Get email delivery of the Cadence blog featured here
When it comes to package design, spacing often reigns supreme. The location readout in the bottom status bar of the tool will always tell you where your cursor is in the design; this can show either absolute or relative mode (in which case coordinate values are relative to the previous pick). Likewise, dimensioning data can be added to your design that gives indications of something’s length, the distance between two elements, and other critical information.
The first indicator is very transient. It is real-time and updated constantly. The latter is permanent. It moves and adjusts as design elements are repositioned around the substrate. What do you do if you want a visual indicator of lengths – beyond strictly horizontal and vertical – for reference while constructing objects? Rulers that are a permanent part of the design, but on layers that won’t be exported during any manufacturing, typically, and serve as guidelines for your work?
The SiP Layout tool offers just what you need with its add ruler command. Available with the RF Structure Editing option license (this feature is most frequently requested by designers working on these types of modules), the ruler commands provide a simple interface to draw and erase rulers anywhere in your design. Add rulers for constructing a spiral resistor to exacting dimensions, or use them as visual indicators of paper size, like your favorite word processing program. Your applications will be as varied as the rules that can be created.
To learn more, read on, as we look at these commands which you may not have noticed before.
Your only requirement for using rulers is a license of the SiP Layout product and an option license for RF Structure Editing. With this option checked out, you will notice an additional menu at the top of your main canvas window, as shown here:
Located next to the Help menu, this provides a set of commands aimed predominantly at the RF community. Some of the commands, like the rulers we’re discussing today, can prove useful to other team members.
Selecting the command shows you a simple, yet powerful, set of options shown below:
Most fields are self-explanatory. Line lock works as it does in add connect, add line, or any of the other geometry-editing features in the tool. Text size gives you the text block to use for the text markers on the ruler (shown in the width x height value, rather than a text block number, for easy selection).
Major division spacing is perhaps the most-unknown field. Looking at a measuring tape or ruler, you’ll see that numbers aren’t shown at every marker. For imperial measurements, labels usually show at every inch, while for metric, this is often at either the 1 or 5 cm mark. Here, the division spacing indicates where on your virtual rulers these numbers appear. 2000 in the image above means that a text label will exist at every 2000 um along the path.
Also useful is knowing that rulers can be composed of multiple segments. This allows you to “bend” your ruler around corners, loop back on itself, etc. When creating features like spirals, this can be VERY handy. Let’s see your regular measuring tape do that!
Finally, the ruler command works with the Snap pick to pop-up options, allowing you to easily select reference objects/locations in your layout, should the ruler you’re defining be tied to existing geometry features. Note, however, that the ruler won’t move along with that object the way that an associative dimensioning reference would.
Without a doubt, the most important consideration when creating rulers is what they look like, and how do they react in the design. A picture is worth a thousand words, so check out the image below to see two rulers that I’ve defined. One is an odd-angle, single-segment ruler that might be useful when creating any angle fanout routing. The other is a compound, two-segment orthogonal ruler that could be invaluable when constructing a complex plane shape or, yes, a spiral resistor:
All rulers are placed on the SUBSTRATE GEOMETRY / RULER subclass. This allows you to turn them all on or off at once. And, being symbols, you can assign colors to individual rulers if they have a specific meaning in your design.
When created, rulers are automatically flagged as fixed in the database. This allows you to proceed with your design, window select to add/remove objects, etc., without concern for your reference measurements being manipulated.
To remove (or move, if you must) individual rulers, simply remove the fixed attribute and delete them with the Edit – Delete command. When you’re finished with rulers, you can also use the Delete All Rulers command, under the Add Ruler in the menu shown earlier, to clear all ruler objects from the design in one quick and easy action.
Do you use the ruler commands today? What role do they serve in your design flow? And, if you don’t, is there a purpose you can see them fitting that would speed your design work? We’d love to hear about your experiences and how the tool can be improved!