Common PCB design mistakes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a common mistake related to component placement on a PCB?

Placing components too close together can cause soldering problems and make troubleshooting difficult.

beginner

Why is poor trace routing a frequent PCB design error?

Poor trace routing can cause signal interference, increased resistance, and can affect the overall performance of the circuit.

intermediate

What mistake involves ignoring power and ground planes in PCB design?

Not using proper power and ground planes can lead to noise issues and unstable voltage levels in the circuit.

intermediate

How can incorrect drill hole sizes affect a PCB?

Using wrong drill hole sizes can cause poor mechanical fit for components and unreliable electrical connections.

beginner

What is the risk of not following design rules for spacing and clearance?

Ignoring spacing and clearance rules can cause short circuits and manufacturing defects.

What happens if components are placed too close on a PCB?

A Power consumption decreases

B The PCB becomes cheaper to produce

C Signal speed increases

D Soldering becomes difficult and troubleshooting is harder

Placing components too close can cause solder bridges and makes it hard to fix issues.

Why is proper trace routing important in PCB design?

A To reduce signal interference and resistance

B To increase the size of the PCB

C To make the PCB heavier

D To avoid using ground planes

Good trace routing helps signals travel cleanly and reduces electrical problems.

What is a consequence of not using power and ground planes correctly?

A Lower manufacturing cost

B Faster signal transmission

C Noise and unstable voltage levels

D Better mechanical strength

Power and ground planes stabilize voltage and reduce noise in circuits.

Incorrect drill hole sizes can cause:

A Poor mechanical fit and unreliable connections

B Faster assembly

C Improved signal quality

D Lower power consumption

Drill holes that are too big or small affect component mounting and electrical contact.

Ignoring spacing and clearance rules may lead to:

A Improved signal speed

B Short circuits and manufacturing defects

C Reduced PCB size

D Better heat dissipation

Proper spacing prevents electrical shorts and helps manufacturing quality.

List three common mistakes made during PCB component placement and explain why they cause problems.

Think about how placement affects soldering, troubleshooting, and heat.

Explain why power and ground planes are important in PCB design and what issues arise if they are not used properly.

Consider how electricity flows and how noise affects circuits.

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