Reliability of Through-Package-Vias From via-First Processing With Ultra-Thin Glass

Reliability of through-package vias (TPVs) in 100-μm glass, prefabricated with an innovative via-first process, is investigated through systematic modeling, design, fabrication, and reliability characterization. Finite element models were built to assess the impact of this novel process on stress and strain distribution in TPV structures. Thermomechanical simulations were carried out to provide design guidelines for reliable TPVs. In order to experimentally validate the predictions from simulations, test samples containing metallized TPVs with 60 μm diameter were fabricated with 100-μm thick glass. To assess the reliability of TPVs, daisy chains were fabricated and subjected to thermal cycling between -55 °C and 125 °C. TPV daisy chain resistances were measured at regular thermal cycling intervals to detect initiation of failures during reliability characterization. As predicted from mechanical modeling, changes in resistance were experimentally observed to be less than the chosen failure criterion, indicating no failures. Detailed mechanical failure analysis by scanning electron microscopy revealed elimination of delamination and crack failures in contrast to those observed in via-first bare glass interposers. This is attributed to the reduced stress and enhanced adhesion with the polymer layers.