Surface mount technology (SMT) is an electronic packaging technology wherein the leads of electronic components are soldered directly to metallized pads on the surface of a printed circuit board (PCB). The SMT with leadless ceramic chip carriers (LCCCs) is used to design, fabricate, and assemble affordable, high-speed, high-density electronic modules with reduced size and weight and improved electrical performance. In surface mount devices, the LCCCs are soldered directly onto the fabric composite PCB substrate. New high-performance composite substrate materials must be developed to take full advantage of SMT. Fabricating a PCB that will perform reliably throughout its intended life is also an increasingly important requirement, especially if the goal is to satisfy the high reliability required in military applications. Consequently, SMT is driving the development of PCB substrate materials with improved thermal and electrical properties. In our continuing effort to meet these military demands, we evaluated high-temperature resistant/high-performance acetylene-terminated polyimide composites for use in SMT PCBs. This paper focusses on the processing and on the thermal, thermomechanical, and dynamic mechanical properties data developed for these acetylene-terminated polyimide composites for their potential evaluation as PCBs. The characterization includes such properties as in-plane coefficient of thermal expansion (CTE), out-of-plane CTE, and glass transition temperature (Tg), which determine the solder joint reliability, plated-through-hole (PTH) reliability, and dimensional stability.