Checking unconnected copper in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This data shows PCB nets with their pad counts and copper area in square millimeters. 'NC' nets have zero pads but some copper area, indicating possible unconnected copper.

Cell	Value
A1	Net Name
B1	Pad Count
C1	Copper Area (mm2)
A2	GND
B2	10
C2	50
A3	VCC
B3	8
C3	40
A4	NC1
B4	0
C4	5
A5	NC2
B5	0
C5	3
A6	SIGNAL1
B6	5
C6	20

Formula Trace

=FILTER(A2:A6, (B2:B6=0) * (C2:C6>0))

Step 1: B2:B6=0

Step 2: C2:C6>0

Step 3: (B2:B6=0) * (C2:C6>0)

Step 4: FILTER(A2:A6, [FALSE, FALSE, TRUE, TRUE, FALSE])

Cell Reference Map

     A       B       C
1  Net    Pad Ct  Copper
2  GND       10      50
3  VCC        8      40
4  NC1        0       5
5  NC2        0       3
6  SIGNAL1    5      20

References:
- B2:B6 for Pad Count
- C2:C6 for Copper Area
- A2:A6 for Net Names

The formula uses pad counts and copper area columns to find nets with zero pads but positive copper area, then returns their net names.

Result

     A       B       C
1  Net    Pad Ct  Copper
2  GND       10      50
3  VCC        8      40
4  NC1        0       5  <-- Unconnected copper
5  NC2        0       3  <-- Unconnected copper
6  SIGNAL1    5      20

Result: Filtered list shows NC1 and NC2 as unconnected copper nets.

The result highlights nets NC1 and NC2 as having copper but no pads, indicating unconnected copper areas on the PCB.

Sheet Trace Quiz - 3 Questions

Which nets have zero pads according to the formula evaluation?

A NC1 and NC2

B GND and VCC

C SIGNAL1 only

D All nets

Key Result

FILTER(range, (condition1) * (condition2)) returns items meeting both conditions

Practice

1.

What is the main purpose of checking unconnected copper in a PCB design?

easy

A. To find copper areas not linked to any circuit path

B. To verify the power supply voltage levels

C. To check the color of the copper layer

D. To measure the thickness of the PCB substrate

Solution

1. Step 1: Understand unconnected copper meaning

   Unconnected copper means copper areas on the PCB that do not connect to any circuit trace or pad.

2. Step 2: Identify the purpose of checking it

   Checking helps find these areas to avoid manufacturing issues or electrical problems.

3. Final Answer:

   To find copper areas not linked to any circuit path -> Option A

4. Quick Check:

   Unconnected copper = Find unlinked copper areas [OK]

Hint: Unconnected copper means no electrical link [OK]

Common Mistakes:

• Confusing unconnected copper with power checks
• Thinking it relates to PCB color or thickness
• Assuming it checks signal integrity

2.

Which PCB software feature is typically used to detect unconnected copper?

easy

A. Design Rule Check with unconnected copper enabled

B. 3D rendering of the PCB layout

C. Schematic capture tool

D. Bill of Materials generator

Solution

1. Step 1: Identify the tool for design validation

   Design Rule Check (DRC) is used to validate PCB layout rules including unconnected copper.

2. Step 2: Confirm feature for unconnected copper

   Enabling unconnected copper check in DRC finds isolated copper areas.

3. Final Answer:

   Design Rule Check with unconnected copper enabled -> Option A

4. Quick Check:

   DRC + unconnected copper = detection tool [OK]

Hint: Use DRC with unconnected copper option [OK]

Common Mistakes:

• Confusing 3D rendering with error checking
• Thinking schematic capture finds copper issues
• Assuming BOM generator checks layout errors

3.

Given this PCB design snippet, what will the Design Rule Check report if unconnected copper check is enabled?

Layer: Top Copper
Area: Large copper pour not connected to any pad or trace

medium

A. No errors, copper pour is valid

B. Error about missing drill holes

C. Warning about unconnected copper area

D. Message about incorrect layer stackup

Solution

1. Step 1: Analyze the copper pour connection

   The copper pour is large but not connected to any pad or trace, so it is isolated.

2. Step 2: Understand DRC behavior with unconnected copper

   DRC with unconnected copper check enabled will warn about isolated copper areas to prevent manufacturing issues.

3. Final Answer:

   Warning about unconnected copper area -> Option C

4. Quick Check:

   Isolated copper = DRC warning [OK]

Hint: Isolated copper triggers DRC warning [OK]

Common Mistakes:

• Assuming no error if copper is large
• Confusing unconnected copper with drill hole errors
• Thinking layer stackup affects copper connection warnings

4.

In a PCB design, the DRC reports unconnected copper errors, but you believe all copper is connected. What is a likely cause?

medium

A. The drill holes are too large

B. Copper areas are connected only by very thin traces below minimum width

C. The schematic is missing components

D. The PCB software is outdated and cannot detect copper

Solution

1. Step 1: Consider connection rules in DRC

   DRC may flag copper as unconnected if connections are below minimum trace width or clearance rules.

2. Step 2: Evaluate other options

   Outdated software or schematic issues do not cause unconnected copper errors directly; drill hole size is unrelated.

3. Final Answer:

   Copper areas are connected only by very thin traces below minimum width -> Option B

4. Quick Check:

   Thin traces below rules cause unconnected copper errors [OK]

Hint: Check trace width meets minimum DRC rules [OK]

Common Mistakes:

• Blaming software version without checking design
• Confusing schematic errors with copper connectivity
• Assuming drill hole size affects copper connection

5.

You have a PCB with multiple copper pours. Some pours are unconnected but intended as isolated ground planes. How should you handle unconnected copper checks to avoid false errors?

hard

A. Increase the copper thickness to connect automatically

B. Disable all unconnected copper checks permanently

C. Remove the copper pours to avoid errors

D. Use net isolation or assign the copper pours to a specific net in the PCB software

Solution

1. Step 1: Understand isolated copper pours purpose

   Isolated ground planes are intentional and should be assigned to a net or isolated properly in the PCB software.

2. Step 2: Configure DRC to recognize isolated nets

   Assigning copper pours to nets or using net isolation settings prevents false unconnected copper errors.

3. Step 3: Evaluate other options

   Disabling checks removes useful validation, removing pours loses design intent, increasing thickness does not connect isolated areas.

4. Final Answer:

   Use net isolation or assign the copper pours to a specific net in the PCB software -> Option D

5. Quick Check:

   Assign nets to isolated copper to avoid false errors [OK]

Hint: Assign nets to isolated copper pours [OK]

Common Mistakes:

• Disabling checks instead of configuring nets
• Removing copper pours losing design function
• Thinking copper thickness auto-connects areas