Keyboard PCB: The Design, and Factors Necessary to Build One

Introduction to Keyboard PCB Design

A keyboard PCB (Printed Circuit Board) is the foundation of any custom mechanical keyboard project. It houses the switches, microcontroller, and other electronic components that make a keyboard functional. Designing a keyboard PCB requires careful planning, attention to detail, and knowledge of various factors that influence its performance and usability.

In this article, we will dive deep into the world of keyboard PCB design, exploring the essential elements, design considerations, and the steps involved in creating a fully functional keyboard PCB from scratch.

Understanding the Basics of Keyboard PCB

Before we delve into the design process, let’s familiarize ourselves with the basic components of a keyboard PCB:

Key Components

1. Switches: The mechanical switches that register key presses and provide tactile feedback to the user.
2. Diodes: Used to prevent ghosting and ensure proper key registration.
3. Microcontroller: The brain of the keyboard, responsible for processing key presses and sending data to the computer.
4. Resistors and Capacitors: Used for various purposes, such as pull-up resistors for the matrix and decoupling capacitors for the microcontroller.
5. USB Connector: Allows the keyboard to connect to a computer or other devices.

Keyboard Matrix

A keyboard matrix is a grid-like arrangement of switches that enables the microcontroller to detect key presses efficiently. Each switch is connected to a unique combination of a row and a column in the matrix. When a key is pressed, the microcontroller scans the matrix to determine which switch was activated.

Example of a 3×4 keyboard matrix

Designing the Keyboard PCB

Now that we have a basic understanding of keyboard PCB Components, let’s walk through the design process step by step.

Step 1: Planning and Layout

1. Determine the keyboard size and layout: Decide on the number of keys, their arrangement (e.g., ANSI, ISO), and any additional features like a numpad or function keys.
2. Choose the switch type: Select the mechanical switches that best suit your preferences (e.g., Cherry MX, Kailh, Gateron).
3. Create a schematic: Use PCB design software (e.g., KiCad, Eagle) to create a schematic diagram of the keyboard, including the switch matrix, microcontroller, and other components.

Step 2: Component Selection

1. Microcontroller: Choose a microcontroller that has enough I/O pins for your matrix and supports USB communication (e.g., ATmega32U4, STM32).
2. Diodes: Select diodes with low forward voltage drop and adequate current rating (e.g., 1N4148).
3. Resistors and Capacitors: Choose appropriate values for pull-up resistors (e.g., 10kΩ) and decoupling capacitors (e.g., 0.1μF).
4. USB Connector: Select a USB connector that matches your desired form factor (e.g., USB-C, Mini-USB).

Step 3: PCB Layout

1. Create a new PCB layout: Use the PCB design software to create a new layout based on your schematic.
2. Place components: Arrange the components on the PCB, ensuring proper spacing and orientation.
3. Route traces: Connect the components using copper traces, following good PCB design practices (e.g., minimizing crosstalk, ensuring adequate trace width).
4. Add silkscreen and solder mask: Include informative silkscreen labels and apply solder mask to protect the PCB.

Step 4: Prototyping and Testing

1. Order PCB Prototypes: Send your PCB design files to a PCB manufacturer for fabrication.
2. Assemble the prototype: Solder the components onto the PCB, following the schematic and layout.
3. Test and debug: Test the assembled keyboard for functionality, checking for any shorts, open connections, or other issues.
4. Iterate and refine: Make necessary changes to the design based on the prototype’s performance and user feedback.

Factors to Consider in Keyboard PCB Design

When designing a keyboard PCB, several factors can impact its functionality, durability, and overall user experience. Let’s explore some of these key considerations:

Keyboard Firmware

The firmware is the software that runs on the microcontroller, handling key scans, debounce, and communication with the computer. Popular keyboard firmware options include:

1. QMK: A highly customizable, open-source firmware that supports a wide range of keyboards and features.
2. TMK: Another open-source firmware that serves as the foundation for QMK.
3. Proprietary Firmware: Some keyboard manufacturers develop their own firmware, often with limited customization options.

Comparison of keyboard firmware options

Switch Mounting Options

The way switches are mounted on the PCB can affect the typing feel and overall build quality. Common switch mounting options include:

1. PCB-mount: Switches are soldered directly onto the PCB, providing a sturdy and stable feel.
2. Plate-mount: Switches are mounted on a separate plate that sits above the PCB, offering a more rigid and consistent typing experience.
3. Hybrid-mount: A combination of PCB-mount and plate-mount, where switches are soldered to the PCB but also secured by a plate.

Keycap Compatibility

Ensure that the switch footprints on your PCB are compatible with the keycaps you intend to use. Common keycap sizes include:

1. 1U: Standard key size (e.g., alphanumeric keys)
2. 1.25U, 1.5U, 1.75U: Larger keycap sizes for modifier keys (e.g., Shift, Enter)
3. 2U, 2.25U, 2.75U: Even larger keycap sizes for special keys (e.g., Spacebar, Numpad Enter)

PCB Thickness and Material

The thickness and material of the PCB can impact its durability and electrical characteristics. Common PCB thicknesses range from 1.2mm to 1.6mm, with 1.6mm being the most popular choice for keyboard PCBs. FR-4 is the most widely used PCB material due to its excellent mechanical and electrical properties.

Electrical Safety and Protection

Implementing proper electrical safety and protection measures is crucial to ensure the longevity and reliability of your keyboard PCB. Some key considerations include:

1. ESD Protection: Use ESD protection components (e.g., TVS diodes) to safeguard the microcontroller and other sensitive components from electrostatic discharge.
2. Short Circuit Protection: Include fuses or resettable fuses to prevent damage from short circuits.
3. Overcurrent Protection: Implement current limiting resistors or polyfuses to protect against overcurrent conditions.

Frequently Asked Questions (FAQ)

1. Can I design a keyboard PCB without prior electronics knowledge?

While it is possible to design a keyboard PCB without extensive electronics knowledge, having a basic understanding of electronic components, circuit design, and PCB layout principles will greatly benefit the process. There are many resources available online, such as tutorials, forums, and open-source projects, that can help you learn and navigate the design process.

2. How much does it cost to manufacture a custom keyboard PCB?

The cost of manufacturing a custom keyboard PCB depends on various factors, such as the PCB size, complexity, number of layers, and quantity. For small quantities (e.g., 1-10 pieces), the cost can range from $20 to $100 per PCB. As the quantity increases, the per-unit cost typically decreases. It’s essential to obtain quotes from multiple PCB manufacturers to find the best pricing for your project.

3. What software is recommended for designing keyboard PCBs?

There are several PCB design software options available, both free and paid. Some popular choices include:

1. KiCad: A free, open-source PCB design suite that offers schematic capture, PCB layout, and 3D viewing capabilities.
2. Eagle: A widely used PCB design software with a free version for small projects and paid versions for more advanced features.
3. Altium Designer: A professional-grade PCB design software with a comprehensive set of tools and features, but it comes with a higher price tag.

Ultimately, the choice of software depends on your budget, project requirements, and personal preferences.

4. How long does it take to design and manufacture a keyboard PCB?

The time required to design and manufacture a keyboard PCB varies depending on the complexity of the design, your experience level, and the responsiveness of the PCB manufacturer. A rough estimate for the design process could range from a few days to several weeks, depending on the aforementioned factors. Manufacturing time also varies but typically takes 1-3 weeks for standard PCB fabrication services.

5. Are there any open-source keyboard PCB designs available?

Yes, there are numerous open-source keyboard PCB designs available online. These designs can serve as excellent starting points for your own projects or as learning resources. Some popular open-source keyboard PCB projects include:

1. Ergodox: A split ergonomic keyboard design with a highly customizable layout.
2. Corne: A compact, split keyboard with a 3×6 layout and support for RGB underglow.
3. Atreus: A 40% ortholinear keyboard designed for portability and efficiency.

You can find these and many other open-source keyboard PCB designs on platforms like GitHub, where the community actively shares and collaborates on projects.

Conclusion

Designing a keyboard PCB is an exciting and rewarding endeavor that combines the art of electronics with the satisfaction of creating a personalized typing experience. By understanding the basic components, following a structured design process, and considering key factors like firmware, switch mounting, keycap compatibility, and electrical safety, you can create a keyboard PCB that meets your unique needs and preferences.

Remember that the keyboard PCB design process is iterative and requires patience, attention to detail, and a willingness to learn and experiment. Don’t be discouraged if your first attempt isn’t perfect—embrace the learning experience and use it to refine your skills and knowledge.

With the information provided in this article and the vast resources available in the keyboard enthusiast community, you are well-equipped to embark on your keyboard PCB design journey. Happy designing, and may your custom keyboard bring you joy and satisfaction for years to come!