SUBSTRATE FOR DIRECT MOUNTING OF INTEGRATED CIRCUIT MODULES

摘要

An improved surface mounting component assembly features an intermediate layer (30) of resilient material between a circuit board substrate (24) and a surface layer incorporating a conductor pattern (22) to which leadless chip carriers (12) are connected by pluralities of solder joints (26). The resilient material is selected such that the modulus of rigidity (G) of the intermediate layer (30) has a maximum value that is defined in terms of the thickness of the intermediate layer, the component size, the cyclic temperature range, and the maximum permissible shear force on the solder joints (26). Selecting a resilient material such that the intermediate layer (30) has a modulus of rigidity within the range defined by Equations (1) and (2) solves the problem of thermal cycling failure of solder joints in surface mounted component assemblies. For example, the elastomer acrylonitrile butadiene can be admixed with one or more adhesives including epoxy resins, polymide resins, and phenolic resins in order to formulate a resilient material having a requisite modulus of rigidity as calculated from Equations (1) and (2) for a particular surface mounted component assembly and application. A representative formulation useful for many aerospace applications is phenolic/acrylonitrile butadiene (1:1). Thermal management problems are alleviated by admixing the resilient material with a dielectric, thermally conductive material such as alumina flour. The alumina flour content of the intermediate layer can range from about 5 volume percent to about 40 volume percent.