  We report the characterisation of printed circuit boards (PCB) metal powder
filters and their influence on the effective electron temperature which is as
low as 22 mK for a quantum dot in a silicon MOSFET structure in a dilution
refrigerator. We investigate the attenuation behaviour (10 MHz- 20 GHz) of
filter made of four metal powders with a grain size below 50 um. The
room-temperature attenuation of a stainless steel powder filter is more than 80
dB at frequencies above 1.5 GHz. In all metal powder filters the attenuation
increases with temperature. Compared to classical powder filters, the design
presented here is much less laborious to fabricate and specifically the copper
powder PCB-filters deliver an equal or even better performance than their
classical counterparts.
