Electronic Design

An Electronic Designer's Guide To Thermal Management

DESIGN-TEAM ORGANIZATION IS CRITICAL FOR SUCCESS:

  • Thermal management must start with the beginning of the project. It can't be as effective if it's started further downstream in the design.
  • Too often, initial component selection is predominantly an electrical engineering function. The packaging engineers then have to "make" it work, sometimes employing expensive solutions.
  • THERMAL-MANAGEMENT DESIGN OPTIONS START WITH COMPONENT SELECTION:

  • Component selection can make a significant impact on the thermal-management solution, so it should be considered early in the design.
  • Printed-circuit-board layout is critical. Copper thickness, via locations, and power plane designs often dictate the solution's performance.
  • Exploit component supplier support and design experience to improve system performance and lower design costs.
  • DESIGNS WITH FANS:

  • Convection heat transfer (fan airflow) covers a broad range of heat flux capacity, depending on the employed technique.
  • To optimize performance, select and design heatsinks and fans together, early in the design.
  • A given fan can deliver only one flow and one pressure in a given system.
  • Fan flow and pressure dictate the performance of the entire convective system.
  • Entertaining alternate techniques, such as heat pipes, confined flow, and closed-circuit liquid cooling, can reduce total system cost in some high-performance products.
  • DESIGNS WITH HEATSINKS:

  • The fin manufacturing process determines the cost and the vendor's ability to optimize the heatsink for the user's specifications.
  • If the fin efficiency is already 80% or better, you can make minimal improvements at best.
  • Often, modifying the fin geometry can improve performance.
  • Serrations boost fin performance by 10% to 20%, but add cost.*
  • Rounded geometries outperform similar sharp-edged fin shapes.*
  • Staggered fins outperform in-line fins.*
  • Interrupted or pin-based fins outperform parallel plate fins.*
  • In low-pressure drop systems, elliptical fins work best.*
  • In high-pressure drop systems, round pins offer the best performance.*
  • DESIGNING WITH TIMS (THERMAL INTERFACE MATERIALS):

  • As power levels and power densities rise, selecting the optimum interface material is as important as the optimum heatsink and fan.
  • Achieving optimum TIM performance requires tradeoffs between its thermal conductivity, rigidity, and thickness.
  • The optimum TIM solution will result in the selection of the highest thermal conductivity material, which enables the largest contact area with the thinnest bondline.
  • First-order interface material selection should be from the data sheet. However, selecting the optimum TIM requires empirical testing due to multiple interrelated variables.
  • IMPROVING OVERALL THERMAL SOLUTION PERFORMANCE MAY REQUIRE ONE OR ALL OF THE FOLLOWING:

  • Reconsider component selection and packaging, which can open up new avenues for heat removal.
  • Optimize the pc-board geometry and layout.
  • Engineer the fan and fin components for optimum per formance.
  • Entertain new cooling techniques that ultimately may lower system cost.
  • Empirically test TIMs to achieve optimum performance.
  • Improve power-management efficiency.
  • Source: M. Behnia, D. Copeland, D. Soodphakdee, "A Comparison of Heat Sink Geometries for Laminar Forced Convection:Numerical Simulation of Periodically Developed Flow," The Sixth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems, ITHERM '98, Seattle, Wash.

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