AN66308 - CY8CMBR2044 CapSense® Design Guide, Doc. No. 001-66308 Rev. *F
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4. Electrical and Mechanical Design
Considerations
When designing a capacitive touch sense technology into your application it is crucial to keep in mind that the
CapSense device exists within a larger framework. Careful attention to every detail, including PCB layout, user
interface, and end-user operating environment, leads to robust and reliable system performance. For in-depth
information, refer to
Overlay Selection
Equation 1 was presented for finger capacitance
Where:
ε
0
= Free space permittivity
ε
r
= Dielectric constant of overlay
A = Area of finger and sensor pad overlap
D = Overlay thickness
To increase the CapSense signal strength, choose an overlay material with a higher dielectric constant, decrease the
overlay thickness, and increase the button diameter. The
helps you to design a robust and reliable
CY8CMBR2044 solution, as discussed in the chapter
Table 4-1. Overlay Material Dielectric Strength
Material
Breakdown Voltage (V/mm)
Min. Overlay Thickness at 12 kV (mm)
Air
1200
–2800
10
Wood
– dry
3900
3
Glass
– common
7900
1.5
Glass
– Borosilicate (Pyrex
®)
)
13,000
0.9
PMMA Plastic (Plexiglas
®
)
13,000
0.9
ABS
16,000
0.8
Polycarbonate (Lexan
®
)
16,000
0.8
Formica
18,000
0.7
FR-4
28,000
0.4
PET Film
– (Mylar
®
)
280,000
0.04
Polymide film
– (Kapton
®
)
290,000
0.04
Conductive material cannot be used as an overlay because it interferes with the electric field pattern. Therefore, do
not use paint containing metal particles.
