Principal Mechanical Engineer

About Commonwealth Fusion Systems

Commonwealth Fusion Systems is on a mission to deliver the urgent transition to fusion energy. Combining decades of research, top talent, and new technologies, we’re designing and building commercially viable fusion power plants. And we're working with policymakers and suppliers to build the energy industry of the future. Since 2018, we’ve raised nearly $3 billion in capital, making us the largest and leading private fusion company in the world.

We’re looking for a Principal Mechanical Engineer to join our R&D and equipment design team to help build the next generation of thin‑film deposition technology. You will be responsible for the end‑to‑end design, integration, and implementation of advanced thermal vacuum deposition systems and complex R&D machinery.

This role requires you to be a technical expert who can drive innovative architecture while maintaining the procedural discipline necessary for high‑performance hardware. If you enjoy solving complex thermal‑mechanical problems in vacuum environments and mentoring others in a collaborative, fast‑paced setting, this is your opportunity to make an impact.

• Lead System Design:
  Drive the design, integration, and validation of advanced R&D equipment for thin‑film processing
  • Define Requirements:
    Establish system‑level requirements and innovative design concepts that directly correlate mechanical precision to final thin‑film product quality
  • Standardize Best Practices:
    Implement and maintain engineering workflows, and best practices using semiconductor standards as your guide
  • Lead Design Reviews:
    Conduct rigorous reviews for overall mechanical systems and sub‑systems, emphasizing manufacturability (DFx) and best practices for mechanical design
  • Collaborate & Interface:
    Generate and maintain critical interfaces with cross‑functional teams, including scientists, vacuum specialists, and electrical engineers
  • Project Accountability:
    Report on project milestones to stakeholders, ensuring delivery of on‑time and in‑spec outcomes
  • Mentor Talent:
    Coach engineering staff on technical delivery, procedural discipline, and professional development
  • Get Things Done:
    Act with speed to drive projects from concept through assembly, testing, and implementation

• Master’s degree in Mechanical Engineering or a related field (or equivalent industrial experience)
• 15+ years of experience in the design and implementation of complex R&D systems or semiconductor manufacturing equipment
• Proven capability in high‑temperature structural design and complex thermal management within vacuum environments
• Deep understanding of vacuum architecture, including material out gassing, seal integrity, and pump‑down optimization
• Expertise in 3D modeling (Solid Works and/or NX) and FEA/Thermal simulation tools (COMSOL, ANSYS)
• Ability to bridge the gap between design and the shop floor, including experience with manual/CNC machining, prototyping, and hardware troubleshooting
• Experience selecting and qualifying global vendors for specialized components or custom sub‑systems
• Demonstrated ability to lead effectively in both direct and matrixed organizational structures
• Experience designing or integrating roll‑to‑roll (R2R) systems for material processing
• Prior success building first‑of‑kind or experimental tools for semiconductor R&D or thin‑film deposition
• Familiarity with SEMI, ASME, ASTM, and other industry‑standard mechanical codes
• Experience designing precision motion and motor‑controlled systems within challenging environments
• Ability to occasionally lift up to 50 pounds
• Perform activities such as stooping, climbing, standing, or sitting for extended periods of time
• Dedication to safety to mitigate industrial hazards that may include heat, cold, noise, fumes, strong magnets, lead (Pb), high voltage, and cryogenics
• Willingness to travel or work required nights/weekends/on‑call occasionally

At CFS, we excel in fast‑paced environments, driven by our values of integrity, execution, impact, and self‑critique. As we grow, we’re eager to bring on mission‑driven folks who offer diverse perspectives and fresh ways to tackle challenges. We value diversity deeply and are proud to be an equal opportunity employer by choice. We consider all qualified applicants equally, regardless of race, color, national origin, ancestry, citizenship status, protected veteran status, religion, physical or mental disability, marital status, sex, sexual orientation, gender identity or expression, age, or any other basis protected by law.

This role requires compliance with U.S. laws concerning the export of controlled or protected technologies or information (collectively, “Export Control Laws”). Any offer of employment will be contingent on the need for compliance with such Export Control Laws.