2015
Application Note | CST AG
Lead Frame Package Layout
and EM Simulation using
CAD Design Software and
CST STUDIO SUITE
Lead frame packages are an established packaging technology for many types of applications, due to their
manufacturing and cost advantages. When the limits of this technology are pushed, careful analysis of these
packages using state-of-the-art design and simulation tools becomes essential. This technical white paper
describes a workflow of rapid design and simulation for lead frame packages using CAD Design Software’s (CDS)
Electronics Packing Designer (EPD) software, and CST STUDIO SUITE®.
With the focus of CDS on design tools for lead frames and CST in
3D electromagnetic simulation, it was natural that these two companies came together to provide a joint solution for lead frame
package design. Starting from the AutoCAD environment that
most lead frame packages are designed in, the EPD tool from CDS
processes vector artwork into intelligent entities using customer
supplied net lists, and can create a full 3D model with ports set up
ready for export to CST STUDIO SUITE tool. Within CST STUDIO
SUITE, the user is able to get fast and accurate analysis results using a variety of solver technologies. The whole workflow requires
minimal user interaction and is optimized to enable the designer
to perform effective virtual prototyping.
Convert DXF into Intelligent Layout
When importing a DWG/DXF of a lead frame package into EPD, it
will arrive as raw data and vector lines that need to be prepared for
adding intelligence to the design. Using set procedures and semiautomatic commands, lines will become Joined-Closed Polylines.
Each entity type (traces, pins numbers, pads, power bars, etc.) will
be separated into individual layers. Any text (font) in the design
may also be captured and will be assigned to their respective pad
or lead. Each entity type will contain the embedded attribute information and finally the design is blocked.
Electric field distribution for single ended excitation of one net of a package, designed in CDS EPD and simulated in CST STUDIO SUITE.
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Application Note | CST AG
Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITE
Figure 1: Converting simple layout geometry into electrically and mechanically
Figure 2: The definition of bond wires in the model.
intelligent Lead Frame design.
1.5825
1.2125
1.5800
Figure 3: A close-up of the bond wires in schematic view (top) and 3D (bottom).
The EPD design environment has tools to set define units and material stackup information. This information will be used to create
the 3D model in CST STUDIO SUITE.
Link to CST STUDIO SUITE
3D Wire Bond Rule Checking
EPD has an advanced built-in Design Rule Checker (DRC) that can
be used to check the design against any number of built-in design
rules as well as customer-specific ones. These can be lead frame
construction-based rules, die-based rules , bond wire-based rules
or any combination of these. This way, the design can be verified
against specific rules that check for manufacturing issues and
corrected prior to sending the design for analysis and onward to
manufacturing. This can reduce time-to-market and helps prevent
costly manufacturing issues.
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Figure 4: The imported model in CST STUDIO SUITE. Bond wires are shown in blue.
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Once the design has been modified according to the design
rules, and the model has been prepared with ports, stackup
and bond wires, it can be exported for simulation. CDS links to
CST STUDIO SUITE by writing a native CST file and therefore no
further data translation is required. As well as the geometry, this
file also saves the material parameters and data , and the information about nets is used to generate ports automatically.
As a result, this model can be directly simulated as is within CST. If
changes are desired, these can be made in the CST STUDIO SUITE
Application Note | CST AG
Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITE
modeler, and the model includes all the history information.
The System Assembly and Modelling (SAM) framework in
CST STUDIO SUITE can be used to combine this model with models representing PCBs and chips, allowing a simulation of multiple
components or even the entire system.
The time domain solver can also be used to investigate timedomain reflectometry (TDR) and time domain cross-talk. This can
help designers to pinpoint impedance discontinuities that are
causing increased cross-talk or reflection. The TDR result can be
automatically optimized in a similar fashion as S-Parameters.
One special benefit of 3D simulation is that the results aren’t just
limited to one-dimension data sets such as S-Parameters and port
signals, but can also include a complete visualization of surface currents and volumetric electric and magnetic fields. Figure 5 clearly
shows how the electric field extends beyond the single net of excitation. This insight into the fundamental electromagnetic behavior
helps the engineer to make better informed design changes.
Layout Modification
Figure 5: Electric field distribution for single ended excitation of one net.
3D EM Simulation
Multiple solvers are available for the EM analysis of the lead frame.
S-Parameters, which are commonly used for package analysis, can
be extracted using either the time domain solver or the frequency
domain solver. This data can be used to analyze crosstalk between
different critical nets. If the model includes pre-defined design
parameters, the built-in optimizers can be used to adjust these
parameters automatically to meet the link specification.
As described in the previous section, simulation can reveal issues
with the engineering design that will need to be fixed. Lead frame
packages can be challenging due to their small size and the need
to maintain equal spacing. As designs are created or intelligized
in the EPD design environment, complex calculations need to be
performed to produce quick results. Using the intelligent artwork,
one can use the software to quickly optimize and easily update
the spacing between leads, modify their positions and pull back
leads. After these modifications, re-running the DRC rules can confirm that manufacturing rules are within guidelines. The updated
design can then be exported back to CST, either as a complete
model or in the form of individual nets.
Figure 6: Design layout after the lead width has been parametrically changed to mitigate design issues discovered by the analysis in CST MWS.
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Application Note | CST AG
Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITE
About CST
Founded in 1992, CST offers the market’s widest range of
3D electromagnetic field simulation tools through a global
network of sales and support staff and representatives. CST
develops CST STUDIO SUITE, a package of high-performance
software for the simulation of electromagnetic fields in all
frequency bands, and also sells and supports complementary
third-party products. CST’s customers are market leaders
in industries as diverse as telecommunications, defense,
automotive, electronics and healthcare. Today, the company
enjoys a leading position in the high-frequency 3D EM
simulation market and employs 260 sales, development,
and support personnel around the world.
About CDS
CAD Design Software specializes in customized software
that is tailored to each customers’ specific needs. From
customization of our powerful design suites, to major
proprietary custom software development, CDS develops
EDA layout software to meet your design and manufacturing
needs, rather than requiring you to do things our way. We
work hard to reduce your time to market and simplify your
design methodology, not make it more complex.
Authors
Martin Schauer
Mario Rocha
Engineering Support Manager
CST of America (West Coast Region)
Senior Product Manager
CAD Design Software
CST AG
Bad Nauheimer Str. 19
64289 Darmstadt
Germany
info@cst.com
http://www.cst.com
Trademarks
CST, CST STUDIO SUITE, CST MICROWAVE STUDIO, CST EM STUDIO, CST PARTICLE STUDIO, CST CABLE STUDIO, CST PCB STUDIO, CST MPHYSICS STUDIO,
CST MICROSTRIPES, CST DESIGN STUDIO, CST BOARDCHECK, CST EMC STUDIO, PERFECT BOUNDARY APPROXIMATION (PBA), and the CST logo are trademarks or registered trademarks of CST in North America, the European Union, and other countries. Other brands and their products are trademarks or
registered trademarks of their respective holders and should be noted as such.
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