6 layers65 × 85 mm

Trackball
efogtech/endgame-trackball-hardware
Because it's cheaper than 4 layers. Yes, seriously.
260 parts26
Boards in 2 GitHub repositories, designed in KiCad, that use the TS3USB30RSW by Texas Instruments (-40℃~+85℃ 1 10Ω 250ps 25ns 2:1 30ns 3V~4.3V 7pF 955MHz UQFN-10(1.4x1.8) Analog Switches, Multiplexers ROHS). See how each wires it, with its parts, size, README and files; the TS3USB30RSW’s symbol, footprint and pinout are on its own page.