An example sensor interposer employing castellated through-vias formed in a PCB includes a planar substrate defining a plurality of castellated through-vias; a first electrical contact formed on the planar substrate and electrically coupled to a first castellated through-via; a second electrical contact formed on the planar substrate and electrically coupled to a second castellated through-via, the second castellated through-via electrically isolated from the first castellated through-via; and a guard trace formed on the planar substrate, the guard trace having a first portion formed on a first surface of the planar substrate and electrically coupling a third castellated through-via to a fourth castellated through-via, the guard trace having a second portion formed on a second surface of the planar substrate and electrically coupling the third castellated through-via to the fourth castellated through-via, the guard trace formed between the first and second electrical contacts to provide electrical isolation between the first and second electrical contacts.