Sr. Thermal Systems 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.

To support our extraordinary teams who build great products and contribute to our growth, we’re looking to add a Senior Thermal Systems Engineer located in Littleton, MA.

Reporting to the Product Manager the Senior Thermal Systems Engineer will own the end-to-end architecture, analysis, validation, and deployment of direct-to-chip (D2C) cooling systems used to cool high-TDP CPUs/GPUs/accelerators. They will be the technical leader partnering with Product Management, Mechanical/Electrical Engineering, Manufacturing, Quality, Reliability, and key customers to deliver robust, scalable products that meet performance, reliability, and cost targets.

What a typical day looks like:

Own thermal architecture & modeling

• Define system-level thermal requirements (TDP range, ΔT, coolant temperature, flow rate, pressure drop, acoustic & power budgets).
• Apply first principles in fluid dynamics and heat transfer to analyze design concept thermal performance
• Build and validate 1D/3D models (e.g., FloEFD, Icepak, MacroFlow, ANSYS Fluent, COMSOL) for cold plates, manifolds, quick-disconnects (QDs), pumps, and CDUs.
• Perform sensitivity trade-offs (flow distribution, fin geometry, microchannel optimization, TIM selection, manifold topology).
  
  

Design liquid cooling subsystems

• Specify and refine cold plates, CDUs, manifolds, hoses/QDs, reservoirs, filters, sensors, and controls.
• Collaborate with ME/EE on mechanical stack-up, materials, corrosion mitigation (galvanic compatibility), and leak risk reduction.
• Define DFX (DFM/DFA/DFT) and lead EVT/DVT/PVT from prototypes to mass production.
  
  

Validate and qualify

• Develop test plans for thermal performance, pressure integrity, leak detection, long-term reliability (HALT/HASS), and contamination control (particulates, biogrowth).
• Execute lab and rack-scale testing (pump curves, flow balance, ΔP mapping, heat load emulation, transient behavior).
• Drive failure analysis and corrective actions (FMEAs, 8D/PPS).
  
  

Partner across the business

• Work with Product Management on PRDs, roadmaps, and business cases.
• Support manufacturing process development (leak/pressure test stations, purge and fill, cleanliness criteria) and supplier selection/qualification.
• Engage with customers: define requirements, run pilots, analyze fleet telemetry, and support deployment at scale.
  
  

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

• BS/MS in Mechanical Engineering or Aerospace Engineering or related field (PhD a plus).
• 5 years experience in thermal design/validation for high-power electronics (preferably data center/server/HPC).
• Excellent first principles knowledge in fluid dynamics, thermodynamics, and heat transfer
• Proven expertise in liquid cooling, including CFD, pressure drop/flow modeling, and thermal metrology.
• Hands-on with lab instrumentation (flow meters, pressure transducers, thermocouples/RTDs, DAQ, leak detectors) and test automation (Python, LabVIEW, or similar).
• Experience bringing products from EVT → DVT → PVT → ramp, including DFX and supplier engagement.
• Excellent technical communication and documentation skills.
  
  

BO18

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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).