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Microvias and flex-an enabling MCM-L technology

The evolution of electronic packaging technologies and the need for smaller hand held consumer electronics are two factors which are forcing designers to require increasingly higher densities on PCBs. PCB manufacturers are being challenged to produce boards with smaller feature sizes using advanced processing techniques to allow for the use of current advanced packages. One solution to the circuit density requirement is to reduce the diameter of the via and the associated pad at the design phase, but maintain producibility at board fabrication. Advances in both material and processing capabilities have made flex materials an attractive alternative for use on low cost MCM-L applications. This paper describes and compares two methods of producing micro-vias in flexible laminate materials. Data collected to compare the two methods is presented to determine if there is a difference in the reliability of laser versus plasma formed micro-vias. An actual application for a tactical missile electronics module that incorporates micro-vias on flex based materials is discussed, along with how the micro-via approach helped accomplish the required wiring density. Several other examples of how the incorporation of MCM-L technology with micro-vias enabled the redesign of ceramic modules to laminate based packaging are presented. Design rules for via diameter and pad diameter are discussed. Thermal cycling and thermal shock evaluations are performed on a test vehicle that represents wiring densities and techniques that are employed in production. Test conditions and conclusions are presented.