SUBJECT: Ph.D. Proposal Presentation
BY: Sangbeom Cho
TIME: Friday, November 20, 2015, 9:00 a.m.
PLACE: MRDC Building, 4211
TITLE: Modeling, Design and Demonstration of Vapor Chamber for Glass Interposer in Mobile Microsystem Application
COMMITTEE: Dr. Yogendra Joshi, Co-Chair (ME)
Dr. Rao Tummala, Co-Chair (ECE)
Dr. Suresh Sitaraman (ME)
Dr. Samuel Graham (ME)
Dr. Venky Sundaram (ECE)


As demands on performance for mobile electronics continue to increase, traditional packaging technology is facing its limit in number of input/outputs (I/Os) and thermal challenges. Glass interposers offer many advantages over silicon interposers as well as previous packaging technology for mobile electronics, including ultra-high electrical resistivity, low loss, and lower cost at processed interposer levels. However, glass has a relatively low thermal conductivity (~1 W/m∙K), compared to Si (~150 W/m∙K). This limitation can potentially be overcome by incorporating copper structures and cooling technology that can dissipate heat efficiently.
The main objective of this thesis is to characterize the effect of copper structures on the thermal performance of glass interposers and develop an ultra-thin cooling device for its mobile application, which makes its performance comparable with silicon interposers.
In the initial phase of this research, the effects of copper structures, such as copper through-package-vias (TPVs) and copper traces in redistribution layer (RDL), on the thermal performance of glass interposers were studied through simulation. The results were compared with experimental results. Parametric study on 2.5D interposer showed that as more copper structures are incorporated in glass interposers, the performance of silicon and glass interposer becomes closer, showing 31% difference in thermal resistance, which showed 53% difference initially without any copper structures in both interposers.
We propose to next study the effect of vapor chamber (thickness: ~1 mm) integrated PCB on the thermal performance of glass interposer. To optimize the device performance, a numerical model for vapor chamber will be developed by using a Brinkman–Forchheimer extended Darcy model for liquid-vapor interface region in conjunction with continuity, momentum and energy equations for the vapor and wick regions, and a conduction analysis in the wall. Our preliminary modeling study by using thermal resistance value acquired from the literature, shows that the vapor chamber can make the glass and silicon interposer thermal performance similar. The design of the chamber will be determined based on the parametric study by using a developed model, and the results will be compared with experimental results.