surface of the housing means once the seal 30 has been installed a removable cover 32 is disposed along and over the channel shaped housing means and the access means and removably secured thereto by further conventional screws 34 threaded into attachment means 11 in portion c of the housing means as can be discerned from this drawing a modular mounting apparatus for substrate means bearing planar circuit means including a housing means means including the substrate means bearing the planar circuit means and means removably disposed along both the housing means and the access means which permits removal and replacement of the substrate is provided this of course is an object of the subject invention as can also be discerned from the drawing of fig1 the apparatus may also include an additional member 36 defining a mode suppressor and is preferably an epoxy iron powder loaded lossy dielectric or similar member for absorbing both radio frequency energy and electromagnetic energy this member is secured to cover member 32 for example assume that the substrate marked x included a planar circuit such as an oscillator operating in the microwave frequency range member 36 would be secured to cover member 32 directly above substrate x so that when cover member 36 is secured to the housing means 10 the absorber would prevent radiation therefrom member 36 in the preferred embodiment is secured to the cover with an epoxy adhesive also shown in fig1 are a plurality of additional access means 38 for disposal into access ports 13 additional signal power etc connections may be made to the planar circuits by parallel gap welding a thin gold ribbon to the circuit leads these additional access.