If you're in a hurry, just scroll down through the pictures on this
Created for efficient electronics thermal analysis
From the beginning, the Sauna program was created exclusively for the
thermal simulation of electronic components and systems. The program
contains extensive libraries of the components and materials actually
used in the electronics industry.
The target user for Sauna is a busy design engineer, either an
electrical engineer or a mechanical engineer. These engineers don't
have the time to spend a week or two learning a complex CFD (computational
fluid dynamics) package. With Sauna, training times are defined in hours,
not days or weeks.
Thermal network method: easy to understand and use
Array of nodes and thermal resistors
in wireframe display mode
At the most basic level, Sauna is based on a network of nodes and
thermal resistors (also known as the finite difference method). All
mechanical and electrical engineers understand this method. But, of
course, assigning values to all those resistors and capacitors can be
a nightmare. While some engineers persist and perform spreadsheet
thermal analysis, the Sauna program provides a much more accurate and
With Sauna you rarely work with individual nodes and resistors.
Instead, you work with the high level building blocks of plates and
boards. For example, to define the backplate of a heat sink, you
simply specify the dimensions and pick a material and surface type.
Sauna then creates a "plate assembly" which includes an array of
nodes and resistors. If you need to switch material or enlarge the
plate, you modify the plate assembly properties and Sauna
automatically updates the resistor and capacitor values. It is an
easy and intuitive process.
Heat sink modeling
Simple heat sink in shaded
Irregular heat sink with module stackup
Heat sinks (heatsinks) are probably the easiest thing to model with
Sauna. After defining the baseplate, you can add fins with a single
command. To define the heat load, you pick a standard package from
Sauna's library, or you can define a custom sized device. Normally,
the user provides the Rjunction-to-case (Rjc) found on the device
datasheet. However, if you're just doing a quick model, you can work
with a typical Rjc provided automatically by Sauna. As the last step, you
will add "float resistors" to provide a convection and radiation
path to the room.
To obtain temperatures, you only need to specify the room temperature
and a cooling mode. Sauna handles all the details of calculating
temperature-sensitive heat transfer coefficients. And Sauna
automatically includes a sophisticated gray radiation analysis which
includes the effects of shielding between fins. In just a few moments
you will have results.
If temperatures are not at desired levels, you have many options for
optimizing the design. You can easily modify fin spacing or fin thickness
or fin length. You can also easily reposition the heat sources,
thicken the baseplate or change materials. Sauna is the premier
what-if tool for heat sinks.
Besides simple heat sinks, you can use Sauna's 3D modeling
capabilities to analyze complex heat sink shapes. You can also
create detailed stackups of the components. Transient and duty cycle
analysis can also be performed.
Circuit board (PCB) modeling
Initial pad layout
PCB with components and
connecting traces and pads
Temperature contours make it easy
to identify hotspots
Evaluate thermal relief configurations
As you will see, Sauna has unique features for PCB thermal simulation.
As the first step in a PCB thermal analysis, you will define a "board
assembly" for one of the laminate layers in the board stackup. As
with heat sink modeling, you simply choose a material (usually FR4)
and define dimensions. Sauna handles the details of creating
individual nodes and resistors.
The second step is to create component pads. Sauna includes a
library of standard pad configurations for a variety of components,
including DPAK's, SOT-223, TOLL, duals (SOIC, PSOP), quads (MQFP,
LQFP, QFN), LED packages and more. For the dual and quad components, you
can choose between a heat slug and non-heat slug version. When pads
are created, you can optionally add an oversized heatsinking pad and/or
create a trace flareout. Very quickly, you will have a basic pad
layout on the board.
With the copper pads on the board, you are ready to add components.
For PCB modeling, you would normally use "enhanced heat
sources". The enhanced heat source provides for a thermal connection
between the junction and each lead pad on the board. And, when
necessary, each of these thermal connections can have a unique
resistance value. Besides the lead connections, the enhanced source
also provides for heat transfer from the top of the component body
and another thermal path down into the board. With an enhanced
source, the simulation will incorporate heat flow from all surfaces
of the package.
After adding enhanced sources, you will create interconnecting
traces and pads between components. In general,
you do not need to exactly replicate the physical layout because
pads have limited cooling impact when the trace length is greater
than 15-20 mm. So if components are separated by 30 mm or so, there
is a good deal of thermal isolation. This is particularly true for
components with heat slugs on a multilayer board. So while your
Sauna analysis will include traces, pads and vias in key areas, you
will probably not exactly duplicate a physical layout. As you gain
experience with Sauna, you will quickly learn how to apply a few
basic rules to keep the thermal model simple while maintaing good
When you have interconnected the components, you have a model for a
single layer board and the job is complete for those users that work
with single layer boards. But, of course, most users have at least 4
copper layers. So you need
to create internal layers. As you might guess, Sauna
has a command to perform this is a single step. (Note that internal layers
can be modeled full plane, or with traces and pads.)
Finally, you will create thermal vias in key areas to connect heat slug
components with ground and/or power planes. While a board will
typically have between hundreds and thousands of small diameter vias,
in a Sauna model you simply define a via size and density over a
specific area of a laminate layer. This approach provides good
accuracy while keeping model size small and calcuation times short.
At this point the model is complete.
To obtain temperatures, you add float resistors to provide
convection and radiation to the room envirnoment. As with heat
sinks, you can analyze for natural or forced air cooling.
After obtaining temperatures, you can use Sauna to optimize your
thermal design. You can easily modify thermal via density,
heatsinking pad size, adjust copper weights and shift heat sources.
Transient and duty cycle analysis can also be
Basic box modeling
Finned box, easy to model
Since Sauna includes a "create box" command, a box model can be
created in less than a minute. You can add fins and components to
any of the box surfaces. If all heat generating
components are mounted to the outer walls of the box, the thermal
model can be completed quickly.
Boxes with internal boards, and more
Contours for complex box
As you know, most electronic products consist of boxes with one or more boards
inside. While it is certainly useful to simulate a circuit
board or a basic box, the real goal is to have an
integrated model which includes both the box and internal boards.
Sauna can do this.
With some software packages, it is assumed that a box-with-board
model is too complicated to include trace-by-trace details on the
board. But Sauna has met this challenge. You can also have internal
boxes (the "box in box" problem) and you can have the board interact
with the walls through brackets, component leads, edge guides and
standoffs. And the model can be created in a reasonable time frame
(frequently less than one hour) and the calculation completed in a minute or
two on a standard Windows computer.
To simulate the heat transfer within the box, Sauna has the
specialized convection correlations for internal convection (natural
or forced). Thermal radiation is particularly important inside
boxes. Sauna handles this with integrated gray radiation, including
automatic view factor calculation. Once the convection and radiation
networks has been defined by the user, Sauna handles all the
necessary details of this complex, non-linear calculation.
When the temperature calculation is complete, you have many tools
to refine and optimize the design. If the model is particularly
complex, you can use Sauna's layering system to isolate portions
of the model. You can also create separate models for portions
of the box, then "append" the model together. Of course, all of the editing
tools for heat sinks and board are still at your disposition.
In short order, you will have an optimized thermal design.
Transient, duty cycle and power shutback
Duty cycle analysis
In the real world, many products are subjected to duty cycle
conditions, where power (or boundary temperatures) vary with time.
Sauna provides "control elements" which let you define a variation
of wattage (or boundary temperature) with time. You can prescibe
simple square waves or you can use Sauna's
scripting language to define highly complex power vs. time curves.
The same control element feature can be used to define power shutback.
There are many other possibilities.
Quick and dirty thermal?
As you have seen on this webpage, Sauna can be used to created highly
detailed models. But sometimes, all you want is a quick answer. For
example, you may be asking: "do I need a fan to dissipate 100 watts
in my box?". You may also be wondering: "what happens when a heat sink
is turned upside down?" or "what is the end-to-end thermal resistance of
a copper trace?". Sauna is an excellent tool for answering these
questions. To learn more, see Quick And Dirty
First class technical support
Sauna is moderately priced (from US$ 995.00). Yet we still provide
friendly, expert technical assistance. And you can see for yourself,
just call (734-761-1956) or email with any question. It's the same team for pre-sale and after-sale