adjacent trace capacitance (horizontal)

Question

I find a lot of online tools to calculate the capacitance between two traces (or a trace and a plane) on opposite pcb layers. One such tool can be found here: http://chemandy.com/calculators/rectangular-capacitor-calculator.htm

However, I would like to calculate the capacitance between adjacent traces on the pcb. Something like this:

Has anyone an idea how to do this?

EDIT :
Imagine the following example:

• Two tracks run parallel for 10 mm.
• Each track is 0.2 mm wide.
• The distance between both tracks is also 0.2 mm.
• Copper thickness is about 20 µm.
• Board thickness is 1.6 mm.
• PCB material is standard FR4.
• One track is signal, the other Gnd.
• There are no other tracks in the area, nor any (Gnd-) planes.

Answer 1

• This is determined by copper thickness, gap, dielectric constant, d and length and thus there is incremental C and L with resulting impedance , Zo for a coplanar microstrip and thus C can be computed from this. For Zo=50R it is about 3.3pF /" or 1.3pF/cm

• So compute Zo from a coplanar stripline calculator (complex) then compute C from Zo as shown here. This assumes other conductors are >10x further away. If not then you have a mesh of calculations ;)

• If you can't find a coplanar stripline tool, try this formula.

\$ C [pf/cm] = 0.12 * \dfrac{t}{w} + 0.09 * (1+d)*log_{10}(1 + \dfrac{2w}{g} + \dfrac{w}{g}^2)\$

• w = width of track [mm]
• t = thickness of track [um]
• d = dielectric constant ~ 4.2 FR4
• g = gap [mm]

hopefully, I got the units correct...you do the math on a 50R pair.

The second term dominates. Using k=3.5 (kapton), w=10 mm, s = 0.5 mm, t = 2 microns, the capacitance is 1.1 pf/cm

Reference https://www.physicsforums.com/threads/capacitance-of-coplaner-adjacent-plates.130876/

Answer 2

I use ATLC for this. You can also draw your own setup (with the correct colours) and have it solve that. http://atlc.sourceforge.net/