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Applications of CFD tools in PCB, Board-level and Chassis Level Thermal Simulations

Electronics Cooling

There are vast range of applications of thermal simulations in electronics industry dealing with Printed Circuit Board (PCB), Board and chassis level simulation, thermal management of data centres ...


Types of Simulations

  • PCB Level:
  • Board Level:
  • Chassis Level:
  • Rack Level in Data Centres:

Commercial Tools

  • ANSYS ICEPAK:
  • SIEMENS FloTHERM:

Some key features of such simulations are usage of Intermediate Data Format (IDF) and Incremental Data eXchange (IDX) files that have been exported from an ECAD package. These files contain informations of traces in PCB. In ANSYS ICEPAK, while importing traces the default materials are Cu-pure for metal and FR-4 for dielectric. PCB construction is a layered design along the thickness direction and hence the thermal conductivity is necessarily orthotropic. Here, the conductivity value along the thickness direction - known as through-the-plane conductivity is far less than in-the-plane conductivity values. These softwares are meant for electronics industry only and hence contains lots of objects related to this applications to fasten the simulation process. They can be summarized as follows:
  • Primitive - Fundamental geometric entities in FloTHERM and ICEPAK: Cuboids, Prisms and Flow Resistances
  • SmartPart - Object parametrically created out of Primitives: e.g. Enclosure, fan, PCB, cylinders, volume or surface heat source, heat sinks (described by base dimension, number of fins, fin width and fin height), perforated plate (fully designated by hole size and arrangement, pitch, free area ratio)
  • Assembly - A group of Primitives, SmartParts and Sub-Assemblies
  • Attribute - A property that can be attached to Primitives and SmartParts (e.g. material properties)
Primitives defined in ICEPAK
ICEPAK Primitives
Reading Mechanical CAD (MCAD) data
  • The MCAD data can be read either in their native format such as ProE, Solidworks or CATIA files (parts and assemblies) or neutral formats such as IGES, STEP or PARASOLID.
  • After initial defeaturing (removal of chamfers and fillets) and simplifications (removal of small holes, branding logos, part identifiers), the MCAD geometry needs to be converted into ICEPAK / FloTHERM entities.
  • Simplification is permissible to the to the extent where the geometry could be created manually using primitives and smart-parts in ICEPAK / FloTHERM!
  • The converion into ICEPAK / FloTHERM entities is a process of replacing a detailed geometry say perforated plate with a plate of same size without perforation and specifying the perforation details as attributes to the ICEPAK / FloTHERM entities.

Mesh generation process and recommedations
  • The components are mostly represented at voume with sharp corners such as cuboid and rectangles. A cut-cell method also known as trimmer mesh or Cartesian mesh or snappyHexMesh (in OpenFOAM) is used in ICEPAK and FloTHERM.
  • For printed circuit boards as in any surface with a significant amount of heat flux, 3 cells in the 1st millimeter above the board (air volume) and 3 cells in the 1st millimeter below the board (solid volume).
  • Maintain aspect ratio of cells < 100.
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