This paper describes the work done at JHU/APL in the development of a new spacecraft bus architecture. The development of an Integrated Electronics Module (IEM) is discussed from the system and thermal design perspective. The IEM work is a first step in a process aimed at integrating the core electronics into the spacecraft structure. A description of the composite IEM card cage built during this development program is given. The design requirements for that card cage are given. Discussions of the effective thermal conductivity of composites, and the qualification of aluminum/composite joints are included, along with results for coupon and system tests performed.