You need detailed drawing to produce membrane switch. Here is a comprehensive guide to the essential steps involved in creating a complete and accurate membrane switch drawing.

1. Graphic Overlay

The first stage of the design process focuses on the user's experience and the visual aesthetics of the switch. This involves:

Key Layout and Functionality

Please determine the number of buttons, their arrangement, and the function of each. Consider user ergonomics and the logical flow of operations. The spacing between keys is critical; a minimum of 0.1 inches is typically recommended to ensure proper switch function and to accommodate the underlying circuitry.

Graphic Design and Artwork

You create the visual design of the overlay, including colors, logos, and button iconography. Most manufacturers accept vector-based file formats like Adobe Illustrator (.ai) or CorelDRAW (.cdr).

Specify colors using a standardized system like the Pantone Matching System (PMS) to ensure color accuracy. If using digital printing, be aware that PMS color matching might not be exact and may require a sample for approval.

Windows and Lighting

Check if the design requires transparent windows for displays like LCDs or LEDs. Specify the size, location, and desired finish of these windows (e.g., clear, anti-glare). If backlighting is needed, determine the type—such as LEDs for individual key illumination or electroluminescent (EL) panels for uniform backlighting—and indicate the areas to be lit.

2. Electrical Design

With the user interface defined, the next step is to design the underlying electrical circuit that will make the switch functional.

Circuit Schematic

The two primary types of circuit layouts are matrix and common bus. A matrix layout uses a grid of rows and columns (X-Y) and is ideal for keyboards with many keys as it reduces the number of required tail connections. A common bus layout connects one side of all switches to a single common line (ground), which is simpler for designs with fewer keys.

Circuit Tail and Connector

The flexible tail is the ribbon-like extension that connects the membrane switch to the main printed circuit board (PCB). You must specify the tail's length, its exit location from the switch assembly, and the type of connector it will use.

Common connector types include ZIF (Zero Insertion Force) and locking connectors. The pinout of the tail, which details the function of each conductor, must be clearly defined in the drawing.

3. Raw Materials & Construction

The longevity and performance of a membrane switch are heavily dependent on the materials used in its construction. The drawing must detail the material for each layer.

Overlay Material

Polyester (PET) is a popular choice due to its durability and resistance to chemicals and fatigue, often rated for millions of actuations. Polycarbonate (PC) is another option, though typically with a lower actuation life. The thickness and surface finish (e.g., gloss, matte, textured) of the overlay should be specified.

Adhesives

High-quality adhesives, often from manufacturers like 3M, are crucial for bonding the various layers of the switch together and for mounting the final assembly to the product enclosure. The specific adhesive type should be chosen based on the application's environmental conditions and the surface it will be mounted on.

Circuitry Substrate

The circuit layers are typically printed on a flexible polyester substrate using conductive silver or carbon inks. For more complex designs with tight trace spacing, etched copper on a polyimide film (Kapton) can be used.

4. Mechanical & Functional Details

The last step before completing the drawing is to define the physical and functional characteristics of the switch.

Tactile Feedback

Decide whether the buttons should have a tactile "snap" when pressed. This is often achieved by incorporating metal or polyester domes under the keys. The actuation force (the pressure required to close the switch) should be specified, as it can be customized.

Embossing

To enhance the user's ability to locate keys by feel, the overlay can be embossed. Common styles include pillow embossing (raising the entire key area) and rim embossing (raising only the border of the key).

Tolerances

The drawing must include dimensional tolerances for all critical features, such as the overall size, cutout locations, and key-to-key spacing. Standard tolerances are typically around +/- 0.010 inches, but tighter tolerances may be required for specific applications.

By systematically addressing these key design stages and meticulously documenting every detail in the final drawing, you can ensure a smooth transition from design to production, resulting in a high-quality, reliable membrane switch that meets all your specifications.