SUBJECT: Ph.D. Dissertation Defense
BY: Sangbeom Cho
TIME: Friday, March 2, 2018, 3:00 p.m.
TITLE: Thermal Performance Enhancement of Packaging Substrates with Integrated Vapor Chamber
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, 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 silicon (~150 W/m∙K), which may cause thermal related issues. The main objective of this thesis is to overcome the limitation associated with low thermal conductivity of glass by incorporating copper structures and additional cooling technology that can spread heat efficiently. To meet the objective, this study focuses on characterizing the effect of copper structures on the thermal performance of glass interposers and demonstrating ultra-thin (< 1 mm) cooling device, which makes the performance of glass substrate comparable with silicon. The first part of this research investigates 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 through numerical and experimental approaches. In the second part, a thermal model of glass interposer mounted on the vapor chamber integrated PCB is developed using multi-scale modeling approach to study the effect vapor chamber. The third part of this thesis explains design, fabrication, and performance of the prototype vapor chamber embedded PCB. Copper micropillar wick structure is fabricated on PCB with electroplating process, and its wettability is enhanced by silica nanoparticle coating. Design of the wick for the vapor chamber is determined based on capillary performance and permeability test results. The prototype of vapor chamber integrated PCB is fabricated through successful completion of following tasks: mechanical design and fabrication of condenser, device sealing, and device vacuuming and charging with working fluid. The performance of the device is tested using a test section with 2 mm by 2 mm heat source. Test results show that thermal performance of the prototype is better than copper plated PCB with the same thickness.