Trace width calculator usage in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This data represents inputs for a PCB trace width calculator: current in amperes, allowed temperature rise in Celsius, copper thickness in ounces, and the output trace width in mils (thousandths of an inch).

Cell	Value
A1	Current (A)
B1	Temperature Rise (°C)
C1	Copper Thickness (oz)
D1	Trace Width (mil)
A2	3
B2	20
C2	1
D2

Formula Trace

D2 = 0.048 * (A2 ^ 0.44) * (B2 ^ 0.725) / (C2 ^ 0.725)

Step 1: A2 ^ 0.44

Step 2: B2 ^ 0.725

Step 3: C2 ^ 0.725

Step 4: 0.048 * 1.681 * 8.132 / 1

Step 5: D2 = 0.656

Cell Reference Map

    A      B      C      D
1 |Current|Temp   |Copper |Trace 
  |(A)    |Rise   |Thickness|Width 
2 |  3    |  20   |   1    |  ?   

Arrows: D2 depends on A2, B2, C2

Cells A2, B2, and C2 provide inputs for the formula calculating D2, the trace width.

Result

    A      B      C      D
1 |Current|Temp   |Copper |Trace 
  |(A)    |Rise   |Thickness|Width 
2 |  3    |  20   |   1    | 0.656

The calculated trace width in cell D2 is 0.656 mil, based on the inputs.

Sheet Trace Quiz - 3 Questions

What is the value of 3 raised to the power 0.44 in the calculation?

A 3.000

B 0.44

C 1.681

D 2.000

Key Result

Trace width = 0.048 * (Current ^ 0.44) * (Temperature Rise ^ 0.725) / (Copper Thickness ^ 0.725)

Practice

1. What is the main purpose of using a trace width calculator in PCB design?

easy

A. To calculate the length of the PCB trace

B. To determine the correct width of a PCB trace based on current and temperature

C. To find the number of layers in a PCB

D. To measure the thickness of the PCB substrate

Solution

1. Step 1: Understand the function of a trace width calculator

   A trace width calculator helps designers find the right width for PCB traces to safely carry electrical current without overheating.

2. Step 2: Identify the key inputs and outputs

   The calculator uses inputs like current, temperature rise, and copper thickness to output the correct trace width.

3. Final Answer:

   To determine the correct width of a PCB trace based on current and temperature -> Option B

4. Quick Check:

   Trace width calculator = Correct trace width [OK]

Hint: Trace width calculator finds safe trace width for current [OK]

Common Mistakes:

• Confusing trace width with trace length
• Thinking it calculates PCB layers
• Assuming it measures substrate thickness

2. Which of the following inputs is NOT typically required by a trace width calculator?

easy

A. Current flowing through the trace

B. Temperature rise allowed

C. Number of PCB layers

D. Copper thickness

Solution

1. Step 1: List typical inputs for trace width calculation

   Common inputs are current, temperature rise, and copper thickness because they affect trace heating and resistance.

2. Step 2: Identify the irrelevant input

   The number of PCB layers does not affect the width calculation of a single trace.

3. Final Answer:

   Number of PCB layers -> Option C

4. Quick Check:

   Trace width inputs exclude PCB layers [OK]

Hint: Trace width calculator ignores PCB layer count [OK]

Common Mistakes:

• Including PCB layers as input
• Confusing copper thickness with substrate thickness
• Ignoring temperature rise input

3. A trace width calculator is given these inputs: current = 3A, temperature rise = 10°C, copper thickness = 35µm. What is the expected effect on the calculated trace width if the temperature rise allowed is increased to 20°C?

medium

A. The calculator will return an error

B. The required trace width will increase

C. The required trace width will stay the same

D. The required trace width will decrease

Solution

1. Step 1: Understand temperature rise effect on trace width

   Allowing a higher temperature rise means the trace can safely run hotter, so less width is needed to carry the same current.

2. Step 2: Analyze the change from 10°C to 20°C

   Doubling the allowed temperature rise reduces the required trace width because the trace can dissipate heat more.

3. Final Answer:

   The required trace width will decrease -> Option D

4. Quick Check:

   Higher temp rise allowed = smaller trace width [OK]

Hint: More temp rise allowed means narrower trace [OK]

Common Mistakes:

• Assuming width increases with temperature rise
• Thinking width stays constant
• Expecting an error from input change

4. You used a trace width calculator but got an unusually small width result for a 5A current. Which of the following is the most likely error?

medium

A. Current input was accidentally entered as 0.5A

B. Temperature rise allowed was set too high

C. Input copper thickness was set too low

D. Trace length was entered instead of current

Solution

1. Step 1: Understand how current affects trace width

   Lower current input reduces required trace width because less heat is generated.

2. Step 2: Identify input error causing small width

   Entering 0.5A instead of 5A drastically lowers the calculated width, causing an unusually small result.

3. Final Answer:

   Current input was accidentally entered as 0.5A -> Option A

4. Quick Check:

   Lower current input = smaller width [OK]

Hint: Check current input carefully for typos [OK]

Common Mistakes:

• Confusing copper thickness effect
• Ignoring current input errors
• Mixing trace length with current

5. You need to design a PCB trace to carry 10A with a maximum temperature rise of 15°C and copper thickness of 70µm. If the calculator suggests a trace width of 3mm, but your PCB manufacturer only supports widths up to 2mm, what is the best solution?

hard

A. Use multiple parallel traces to share current

B. Ignore the width limit and use 3mm anyway

C. Increase temperature rise allowed to 30°C without consulting specs

D. Increase copper thickness or reduce current to meet width limits

Solution

1. Step 1: Understand the constraint and requirement

   The required width (3mm) exceeds manufacturer limit (2mm), so direct use is not possible.

2. Step 2: Evaluate practical solutions

   Increasing copper thickness or reducing current may not be feasible; ignoring limits or raising temperature without specs risks failure.

3. Step 3: Use multiple parallel traces

   Splitting current across parallel traces each within width limits safely meets current and temperature requirements.

4. Final Answer:

   Use multiple parallel traces to share current -> Option A

5. Quick Check:

   Parallel traces solve width limit issues [OK]

Hint: Split current with parallel traces if width limit exceeded [OK]

Common Mistakes:

• Ignoring manufacturer width limits
• Raising temperature rise without specs
• Assuming copper thickness can always be increased