  Mu3e is an upcoming experiment at Paul Scherrer Institut in the search for
the strongly suppressed decay of $\mu\rightarrow eee$. It will use an
ultra-lightweight silicon pixel detector using thinned HV-CMOS MAPS chips.
Multiple Coulomb scattering is further kept under control with using high
density interconnects made of aluminium and operating the detector in a helium
atmosphere. More than 1 m2 of instrumented surface will produce about 3.3 kW of
heat ($\leq$ 250 mW/cm2). Traditional cooling approaches are in conflict with
the low-mass requirements, hence a gaseous helium flow cooling system will be
implemented. This talk will give a report on the successful data transmission
tests with the aluminium interconnects at target speeds of 1.25 Gbit/s under
realistic condition. The final proof-of-concept of the helium cooling has been
achieved with comprehensive cooling simulations and successfully confirmed with
laboratory measurements using a full-scale mock-up of the vertex pixel
detector.
