In this paper, the patch concept is applied to the design of millimeter-wave band-pass filters in BiCMOS 55 nm technology. The operation frequencies are 120 GHz and 200 GHz, respectively. A via- and slot-based approach makes filters very compact, albeit patch-based, through a multi-mode approach. At 200 GHz, the side of the patch is only 194 μm long, or about a quarter wavelength, compared to half a wavelength for a conventional patch. The dependence of performance on the thickness of the Back-End-Of-Line is studied, and the design method is detailed. The performance is very good, with for example a filter operating at 200 GHz with a relative bandwidth of 23% and insertion loss of 3 dB. Finally, the prospect of using a thicker Back-End-Of-Line, offered as an option in 55-nm BiCMOS technology, makes it possible to show that even better performance can be achieved, with insertion loss below 3 dB.