Key Considerations for Designing Keypad PCB Design

What is a Keypad PCB?

A keypad PCB is a circuit board that hosts the electronic components necessary for a keypad's operation. It serves as the foundation for connecting switches, microcontrollers, and other elements that facilitate user input. The design of a keypad PCB significantly influences its performance, reliability, and overall functionality.

Keypad circuit boards are widely used in everyday products, such as remote controls, car window buttons, and elevator buttons. They are inexpensive to produce and offer excellent conductivity and wear resistance. The keys are covered with conductive gold or carbon oil to prevent the copper surface from oxidizing in the air. Once assembled, a metal dome is placed over the key area. The metal dome is a metallic snap dome used in tactile switches and serves the function of conducting or breaking the circuit. When the dome is pressed down, it connects the intersecting keypad lines, and when released, the dome springs back, breaking the connection, thus enabling signal transmission or the execution of the product's function.

Now that we understand how a keypad works, let's discuss the key points to consider when designing keypads:

1. Key Size and Position

The size and position of the keys should be designed reasonably to match the metal dome and take ergonomics and ease of use into account. Insufficient or excessive space can affect the user experience and operational accuracy.  

2. Avoid Short Circuits

Avoid routing other exposed copper lines near the key area to prevent the metal dome from causing a short circuit when pressed.  

3. Ensure Proper Ventilation

Ensure proper airflow around the key area. Without ventilation, the metal dome might not spring back, behaving like a suction cup.  

4. Maintain Flat Key Areas

Key areas should be flat. Since tin-sprayed surfaces can be uneven, avoid using tin spray. Instead, opt for gold plating, carbon oil, or immersion gold (while immersion gold has the same flatness as gold plating, its wear resistance is not as good).  

5. Key Area Spacing

The gap between key areas should not be too narrow. It is recommended to maintain a gap of more than 10 mil (for carbon oil designs, more than 20 mil).

6. Solid Open Window Design  

It is preferable to design the key area with a solid open window, meaning "there should be no ink in the middle of the key area." Even a slightly thicker layer of ink in the middle can make the key harder to press or malfunction. Long-term friction from pressing can also cause the ink to wear off, with ink particles sticking to the key area, leading to key failure.  

Summary

Avoid tin spraying on key areas, maintain reasonable spacing, ensure no ink in the middle of key areas, and design solid open windows for the keys.

Designing a keypad PCB involves careful consideration of factors like key size, position, material choice, and spacing. By focusing on these elements, you can create a durable and reliable keypad that enhances user experience while maintaining the longevity of the device. Whether you’re designing for consumer electronics, automotive applications, or industrial controls, following these guidelines will help you achieve the best possible results.