Impedance-controlled traces in PCB Design - Cell-by-Cell Formula Trace

Sample Data

Sample PCB trace parameters: width, dielectric height, dielectric constant, and impedance to be calculated.

Cell	Value
A1	Trace Width (mil)
B1	Dielectric Height (mil)
C1	Dielectric Constant
D1	Impedance (Ohms)
A2	10
B2	5
C2	4.5
D2
A3	15
B3	5
C3	4.5
D3
A4	20
B4	5
C4	4.5
D4

Formula Trace

Impedance = (87 / sqrt(Dielectric Constant + 1.41)) * ln(5.98 * Dielectric Height / (0.8 * Trace Width + Thickness))

Step 1: sqrt(C2 + 1.41)

Step 2: 87 / 2.43

Step 3: 0.8 * A2 + Thickness

Step 4: 5.98 * B2 / 9.4

Step 5: ln(3.18)

Step 6: 35.8 * 1.16

Cell Reference Map

    A       B       C       D
1 |Width |Height |Diel.  |Imp.  |
2 | 10   |  5    | 4.5   |      |
3 | 15   |  5    | 4.5   |      |
4 | 20   |  5    | 4.5   |      |

Arrows: D2 depends on A2, B2, C2, and Thickness (constant 1.4)

Impedance in D2 is calculated using trace width (A2), dielectric height (B2), dielectric constant (C2), and a fixed thickness value.

Result

    A       B       C       D
1 |Width |Height |Diel.  |Imp.  |
2 | 10   |  5    | 4.5   |41.53 |
3 | 15   |  5    | 4.5   |      |
4 | 20   |  5    | 4.5   |      |

The impedance for the first trace (row 2) is calculated as 41.53 Ohms using the formula.

Sheet Trace Quiz - 3 Questions

What is the result of sqrt(Dielectric Constant + 1.41) for C2=4.5?

A 2.43

B 3.91

C 1.41

D 4.5

Key Result

Impedance = (87 / sqrt(Dielectric Constant + 1.41)) * ln(5.98 * Dielectric Height / (0.8 * Trace Width + Thickness))