What are Conductive Contact in Rubber Keypads?

Conductive pill is the contact medium between the rubber keypad and PCB board. A typical silicone rubber keypad involves designing a flex key webbing around the perimeter of the button. When the key is pressed, the flex key webbing allows the center of the key to make contact with the circuit, then produces a tactile response for user.

In rubber keypads, there are typically two methods of making contact with the actual switch: dome switches or conductive pills. 

The basic raw material of conductive pills are typically manufactured from a silicone.

There are four prevalent conductive materials—carbon black, gold-coated, silver-coated, and nickel particles.

Carbon Black Particles (Conductive "Black Dots")

· ‌Composition

Amorphous carbon clusters (10-50μm) with sp⊃2; hybridized structures

· ‌Conductivity‌ 

10⊃2;–10⊃3; Ω·cm

· ‌Advantages‌

Cost-effective.

Stable contact resistance over 1 million cycles.

· ‌Limitations‌

Susceptible to arcing in high-voltage (>12V) applications.

15-25% resistance drift under 85°C/85% RH aging tests.

· ‌Application Example

The most common conductive way. Such as, TV remote controls, etc. Silicone rubber keypad for electronic products. 

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Smooth Surface Carbon Pill

Texture Surface Carbon Pill

Gold-Coated Particles(Conductive Glod Pills)

· ‌Structure‌

Polymer cores (30-80μm) with 0.2-0.5μm gold plating

· ‌Conductivity‌

5-20 mΩ·cm (Ohmic behavior)

· ‌Key Metrics‌

Contact resistance <100mΩ maintained after 10⁶ cycles

Corrosion resistance up to 200°C (ideal for automotive ECUs)

· ‌Trade-offs‌

Material cost higher than carbon

Requires pulse plating for uniform coverage

· ‌Application

Silicone rubber keypad for auto industry, medical device

Silver-Based Conductive Pills

· ‌Variants‌

Ag flakes (1-10μm): 1.6×10⁻⁶ Ω·cm (near-bulk sliver conductivity)

AgNW (nanowires): 80% transmittance at 10Ω/sq for transparent keypads

· ‌Failure Modes‌

Sulfur-induced tarnishing reduces conductivity by 40% in 500hr H₂S tests

Migration risk under >50% strain

· Application

Ag-PDMS composites enabling stretchable input devices.

Nickel Conductive Elements

· ‌Design‌: Electroless Ni-P coatings (3-8μm) on silicone cores

· ‌Performance‌

Initial resistivity: 50-100 μΩ·cm

20% resistance increase after 500 thermal cycles (-40°C↔125°C)

· ‌Cost-Benefit‌

Cheaper than gold pill

Limited to non-critical DC circuits <100mA

· ‌Industrial Application

White goods control panels with IP54 sealing.

Necessary tool for conductive rubber keypad.

How to produce Conductive Rubber Keyboard?