It is not an easy decision to embark on a PhD journey, and that too in an entirely new area, after working with top brands in the manufacturing industry for 7 years !

Sasi Kumar Tippabhotla (PhD), our next pathbreaker, Scientist at the Institute of Microelectronics, Singapore, conducts mechanical modelling, simulations and material characterizations for improving the reliability of current and future microelectronics packages (integrated chips used in computers, mobile phones, automotives, etc).

Sasi talks to Shyam Krishnamurthy from The Interview Portal about his PhD on quantitatively characterising the processes that induce residual stress in silicon solar cells during different process steps of solar PV module fabrication.

For students, semiconductors and microchips form the backbone of technologies that we depend on in our daily life, and so it is important to predict their failure mechanisms in order to enhance product performance.

Sasi, can you tell us about your background?

I grew up in a small village in Andhra Pradesh, India. My father was a Telugu teacher in the government. high school and my mother is a housewife. During my childhood, I was fascinated by how things like cars and aeroplanes work. This interest was the first stepping stone for me to pursue mechanical engineering. 

My teachers in primary school, who are also my father’s colleagues, suggested that my father apply to Jawahar Navodaya Vidyalaya (JNV), the national level schooling system provided by the Govt. of India in order to impart quality education to bright rural students, free of cost. There is only one JNV per district in every state (except TN, I guess) where they teach from 6th to 12th. In those days, the selection was based on  a national level entrance test conducted for students in 5th standard, and they selected only 60 students per year per district. Fortunately, I was one of the selected students for the batch from 1992-1999.

The quality of schooling at JNV can be termed as world class. There, the focus is definitely NOT on grades, but on the overall development of students. As per my knowledge, all the JNV alumni are doing very well.

What did you do for graduation/post graduation?

I did my B.Tech (from G.I.E.T., Rajahmundry, then affiliated to J.N.T.U., Hyderabad), M.S. (from IIT Madras) in Mechanical Engineering, and PhD (from Singapore University of Technology and Design (SUTD)) in Engineering Design.

As I had mentioned earlier, my schooling never focused on cracking entrance exams. So, my score in the engineering entrance exam was not that great. Still, I managed to get admission in B.Tech (Mech. Engg.) through govt. quota (for general category) with minimal fee.

Thanks to JNV teachers, I could self-study most of my engineering courses, using the prescribed (recommended) textbooks. I also realized that engineering needs to be learnt with a focus on practical applications. This helped me to choose the courses that were important for my preferred specialization, machine design,  and study them with special focus. I used to study these subjects throughout the semester, byte by byte to gain a sound understanding of the concepts and spend time to revise them before exams. I never used to prepare based on important questions/topics, because that approach might give good grades but not sound knowledge.

During my under graduation, I also gave special attention to the way I wrote the exams. This is the area that many good students fail to focus on. I used to attempt the questions in the order of my confidence and would ensure I answer the first two questions with utmost care, good handwriting, and no strike offs. I also used to write my answers in the form of bullet points, not long paragraphs. Wherever possible, I used to sketch schematics, that help to shorten descriptive answers and save time while adding more clarity.

With my approach, I topped the class with the highest GPA and also secured a decent GATE score. I also took the opportunity to lead my final year project, through which I got a great deal of understanding of working of a steam turbine power plant.

Again, my GATE score was not sufficient enough to get me direct admission to the M.Tech programs at IITs. But I could secure admission in the M.S. (by Research) program with MHRD scholarship at IIT Madras. For this program, they use both GATE score and academic GPA for initial screening. The final selection is through a written test and a subsequent interview by a panel of faculty members of concerned department of IITM.

Can you explain your master’s thesis at IIT Madras?

In my initial days at IITM, it was really difficult for me to match the standards of the IIT system of teaching. I could only manage above average grades and I was very upset. My master’s supervisor then told me to focus on the research work and not to give too much attention to the grades. He encouraged me to enjoy doing research, which also included learning the necessary topics and skills. He actually boosted my confidence with his words. With this, I could get great results in a short time and also perform well in the courses of subsequent semesters. In the process I also secured the prestigious DAAD-IIT Masters Exchange Fellowship 2006-2007.

In Germany, I worked with the prestigious research group, which develops the German (VDI) standards for bolted joint design at the Technical University Berlin and continued my research work on finite element simulation of bolted joints. I worked and interacted with researchers and students from many nationalities and cultures, which was a great experience. I also travelled to many places in Germany like Munich, Stuttgart, Dresden, etc. This valuable international exposure boosted my confidence and also seeded my aspiration to pursue a PhD at a later stage. 

I worked on finite element simulation of bolted joints for my master’s thesis. Bolted joints are the common mechanical connections we encounter in our everyday life. Many of our household appliances use nut and bolts or screws for connections. In machinery, these bolted joints are used to connect different components and hence they form the critical load path of a structure. If these joints are not designed properly, they could lead to machinery failure and sometimes could lead to catastrophic accidents as well. I worked on simulating the member stiffness, which is an important parameter for estimation of load sharing between the bolt and the joined members. 

Finite element (FE) simulation is a numerical method to convert the structure or the machine component virtually into a number interconnected finite pieces (called elements) and obtain the load deformation relationship, under given loading conditions. First the solution is obtained at each element numerically and then we assemble the individual element solution based on its position and interconnection with other elements to obtain the global solution for the structure. FE simulations are used widely in the aerospace, automotive, energy and oil & gas industries to predict the product behaviour and its lifetime utility even before making it. This reduces product development costs and lead times.

Finally, the results from my master’s research work were published in the prestigious ASME Journal of Mechanical Design. This publication highlighted my capability of conducting high quality research and helped me to get my PhD admission later.

After my masters, I worked in Bangalore for different companies in the field of mechanical design and FE analysis for 7 years to gain valuable industrial experience before embarking on a PhD journey.

In September 2014, I joined the Singapore University of Technology and Design (SUTD) in order to pursue a PhD with the university graduate fellowship. During my PhD, I worked on the thermo-mechanics of solar photovoltaic modules. I used both experimental and simulation approaches to study the mechanical stresses and fracture of the solar PV modules. Our seminal work highlighted the importance of such research studies and motivated many research groups later on to pursue this topic. I published four first author research papers in highly reputed international journals in the field of solar energy and photovoltaics. I also presented my work in many prestigious conferences including the PVRW by NREL, USA, ICMAT by MRS Singapore, EPTC by IEEE Singapore. I also received the best student poster award from MRS Singapore in ICMAT-2017. I am also one of the finalists of the 1st Singapore National 3 Minute Thesis Competition held at NTU.

What were some of the factors that influenced you to take up such a career path in research?

I wanted to be an engineer who makes stuff like cars, aeroplanes, etc. So I chose mechanical engineering for my under graduation. I further specialized in Mechanical Design during my master’s at IIT Madras and worked as a mechanical design engineer at different multinational companies like GE, Caterpillar, and Delphi. 

During schooling at JNV, I was influenced by my physics teacher and the way he related to physics phenomena with real life examples. This helped me throughout my studies and professional career.

During my masters at IITM, I was motivated by my professor to pursue excellence in anything I did, research aptitude, and also mechanical simulations. He also mentored me on my career path. 

While working for GE as a gas turbine structural design engineer, I learned practical engineering and application of fundamentals to address a real-life problem. I also learned the importance of different stakeholders in an engineering product company, like suppliers, manufacturers, product service providers, cross-functional design teams, and most importantly, customers. I also completed green belt certification in design for lean six sigma at GE and also co-invented 3 US patent applications filed by GE. I got several recognitions/awards (project of the month and project of the quarter and hats-off), which constantly boosted my morale to perform better.

Later, I moved to Caterpillar, where I worked on IC engine fuel systems for nearly 1.5 years and then moved to Delphi as a technical leader to work on mechanical analysis of automotive electronic systems. The commonality in all these positions was mechanical design and also the focus on “Energy”. I realized that these systems contribute to the emissions to a great deal and pollute the environment. So, I decided to pursue research in the field of renewable energy sources like wind, solar, etc.

As a result, I choose to work on the mechanics of solar photovoltaic modules for my PhD. 

I can say, admission to Jawahar Navodaya Vidyalaya (JNV) and IITM are the biggest turning points in my life. JNV influenced the way I learned and once I joined IITM, rest of the things fell in place. I was constantly inspired by an elder cousin, who was a brilliant student, and had studied at JNV and IITM.

How did you plan the steps to get into the career you wanted?

My schooling at JNV gave me a sound understanding of science, especially physics. This helped me to excel during my under graduation, especially in my favourite subjects like engineering mechanics, machine design, etc. My final year project on the steam turbine governing system at Vijayawada thermal PowerStation helped me to gain practical understanding of heavy machinery maintenance and operation. This in turn helped me to secure a master’s admission at IITM with a full research scholarship from MHRD.

At IITM, encouragement and guidance from my professor helped me to produce high quality results in a short time, which in turn helped me to get selected for the prestigious DAAD scholarship. My masters research work at IITM was on finite element analysis of bolted joints using Ansys software. This methodology can be applied to any product/ system/ sub-system in general to simulate the response of the systems to a certain design/material parameters. This helps to optimize the product and also reduce the number of experimental runs, as they involve real materials, high cost and lead time and planning. Knowledge and experience of such processes is essential in the modern product development process. 

So, based on my above work, I easily got an employment offer from GE.

At GE, I worked as a gas turbine structures design engineer. I realized that the John F. Welch Technology Centre (JFWTC) at GE is a great place to start working. It is the hub of virtual product development for GE’s flagship products like aero engines, gas turbines, steam turbines, etc. I worked there with an open mindset to learn as much as possible and contribute to the maximum extent. I got very good encouragement from the GE leadership which led me to assume leadership in my first project itself where I developed a new analysis procedure for a repair fix. I also got the opportunity to become a complete design engineer  and hardware owner to manage a portfolio of components from drawings to the deployment, and field service. This helped me to gain a sound understanding of the product life cycle management, design for manufacturing, GD&T, systems integration, vendor management, handling supplier and manufacturing non-conformances and field issues. This is a very valuable practical domain knowledge which no university can offer. 

Another great advantage of working for GE is the opportunity to present the work to the chief engineers directly in the design reviews. This helps to a great extent to develop ones technical presentation and storytelling skills.

At Caterpillar (CAT), I worked for the IC engine fuel systems analysis team at the EDC India, Chennai/Bangalore. Unlike GE, this is limited to finite element analysis only. I was mainly working on structural and thermo-mechanical integrity assessment of fuel injector system and components. However, I embarked on this role to widen my domain knowledge to the field of IC engines and also learn a wide gamut of analyses. Earlier at IITM and GE, I used Ansys software for FEA and MATLAB for some coding. Here at CAT, I learned Abaqus and HyperMesh for FEA. These credentials increased my employability.

Next, at Delphi, I got the opportunity to plan and work independently on analysis projects as a Technical Leader. Here I worked on mechanical analysis of automotive electronic systems. Working at Delphi, I gained a lot of experience on vibration analyses like modal analysis, harmonic response analysis, random vibration analysis, and impact analysis. These are the new additions to my simulation portfolio. 

However, my stint at Delphi was rather  short, as I got admission for a PhD program at SUTD, Singapore.

What was your PhD research focused on?

At SUTD, I worked on thermo-mechanics and fracture of solar photovoltaic modules. The project is planned to be based on synchrotron X-ray microdiffraction (uSXRD) experiments to study the evolution of residual stress in the silicon solar cells during the module manufacturing process cycle. However, with my simulation expertise, I quickly modelled the system using FEA and simulated the stress evolution process. This helped us to plan our experiments at Lawrence Berkeley National Laboratory (LBNL, Berkely, USA) to get excellent results and publications. I also helped to validate the product testing observations of REC Solar, Singapore using my experimental and simulation-based research during my internship program. For my research, I also learned several mechanical characterization skills such as Mechanical/Fracture testing, Dynamic Mechanical Analysis for polymeric materials, Nanoindentation, scanning electron microscopy, statistical data analysis, etc. 

The end goal of my PhD was to quantitatively characterise the processes that induce residual stress in the silicon solar cells and also to elucidate the stress evolution during different process steps of solar PV module fabrication.

I also worked on a minor project to design a lithium-ion battery test cell to enable uSXRD experiments during a research internship at the Massachusetts Institute of Technology (MIT), Boston, USA. I also learned to work on a glove box to assemble this battery test cell. I performed uSXRD experiments in close collaboration with research groups in MIT and LBNL Berkely to get some exciting results, published in the Journal of Materials Research.

I also got an opportunity to work on a 6-month internship related to crystalline silicon solar cells at the Anhalt University of Applied Sciences, Koethen, Germany by invitation from the University President. I was introduced to him by my supervisor, and he was impressed with my research work. However, I couldn’t complete this work as I fell sick after going to Germany. These health issues delayed my PhD by at least 1 year. I realized that it is important to take care of health. Especially, since a PhD involves working under a lot of pressure, taking personal responsibility for results, having teaching assistant responsibilities, and overworking late nights. These things could easily lead to health issues.

How did you get your first break?

As a fresh undergraduate, I got selected for the post of Assistant Design Engineer at Mecon Limited, Ranchi, Jharkhand. This was my first break, purely based on my academic score and performance in the interview. However, I was already motivated to join the master’s program at IITM. I still joined Mecon because my parents advised me to take the existing offer as my MS admission at IITM was not yet confirmed (I was very confident of getting admitted though). I got the admission letter from IITM 10 days after joining Mecon. I wanted to resign and felt that the management would be upset with me. On the contrary, they gracefully accepted my resignation and wished me all the best for my studies at IITM. I worked there only for 20 days, for which they sent me the pay check also.

After my masters, I got my first break through job referral. My senior working for GE forwarded my resume, as I was in Germany and not able to attend the campus recruitment.

For a fresh PhD, getting an industry job is tough. In my case, I worked for 7 years before PhD and all that experience was useful. In fact, I got postdoctoral opportunities in Singapore and Europe. However, I couldn’t find a suitable job that were a match to my interests and qualifications. Also, I wanted to go back to India due to personal reasons. The position at QuEST (they work for Rolls-Royce) is based on my experience on gas turbines and stress analysis. My PhD qualification gave me an edge in understanding and analysing any problem quickly and helped in my additional responsibility as a technical reviewer.

I joined Entrepreneur First as a founder to explore possibilities of starting up a technology company in the solar PV and thermoelectric fields. Though I couldn’t realize that, it was a great learning about how start-ups are founded and how they are funded, etc.

What were some of the challenges you faced? How did you address them?

When I joined my first job, I was overwhelmed looking at the 

Challenge 1: English Language. 

When I joined JNV in 6th class, I could barely utter a few words in English, leave alone a small sentence. I could barely manage to get pass marks in the 6th class final exams. I realized that I would be in trouble as the medium of instruction changes from mother tongue to English from 9th class onwards. I had only 2 years to improve. I spent additional time on English, practised by talking to myself and to my friends in English, reading story books in English and trying to rewrite in my own words. This helped me tremendously to the extent that I started speaking well and also secured >85% in my 7th class final exams. In my 11th class, I also participated in the regional level national youth parliament competition to play the role of opposition leader, where I delivered several long speeches in English including a no-confidence motion. I got appreciation from the ministry of parliamentary affairs, Govt. of India for the same.

Challenge 2: Adapting to the Corporate Environment (in my first job at GE). I felt completely lost on my first day at GE. I became nervous, looking at the posters that depict the past achievements of various teams and the busy working environment. It took a week for me to get accustomed to the team and get a basic understanding of how everything worked. I spent a lot of my free time at the office, reading the design practices, analysis decks, presentations, etc. to get up to speed quickly. I also never hesitated to approach colleagues and even senior people to clarify my doubts and gain an understanding of my work. However, it took me quite some time to understand all the acronyms and the accent of foreign counterparts during meetings.

Challenge 3: Balancing research and industry projects in my current job. Research work requires deeper understanding of the topic and attention to even minute details and outliers, whereas industry projects need certain execution speed to deliver appropriate results within the deadlines, which often needs simplified models for adaptation. We often resort to our past experiences to make necessary simplifications to deliver results on time. So, handling both types of projects at the same time needs proper planning and a balanced mindset. I am still working on this challenge.

Where do you work now? Tell us about your role

I currently work as a scientist in the Advanced Microelectronics Packaging domain at the Institute of Microelectronics, Singapore. I conduct mechanical modelling, simulations and material characterizations for improving the reliability of current and future microelectronics packages (integrated chips used in computers, mobile phones, automotives, etc.)

This is in line with my career aspiration of being a mechanical design engineer. As a mechanical design engineer, I look at any product or process from a failure prevention perspective. We use simulations to predict the failure mechanisms and design/process/material modifications or selections to avoid failures and enhance product performance.

What are the skills required in your role? How did you acquire them?

The skills I acquired from my academics as well as my industrial experience are all useful in my current job. In reality, though I do not have much knowledge of electronics or semiconductors, as a mechanical engineer, I know that any product would have developed in-built strains as a result of processing and is typically subjected to additional strains/stress from regular operation and the environment. My day-to-day job as a packaging simulation scientist is to characterize the material behaviour and use that in numerical models to simulate the stress, strain and failure modes of the product.

In this job, I get to work on cutting edge chip technologies that decide the future of the microelectronics/semiconductor industry. We work with several industrial partners to develop such new technologies. So this job is very exciting.

How does your work benefit society? 

There will be tremendous impact. The society will benefit from the developments in computing and mobile communications, and our work on semiconductors and microelectronic chips forms the backbone of such technologies. In the future, our work will help in the development of devices that could improve medical technology, through IOT sensors, haptic devices, robotic surgeries, etc. They also help in the electric vehicle technologies to reduce pollution.

Tell us an example of a specific memorable work you did that is very close to you!

The one that is very close to me is my first project at my first job at GE.

I joined the project team as a new trainee engineer to support the analysis. This project was about developing a repair for a casing that sees a high thermal gradient during gas turbine start-up and cooldown. I realized that we didn’t have an analysis methodology for simulating heat transfer through bodies joined by sliding contacts. I worked with the thermal analysis team and the consulting engineer in the US to develop a methodology which later became a standard process for similar projects. As a fresher, I did not have much analysis or product knowledge. I worked long hours to read available reports, discuss with peers and domain experts and arrived at a physically reasonable methodology within a few months of my joining GE. All this I did with a curiosity to learn and determination to solve the problem. My team and the leadership felt very proud and gave me a Hats-off award.

Your advice to students based on your experience?

Give more importance to the experience than the end result

Good grades are needed but sound knowledge is the ultimate goal.

Choose the field based on interest, not based on other factors

Future Plans?

I prefer to go with the flow and perform well in my current job.