Chip on Board Technology for Low Cost Multi-Chip-Modules

Multi-Chip-Module on a laminated epoxy-glass substrate (MCM-L) meets the demand for a low cost miniaturized module when many functions with different technologies need to be integrated in a single standard package. The following paper presents two original MCM-L designs using Chip On Board (COB) technology. Both are made on the same kind of modified multilayer glass epoxy ; one is equiped with J lead ouput pins allowing the mounting of dice on both faces, the second is very thin with dice mounted on the top face and bumps on the bottom face allowing direct soldering on the motherboard like other Surface Mount Device (SMD) components. These two kinds of MCM modules with Jedec standard dimensions are now pushed into production. Mounting procedure as well as qualification program and test approach are described. To ensure reliability of such MCMs it becomes important to know exactly the maximal stress and deformation induced by thermal or mechanical cycles during mounting procedure. The use of the Finite Element Method (FEM) for design optimization is explained. This method allows the calculation of deformation, stress and temperature distribution in the whole module during the development phase. The results of such simulation are presented here.