Virtuoso Meets Maxwell: Magic! – Dynamic Voiding in Virtuoso RF Solution

11 Aug 2020 • 7 minute read

'Virtuoso Meets Maxwell' is a blog series aimed at exploring the capabilities and potential of Virtuoso RF Solution and Virtuoso MultiTech. So, how does Virtuoso meets Maxwell? Now, the Virtuoso platform supports RF designs, and the RF designers measure the physical and radiation effects by using the Maxwell's equations. In addition to providing insights into the useful software enhancements, this series broadcasts the voices of different bloggers and experts about their knowledge and experience of various tools in the Virtuoso IC-Packaging world along with the nuances of RF, microwave, and high frequency designs. Watch out for our posts on Mondays.

While SiP Layout Option is – and continues to be – one of the most complete solutions for package design, the Virtuoso RF Solution gives access to a constantly increasing set of package layout authoring capabilities inside the Virtuoso Layout Suite. Having both IC and package inside the same design platform enables Virtuoso users to do package layout in their preferred design environment. An innovative co-design environment reduces the design cycle and eliminates error-prone manual steps to align the IC with the package. Full interoperability with SiP allows designers to switch between Virtuoso RF Solution and SiP Layout Option, and to work in an environment of their choice, the one they feel most comfortable. To allow seamless working on same design using different tools, it is very beneficial to have most of the functionalities available in both tools. Cadence is working hard on a smooth and user-friendly flow, and we are almost there.

Today I want to introduce and to illustrate one amazing feature, that is well established in SiP Layout Option, supported in Virtuoso RF Solution for package design by now, but so far not available in the Virtuoso IC layout environment.

Package design in SiP Layout Option has solved this by a very elegant solution. Metal shapes can be either of type drawing or dynamic. Drawing is used for routing or custom shapes, that are placed in static manner, while dynamic type shapes are special. Think about a metal plane connected to a certain net that is dynamically cut off to avoid shorts with any routing of different connectivity. This to happen is called voiding. Routing of purpose drawing stays as placed (either manual or by routing tools) while the dynamic type shape opens up and remains only on the non-taken area. Of course, any DRC rules are fully respected. This well-established concept for package design is available also in Virtuoso RF Solution.

Let’s have a walkthrough:

In Virtuoso RF Solution, you can choose metal shapes with either purpose drawing or dynamic.

Prior to ICADVM18.1 ISR12, drawing a metal rectangle with purpose dynamic looks like a metal rectangle drawn with purpose drawing. That could cause some confusion.

Beginning with ICADVM18.1 ISR12 during import sip to Virtuoso RF Solution, different stipple patterns are used for dynamic and drawing purposes, which makes it easier to identify what is static or dynamic.

Let’s assume we assign both to be connected to net ‘gnd’.

Connectivity can be defined, either via shape properties as here (manual), or net connectivity gets inherited by shape overlapping (XL auto connect).

If any routing is done, of a net different to ‘gnd’, and it overlaps these rectangular shapes two nets are shorted and dynamic markers flag it correctly.

The concept of dynamic shape and its benefits will become obvious if voiding is triggered by the RF-Module menu.

The user may void all dynamic shapes at once or only selected ones.

The dynamic shape frees up the area around the routing path (curved path objects with purpose drawing).

Voiding results in a DRC clean cut out of the made routing.

Just to mention a difference to SiP Layout Option, in Virtuoso RF Solution this is a manually triggered action, while in SiP Layout Option, dynamic shapes get updated on the fly when routes changing.

A closer look in the single shapes shows clearly their relation. The voided area is derived as a new layer of name <orgLayer>_VOID. See below the M1 and M1_VOID of given example, M1_VOID represents the pure overlap area of path route (purpose drawing) plus the DRC min spacing distance. The M1 of purpose dynamic that is displayed is simply derived as <drawing NOT void>.

The voiding principle can be applied also to multiple dynamic shapes on different nets overlapping each other. This becomes a real scenario, if several dynamic shapes with different net assignments (e.g. ‘gnd’ or ‘vdd’) are used and overlap.

In this case, Virtuoso RF Solution makes use of an OA property called ‘priority’ to define the voiding order. The shape with higher priority value voids the one with lower value. It might be of interest to know, if a shape is generated newly (create or copy), it gets next lowest priority of all dynamic shape priorities already existing in design.

In the example below, two rectangular shapes of dynamic purpose with different net assignments are overlapping each other.

By SKILL vrfSipGet(), the given priority of selected shape can be checked:

Select shape in layout
Run in CIW: vrfSipGet(css() "priority")

The ‘gnd’ shape has the priority of “-2”, while the ‘vdd’ one has a priority of “-3”. The higher priority dominates the lower priority. Following this rule, the ‘vdd’ shape gets voided on the overlap to ‘gnd’ shape.

If you like to modify current priorities, to change voiding order, you can raise or lower the priority of a selected shape by following SKILL APIs:

vrfLowerPriority() - redefines shape priority to one lower as current lowest

vrfRaisePriority() - puts selected shape priority to one higher as current highest

Let’s exercise it.

Select the shape to modify, here the ‘vdd’ shape (currently priority "-3")
Run in CIW: vrfRaisePriority(css() )
check new priority in CIW: vrfSipGet(css() "priority")

The priority has changed from “-3” to “1”, as “-2” and “-1” are taken already by other shapes and “0” is not a valid value.

As expected, the ‘gnd’ shape with lower priority value is now voided.

SiP Layout Option uses exactly same principle to decide the voiding order of dynamic shapes, but don’t get confused! Although priority values are not directly mapped between SiP Layout Option and Virtuoso RF Solution when running sip2oa or oa2sip (interoperability), the relative order of priorities is ensured to be the same. The voiding results in Virtuoso RF Solution will be the same as in SiP Layout Option.

At last one special, but important use case should be mentioned.

There might be the need to turn a dynamic shape into a static one. In package design, this is used to prevent any accidentally shape modifications shortly before or after sending data to manufacturing. In SiP Layout Option, this can be achieved by changing dynamic type shapes to static type shapes.

Starting with ICADVM18.1 ISR13, the same capability will be available in Virtuoso RF Solution. By using the menu RF Module – Convert Selected Dynamic Shapes or the SKILL API leConvertSelectedDynamicShapes, it is now possible to translate dynamic and voided shapes to proper curved polygon shapes with the same connectivity.

I hope, you enjoyed the tour and will benefit from metal voiding solution in Virtuoso RF Solution based on dynamic purpose in your package design.

Kai Schiller

About Virtuoso Meets Maxwell

Virtuoso Meets Maxwell series includes posts about the next-generation die, package, and board design flow with a focus on reinventing and optimizing the design process to ensure that the designer remains a designer! Keep watching!

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