Materials, processes and reliability evaluation of photodielectrics for sequential circuit application

High-density sequential buildup printed wiring board (PWB) is well-known for its high wiring density and capability of mounting high-I/O-count chips. It is one of the most significant technologies being actively pursued by PWB manufacturers worldwide. The key to this technology is the application of polymer thin-films as the interlayer dielectrics which allow for buried/blind microvia interconnection and fine-line patterning. Among the many via formation alternatives, photodielectric method is the most promising in terms of compatibility with the existing manufacturing, simple process and low cost. In this paper, the results and experience on the fabrication and reliability tests of the circuit boards being developed jointly by AMP Circuits and Georgia Tech are reported. Motorola Reliability Test Vehicle-2.2 (MRTV-2.2) was employed for the process evaluation and reliability tests. Two types of photodielectrics were chosen as the interlayer dielectrics and for microvia formation, one liquid film and the other dry film. Metallization is performed by electroless flash followed by panel plating. Materials and process issues critical to the high-density capability, and reliability of sequential buildup circuit boards are addressed. Further investigation and improvements are being proposed and pursued. This investigation is part of the Consortium on Vehicle Electronics funded, in part, by DARPA under the agreement number MDA972-95-3-0021. This consortium was established to define and develop materials and processes that can support low cost, robust packaging for vehicle and other applications. Key to the CVE effort are MCM-L substrates that are substantially lower in cost than those currently available