Thick film/flip chips - A systems approach

This paper deals with the thick-film hybrid integrated circuit process currently being used to realize complex circuit functions in hybrid form. The thick-film technology, active device attachment, and packaging all play important roles in the overall systems approach. A description of the various processes will be presented starting with the ceramic substrate and ending with the completed package. Extensive use is made of computer-controlled laser trimming for both static trimming of resistors and functional trimming of modules after assembly. When properly used, the laser is a powerful tool. Active devices are attached using a solder-reflow technique. All of the connections on the active devices are terminated using solder bumps connsisting of a tin/lead alloy. There are corresponding land areas on the ceramic substrate that have been coated with a tin/lead solder. The land areas on the substrate are designed in such a way as to restrict the solder wetting to the small area around the terminal similar to the IBM, "controlled collapse" process. The techniques employed result in thick-film hybrid integrated circuits that are economical, reliable, high in yield, and offer considerable flexibility to the hybrid manufacturer.