Feature List

Sauna at a glance

created for the thermal simulation of electronic equipment
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 architecture 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    Control elements    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 (trace 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:
  - convert to layer-by-layer with Stackup command
  - for quick analysis, use the approximate via densities
    - none
    - low
    - medium
    - high
    - very high
    - infinite
  - for a more detailed analysis, use exact layer-to-layer resistance from Toolbox
  - 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 automatically updated
- reverse flow direction
- extend a flow path
heat sink flow network
- specify fan or assign flow
- for fan, flow is calculated automatically based on fin characteristics
- obtain temperature rise at intermediate points in 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
- subdivide assemblies at an arbitrary coordinate
- 4 types of slices (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
stackup
- subdivide into layers
- heat loads are placed on user-specified layer
- joins to adjacent assemblies are maintained
- boards
  - convert planar model to layer-by-layer model
  - for quick analysis, use the approximate via densities
    - none
    - low
    - medium
    - high
    - very high
    - infinite
  - for a more detailed analysis, use exact layer-to-layer resistance from Toolbox
- plates
  - user chooses number of layers in final stackup
  - useful for detailed chip modeling

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
- ordinary
  - join layered assemblies
  - interface types: zero resistance, die attach epoxy, flat/dry, flat/greased, solder, thin air gap, special
- via approximation
  - used for quick analysis of multilayer circuit board (uses typical properties for plating thickness, via diameter, etc.)
  - types
    - none
    - low
    - medium
    - high
    - very high
    - infinite
  - for more detailed analysis, use ordinary stack join with exact resistance obtained from Toolbox

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
R_max/R_min 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 path to ambient
- wattage and fixed temperature inconsistencies
- out of range on convection correlations
- incomplete joins
- islands in model

Control elements

time base
- wattage can vary with time (q vs. time control element)
- fixed node (boundary temperature) can vary with time (temperature vs. time control element)
- use these control elements for duty cycle problems where a predetermined set of on/off and environmental conditions exist
- simulate square waves, ramps, pulses and arbitrary user-defined waveforms
- characteristics specified with menus or by writing a script
- with scripts, virtually any waveform can be defined
- existed in earlier Sauna versions as duty cycle elements
temperature base
- wattage vs. temperature
  - control types
    - simple linear shutback
    - thermostat, use for simple control
    - complex, fully defined by user
  - remote reference temperature allowed
  - calculate component operating point during partial shutback
  - obtain plots of wattage vs. time
  - can be combined with time-based control
- temperature vs. temperature
  - control types
    - on/off, use to activate a cooling mode, such as a temperature controlled fan
    - ΔT, use to establish a ΔT between parts of the model, as for a thermoelectric application
    - complex, fully defined by user
  - absolute temperature and ΔT options
  - can be combined with time-based control
wattage base
- wattage can vary based on heat flow into a node (q vs. q control element)
- control types
  - simple scale
  - complex
- use these control elements for thermoelectric applications
- can be combined with time-based control and temperature-based control
since Sauna's solver is very fast, it is ideally suited for handling complicated control element 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
surface assembly
- create on face or edge
- assembly can be "thin" or with a user specified thickness
- material can be the same or user-specified
- useful for many situations
  - define boundary conditions
  - quickly convert a board to a metal-backed structure
  - quickly add insulation to the outside of a box
  - add a gap filler pad between a board and a box wall
  - allows for conversion of a board to a plate
  - useful when defining chip stackups
float resistors
- modify dissipation mode and air velocity
- specify special flow length
- specify laminar or turbulent flow (default is Sauna calculates transition)
- h vs. length (use average or h varies with length)
- convert between certain float resistor types
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 provide dimensions, cooling modes, material properties, etc.
heat load reports
- provides detailed information about the position and characteristics of point heat sources and distributed wattage
- input report: heat load before considering the effects of control elements
- final report: heat load at the end of the analysis, which includes duty cycle and power shutback effects
- transient report: heat load vs. time (text, graph or export spreadsheet data)
temperature reports
- indicate maximum, minimum, and averages for all heat sources, internal ambients, and assemblies
- current report: steady state temperatures or final step in transient analysis
- transient report: temperature vs. time (text, graph or export spreadsheet data)
mass reports provide weight, mass and thermal capacitance

Graphics export

Postscript files
BMP files
Windows meta files
"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 (400+ pages) with many tutorials
context sensitive help
- complete description of every menu
- one-click access
- all acronyms are defined
- reference pictures available for many operations
technical support area on website for technical notes
training sessions available (one day training session included at no charge for Sauna Modeling System)