M.S. Thesis Presentation by Gnyaneshwar Ramakrishna

(Dr. Suresh Sitaraman, advisor)

"Physics-Based Modeling Methodology for Reliability of Microvias"


Rapid advances in electronic industry have lead to higher I/O, finer pitch and smaller footprint off chip interconnects to meet the cost, performance and size requirements. Microvia substrate technologies will play a crucial role in the printed wiring board (PWB) industry to accommodate these high I/O chips. According to the Interconnect Technology Roadmap for Semiconductors (ITRS) for packaging and assembly, by year 2012, it is necessary to fabricate microvias with pads as small as 18 µm with a pitch of 50 µm to meet electronic packaging requirements. As the feature size continues to reduce and the density continues to increase, there is a compelling need to understand the thermo-mechanical reliability of microvias.

The objective of this study is to develop an experimental and theoretical program to understand and predict the thermo-mechanical reliability of the microvias. The theoretical program aims to develop a physics-based modeling methodology to predict fatigue cracking of the microvias, taking into consideration the process and failure mechanics. The physics-based models have been used to understand the effect of geometry, dielectric material, and fabrication process parameters on microvia reliability. In addition, the models have been extended to address the material behavior at small scales, by developing an algorithm that can be used with the conventional finite element codes, to study the mechanics of behavior of microvias with reduced feature size. The experimental aspect of this program involves fabrication of the microvia test vehicles in a class 1000 clean room facility, to understand the effect of process parameters on yield and reliability of the microvias. The fabricated test vehicles were then subjected to reliability testing. The experimental data were used to validate the results from the theoretical program. Based on the results from the physics-based design methodology, design guidelines have been developed for fabricating thermo-mechanically reliable microvias.