Principal Thermal Mechanical R&D Engineer

Flex is the diversified manufacturing partner of choice that helps market-leading brands design, build and deliver innovative products that improve the world.

A career at Flex offers the opportunity to make a difference and invest in your growth in a respectful, inclusive, and collaborative environment. If you are excited about a role but don't meet every bullet point, we encourage you to apply and join us to create the extraordinary.

Job Summary

To support our exceptional teams in building innovative products, we are seeking a Principal Thermal/Mechanical R&D Engineer based in Littleton, MA. Reporting to the Sr. Director of Research & Development, the Principle Thermal/Mechanical R&D Engineer role is responsible for creating and implementing advanced, cost-effective thermal and mechanical designs that deliver outstanding product performance from early development through full-scale production. The Principal Engineer will provide technical leadership and mentorship while applying deep expertise in mechanical design, fluid dynamics, and heat transfer. In addition, this position will work closely with customers to deliver JetCool's cutting-edge cooling solutions and foster strong technical relationships.

What a typical day looks like:

• Drive innovation by introducing new ideas and critical thinking to advance cooling technologies for improved performance, manufacturability, and reliability.
• Lead the conceptual design, analysis, and optimization of complex fluid systems, including pumps, fluids, tubing, and heat exchangers, for next-generation processors.
• Perform advanced fluid flow simulations, analyses, and validation tests to ensure optimal performance under various operating conditions while collaborating with customer and cross-functional teams to integrate fluid systems into overall product designs.
• Develop and review engineering specifications, and documentation for fluid system and heat transfer components and assemblies, ensuring compliance with industry standards and regulatory requirements.
• Oversee prototype fabrication, testing, and validation, diagnosing and resolving technical issues during development phases and provide technical guidance and mentorship to junior engineers.
• Assist in maintaining a strong best practice culture and driving additional foundational knowledge and IP through research.
• Identify technical gaps, advocate for R&D initiatives, IP, and lead research projects to maximize product impact and value.

The experience we're looking to add to our team:

• Master's (Thesis required) degree in Mechanical Engineering or related field.
• Minimum of 7 years of post-collegiate experience in designing and engineering thermal fluid systems, preferably within the data center cooling, automotive, combustion, aerospace, medical, or nuclear industries.
• Profound expertise in fluid dynamics, thermodynamics, and heat transfer, with a strong foundation in engineering principles.
• Strong analytical and problem-solving skills, with the ability to effectively troubleshoot and optimize fluid system performance.
• Impacts the medium-term (semi-annual/annual) direction and financial or operational success of the function. Approves and/or creates functional processes or technologies. Executes and provides input to functional strategic plans and objectives for site. Assists in developing plans for structuring and implementing major initiatives.
• Excellent communication skills to convey complex technical concepts to both technical and non-technical audiences.
• Be a good person and a good team player.
• Demonstrates skills in teaching/leading and/or mentoring. Models appropriate behavior in support of Flex values.

Job Category
Design, Process & Technology Engineering

Required Skills:

Optional Skills:

Flex is an Equal Opportunity Employer and employment selection decisions are based on merit, qualifications, and abilities. We do not discriminate based on: age, race, religion, color, sex, national origin, marital status, sexual orientation, gender identity, veteran status, disability, pregnancy status, or any other status protected by law. We're happy to provide reasonable accommodations to those with a disability for assistance in the application process. Please email accessibility@flex.com and we'll discuss your specific situation and next steps (NOTE: this email does not accept or consider resumes or applications. This is only for disability assistance. To be considered for a position at Flex, you must complete the application process first).

Client-provided location(s): Flexible / Remote

Job ID: Flex-WD214161

Employment Type: FULL_TIME

Posted: 2026-01-20T19:27:47