Fabrication of the Grafted Multilayer SMT-1990 Boards in the Whippany High Density Facility.

The trend toward surface mount technology (SMT) has increasingly stressed many areas in circuit-pack manufacturing, such as CAD tools, printed wiring board (PWB) manufacturing, electrical tests, and component assembly. The SMT-1990 is a test vehicle to address whether current design and manufacturing capabilities can meet the need for SMT in the 1990 time frame, and identify key technology elements for future development. The SMT-1990, a shrunken version of the existing SBC (single board computer) board, has a circuit density of 144 compterms/square inch. Grafted multilayer (GML) was one of the technologies used to build the SMT-1990 boards, the others being the laminated multilayer (LML) and the composite grafted multilayer (CGML). Nine GML SMT-1990 boards were completed in the Whippany High Density Facility (HDF). Of the nine boards, five passed the final bare board test. These boards were used as the "golden boards" to test the LML SMT-1990 boards. Five GML boards were sent to Oklahoma City Works for component assembly. Most of the challenging features in the SMT-1990, such as 6-mil buried vias, 8-mil semi-buried vias, 6-/10-mil stacked vias, 4-/5- mil lines/spaces, and short runs of 3-/3.5-mil lines/spaces, were made without noticeable difficulty. The registration capability of the HDF was not adequate for the 13.5-mil through- hole vias because in the SMT-1990 design, the misregistration (with respect to drilled-hole locations) of all four signal layers must be