Thermal relief for through-hole pads in PCB Design - Real Business Scenario

Scenario Mode

👤 Your Role: You are a PCB design engineer working on a new circuit board layout.

📋 Request: Your manager wants you to analyze the impact of thermal relief patterns on soldering quality and heat dissipation for through-hole pads.

📊 Data: You have data on pad sizes, thermal relief spoke counts, solder joint temperatures, and heat dissipation measurements from test boards.

🎯 Deliverable: Create a report with charts showing how different thermal relief designs affect solder joint temperature and heat dissipation, and recommend the best pattern.

Sample Data

Pad Size (mm)	Spoke Count	Solder Joint Temp (°C)	Heat Dissipation (W)
1.0	4	230	1.2
1.0	6	225	1.4
1.0	8	220	1.5
1.5	4	235	1.3
1.5	6	228	1.6
1.5	8	222	1.7
2.0	4	240	1.4
2.0	6	230	1.8
2.0	8	225	2.0

1

Step 1: Organize the data by pad size and spoke count to prepare for analysis.

Create a pivot table with Rows = Pad Size (mm), Columns = Spoke Count, Values = Average of Solder Joint Temp (°C) and Average of Heat Dissipation (W).

Expected Result

Pivot table showing average solder joint temperature and heat dissipation for each pad size and spoke count combination.

2

Step 2: Create a line chart to visualize how solder joint temperature changes with spoke count for each pad size.

X-axis = Spoke Count, Y-axis = Average Solder Joint Temp (°C), Series = Pad Size (mm).

Expected Result

Line chart showing decreasing solder joint temperature as spoke count increases for all pad sizes.

3

Step 3: Create a second line chart to visualize heat dissipation changes with spoke count for each pad size.

X-axis = Spoke Count, Y-axis = Average Heat Dissipation (W), Series = Pad Size (mm).

Expected Result

Line chart showing increasing heat dissipation as spoke count increases for all pad sizes.

4

Step 4: Calculate the percentage change in solder joint temperature and heat dissipation from 4 spokes to 8 spokes for each pad size.

Percentage Change = ((Value at 8 spokes - Value at 4 spokes) / Value at 4 spokes) * 100 for both metrics.

Expected Result

Table showing percentage decrease in solder joint temperature and percentage increase in heat dissipation for each pad size.

5

Step 5: Summarize findings and recommend the optimal spoke count balancing soldering quality and heat dissipation.

Review charts and percentage changes to identify spoke count with best trade-off.

Expected Result

Recommendation to use 6 spokes for best balance between lower solder joint temperature and improved heat dissipation.

Final Result

Thermal Relief Analysis Report

Pad Size (mm) | Spokes | Solder Temp (°C) | Heat Dissipation (W)
---------------------------------------------------------------
1.0           | 4      | 230              | 1.2
1.0           | 6      | 225              | 1.4
1.0           | 8      | 220              | 1.5
1.5           | 4      | 235              | 1.3
1.5           | 6      | 228              | 1.6
1.5           | 8      | 222              | 1.7
2.0           | 4      | 240              | 1.4
2.0           | 6      | 230              | 1.8
2.0           | 8      | 225              | 2.0

Key Insights:
- Increasing spoke count reduces solder joint temperature by up to 6.25%.
- Heat dissipation improves by up to 42.9% with more spokes.
- 6 spokes offer a good balance between thermal relief and heat transfer.

Recommendation:
Use 6 spokes for thermal relief on through-hole pads to optimize soldering quality and heat management.

✓Solder joint temperature decreases as spoke count increases, improving soldering quality.

✓Heat dissipation increases with more spokes, enhancing thermal performance.

✓6 spokes provide the best balance between temperature reduction and heat dissipation.

✓Larger pad sizes show greater improvements with increased spoke count.

Bonus Challenge

Analyze how different spoke widths affect solder joint temperature and heat dissipation for a fixed spoke count.

Show Hint

Add spoke width as a new variable in your data and create similar pivot tables and charts to compare its impact.

Practice

1. What is the main purpose of thermal relief in through-hole pads on a PCB?

easy

A. To prevent any electrical connection

B. To increase electrical resistance

C. To make the pad larger

D. To control heat flow for better soldering

Solution

1. Step 1: Understand thermal relief function

   Thermal relief uses thin copper spokes to connect pads to planes, controlling heat flow.

2. Step 2: Identify the main goal

   This control helps soldering by preventing heat from dissipating too quickly.

3. Final Answer:

   To control heat flow for better soldering -> Option D

4. Quick Check:

   Thermal relief = better soldering heat control [OK]

Hint: Thermal relief balances heat for soldering, not resistance [OK]

Common Mistakes:

• Thinking thermal relief increases resistance
• Assuming it makes pads bigger
• Believing it blocks electrical connection

2. Which of the following correctly describes the copper connection in thermal relief for through-hole pads?

easy

A. Thin copper spokes connecting pad to plane

B. Solid copper plane connection

C. No copper connection at all

D. Thick copper bars around the pad

Solution

1. Step 1: Recall thermal relief design

   Thermal relief uses thin copper spokes, not solid or thick bars, to connect pads.

2. Step 2: Match description to options

   Only thin copper spokes correctly describe the connection method.

3. Final Answer:

   Thin copper spokes connecting pad to plane -> Option A

4. Quick Check:

   Thermal relief = thin spokes connection [OK]

Hint: Thermal relief uses spokes, not solid or thick copper [OK]

Common Mistakes:

• Choosing solid copper connection
• Thinking there is no copper connection
• Confusing thick bars with spokes

3. Given a PCB pad connected to a copper plane with thermal relief, what is the expected effect on soldering time compared to a solid connection?

medium

A. Soldering time decreases due to heat dissipation control

B. Soldering time decreases because of more copper

C. No change in soldering time

D. Soldering is impossible with thermal relief

Solution

1. Step 1: Understand heat flow in thermal relief

   Thermal relief limits heat flow to the plane, slowing heat loss from the pad.

2. Step 2: Relate heat flow to soldering time

   Less heat loss means the pad stays hot longer, allowing solder to melt faster, decreasing soldering time.

3. Final Answer:

   Soldering time decreases due to heat dissipation control -> Option A

4. Quick Check:

   Thermal relief slows heat loss = shorter soldering [OK]

Hint: Thermal relief slows heat loss, so soldering takes shorter [OK]

Common Mistakes:

• Assuming soldering time increases
• Thinking thermal relief has no effect
• Believing soldering is impossible

4. A PCB designer notices that the thermal relief spokes are too thick, causing excessive heat loss during soldering. What is the best fix?

medium

A. Increase the number of spokes

B. Reduce the width of the thermal relief spokes

C. Remove thermal relief and use solid copper

D. Add more vias around the pad

Solution

1. Step 1: Identify problem cause

   Thick spokes conduct more heat, causing excessive heat loss.

2. Step 2: Choose appropriate fix

   Reducing spoke width lowers heat conduction, improving soldering heat retention.

3. Final Answer:

   Reduce the width of the thermal relief spokes -> Option B

4. Quick Check:

   Thinner spokes = less heat loss [OK]

Hint: Thinner spokes reduce heat loss, fix soldering issues [OK]

Common Mistakes:

• Increasing spokes increases heat loss
• Removing thermal relief worsens heat control
• Adding vias does not fix spoke thickness

5. A PCB has a through-hole pad connected to a large ground plane. The thermal relief uses four spokes. If the designer changes to two spokes, what is the likely impact on soldering and electrical performance?

hard

A. No change in soldering; electrical resistance increases greatly

B. Soldering becomes harder; electrical resistance slightly increases

C. Soldering improves; electrical resistance slightly increases

D. Soldering impossible; electrical connection lost

Solution

1. Step 1: Analyze spoke count effect on heat flow

   Reducing spokes from four to two reduces heat conduction paths, retaining more heat in the pad, improving soldering.

2. Step 2: Analyze spoke count effect on electrical resistance

   Fewer spokes slightly increase electrical resistance but usually remain acceptable.

3. Final Answer:

   Soldering improves; electrical resistance slightly increases -> Option C

4. Quick Check:

   Fewer spokes = improved soldering + slight resistance rise [OK]

Hint: Fewer spokes reduce heat flow (improve soldering) and increase resistance slightly [OK]

Common Mistakes:

• Thinking soldering becomes harder with fewer spokes
• Thinking electrical resistance decreases
• Believing electrical connection is lost