The Proximity of Microvias to PTHs and Its Impact on the Reliability

Category: Circuit Board Technology
Post Date: July 20, 2004
Author(s): Anthony A. Primavera, PhD - Universal Instruments, Surface Mount Technology Lab; and Jaydutt Joshi - Conexant Systems Inc.

Description
High Density Interconnect (HDI) technology is fast becoming the enabling technology for the next generation of small portable electronic communication devices. These methods employ many different dielectrics and via fabrication technologies. In this research, the effect of the proximity of microvias to Plated Through Holes (PTHs) and its effect on the reliability of the microvias was extensively evaluated. The reliability of microvia interconnect structures was evaluated using Liquid-To-Liquid Thermal Shock (LLTS) testing (-55 o C to +125 o C). Comprehensive failure analysis was performed on microvias fabricated using different via fabrication technologies. Test vehicles that were manufactured by multiple vendors were used in this study. The test vehicles incorporated microvias that were fabricated using different laser ablation and photoimaging technologies. Laser technologies, such as YAG laser drilling and YAG-CO2 laser drilling, in non-glass reinforced and glass reinforced dielectric materials were evaluated. The resistance of the via chain was measured at various stages of LLTS testing. Samples that failed were subjected to non-destructive and destructive analysis in order to fully understand the failure mechanism. The effect of the plating thickness, via fabrication technology, dielectric material, and the effect of the proximity of microvias to the PTHs on the fatigue life was studied. It was found that the location of microvias vis-à-vis PTHs did have an effect on the reliability of microvias.

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