Development of an HDI photovia process for portable products

The use of a “microvia” process for the fabrication of high density printed circuit boards and IC packages offers many advantages in terms of producing high interconnect density, cost competitive substrates for portable communications products. Motorola has put into production a sequential build HDI process that uses photoimageable dielectrics and semi‐additive copper metallization on a PWB substrate. Design capabilities for the current HDI process are 100μm/100μm line/space and 125μm /250μm via/pad. Plated through holes in the substrate are filled with a screen printable ink so that traces can be routed over the through hole area. This design capability meets routing and reliability requirements for current Motorola portable products. Future PWBs and IC packages, however, will need higher density features and higher performance materials. These features include finer line width, multiple HDI layers for routing dense SMT packages, low loss dielectrics for RF circuitry, higher Tg, and lower moisture dielectrics for DCA and IC package assembly.