D1	Connection Status
E1	ERC Result
A2	VCC
B2	Output
C2	Input
D2	Connected
E2	Pass
A3	GND
B3	Output
C3	Output
D3	Connected
E3	Fail
A4	SIGNAL1
B4	Input
C4	Input
D4	Connected
E4	Fail
A5	SIGNAL2
B5	Output
C5	Input
D5	Not Connected
E5	Fail

Formula Trace

IF(AND(D2="Connected", OR(AND(B2="Output", C2="Input"), AND(B2="Input", C2="Output"))), "Pass", "Fail")

Step 1: D2="Connected"

Step 2: AND(B2="Output", C2="Input")

Step 3: AND(B2="Input", C2="Output")

Step 4: OR(TRUE, FALSE)

Step 5: AND(TRUE, TRUE)

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

Cell Reference Map

    A       B        C           D           E
1 | Net   | Pin 1  | Pin 2    | Connection | ERC
  | Name  | Type   | Type     | Status     | Result
--------------------------------------------------
2 | VCC   | Output | Input    | Connected  | Pass
3 | GND   | Output | Output   | Connected  | Fail
4 | SIGNAL1| Input  | Input    | Connected  | Fail
5 | SIGNAL2| Output | Input    | Not Connected | Fail

The formula references cells B2, C2, and D2 to check pin types and connection status for the net 'VCC'. These cells determine if the ERC result in E2 is 'Pass' or 'Fail'.

Result

    A       B        C           D           E
1 | Net   | Pin 1  | Pin 2    | Connection | ERC
  | Name  | Type   | Type     | Status     | Result
--------------------------------------------------
2 | VCC   | Output | Input    | Connected  | Pass
3 | GND   | Output | Output   | Connected  | Fail
4 | SIGNAL1| Input  | Input    | Connected  | Fail
5 | SIGNAL2| Output | Input    | Not Connected | Fail

The final ERC results show 'Pass' for the valid output-to-input connected net (VCC) and 'Fail' for nets with invalid pin type connections or not connected status.

Sheet Trace Quiz - 3 Questions

What does the formula check first in the ERC evaluation?

A If the net name is 'VCC'

B If both pins are 'Output'

C If the connection status is 'Connected'

D If the ERC result is 'Pass'

Key Result

IF connection is 'Connected' AND pin types are Output-Input or Input-Output THEN 'Pass' ELSE 'Fail'

Practice

1. What is the main purpose of Electrical Rules Check (ERC) in PCB design?

easy

A. To generate the bill of materials automatically

B. To check the physical dimensions of the PCB

C. To find electrical mistakes like unconnected pins early in the schematic

D. To simulate the circuit's electrical behavior

Solution

1. Step 1: Understand ERC's role in PCB design

   ERC is used to detect electrical issues such as unconnected pins or conflicting connections in the schematic.

2. Step 2: Differentiate ERC from other checks

   Physical dimension checks and simulations are separate processes, not part of ERC.

3. Final Answer:

   To find electrical mistakes like unconnected pins early in the schematic -> Option C

4. Quick Check:

   ERC = Find electrical mistakes early [OK]

Hint: ERC finds electrical errors in schematics before layout [OK]

Common Mistakes:

• Confusing ERC with physical layout checks
• Thinking ERC simulates circuit behavior
• Assuming ERC generates manufacturing files

2. Which of the following is the correct way to run an ERC in most PCB design software?

easy

A. Click the 'Run ERC' button after completing schematic edits

B. Export the schematic as PDF and review manually

C. Run a 3D visualization of the PCB

D. Generate Gerber files before running ERC

Solution

1. Step 1: Identify the ERC execution method

   Most PCB tools have a dedicated 'Run ERC' button or menu option to start the electrical rules check.

2. Step 2: Eliminate incorrect options

   Exporting PDFs, 3D visualization, and generating Gerber files are unrelated to running ERC.

3. Final Answer:

   Click the 'Run ERC' button after completing schematic edits -> Option A

4. Quick Check:

   Run ERC via dedicated button [OK]

Hint: Run ERC using the software's dedicated button [OK]

Common Mistakes:

• Thinking ERC runs automatically without user action
• Confusing ERC with file export or visualization
• Running layout checks instead of ERC

3. After running ERC, you see an error: Pin 'IN' on U1 is unconnected. What does this mean?

medium

A. The pin 'IN' is connected correctly and no action is needed

B. The pin 'IN' is connected to multiple nets causing a short

C. The component U1 is missing from the PCB layout

D. The pin named 'IN' on component U1 has no wire connected to it

Solution

1. Step 1: Interpret the ERC error message

   The message says the pin 'IN' on component U1 is unconnected, meaning no wire or net is attached to it.

2. Step 2: Understand implications

   An unconnected pin usually indicates a missing connection that may cause circuit malfunction.

3. Final Answer:

   The pin named 'IN' on component U1 has no wire connected to it -> Option D

4. Quick Check:

   Unconnected pin means no wire attached [OK]

Hint: Unconnected pin means no wire attached to that pin [OK]

Common Mistakes:

• Assuming unconnected means short circuit
• Confusing missing PCB part with schematic connection
• Ignoring ERC errors thinking they are warnings

4. You ran ERC and got multiple errors about conflicting pin connections. Which step should you take to fix this?

medium

A. Ignore the errors and proceed to PCB layout

B. Check the schematic for pins connected to multiple nets and correct wiring

C. Delete the entire schematic and start over

D. Run a 3D model check instead

Solution

1. Step 1: Analyze ERC conflict errors

   Conflicting pin connections mean pins are wired to more than one net, which is invalid.

2. Step 2: Correct schematic wiring

   Review and fix the wiring in the schematic to ensure each pin connects to only one net.

3. Final Answer:

   Check the schematic for pins connected to multiple nets and correct wiring -> Option B

4. Quick Check:

   Fix wiring conflicts in schematic before layout [OK]

Hint: Fix wiring conflicts in schematic, don't ignore ERC errors [OK]

Common Mistakes:

• Ignoring ERC errors and continuing
• Deleting schematic unnecessarily
• Confusing ERC errors with layout issues

5. You have a complex schematic with multiple power nets. ERC reports a warning that a power pin is connected to a net with a different voltage level. What is the best approach to resolve this?

hard

A. Verify the power net assignments and ensure pins connect only to nets with matching voltage levels

B. Ignore the warning if the circuit works in simulation

C. Connect all power pins to a single net regardless of voltage

D. Remove the power pins from the schematic

Solution

1. Step 1: Understand power net voltage warnings

   ERC warns when a power pin connects to a net with a different voltage, which can cause damage or malfunction.

2. Step 2: Verify and correct net assignments

   Check that each power pin connects only to the correct net matching its voltage level to avoid conflicts.

3. Step 3: Avoid unsafe shortcuts

   Ignoring warnings or connecting all power pins to one net can cause serious issues.

4. Final Answer:

   Verify the power net assignments and ensure pins connect only to nets with matching voltage levels -> Option A

5. Quick Check:

   Match power pins to correct voltage nets [OK]

Hint: Match power pins only to nets with correct voltage [OK]

Common Mistakes:

• Ignoring ERC voltage warnings
• Connecting different voltage nets together
• Removing essential power pins