Electronics that support aircraft, military, and space applications, as well as the consumer portables industry are increasingly calling for lighter-weight systems. With this, flex circuits are being used in lieu of heavier weight rigid circuit boards and flex is finding its way into increased applications. Flex offers a substrate material that is significantly lighter in weight, thinner, and more compliant than traditional rigid circuit board materials. Numerous methods of fabricating multilayer flex circuits exist; most of which involve using a n adhesive material to bond the individual patterned film layers together to create the multilayer circuit. Thus adhesives are commonly used to bond conductive foils to polyimide films, cover-layers to patterned circuits, and patterned films together to form multilayer circuits. However, adhesives can be problematic if they fail, ultimately leading to wrinkling, voids or delamination of the circuit. Numerous advantages can be gained from fabricating flex circuits without adhesives. Some of these advantages include: a reduction of materials and processing costs, lighter end-weight circuits, increased circuit flexibility, circuits with less z-axis expansion, and a matched coefficient of thermal expansion between the circuit layers. NASA Langley Research Center has developed a unique polyimide material called Langley Research Center - Soluble Polyimide or 'LaRC-SI' which can be used to make lightweight, adhesiveness flex circuits. LaRC-SI films can be bonded together simply by applying heat and pressure, and require no additional adhesive material for lamination. Once the LaRC-SI films are heated and pressed together, the individual films fuse together forming a monolithic film. Additionally, LaRC-SI flex circuits can be bonded directly to structures without the use of adhesives, simply by using a thermal compression technique. This technique provides a means of fabricating a multifunctional structure with many advantages, among the most obvious being optimized use of space.