Trace width for current capacity in PCB Design - Real Business Scenario

Scenario Mode

👤 Your Role: You are a PCB design engineer working on a new electronic device.

📋 Request: Your manager wants you to determine the correct trace widths on the PCB to safely carry specified current loads without overheating.

📊 Data: You have a table listing different current values (in Amperes) and the corresponding recommended trace widths (in mils) for a 1 oz copper thickness PCB.

🎯 Deliverable: Create a report with a clear table and a line chart showing the relationship between current and trace width. Include a calculated measure for the minimum trace width needed for a given current.

Sample Data

Current (A)	Trace Width (mils)
1	10
2	20
3	30
4	40
5	50
6	65
7	80
8	95
9	110
10	125

1

Step 1: Load the sample data into your BI tool as a table with columns 'Current (A)' and 'Trace Width (mils)'.

Import the data as-is from the sample_data HTML table.

Expected Result

A table with 10 rows showing current values from 1A to 10A and their corresponding trace widths.

2

Step 2: Create a line chart to visualize the relationship between Current and Trace Width.

Set X-axis to 'Current (A)', Y-axis to 'Trace Width (mils)'.

Expected Result

A smooth increasing line showing trace width growing as current increases.

3

Step 3: Create a calculated measure to find the minimum trace width needed for any given current input.

Use interpolation or lookup to find trace width for input current. For example, in DAX: TraceWidthForCurrent = LOOKUPVALUE('Table'[Trace Width (mils)], 'Table'[Current (A)], SELECTEDVALUE('Input'[Current]))

Expected Result

When input current is 5A, the measure returns 50 mils; for 7A, returns 80 mils.

4

Step 4: Add a slicer or input box for the user to select or enter a current value to see the required trace width.

Connect the slicer/input to the calculated measure from step 3.

Expected Result

User can select current 3A and see trace width update to 30 mils dynamically.

5

Step 5: Format the report with clear labels, titles, and units for accessibility and clarity.

Add chart title 'Trace Width vs Current', axis titles 'Current (A)' and 'Trace Width (mils)'. Ensure color contrast is high.

Expected Result

A clean, readable report suitable for presentation to engineering team.

Final Result

Trace Width vs Current (A)

Current (A) | Trace Width (mils)
------------|--------------------
1           | 10
2           | 20
3           | 30
4           | 40
5           | 50
6           | 65
7           | 80
8           | 95
9           | 110
10          | 125

[Line chart showing an upward slope from 10 mils at 1A to 125 mils at 10A]

User input: 5A -> Required Trace Width: 50 mils

✓Trace width increases roughly linearly with current to prevent overheating.

✓For currents above 5A, trace width grows faster to handle heat dissipation.

✓Using this data helps ensure PCB traces are designed safely for electrical loads.

Bonus Challenge

Extend the report to include trace width recommendations for different copper thicknesses (e.g., 2 oz copper).

Show Hint

Add a new column for copper thickness and adjust trace width values accordingly using industry formulas or tables.

Practice

1. What is the main reason to choose the correct trace width in PCB design?

easy

A. To increase the signal speed on the trace

B. To make the PCB look visually appealing

C. To reduce the cost of copper used in the PCB

D. To ensure the trace can safely carry the required current without overheating

Solution

1. Step 1: Understand trace width purpose

   Trace width determines how much current a PCB trace can carry safely without overheating.

2. Step 2: Identify the main safety concern

   Overheating can damage the PCB and cause failure, so correct width prevents this.

3. Final Answer:

   To ensure the trace can safely carry the required current without overheating -> Option D

4. Quick Check:

   Trace width controls current safely [OK]

Hint: Trace width prevents overheating by carrying current safely [OK]

Common Mistakes:

• Thinking trace width is for aesthetics
• Assuming trace width reduces cost only
• Believing trace width affects signal speed directly

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

easy

A. TraceWidth = 10mm + Current * 0.5

B. TraceWidth = 10 mils

C. traceWidth = '10mil'

D. Trace_Width = 10mil

Solution

1. Step 1: Recognize standard units for trace width

   Trace width is commonly specified in mils (thousandths of an inch) or mm, with a space before the unit.

2. Step 2: Identify correct syntax for specification

   TraceWidth = 10 mils uses a numeric value followed by a space and unit 'mils', which is clear and standard.

3. Final Answer:

   TraceWidth = 10 mils -> Option B

4. Quick Check:

   Standard unit with space = correct [OK]

Hint: Use numeric value plus unit with space (e.g., 10 mils) [OK]

Common Mistakes:

• Using quotes around units incorrectly
• Combining units without space
• Using non-standard unit names

3. Given a PCB trace carrying 3A current with a temperature rise limit of 10°C, which trace width is closest to the recommended value using IPC-2152 guidelines?

Options are based on typical IPC-2152 charts for external layers.

medium

A. 30 mils

B. 15 mils

C. 50 mils

D. 70 mils

Solution

1. Step 1: Refer to IPC-2152 chart for 3A current and 10°C rise

   According to IPC-2152, a 3A current with 10°C rise typically requires about 25-35 mils trace width on external layers.

2. Step 2: Match closest option

   Among given options, 30 mils fits best within the recommended range.

3. Final Answer:

   30 mils -> Option A

4. Quick Check:

   3A current needs ~30 mils width [OK]

Hint: Use IPC-2152 chart ranges for current and temp rise [OK]

Common Mistakes:

• Choosing too narrow trace causing overheating
• Picking overly wide trace wasting PCB space
• Ignoring temperature rise in calculation

4. A designer used the formula TraceWidth = Current * 10 to calculate trace width in mils. The trace carries 2A current. The calculated width is 20 mils. However, the trace overheats during testing. What is the likely error?

medium

A. The formula does not consider temperature rise and copper thickness

B. The current value should be squared in the formula

C. Trace width should be in mm, not mils

D. The formula should multiply current by 5, not 10

Solution

1. Step 1: Analyze the formula used

   The formula is a simple linear multiplication ignoring key factors like temperature rise and copper thickness.

2. Step 2: Understand why overheating occurs

   Without considering temperature rise and copper thickness, the trace width may be underestimated, causing overheating.

3. Final Answer:

   The formula does not consider temperature rise and copper thickness -> Option A

4. Quick Check:

   Missing temp rise and copper thickness causes errors [OK]

Hint: Always include temperature rise and copper thickness in calculations [OK]

Common Mistakes:

• Using oversimplified formulas
• Ignoring units consistency
• Assuming linear scaling is enough

5. You need to design a PCB trace for a 5A current on an internal layer with a maximum temperature rise of 20°C. Using IPC-2152 guidelines, which approach is best to determine the correct trace width?

hard

A. Use the external layer chart and double the width value

B. Use a fixed 50 mil width for all internal traces carrying above 4A

C. Use the internal layer chart and adjust for copper thickness and temperature rise

D. Calculate width by dividing current by temperature rise

Solution

1. Step 1: Identify correct IPC-2152 chart for internal layers

   Internal layers have different heat dissipation, so use the internal layer chart for accurate width.

2. Step 2: Adjust for copper thickness and temperature rise

   Consider copper thickness and max temperature rise to find precise trace width for 5A current.

3. Final Answer:

   Use the internal layer chart and adjust for copper thickness and temperature rise -> Option C

4. Quick Check:

   Internal layer needs specific chart and adjustments [OK]

Hint: Use internal layer IPC-2152 chart with copper and temp adjustments [OK]

Common Mistakes:

• Using external layer data for internal traces
• Applying fixed widths without calculation
• Ignoring copper thickness effect