Silicone Keypad Finishes & Design Options

Positive Tactile Feel

  • Many designers seek a stronger tactile response than traditional carbon pill keypads. Keyflex silicone keypads deliver this through:
  • Tact switch integration: Mounted on the PCB, with the stem seated behind the silicone key.
  • Snap dome switches: A cost‑effective alternative to tact switches, using metal domes on adhesive layers. This reduces PCB costs and allows simple peel‑and‑stick installation.
  • Enhanced design flexibility: Force and feedback are not limited to the diaphragm, enabling broader design scope.

Laser Etched Silicone Keypads

  • Laser etched keypads combine durability with precision:
  • Start with translucent coloured silicone printed with the keytop design.
  • Apply a protective silicone paint layer, cured for stability.
  • Use computer‑controlled lasers to etch away paint, revealing translucent ink.
  • Produce high‑quality, repeatable characters that remain legible and consistent across multiple keypads.
  • Ideal for backlit keypads, as etched areas transmit light while blocking excess spillage.

Multi‑Coloured Keypads

  • Multiple colours within one keypad using Pantone or RAL matching systems.
  • Client colour swatches can be matched.
  • Colour applied directly to the key reduces cost and prevents ink wear.

Wear‑Resistant Coated Keypads

  • Protective coating applied after curing safeguards printing and spraying.
  • Recommended for high‑usage or harsh environments to prevent ink wear.

Epoxy Coated Silicone Keypads

  • Clear epoxy displays printed ink, or can be sprayed and laser etched.
  • Available in gloss or matte finishes.

Plastic Keycap Options

  • For applications requiring plastic keycaps, options include:
  • Multiple colours and shapes
  • Printed or engraved key information
  • Clear keycaps for interchangeable labels, offering maximum versatility
  • Actuation force and tactile feedback can be tailored to meet user requirements, ensuring the keys deliver the desired “feel” for everyday use.

Thermoformed Keypads

  • Made from polycarbonate or polyester, rear‑printed and thermoformed.
  • Ideal for compact handheld devices requiring closely pitched keys.

Construction & Design Features

  • Individual Key Design
  • Key styles vary by function and aesthetics. Options include legends, backlighting, and custom shapes.

Snap Ratio

  • Directly linked to tactile feel.
  • Recommended ratio: 40–60% for balance between tactile response and lifespan.

Tactile Feedback

  • Membrane shape and size can be tailored.
  • Typical recommendation: 125–150 grams actuation force with 40–60% snap ratio.

Switch Life

  • Influenced by membrane style and silicone durometer.
  • Higher durometer, increased force, or longer stroke reduces lifespan.

Contact Solutions

  • Keyflex offers three types of contacts:
  • Carbon pill contacts: Most common, >10 million operations,
  • Circular (1.5–10mm diameter, 0.4–0.6mm thickness) or oval shapes available.
PCB Design Considerations
  • Rubber keymats are reliable, but PCB design must account for environmental conditions to ensure long‑term performance.

Mechanical Drawings & Quotation

  • Preferred quoting method: 3D drawings (STP or IGES).
    Alternatively, provide 2D drawings or sketches with details such as:
  • Overall keypad size & base thickness
  • Keytop dimensions & heights
  • Contact size
  • Mounting hole & boss details
  • Keypad/switch colours
  • Stroke/travel & actuation force
  • Snap ratio & electrical specs
  • Material specifications
  • Graphic colours & artwork
General Specifications of Silicone Keypads Operating & Performance Characteristics
  • Operating Temperature: –15°C to +50°C
  • Storage Temperature: –30°C to +70°C
  • Operating Force: 50–350 grams
  • Cycle Life: 300,000 to 30 million operations
  • Contact Resistance: < 100 ohms at 5mA @ 12VDC
  • Contact Rating: 5mA @ 12VDC
  • Contact Bounce: < 12 milliseconds
  • Insulation Resistance: > 10¹² ohms @ 500VDC
  • Break Voltage: > 25–30 KV/mm
  • Key Options: Colour, size, shape, tactile feedback, and print colour available

Conductive Rubber Properties

  • Specific Gravity: 1.06 – 1.18
  • Hardness (Shore A): 60 – 65
  • Tensile Strength: 65 kg/cm
  • Elongation: 300%
  • Compression Set: 15 – 25%
  • Volume Resistivity: 4 ohm‑cm

Insulative Rubber Properties

  • Specific Gravity: 1.10 – 1.40
  • Hardness (Shore A): 35 – 80
  • Tensile Strength: 50 – 80 kg/cm
  • Elongation: 400%
  • Compression Set: 18 – 20%

Volume Resistivity:

  • Room Temperature: 2 × 10¹⁴ ohm‑cm
  • After 24 Hours @ 150°C: 3 × 10¹⁴ ohm‑cm
Standard Conductive PIL Sizes
  • Conductive PILs can be produced to almost any design, including centre‑removed PILs for backlighting with LEDs mounted under the switch centre.

Dimensional Guidelines

  • Minimum Radius: 0.25–0.5 mm depending on design
  • Minimum Diameter: 1.5–3.0 mm
  • Plastic Moulding:
    • If H < 7 mm → minimum radius 0.5 mm
    • If H > 7 mm and < 10 mm → minimum radius 0.9 mm
  • Wall Thickness: Minimum 0.2 mm, typical 0.15 mm

Typical Tolerances (mm)

  • Normal:
    • L < 10 → ±0.1
    • L 10–20 → ±0.15
    • L 20–30 → ±0.20
    • L 30–50 → ±0.25
    • L 50–100 → ±0.50
    • L > 100 → ±1.0%

Critical:

  • ±0.05 to ±0.5% depending on length
Standard Conductive PIL Dimensions
  • Conductive PILs can be manufactured in virtually any design, including centre-cut configurations for LED backlighting beneath the switch centre.

Dimension Guidelines

Minimum Radius: 0.25–0.5 mm (Based on Design Requirements)

Minimum Diameter: 1.5–3.0 mm

Plastic Moulding Guidelines:
If H < 7 mm → Recommended Minimum Radius: 0.5 mm
If H > 7 mm and < 10 mm → Recommended Minimum Radius: 0.9 mm

Wall Thickness Range:
Minimum Thickness: 0.2 mm
Typical Thickness: 0.15 mm

Typical Application Specifications

Silicone Keypad Tooling & Manufacturing

Precision Compression Moulding

All Keyflex conductive rubber keypads and switches are manufactured using compression moulding in high‑precision carbon steel tools. We use non‑toxic, highly elastic silicone rubber compounds to ensure durability and safety.

  • Process overview: Compression moulds consist of a bottom tool and a top tool (similar to a waffle iron).
  • Cycle time: Typical cycle time for silicone keypads is 5–10 minutes, longer than plastic moulding due to material properties.
  • Post‑curing: After moulding, keypads undergo a two‑hour post‑curing cycle at 200°C. This step is critical to:
  • Remove catalyst and oxidant residue
  • Stabilize silicone’s physical properties
  • Enhance thermal stability for long‑term performance

Tool Cavities

  • Keyflex tooling can be designed with single or multiple cavities:
  • Single cavity tools: Lower upfront cost, suitable for small production runs.
  • Multiple cavity tools: Higher tooling cost but reduced production cost per keypad.
  • High‑volume production: Moulds with up to 100 cavities are possible depending on design requirements.

Tool Modification Considerations

  • Modifying compression moulds requires careful planning:
  • Steel removal: Existing moulds can be modified by cutting away steel, effectively adding material to the part.
  • Steel addition: Adding steel inserts is highly difficult and not recommended.
  • Design importance: Initial part design must account for potential modifications to avoid costly tooling changes.