Thermal relief for through-hole pads in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This table shows through-hole pad properties including pad diameter, copper area connected, thermal relief width, and number of thermal relief spokes.

Cell	Value
A1	Pad ID
B1	Pad Diameter (mm)
C1	Copper Area Connected (mm²)
D1	Thermal Relief Width (mm)
E1	Thermal Relief Spokes
A2	P1
B2	1.2
C2	50
D2	0.3
E2	4
A3	P2
B3	1.0
C3	30
D3	0.25
E3	3
A4	P3
B4	1.5
C4	70
D4	0.35
E4	5

Formula Trace

Thermal Relief Area = (Pad Area) - (Spokes Area) Where: Pad Area = π * (Pad Diameter / 2)^2 Spokes Area = Number of Spokes * (Thermal Relief Width * Pad Diameter)

Step 1: Pad Area for P1 = π * (1.2 / 2)^2

Step 2: Spokes Area for P1 = 4 * (0.3 * 1.2)

Step 3: Thermal Relief Area for P1 = 1.130976 - 1.44

Step 4: Pad Area for P2 = π * (1.0 / 2)^2

Step 5: Spokes Area for P2 = 3 * (0.25 * 1.0)

Step 6: Thermal Relief Area for P2 = 0.785398 - 0.75

Step 7: Pad Area for P3 = π * (1.5 / 2)^2

Step 8: Spokes Area for P3 = 5 * (0.35 * 1.5)

Step 9: Thermal Relief Area for P3 = 1.767145 - 2.625

Cell Reference Map

     A       B       C       D       E
  +-------+-------+-------+-------+-------+
1 | PadID |  Dia  |  CuA  |  TRW  | Spokes|
  +-------+-------+-------+-------+-------+
2 |  P1   |  1.2  |  50   |  0.3  |   4   |
  +-------+-------+-------+-------+-------+
3 |  P2   |  1.0  |  30   | 0.25  |   3   |
  +-------+-------+-------+-------+-------+
4 |  P3   |  1.5  |  70   | 0.35  |   5   |
  +-------+-------+-------+-------+-------+

References used:
- Pad Diameter (B2:B4)
- Thermal Relief Width (D2:D4)
- Thermal Relief Spokes (E2:E4)

This map shows the cells used in the thermal relief area calculation: pad diameter, thermal relief width, and number of spokes for each pad.

Result

     A       B       C       D       E       F
  +-------+-------+-------+-------+-------+---------+
1 | PadID |  Dia  |  CuA  |  TRW  | Spokes| TR Area |
  +-------+-------+-------+-------+-------+---------+
2 |  P1   |  1.2  |  50   |  0.3  |   4   | -0.309  |
  +-------+-------+-------+-------+-------+---------+
3 |  P2   |  1.0  |  30   | 0.25  |   3   |  0.035  |
  +-------+-------+-------+-------+-------+---------+
4 |  P3   |  1.5  |  70   | 0.35  |   5   | -0.858  |
  +-------+-------+-------+-------+-------+---------+

Column F shows the calculated thermal relief area for each pad.

The final result column (F) shows the thermal relief area for each pad, calculated by subtracting the spokes area from the pad area.

Sheet Trace Quiz - 3 Questions

What is the pad area for pad P1?

A 1.44

B 1.130976

C 0.785398

D 2.625

Key Result

Thermal relief area = pad circular area minus total area of thermal relief spokes calculated as spokes count times width times diameter.