Feature List

Sauna at a glance

  • created for electronic equipment thermal modeling
  • models are composed of the building blocks of boards, plates and plates with fins
  • convection and radiation coefficients calculated automatically
  • underlying modeling method is thermal network (thermal nodes and resistors), but modern architcture means that user rarely specifies a resistor value
  • 3D color graphics with shaded, perspective viewing and temperature contours
  • exceptionally easy to learn and use, much easier than finite element or computational fluid dynamics software

Quick links to Sauna features

Assemblies    Box creation utilities    Float resistors    Flow networks
Subdividing assemblies    Join command    Heat sources
Temperature calculation    Duty cycle transient    Editing    Display modes
Reports    Graphics export    Model export    Toolbox    Support   


Assemblies

  • assemblies are the building blocks from which a comprehensive thermal model is created
  • assembly types
    • circuit board
    • plate (with or without fins)
  • circuit board assembly
    • menus are used to specify copper weight, copper coverage, laminate material, thickness
    • user may also enter his own properties
    • copper coverage (density) can vary across the board
    • simple models are planar (all layers represented with a single board assembly)
    • for more complex problems, "layer-by-layer" analysis is used:
      • each board layer is a separate assembly
      • stack joins are created between layers, with the interface resistance determined by the via (feedthrough) properties
      • via density can be uniform or can vary across the board
  • plate assembly
    • plates may be metallic, ceramic, plastic, semiconductor
    • fins
      • may be added to one or both sides
      • specify fin length, spacing, thickness, orientation
    • menus are used to choose material and surface
    • many materials in library, including CVD diamond, AlSiC and other new materials
    • user may also enter his own properties

Box creation utilities

  • create six-sided box with a single command
  • "Board In Box" command for easy creation of circuit board within a box
  • "Plate In Box" command for easy creation of internal walls within a box

Float resistors

  • float resistors are used for modeling convection and radiation
  • nonlinear characteristics of convection and radiation are automatically taken into account when temperatures are calculated
  • convection
    • natural or forced air convection
    • internal and external flows
    • air temperature range: -60C to +300C (-76F to +572F)
    • specify altitude or air pressure, convection resistors are automatically updated
    • automatic calculation of transition between laminar and turbulent flow
    • calculation of developing flow regime
    • isolated plates, parallel plates, parallel gaps
    • fin array (heat sink) convection
      • natural
        • vertical baseplate/vertical fin channels, Van de Pol & Tierney equation
        • vertical baseplate/horizontal fin channels, equation based on Bilitzky data
        • horizontal baseplate, faces up or down, equation based on Bilitzky data
      • forced: parallel plate with developing flow
    • any number of different convection modes are allowed in one thermal model
  • radiation
    • blackbody
    • gray for the inside of an enclosure
    • automatic calculation of view factors
      • algebraic method for non-obstructed view factors
      • ray tracing for obstructed view factors
      • fast and accurate
      • completely integrated within software, no interfacing to external programs
  • in addition to modeling with float resistors, can also model using constant value resistors
  • automatic connection routines for simultaneous creation of ambient nodes and float resistors

Flow networks

  • flow resistors
    • "one way" resistors
    • fluid types: air, water, special fluid
    • create a single flow resistor or chains of flow resistors
    • error checking insures flow balance and fluid type continuity
  • multiple flow paths and flow branches allowed
  • easy to modify flow networks
    • when editing flow, can specify a flow value or use a scale factor
    • when the flow rate is modified, associated channel convection resistors are automically updated
    • reverse flow direction
    • extend a flow path
  • liquid cooling (cold plates)
    • obtain pipe thermal resistance from Toolbox
    • use generic resistors to incorporate pipe thermal resistance into Sauna model

Subdividing assemblies

  • slice command for subdividing assemblies at an arbitrary coordinate (single line, double line, 2 point, 4 point)
  • use slice to align mesh between adjacent model elements: boards and walls in enclosure, silicon chip and substrate in semiconductor module, etc.
  • subdivide assemblies to increase mesh density in key heat flow areas while using low mesh density elsewhere
  • Sauna understands that subdivided assemblies are part of a larger entity (superassembly); when temperatures are calculated, overall dimensions are used
  • whenever subdividing, Sauna maintains heat source placement, float resistor connections, stack and edge joins

Join command

  • used to provide a thermal connection between assemblies
  • join types: stack and edge
  • joins have an interface type associated with them, so it isn't necessary to create a separate interface layer
  • checks performed for interference and air gaps
  • edge join
    • any two assemblies which share an edge can be joined
    • interface types: zero resistance, insulated card guide, conductive card guide, special
  • stack joins
    • used for multilayer boards, semiconductor modules, solid blocks
    • interface types: zero resistance, die attach epoxy, flat/dry, flat/greased, solder, thin air gap, special
    • for circuit board stackup, interface resistance is based on via density, via size, fill material, etc.

Heat sources

  • footprint heat sources manage device characteristics and contact area
  • Sauna calculates case to sink resistance based on package type, footprint area, and interface type
  • thermal interface types: greased, dry, mica, silicon pad, solder, special
  • thermal parameters library for standard power semiconductor packages
  • heat sources can also be modeled as a detailed "stackup"

Temperature calculation

  • steady state, simple transient, duty cycle transient
  • for simple transient and duty cycle transient, the Sauna Modeling System version is required
  • highly optimized and efficient numerical solvers
  • steady state calculations
    • handled with direct sparse matrix solver
    • automatic iteration to calculate convection and radiation coefficients
    • uses equivalent gray method to accelerate radiation calculation
  • transient calculations
    • two solver methods: implicit or explicit
    • in automatic mode Sauna analyzes model characteristic and chooses either implicit or explicit solver, Sauna may switch between methods during the course of the calculation
    • user can also directly specify the solver method to use
    • convection and radiation coefficients updated at each output time step
  • Rmax/Rmin ratio of 1015 allowed
  • analyze models with small time constants
    • time steps as small as 0.1 microseconds
    • feature size down to 0.1 micron
  • comprehensive error checking
    • interference
    • nodes without connections to ambient
    • wattage and fixed temperature inconsistencies
    • out of range on convection correlations
    • incomplete joins
    • islands in model

Duty cycle transient

  • duty cycle features are leading edge, well ahead of any finite element or CFD program
  • wattage and boundary temperatures may be varied over time
  • duty cycle characteristics specified with menus or by writing a "duty cycle script"
  • menus allow for square wave, ramp and pulse duty cycles
  • with scripts, virtually any duty cycle can be defined
  • wattage duty cycle are based on wattage ratios, so a single duty cycle can control the wattage on many different heat sources as well as distributed heat loads
  • since Sauna's solver is very fast, it is ideally suited for handling complicated duty cycle problems

Editing

  • many advanced editing commands
  • very easy to perform "what-if" modifications
  • any assembly property, such as material or surface type, is modifiable with a single command
  • re-mesh assembly
    • use fine mesh in regions of high heat flow, low mesh density elsewhere
    • can re-mesh in one or both axes
    • when re-meshing, Sauna maintains heat sources, joins and float resistors
  • enlarge/reduce assembly
    • extend to limit point, enter new overall dimension, enter delta dimension, trap delta dimension
    • retain origin, center or endpoint
    • when enlarging/reducing, Sauna maintains heat sources, joins and float resistors
  • float resistors
    • modify dissipation mode and air velocity
    • specify special flow length for controlling h(x)
  • merge command to undo the effects of slicing
  • rotate
  • mirror
  • append one model into another
  • easy to edit fin length, spacing, thickness and orientation to obtain optimum fin dimensions

Display modes

  • orthogonal, perspective and oblique projections
  • wireframe display mode to see node and resistors
  • shaded display mode to show surfaces
  • contour mode to display temperature contours

Reports

  • "English language" reports give a complete description of thermal model and temperature results
  • assembly reports include dimensions, cooling modes, material properties, etc.
  • heat source reports detail the position and characteristics of all heat sources in the model
  • temperature reports indicate maximum, minimum, and averages for all heat sources, internal ambients, and assemblies
  • mass reports provide weight, mass and thermal capacitance

Graphics export

  • Postscript files
  • BMP files
  • Windows meta files (PC only)
  • "temperature vs. time" data in tab-delineated spreadsheet format

Model export

  • SINDA thermal and fluids modeling program
    • SINDA-85 or SINDA/G format
    • SINDA results can be imported into Sauna for post-processing
  • Saber circuit simulation program
    • perform advanced electrothermal modeling

Toolbox

  • perform "classic" heat transfer calculations to obtain h, Gr, Re, etc.
    • isolated plates
    • parallel plates and channels
    • cylinders
    • natural or forced convection
    • handles laminar and turbulent regimes
    • corrects for entrance effects
  • pipe heat transfer calculations
    • fluid types: air, water, special fluid
    • automatically switches between laminar and turbulent
    • corrects for entrance effects
    • analyzes smooth or rough pipes
  • obtain properties from Sauna's libraries
  • calculate conduction resistances
    • rectangular
    • cylindrical/radial
    • cylindrical/axial
    • tube/axial
  • calculate layer-to-layer board resistance which is based on via density and via characteristics.
  • radiation shape factors
  • optimize fin spacing and thickness

Support

  • comprehensive telephone and email support provided, including assistance with modeling strategies and assumptions
  • user manual
    • paper manual provided at no extra cost
    • very complete (380 pages) with many tutorials
  • Sauna includes online menu reference which gives detailed explanation of all menus
  • Sauna includes online error message reference
  • technical support area on website for technical notes
  • training sessions available (one day training session included at no charge for Sauna Modeling System)

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