Interesting fact : Apple’s Mac Studio uses 3+ rigid boards linked by flex-rigid interconnects.

For multiboard projects, treat them as :

Use standardized bus protocols for communication between boards (I2C, SPI, UART, CAN). For power lines, define a standard pinout for your connectors. This prevents mishaps like plugging a 12V power module into a 3.3V logic board.

While the benefits are clear, multiboard design introduces a new layer of complexity to the engineering process.

Defining how signals transition from one board to another via schematics.

Here’s an to Multiboard PCB Design — focusing on why, when, and how to break a single PCB into multiple interconnected boards.

Tools like Altium Designer, Cadence Allegro, and KiCad now feature dedicated multiboard schematic and layout environments, acknowledging that the days of the standalone board are fading.

Free tool hint : has excellent multi-board project support – you can place board outlines in the same 3D viewer.

In the early days of electronics, the "breadboard" was a chaotic mess of wires. As technology advanced, the Printed Circuit Board (PCB) brought order, allowing components to be mounted on a single, rigid substrate. But as electronics have grown more complex, compact, and modular, the industry has moved past the single-board paradigm.