Client Background

Our client is a fast-growing Chinese electric vehicle manufacturer (EV OEM) that launched its first mass-market model in 2023 and has since delivered over 80,000 units. For their second-generation model, the design team wanted to replace the single-piece capacitive touch panel used in the first generation for HVAC and infotainment controls with a hybrid approach — a physical silicone keypad cluster with tactile switches for the primary driving controls (temperature, fan speed, defrost, driving mode), complemented by a central touch display for secondary functions.

The client's research showed that drivers strongly preferred physical buttons for frequently used climate and driving controls — touch screens alone caused higher distraction scores in their internal user studies. SanTeXing was brought in at the concept phase to develop the silicone keypad assembly in parallel with the vehicle's interior development.

The Challenge

Automotive interior components face extreme requirements that go far beyond consumer-grade electronics:

• Temperature range: The dashboard can reach 85°C in summer cabin soak conditions and drop to -40°C in cold climate testing. Standard silicone rubber compounds harden or soften unacceptably across this range.
• Abrasion and wear: Keypad legends must remain legible after 1 million actuations. The surface texture must resist wear from fingernails, rings, and cleaning products over 10+ years of vehicle life.
• UV and ozone resistance: Dashboard components are exposed to UV radiation through the windshield. Without proper formulation, silicone rubber can degrade, discolor, or develop surface cracks.
• Tactile consistency: Actuation force must remain within ±15% of nominal across the entire operating temperature range. Drivers should feel exactly the same click at -20°C as at 40°C.
• Backlighting: RGB LED backlighting with uniform illumination behind each keycap, with no light bleed between adjacent keys, compliant with interior lighting regulations.
• Regulatory: The assembly must pass ECE R118 (fire resistance), RoHS, REACH, and OEM-specific chemical resistance tests (sunscreen, hand cream, coffee, coffee creamer).

Our Solution

SanTeXing engineered a P+R (Plastic + Rubber) composite keypad assembly combining a silicone rubber keypad base with molded plastic keycaps, supported by a stainless steel backplate and PCB-mounted tactile switches:

1. Silicone Rubber Formulation

We developed a custom 60 ± 2 Shore A silicone rubber compound (LSR, liquid silicone rubber) with proprietary UV stabilizers and a hydrophobic surface treatment. The formulation maintains working hardness between 58 and 62 Shore A across the -40°C to +105°C range — a critical performance metric verified through 500-hour thermal cycling tests. The high tear strength (≥25 kN/m) prevents edge tearing during assembly and long-term use.

2. Composite Keycap Design

Each key uses a two-shot molded PC/ABS keycap bonded to the silicone base during the vulcanization process. The keycap features a hard, wear-resistant top surface with UV-cured clear coating and laser-etched legends filled with translucent silicone for backlighting. The underside incorporates a precisely shaped plunger that contacts the tactile switch on the PCB. Keycap hardness is 85 Shore D — resistant to fingernail scratches and cosmetic wear.

3. RGB Backlighting Integration

We designed light guide channels directly into the silicone base layer beneath each keycap. SMT RGB LEDs on the main PCB shine through these channels, with each key's legend illuminated independently. The silicone acts as a built-in light diffuser, eliminating hot spots without a separate light guide plate. Light bleed between adjacent keys is less than 2 lux at 5 mm spacing, verified with a photometer.

4. Tactile Switch Integration

Each key actuates a surface-mount tactile switch (6 × 6 mm, 250 gf nominal, 1 million cycles rated) soldered to the PCB. The silicone keypad's plunger geometry was optimized through FEA simulation to deliver a linear force-displacement curve that, combined with the tactile switch's snap ratio (≥45%), produces a crisp tactile event. Total key travel is 1.2 ± 0.15 mm.

Results

The keypad assembly was validated through an 18-week automotive-grade qualification program:

• AEC-Q100 qualified (Grade 2: -40°C to +105°C operating range).
• Thermal shock (500 cycles, -40°C to +105°C, 30-minute dwell): zero cosmetic or functional defects.
• UV weathering (1000 hours, ISO 4892-2): ΔE ≤ 0.5 color shift, no cracking or tackiness.
• Abrasion testing (100,000 cycles, Taber CS-10F wheels, 250 g load): legend clarity retained with no breakthrough of surface coating.
• Assembly yield exceeded 98% in the first production month, improving to 99.4% by month three.
• The keypad assembly has been in production since Q3 2025, fitted to approximately 35,000 vehicles with a field return rate of 0.06%.

Related Products

This project showcased SanTeXing's custom silicone rubber keypad manufacturing capabilities. See also our automotive membrane switch solutions and FPC for automotive electronics.