Hengchuanqi Fully Automatic Screen Printing Machine: Key Precautions for Membrane Switch Screen Prin

As a touch-sensitive electronic control component, membrane switches are widely used in home appliances, medical devices, and industrial controls. Their surface circuits, key markings, and insulating layers all rely on screen printing. Due to the flexible, smooth nature of film substrates (e.g., PET, PC), the process must balance adhesion, precision, and durability. Core precautions are as follows: 

 1. Substrate Pretreatment: Lay a Solid Adhesion Foundation 

Common substrates are PET (high-temperature/aging resistance) and PC (good flexibility, low cost), with surface tension directly affecting ink adhesion. New substrates must first test surface tension (≥38dyn/cm); if insufficient, corona treatment is required—high-voltage discharge breaks surface molecular structures to boost tension to 40-45dyn/cm. Printing must be completed within 24 hours post-treatment to avoid natural tension decay. 

Cleaning must prevent surface scratches: remove dust with compressed air, then wipe gently with 99% isopropyl alcohol-dampened lint-free cloths (unidirectional wiping to avoid electrostatic recontamination). Protective films on substrates should be peeled off within 1 hour before printing to prevent residual adhesive contamination. 

 2. Screen & Ink: Matching Film Characteristics 

Screens must suit fine patterns (e.g., 0.1mm conductive lines): use 300-420 mesh stainless steel mesh with 10-15μm photoresist thickness to ensure jagged-free edges. Aluminum frames are preferred to avoid deformation-induced pattern offset; maintain 1-3mm screen-to-substrate distance (off-contact) to prevent ink sticking during separation. 

Ink selection must align with functional requirements: 

- Conductive circuits: silver paste ink (silver content ≥70%), with post-curing resistance <0.05Ω/□ (at 20μm thickness). 

- Insulating layers: UV-curable insulating ink, with light transmittance ≥90% and breakdown voltage ≥10kV/mm. 

- Key markings: scratch-resistant PU ink, with pencil hardness ≥3H and no peeling after 5,000 friction tests (500g load). 

Critical notes: PET substrates prohibit ketone-based solvents (to avoid chemical corrosion/cracking); PC substrates require low-temperature curing (≤80℃) to prevent deformation. 

 3. Printing Parameters: Micron-Level Precision Control 

Squeegee configuration is key: use 70-80 Shore A polyurethane squeegees with 60° blade angles (acute angles for sharp lines, obtuse angles for large-area filling). Printing pressure must be 2-5kgf—excess pressure causes screen deformation/ghosting; insufficient pressure leads to incomplete ink transfer/line breaks. 

Squeegee speed: 30-60mm/s. Increase speed for PET (reduce ink penetration time); decrease for PC (avoid pattern stretching due to softness). Maintain constant ambient conditions: 23±2℃, 50±5% humidity—low humidity causes static/ink splattering; high humidity slows drying/sticks screens. 

 4. Curing Process: Balancing Performance & Substrate Tolerance 

Curing parameters vary by ink type: 

- Silver paste ink: infrared drying with three-stage heating (60℃/10min→80℃/20min→120℃/30min) to prevent silver particle oxidation from rapid high-temperature exposure. 

- UV ink: medium-pressure mercury lamp (80-120W/cm) with curing speed 10-15m/min, ensuring UV energy 800-1200mJ/cm² (avoids poor weather resistance from incomplete curing). 

- Solvent-based ink: air leveling for 5-10min, then oven drying at 60℃ for 30min—prohibit forced air drying (causes surface skinning/residual solvents). 

Post-curing, cool to room temperature (≈20min) before further processing to prevent pattern cracking from thermal expansion/contraction. 

 5. Quality Control: Focus on Core Indicators 

- Adhesion: 3M tape (Model 610) applied vertically, peeled rapidly 3 times—ink loss area <1%. 

- Electrical performance: conductive lines after 1,000 thermal shocks (-40℃/30min→85℃/30min) show resistance change rate ≤10%. 

- Chemical resistance: no discoloration/peeling after 24-hour immersion in 75% alcohol. 

- Dimensional accuracy: 2D image measurement shows line width tolerance ≤±0.03mm, position offset ≤±0.05mm. 

Pinholes indicate screen blockages or bubbles; jagged edges require new squeegees and reduced printing speed. 

 6. Special Scenario Handling 

For curved membrane switches (e.g., automotive center console buttons), use curved screen printers with screens bending synchronously with substrate curvature, ensuring uniform pressure distribution. For multi-layer membrane switches, each layer reserves 0.1mm alignment tolerance, with precise lamination via positioning holes (φ2.0±0.02mm). 

The core of membrane switch screen printing is "flexible adaptation"—taming the delicate nature of film materials while ensuring stable electronic functionality. Every detail, from substrate pretreatment to curing parameters, directly determines switch lifespan (typically ≥1 million presses). Only by deeply matching process parameters with material characteristics can the "responsive touch" experience be achieved.