The industrial trend of shrinking microelectronic devices while increasing the density of interconnections places great demands on the substrates upon which these devices are packaged. Multilayer flex circuits will provide the interconnection densities needed to meet these demands in a wide range of packaging and interconnection technologies.This paper discusses the development of ultra-high density flexible circuits. Processes and materials to fabricate fine line pitches from 12.5 pm to 40 Km are examined. Various microvia structures, through hole and blind via, are demonstrated. A test vehicle was designed and built for BGA packages to illustrate the density capability. A four-layer structure is demonstrated by using Z-connection to connect two layer pairs. Electrical, mechanical, and reliability test results are presented to show the selection of flex substrate material, Zconnection methodology and fabrication processes. A cost comparison of high-density flex to alternative substrates is discussed to identify potential Key Worak: $ex, substrate, high dens@, Z-connection
INTRODUCTIONSemiconductor devices have placed an increasing demand on the interconnect density and electrical performance of package substrates. These demands are not static, and are influenced by changes in multiple industries. Silicon shrinks are the primary drivers, hut advances in design tools, system architecture and package assembly also play