The printed circuit board, or PCB, forms the foundation of any mechanical keyboard. Similar to the motherboard inside a computer, the keyboard's PCB acts as a central control hub connecting all the components like switches, controllers, and wiring together.
While visible switches and external features get most of the attention, it's the PCB doing the behind-the-scenes work of translating keypresses into digital signals. But what exactly does a keyboard PCB do, and what factors influence its design and functionality?
In this comprehensive guide, we'll explain the basic inner workings of mechanical keyboard PCBs and diving deeper into common layouts, components, and other specifications that impact performance.
Anatomy of a Keyboard PCB
On a basic level, all keyboard PCBs perform the same core tasks:
- Switch Mounting Points – Holes aligned to PCB switch contacts for secure mounting.
- Controller Chips – Microcontrollers or processors handling input signals.
- Wiring Trace Paths – Circuit routes carrying electrical signals to controller.
- Firmware Flashing – Software configurations reserved on PCB.
- Through-Hole Components – Resistors, capacitors soldered directly onto board.
Additional features like underglow LED support, USB-C ports and extra inputs also rely on the PCB's circuit architecture.
Common Keyboard PCB Layouts
Layout refers to the physical switch placement design. Popular options are:
60%, 65%, TKL, Full Size
– Standard pre-built layouts corresponding to typical keyboard footprints.
Split/Column Staggered
– Keys separated into logical columns for ergonomic hand positioning.
Ortholinear/Grid
– Keys arranged in a grid without staggered rows for uniform functionality.
Custom Form Factors
– Unique layouts like 40% or macropad PCBs for specialized functions.
Hot-Swappable Sockets
– Added compatibility with many switch types without soldering.
Layout influences switch/stabilizer placement, critical for proper functionality.
Controller Chips
The controller chip is the "brain" interpreting inputs. Common ICs (Integrated Circuits) include:
Atmel AVR (ATmega328P)
– Budget-friendly 8-bit chip powering many budget boards.
STM32 "Blue Pill" (STM32F103)
– Popular 32-bit ARM Cortex M3 MCU with larger program space.
Pro Micro/Leonardo (ATmega32U4)
– Arduino-compatible 16-bit chip for macros/QMK firmware support.
Teensy (MK20DX256/MK66FX1M0)
– High-end 32-bit PIC32 chip with USB-C, many GPIO pins for customization.
More powerful chips unlock advanced features but add to cost and complexity.
Firmware and Programming
The controller requires pre-loaded firmware software to function. Common options include:
Bootmagic/VIA
– Configures keys/macros through simple on-board reset sequences.
QMK/TMK
– Highly customizable, community-driven firmware compiled/flashed via computer.
Via
– Online GUI for programming without compiling or flashing needed.
New features/layouts usually require updating firmware to take advantage of chip/PCB capabilities.
Additional Components
Other through-hole parts soldered directly to PCBs include:
Diodes
– Prevent ghosting by isolating adjacent key electrical pathways.
LEDs
– Underglow, indicator lighting powered by board's integrated drivers.
Resistors
– Regulate current flow protecting components from damage.
Regulators
– Convert USB power to safe voltages for chip/switch operation.
Connectors
– USB-C, TRRS jacks, daughterboard linkages enabling peripherals.
Proper component choice depends on PCB specifications and needs.
PCB Material and Finishes
Most boards use standard 1.6mm thick FR-4 fibersglass epoxy laminate. But higher-end options include:
POM/Acrylic
– Dampen sound signature for quieter "thock".
Carbon Fiber
– Looks amazing while adding rigidity to large boards.
Brass/Copper Traces
– Conduct electricity efficiently for reliable performance.
Solder Mask/IPC Class Rating
– Protection against corrosion for longer lifespan.
Endless hobbyist tweaks and customization rely on solid PCB construction.
Final Thoughts
So in summary – while hidden from view, the keyboard PCB acts as the dynamic backbone linking all components together. Its design considerations like layout, chip selection, firmware and construction qualities directly impact the user experience.
With some electronics knowledge, hobbyists can design full custom boards or modify existing ones. And with proper care like cleaning/reprogramming over time, PCBs enable keyboards to function flawlessly for many years of usage.