Common PCB design mistakes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identifying a common PCB layout mistake

Which of the following is a common mistake when placing components on a PCB?

A Placing components too close to each other causing soldering issues

B Using a ground plane to reduce noise

C Routing power traces with sufficient width

D Adding test points for debugging

💡 Hint

Think about what might cause manufacturing or reliability problems.

Placing components too close can cause solder bridges and assembly problems, which is a common PCB design mistake.

🎯 Scenario

intermediate

Troubleshooting signal integrity issues

You notice signal integrity problems on a high-speed PCB. Which design mistake is most likely causing this?

A Using controlled impedance traces

B Placing decoupling capacitors close to IC power pins

C Using long, unshielded traces with many vias

D Implementing proper differential pairs routing

💡 Hint

Consider what affects signal quality and timing on high-speed signals.

Long traces with many vias can cause reflections and signal degradation, leading to signal integrity issues.

🔧 Formula Fix

advanced

Identifying the cause of power noise

Which mistake in PCB power design can cause excessive noise on the power rails?

A Using a solid ground plane

B Not placing enough decoupling capacitors near ICs

C Routing power traces with wide copper areas

D Separating analog and digital grounds properly

💡 Hint

Think about what helps stabilize power supply voltage at the IC.

Insufficient decoupling capacitors cause voltage fluctuations and noise on power rails.

❓ visualization

advanced

Visualizing a PCB trace routing mistake

Which of the following trace routing patterns is a common PCB mistake that can cause EMI problems?

A Differential pairs routed closely with matched length

B Short, perpendicular crossing traces

C Ground traces surrounding signal traces

D Long parallel traces running close together for a long distance

💡 Hint

Think about what causes electromagnetic interference between traces.

Long parallel traces close together can cause crosstalk and EMI issues, a common PCB design mistake.

❓ data_modeling

expert

Modeling PCB layer stackup for signal integrity

Which PCB layer stackup mistake can degrade signal integrity in a high-speed design?

A Placing signal layers adjacent to each other without a ground plane in between

B Including a solid ground plane next to signal layers

C Using alternating signal and ground planes

D Using controlled impedance layers with proper dielectric thickness

💡 Hint

Consider how return current paths affect signal quality.

Signal layers adjacent without a ground plane cause poor return paths and degrade signal integrity.

Practice

1. Which of the following is a common mistake in PCB design related to component placement?

easy

A. Placing components too close causing soldering issues

B. Using correct footprint sizes for components

C. Ensuring clear labeling of components

D. Following manufacturer recommended spacing

Solution

1. Step 1: Understand component placement importance

   Components placed too close can cause solder bridges and assembly problems.

2. Step 2: Identify the mistake

   Placing components too close is a common error that leads to manufacturing defects.

3. Final Answer:

   Placing components too close causing soldering issues -> Option A

4. Quick Check:

   Component spacing = Placing too close [OK]

Hint: Check spacing between parts to avoid solder bridges [OK]

Common Mistakes:

• Ignoring minimum spacing rules
• Not considering solder mask clearance
• Overcrowding components

2. Which of the following is the correct way to define a PCB trace width in a design file?

easy

A. trace_width = '0.5mm'

B. traceWidth = 0.5

C. trace_width: 0.5mm

D. trace-width = 0.5mm

Solution

1. Step 1: Review syntax for trace width setting

   Trace width is often set as a string with units, e.g., '0.5mm'.

2. Step 2: Identify correct syntax

   trace_width = '0.5mm' uses correct assignment with units in quotes.

3. Final Answer:

   trace_width = '0.5mm' -> Option A

4. Quick Check:

   Trace width syntax = '0.5mm' string [OK]

Hint: Use quotes and units for trace width values [OK]

Common Mistakes:

• Omitting units in trace width
• Using invalid variable names
• Missing quotes around string values

3. Given a PCB layout with power and ground traces routed too thin, what is the most likely outcome?

medium

A. Improved signal integrity

B. Reduced electromagnetic interference

C. Increased risk of trace overheating and voltage drop

D. Better mechanical strength of the PCB

Solution

1. Step 1: Understand effects of thin power/ground traces

   Thin traces have higher resistance causing heat and voltage drop.

2. Step 2: Identify the outcome

   Higher resistance leads to overheating and unstable power delivery.

3. Final Answer:

   Increased risk of trace overheating and voltage drop -> Option C

4. Quick Check:

   Thin traces = Overheating & voltage drop [OK]

Hint: Thin power traces cause heat and voltage issues [OK]

Common Mistakes:

• Ignoring current capacity for trace width
• Assuming thin traces are always fine
• Not checking voltage drop in design

4. A PCB designer wrote the netlist but forgot to connect the ground pins of multiple components. What is the best way to fix this error?

medium

A. Change component footprints to larger sizes

B. Increase the trace width of power lines

C. Remove all ground connections to avoid confusion

D. Add a ground plane or connect ground pins with traces

Solution

1. Step 1: Identify the missing connection problem

   Ground pins must be connected to a common ground reference.

2. Step 2: Fix by adding ground plane or traces

   Adding a ground plane or connecting ground pins with traces ensures proper grounding.

3. Final Answer:

   Add a ground plane or connect ground pins with traces -> Option D

4. Quick Check:

   Ground connection fix = Add ground plane/traces [OK]

Hint: Connect all ground pins to a common ground plane [OK]

Common Mistakes:

• Forgetting to connect ground pins
• Assuming power lines replace ground
• Ignoring netlist errors

5. You notice that your PCB design has overlapping vias and traces causing short circuits. What is the best approach to solve this problem while maintaining signal integrity?

hard

A. Increase the number of vias in the overlapping area

B. Re-route traces to avoid via overlap and use design rule checks

C. Ignore the overlap if the PCB passed electrical tests

D. Use thinner traces to fit between vias

Solution

1. Step 1: Identify the cause of short circuits

   Overlapping vias and traces cause electrical shorts and signal problems.

2. Step 2: Apply design rule checks and re-route

   Re-routing traces to avoid overlaps and running design rule checks prevents shorts and maintains signal quality.

3. Final Answer:

   Re-route traces to avoid via overlap and use design rule checks -> Option B

4. Quick Check:

   Fix overlap = Re-route + design rule checks [OK]

Hint: Use design rule checks and re-route to fix overlaps [OK]

Common Mistakes:

• Ignoring via and trace overlaps
• Adding more vias without fixing routing
• Using thinner traces causing signal loss