Reliability studies of ultra-small copper-plated through-package-vias in ultra-thin glass interposers
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The objective of the research is to model and design copper-plated through-package-vias, leading to fabrication of test vehicles for characterization of defects, and validation of models by demonstration of reliability through accelerated lifetime testing. To meet these objectives, this study focusses on four main tasks, a) mechanical modeling and design of TPVs in glass, b) fabrication of test vehicles for reliability characterization, c) reliability characterization of TPVs, and d) analysis of failures to validate the models. Extensive parametric modeling of TPVs is performed to provide design guidelines for reliable TPVs. Three glass package structures are investigated: polymer-laminated glass, bare glass, and TPVs with polymer-liner. Test-vehicles with all the three structures are designed and fabricated. Various TPV formation approaches such as excimer, UV, CO2 lasers and electrical discharge techniques were utilized to fabricate the test-vehicles. Quality of TPVs formed with each of these methods are analyzed through cross-section SEM imaging to identify characteristic defect sizes and geometries corresponding to each method. Thermo-mechanical reliability tests and failure analyses are performed to study TPV reliability. Micro Raman spectroscopy was used to measure stresses in glass packages for the first time. The results from test-vehicle characterization are consistent with the modeling predictions, thus providing a valid set of design rules for reliable TPVs. This thesis, thus, reports the first comprehensive study on reliability of ultra-small TPVs in ultra-thin glass interposers.