August 2020 Newsletter

Director’s Corner

Greetings! Welcome to the PRC Quarterly Newsletter.

Let me start by expressing my deepest grief at the passing away of Congressman John Robert Lewis, Civil Rights Activist and US Representative from Georgia’s fifth congressional district. I have always admired him for his integrity and the “good trouble” he caused to make the United States a better place to live in. When the world leaders bade him farewell at the Atlanta Ebenezer Baptist Church a few blocks from my home, I was in tears. My prayers are with him and his family!

For those not familiar with what we do, we are an academic center based at Georgia Tech (GT) focusing on next generation advanced packaging and system integration. Our team consists of 26 faculty from four schools, 11 research/administrative staff, 40+ graduate students, many undergraduate students, and several visiting engineers. As a team we work with 33 industry/govt. labs and 8 universities on collaborative research and education projects.

Our first virtual Industrial Advisory Board (IAB) meeting was held May 20-21, 2020 and repeated twice to cover our members and collaborators in North America, Europe and Asia. This was attended by 159 people with 105 from industry. This was by far the largest meeting that we have hosted. The meeting consisted of 12 live oral presentations and 35 pre-recorded poster presentations. This meeting was a grand success for us since not only could we present our latest research findings, but these presentations also led to many lively discussions and feedback. In spite of the multiple time zones and many logistics involved, we were able to keep time. Kudos to the PRC organizing team, the presenters and industry partners.

We at GT-PRC continue to make advances in heterogeneous integration with applications in AI, high performance computing (HPC), automotive and wireless communication. More recently we have started working on interposers for space applications with a focus on reliability. This quarter we launched a new short course series with tutorials offered virtually to GT students, staff, faculty and industry members. These tutorials cover the fundamentals of polymers, fine-line interconnect fabrication, electrical/mechanical/thermal design, assembly technologies, machine learning, thermal management, reliability and others in the context of advanced packaging and system integration. We also support a distinguished lecture (DL) series with experts from industry and academia covering varied topics that include both technical and non-technical areas.

And finally, we have a new website. Please check out and provide us with comments and feedback. We provide below some recent research highlights in this newsletter.

Madhavan Swaminathan

Research Highlights

Vapor Phase Infiltration of Polymers for Enhanced Adhesion Strength
Heterogeneous integration with multiple dies is being driven by artificial intelligence (AI) applications. The interposer therefore plays a very important role. GT-PRC has been investing in panel level packaging (PLP) which requires reliable redistribution layer (RDL) fabrication on large substrates. Such an approach can be hindered by warpage and poor adhesion of polymer to copper and copper to polymer layers. In a recent paper published by graduate student S. Dwarakanath, we have shown that increased interfacial adhesion of copper on polymer using vapor phase infiltration of inorganic materials (AlOx) into polymers is possible. Her co-authors are P. M. Raj, N. Kondekar, M. D. Losego, R. Tummala with the paper published in the Journal of Vacuum Science and Technology, 38, 033210, 2020. Read More

Normalized SIMS data for Al+ as a function of depth for an AlOx infiltrated BCB polymer (Left), Contact angle of untreated and VPI-treated BCB (Middle), and Schematic illustration of the proposed mechanism of improved adhesion resulting from VPI treatment (Right)

High Temperature Epoxy Molding Compound
Epoxy molding compound materials with improved high temperature endurance is desirable in high power packages employing wide-bandgap semiconductors in a multitude of applications. Cyanate ester-epoxidized cresol novolac (CE/ECN) copolymer chemistry with varied feed ratios was introduced in this work to produce resins with significantly increased glass transition temperature, decomposition temperature and stability during high temperature (250 ºC) aging as compared to traditional epoxies. Various chemical, thermal and mechanical characterizations were performed to analyze the polymer degradation mechanisms over high temperature aging condition. This work was recently published by graduate student J. Li with co-authors C. Ren, D. An, Y. Ren, K. Moon and C.P. Wong in the paper entitled Systematic evaluation of cyanate ester/ epoxidized cresol novolac copolymer resin system for high temperature power electronic packaging applications, Polymer, Vol 195, 122454, 2020. Read More.

Results from dynamic mechanical analysis (left), thermogravimetric analysis (middle) and 250 ºC aging weight loss of the synthesized CE/ECN copolymers with varied ratio (right).

Inverse Design using Machine Learning
GT-PRC has identified machine learning (ML) as an important constituent of interposer design. In previous work we have shown the use of ML models for addressing forward problems, meaning that the model is used to compute the output based on the input design parameters. Here, we address the inverse problem where given the required output we estimate the input design parameters. A major challenge in inverse modeling is the non-uniqueness problem where a single output response can be due to multiple input parameter combinations. We address this issue by introducing Invertible Neural Networks (INN), which introduces redundant parameters to convert the one-to-many mapping to a one-to-one problem. The redundant parameters enable the estimation of the most likely input parameters that would provide the desired output response. This has been applied to a second-order substrate integrated waveguide (SIW) in D-Band to determine its slot width and slot depth that would support a center frequency of 142 GHz and 2.6 dB/GHz roll-off. The results show that INN predicts 2 possible design candidates that meet the desired performance, one with a traditional two-notch passband response and another with a significantly higher Q-factor without any ripples in the passband. Details of the work was presented at the 2020 International Microwave Symposium (IMS) by graduate student Huan Yu. His co-authors are H. M. Torun, Mutee ur Rehman and M. Swaminathan. Read More.

Design candidates derived using INN (left), frequency response (middle) and Substrate Integrated Waveguide (right)

Sub-THz Transmission Lines on Glass Substrates
Communication beyond 5G (called 6G) supporting data rates over 100 Gbps is under active discussion by the wireless community. This requires frequencies in the sub-THz region that need to be supported in the interposer as part of Heterogeneous Integration. GT-PRC is investigating the use of polymers on glass substrates for such applications. We recently published the first results on the performance of transmission lines integrated into polymer films laminated on glass substrates up to 170 GHz. The insertion loss for co-planar waveguide (CPW) was measured to be 0.21 – 0.275 dB/mm in D-Band (110 – 170GHz), which is comparable or better than other materials and indicates that these materials can be used at sub-THz frequencies for integrating devices. This work was presented at the 2020 IEEE Electronics and Technology Conference (ECTC) by graduate student M. Rehman. His co-authors were S. Ravichandran, S. Erdogan, and M. Swaminathan. Read More.

Polymer on Glass Substrate (Left), measured sample with resonators and transmission lines (Middle) and measured insertion loss of CPW (Right)

Faulty Highlight

Prof. Shimeng Yu has been named as a recipient of the IEEE/ACM Design Automation Conference Under-40 Innovators Award. This award recognizes the top young innovators who have made a significant impact in the field of design and automation of electronics. Yu was recognized at the 57th Design Automation Conference (DAC), held July 20-24 in a virtual format.

Yu is an associate professor in the Georgia Tech School of Electrical and Computer Engineering. He received his B.S. degree in microelectronics from Peking University in 2009 and his M.S. and Ph.D. degrees in Electrical Engineering from Stanford University in 2011 and 2013, respectively. From 2013 to 2018, he was an Assistant Professor at Arizona State University.


Student Spotlight

Majid Ahadi Dolatsara received his B.Sc. degree in Electrical Engineering from K.N.Toosi University of Technology, Tehran, Iran in 2013 and an M.Sc. degree in Electrical Engineering from Colorado State University, Fort Collins, Colorado in 2016. Currently, he is completing his PhD in Electrical Engineering at Georgia Institute of Technology, Atlanta, Georgia. His research interests include Computer Aided Design (CAD) and Machine Learning. Majid is interning at Apple this summer and is planning to graduate shortly. He is seeking job opportunities in Industry.


Congratulations to our 2020 Graduate!

Dr. Kashyap Mohan:
Thesis: Sintered Nanoporous Copper Die-Attach Interconnections: Fabrication and Assembly Demonstration
Employer: Texas Instruments (Dallas, TX)



Upcoming Events

Distinguished Lecture (Virtual) – Prof. Conrad S. Tucker, Arthur Hamerschlag Career Development Professor, Mechanical Engineering & Machine Learning, Carnegie Mellon University, USA. Date: September 23, 2020. This seminar is open to all who are interested. Registration is required.

Short Course – Prof. Vanessa Smet, “Navigating the Interconnection & Assembly Technologies Landscape”. Date: August 12, 2020. This short course is open to GT employees, students and industry members only and registration is required.