www.cst.com

Application Note | CST AG

www.cst.com

Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITELead 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 workfl ow of rapid design and simulation for lead frame packages using CAD Design Software’s (CDS) Electronics Packing Designer (EPD) software, and CST STUDIO SUITE®.

Electric fi eld distribution for single ended excitation of one net of a package, designed in CDS EPD and simulated in 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 com-panies 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 us-ing a variety of solver technologies. The whole workfl ow 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 semi-automatic 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 infor-mation and fi nally the design is blocked.

2015

Application Note | CST AG Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITE

2 www.cst.com

Figure 3: A close-up of the bond wires in schematic view (top) and 3D (bottom).

The EPD design environment has tools to set defi ne units and ma-terial stackup information. This information will be used to create the 3D model in 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-specifi c 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 verifi ed against specifi c 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.

Figure 4: The imported model in CST STUDIO SUITE. Bond wires are shown in blue.

Link to CST STUDIO SUITE

Once the design has been modifi ed 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 fi le and therefore no further data translation is required. As well as the geometry, this fi le also saves the material parameters and data , and the informa-tion 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

Figure 1: Converting simple layout geometry into electrically and mechanically

intelligent Lead Frame design.

Figure 2: The defi nition of bond wires in the model.

1.5800

1.58251.2125

Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITE

3

Application Note | CST AG

www.cst.com

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 mod-els representing PCBs and chips, allowing a simulation of multiple components or even the entire system.

Figure 5: Electric fi eld 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-defi ned design parameters, the built-in optimizers can be used to adjust these parameters automatically to meet the link specifi cation.

The time domain solver can also be used to investigate time-domain refl ectometry (TDR) and time domain cross-talk. This can help designers to pinpoint impedance discontinuities that are causing increased cross-talk or refl ection. The TDR result can be automatically optimized in a similar fashion as S-Parameters.

One special benefi t 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 cur-rents and volumetric electric and magnetic fi elds. Figure 5 clearly shows how the electric fi eld extends beyond the single net of exci-tation. This insight into the fundamental electromagnetic behavior helps the engineer to make better informed design changes.

Layout ModificationAs described in the previous section, simulation can reveal issues with the engineering design that will need to be fi xed. 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 modifi cations, re-running the DRC rules can con-fi rm 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.

Application Note | CST AG Lead Frame Package Layout and EM Simulation using CAD Design Software and CST STUDIO SUITE

4 www.cst.com

About CST

Founded in 1992, CST offers the market’s widest range of 3D electromagnetic fi eld 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 fi elds 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’ specifi c 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 Engineering Support Manager CST of America (West Coast Region)Mario Rocha Senior Product Manager CAD Design Software

CST AGBad Nauheimer Str. 1964289 DarmstadtGermany

info@cst.comhttp://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 trade-

marks 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.