What is a QA Engineer at Celestial AI?

As Generative AI continues to push the boundaries of modern computing, the fundamental architecture of data centers is shifting from systems-on-chip (SOCs) to expansive systems of chips. At Celestial AI, we are pioneering this transition with our Photonic Fabric™, a next-generation optical interconnect technology designed to shatter existing memory and bandwidth bottlenecks. As a QA Engineer (specifically operating as a Test Engineer - ATE & SLT), you are the critical gatekeeper ensuring that this groundbreaking hardware delivers the tenfold increase in performance and energy efficiency we promise to hyperscalers and tier-1 partners.

In this role, your impact is immediate and foundational. You are not just running routine quality checks; you are developing and optimizing the automated test strategies for highly complex semiconductor and optical components. Your work directly influences the yield, reliability, and market readiness of optical interface chiplets, interposers, and Optical Multi-chip Interconnect Bridges (OMIB). By ensuring our hardware functions flawlessly at bandwidths of tens of terabits per second with nanosecond latencies, you empower our customers to optimize their AI accelerators and GPUs for the next era of accelerated computing.

Expect a highly collaborative, fast-paced environment where hardware, firmware, and validation teams intersect. You will be tackling unprecedented engineering challenges at the boundary of digital, analog, and photonic testing. This role requires a blend of deep semiconductor test expertise, strong coding fundamentals, and the agility to thrive in an early-stage startup environment where your technical decisions shape the future of high-performance computing architecture.

Common Interview Questions

Getting Ready for Your Interviews

Preparing for an interview at Celestial AI requires a strategic approach. We want to see how you bridge the gap between theoretical test methodologies and practical, high-yield production realities. Focus your preparation on the following key evaluation criteria:

Technical Depth in ATE & SLT We evaluate your hands-on mastery of Automated Test Equipment (ATE) and System-Level Testing (SLT). You should be able to discuss how you develop, debug, and optimize test programs for complex silicon, demonstrating familiarity with industry-standard platforms and test coverage methodologies.

Hardware Debugging & Failure Analysis Your interviewers will assess your ability to systematically isolate and resolve issues. Strong candidates will demonstrate how they analyze test data to identify root causes, improve yield, and collaborate with hardware and firmware teams to debug failures at both the component and system levels.

Scripting & Automation Proficiency Because efficiency is paramount, we look for your ability to automate data collection and test execution. You must be comfortable writing and debugging test scripts in Python, C/C++, or equivalent languages, proving that you can build scalable test infrastructure rather than relying solely on manual processes.

Adaptability & Cross-Functional Collaboration As an early-stage startup, Celestial AI values engineers who can navigate ambiguity and drive New Product Introduction (NPI). We evaluate your communication skills, your ability to define test requirements alongside design teams, and your readiness to learn emerging domains like integrated photonics testing.

Interview Process Overview

The interview process for the QA Engineer role is designed to rigorously evaluate both your hardware testing fundamentals and your problem-solving agility. You will typically begin with an initial recruiter screen to align on your background, compensation expectations, and overall fit for our startup environment. This is followed by a technical screen with a hiring manager or senior engineer, which will focus heavily on your past experience with ATE platforms, SLT, and your approach to semiconductor testing.

If you progress to the onsite or virtual panel stage, expect a series of deep-dive interviews. These sessions are highly interactive and will cover a mix of architecture discussions, live debugging scenarios, and behavioral questions. You will meet with cross-functional stakeholders—including hardware designers and firmware engineers—who will test your knowledge of communication protocols, boundary scans, and failure analysis. We highly value candidates who can back up their technical claims with data-driven examples of yield improvement and test optimization.

The timeline above outlines the typical progression from your initial application to the final offer stage. Use this visual to pace your preparation, ensuring you review core scripting concepts early on, while saving deep-dives into your past failure analysis case studies for the later panel rounds. Note that because we are a startup, the process can move quickly, and you may have the opportunity to speak directly with technical leadership.

Deep Dive into Evaluation Areas

To succeed, you must demonstrate a deep understanding of semiconductor testing and the specific challenges associated with high-speed, high-bandwidth interconnects. Below are the primary areas where you will be evaluated.

Automated Test Equipment (ATE) & System-Level Testing (SLT)

This is the core of the Test Engineer role. We need to know that you can translate product requirements into robust, high-yield test programs. Interviewers will look for your ability to write, debug, and optimize patterns on standard platforms.

Be ready to go over:

• Platform Experience – Your hands-on work with testers like Advantest, Teradyne, or LTX, including hardware setup and loadboard design considerations.
• Test Optimization – Techniques for reducing test time without compromising test coverage.
• SLT Methodologies – Bridging the gap between structural ATE tests and functional system-level environments.
• Advanced concepts (less common) – Multi-site testing strategies, thermal control during SLT, and handling massive parallel test data.

Example questions or scenarios:

• "Walk me through a time you successfully reduced test time on an ATE platform. What trade-offs did you consider?"
• "How do you ensure correlation between ATE results and SLT performance?"
• "Describe your process for developing a test program for a newly taped-out ASIC."

Failure Analysis & Yield Improvement

At Celestial AI, finding a defect is only the first step; understanding why it happened and how to prevent it is what drives our product forward. You will be evaluated on your systematic approach to root cause analysis.

Be ready to go over:

• Data Analysis – How you use statistical tools and data visualization to identify yield limiters.
• Debug Methodologies – Isolating faults between the device under test (DUT), the test hardware, or the test software.
• Cross-functional Debugging – Collaborating with design and firmware teams to implement corrective actions.
• Advanced concepts (less common) – Silicon characterization across process, voltage, and temperature (PVT) corners.

Example questions or scenarios:

• "You notice a sudden 5% yield drop on a mature production lot. Walk me through your debugging steps."
• "How do you differentiate between a silicon design flaw and a test program error?"
• "Tell me about a time you had to push back on a design team regarding testability requirements."

Communication Protocols & High-Speed Interfaces

Our Photonic Fabric™ interfaces with cutting-edge AI accelerators, meaning you must be fluent in the protocols that govern these interactions.

Be ready to go over:

• Low-Speed Control Protocols – Deep understanding of I2C, SPI, and UART.
• Test Interfaces – Practical application of JTAG (IEEE 1149.1) and boundary scan techniques.
• High-Speed Interfaces – Familiarity with PCIe and the fundamentals of high-speed signal integrity.
• Advanced concepts (less common) – RF testing basics, eye diagram analysis, and jitter tolerance.

Example questions or scenarios:

• "Explain how you would use JTAG boundary scan to verify the connectivity of a complex 2.5D packaged device."
• "What are the common failure modes you look for when testing a PCIe interface?"
• "How do you debug an I2C communication failure on a prototype board?"

Scripting & Test Automation

Manual testing cannot scale. We evaluate your ability to write clean, efficient code to automate data collection, control instruments, and parse complex test logs.

Be ready to go over:

• Python Proficiency – Using Python for instrument control, data parsing (Pandas/NumPy), and automation frameworks.
• C/C++ Skills – Writing low-level test scripts or firmware interactions.
• Data Infrastructure – Automating the pipeline from raw tester data to actionable yield reports.

Example questions or scenarios:

• "Write a Python script to parse a CSV log file and extract devices that failed a specific voltage threshold."
• "How do you manage version control and deployment for your test scripts across multiple ATE setups?"