The invention provides a subassembly to facilitate co-planar vertical surface mounting of subassembly boards. By “vertically mounting” is meant that a subassembly circuit board with a major surface is mounted perpendicular to the major surface of a circuit motherboard. In accordance with the invention, a subassembly for co-planar vertical surface mounting comprises a subassembly board coupled between a pair of base headers. Advantageously one base header comprises a plurality of mounting lugs secured to a transverse element in a co-planar configuration. The other base header conveniently comprises a plurality of connector pins secured to an elongated header element in co-planar configuration. The two headers interlock with the board to provide connection and co-planar support. Edge metallization of the subassembly board can provide enhanced thermal or electrical connection to the underlying portions of one or more lugs.