Matrix Design And Metal Dome Switches For Tactile Membrane Switch Keypads In OEM Designs

It appears you're asking about the design and use of metal dome switches in tactile membrane switch keypads, particularly in OEM (Original Equipment Manufacturer) designs. Here's a breakdown of what you should consider:

1. Function and Components

• Membrane Switch: A membrane switch is a user interface component used to create a man/machine interface [1]. It's an effective way to interface with a product while retaining the benefits of a printed overlay [1].
• It consists of a printed circuit layer, a front overlay, and a rear adhesive [1].
• Metal Dome: A metal dome is a crucial part of the switch [2]. It's made of stainless steel and sometimes referred to as a tactile metal dome [2].
• The metal dome is located on the conductive part of the PCB (printed circuit board) within the silicone membrane keypad [2].
• How it Works: When you press the metal dome, the center collapses and contacts the circuit on the PCB, completing the electrical connection and sending a signal [3][4]. The metal dome provides tactile and audible feedback [3][5].

2. Advantages of Metal Domes

• Tactile Feedback: Metal domes provide a tactile response when pressed, confirming that the input has been registered [4][5]. This is especially important where accuracy is critical, such as in medical or scientific equipment [4].
• Durability: Metal domes are made from high-quality materials like stainless steel, which can withstand repeated use without losing their tactile properties [4]. They are ideal for applications requiring frequent or heavy use, like industrial control panels or medical devices [4].
• Long Lifespan: Metal domes typically have a longer lifespan (1,000,000+ actuations) than common silicone rubber keypads [2][5]. Some are rated for up to five million cycles or more [5].
• Easy Assembly: Using a metal dome array reduces production time because all domes can be placed on the PCB simultaneously [2].
• Hygienic: Dome switches can be designed with a sealed construction, making them suitable for cleanroom, laboratory, and medical environments where resistance to contaminants and easy sterilization are needed [5].

3. Design Considerations

• Actuation Force: This is the amount of pressure required to activate the dome [3]. It can be customized based on user preference and the application [3].
• Typical actuation forces for tactile switches range from 3 to 25 oz [6].
• Light force is suitable for smaller, denser keypads [6].
• Medium force is good for most applications, including medical devices [6].
• Heavy force is best for applications where users may wear gloves, such as in industrial settings [6].
• Material Selection: Choose durable materials resistant to environmental factors and repeated use [7]. Common materials include polyester and polycarbonate [1][8].
• Environmental Factors: Consider the environmental conditions the switch will be exposed to, such as temperature and humidity [7].
• Tactile Feedback: If the design includes raised buttons or embossed keys, make sure they are designed for ergonomic use and can withstand repeated presses [1][7].
• Circuit Design: Aim to reduce resistance and signal interference while maximizing the arrangement of conductive traces for reliable operation [8].
• Connector Compatibility: Ensure compatibility with commonly used connectors like ZIF (Zero Insertion Force) connectors for reliable connections and easy assembly [8].

4. Metal Dome Characteristics

• Size: Dome sizes range from 6mm up to 20mm. The size of the keys on the membrane switch will determine the appropriate dome size [9].
• Shape: Common shapes include round, four-legged, triangle, and oblong [3][9]. Special shapes can be custom-made [2].
• Actuation Force: Ranges from 40g up to 2250g [9].
• Dimple: Some domes have a dimple in the center to improve electrical characteristics and reduce contact bounce [9].

5. Keypad Matrix Design

• Membrane switches can be designed using a common bus or matrix layout [1].
• A matrix array connects the keys in a grid, reducing the number of pins needed [10].

6. Additional Considerations

• Backlighting: Consider backlighting to increase visibility in low-light conditions [8][11]. This can be achieved with LEDs [8][11].
• EMI/RFI Shielding: Consider shielding options to minimize electromagnetic and radio frequency interference [1][11].
• Adhesives: Select appropriate adhesives to bond the layers of the membrane switch together, considering the product's lifespan and the environment it will be used in [1][8].

Membrane Switch Specification:

1)Material---for front or face overlay

Polyester

1.Highly versatile for embossing 2.Highly resistant to chemicals

3.Better durability 4.For internal and external use

Polycarbonate

1.Wide range of surface finishes and thicknesses

2.More cost-effective 3.For internal and external use

2) Embossing--rim embossing pillow embossing dim embpssing

Graphic overlays can be embossed in order to insert domes (tactile), leave space for mechanical keys and provide tactile indications Pedestal embossing

3)Windows ----for display function

1. print colors windows

2.transparent finishes windows

4)Keys/buttons

Tactile keys---with metal dome or poly dome

Non-tactile--silver printing spot

5) Embeded LEDs-

miniature LED, LED colors:white, yellow, orange, green, red, etc.

6)Cable

is an extension of the printed circuit and is used to communicate with your device

7)Types of connector

1.Zero insertion force (ZIF) connector; 2.Female connector; 3.male connector

8) EMI / RFI / ESD Shielding

use an aluminum foil shielding / a clear ITO electrical conductive polyester

9) Adhesive ----mostly used are 3M-double-side glue

10)Backplate---in aluminum, polycarbonate or acrylic

Membrane switch Performance Index:

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