| Objectives | Background | Approach |
Provide understanding of reliability issues associated with
use of Microvia and other Build-up Technologies for advanced
printed wire board construction.
Use of higher density microcircuits and their higher I/O count packages with finer pitch (<20 mils) and high density area arrays (e.g. BGA and micro BGAs) are causing problems (excessive layers) with wiring routing restrictions on conventional printed wire boards with 5 mil lines and spaces. The use of micro vias and other build up board technologies with 1 mil lines and spaces eliminates the wire routing problems for printed wire boards, but there is little data on the long term reliability of these technologies. Emphasis will be placed on thermal cycling failures.
The first year of the project emphasized the understanding of microvias and the associated issues for accessing the long term reliability of microvias under thermal cycling. Available experimental thermal cycling data was carefully searched for and studied. Parametric finite element models of representative structures were developed and analyzed. These results will be used in the development of an analytic design model. This year will concentrate on formulating a design model for estimating the life of a micro via under thermal cycling. The results of the available experimental data and the FEM thermal cycling simulations will be compared to the proposed models. The experimental data used to validate the model will attempt to come from classic oven cycling. Unfortunately the IST thermal cycling test is becoming more and more commonly used to understand micro via reliability. A large portion of the effort will be spent examining IST thermal cycling procudure. IST is a technique where a current is passed through daisy chained series of vias and traces to rapidly heat up a test coupon. An IST thermal cycle only takes 4-5 minutes to complete compared to a traditional oven cycle that takes on the order of an hour to complete. This project will build off the IST project C99-51 done with traditional PTV's to examine and understand the consequences of using IST to experimentally determine the thermal-fatigue life of microvias.