Layout design is all about clearances. Daily challenges come from maintaining consistent space between your differential pair members, calculating the number of routing channels you can squeeze between two vias, or ensuring adequate clearance of bond wires as they cross the edge of your die.

All EDA layout tools provide you with basic measurement commands because of this. If you want to know the gap between two traces, select them and ask. Whatever tool you are using, there will be a command to give you this immediate feedback.

What if you want a more general calculation, though? The minimum separation between vias might be 50um per your manufacturing partner, but in your finished design, are there any pairs of vias placed this close together? Maybe the smallest value you’re using is 75um. Is it possible other, more frugal, manufacturing options could be attainable?

The Min Airgap Function to the Rescue 

For all these questions, there’s the perfect tool available in SiP Layout today, and it can be found under the Display menu: Min Airgap. This command serves a complementary role next to the Measure and Constraint tools in the same menu (that’s, coincidentally, why it is sandwiched between the two).

Show measure can measure the space between any two objects, it can only do two items at a time.  While showing constraints will give you the gap between the two items where you select them – perfect for situations involving constraint regions – and the constraints governing the clearances, it, too, only provides information about two items at a time.

The Min Airgap tool slots between them. It can be run in two item mode, of course, to provide similar gap information to the other two commands (just in the Options panel, rather than a floating window). The real value it adds, however, is the ability to select ANY number of objects and compute the smallest spacing between any part of those selected.

Do you want to figure out the smallest gap between any two bond fingers on the top of your substrate? Turn on bond fingers in the find filter and window all the fingers. You’ll see the minimum gap found, and the canvas will optionally be moved and zoomed to display that exact location where this gap was calculated.

Other information will be shown as well, such as how many of the selected items were defined on the layer in question. If you picked a layer other than your intended reference, change the layer in the Options panel and the gap will be recalculated for that layer. No need to reselect anything! A flow you might not have thought of but can be highly useful is to select ALL the vias in your design and then scroll through the calculation layers from top to bottom. As you step through each, you’ll see the minimum gap between any vias with pads on that layer. A few scrolls of your mouse wheel or clicks of the down arrow key, and you have a comprehensive view of the state of your design.

There is an option to ignore gaps between objects on the same net, as well. This ignores calculations between two vias both on the ground net while still telling you the closest these vias might get to elements on the ground net beside it.  

Presentation of Gap in the Design Canvas

The picture below shows you how the results are displayed to you. After selecting items (I selected four, here), you see how many were defined on the SURFACE layer (2), and what the gap calculated was. The thin white line in the canvas shows where this gap is. Zoom in or out as much as needed to give the needed context to understand what options you might have to increase the gap.

Sometimes, the simplest tools can be the most valuable. Calculating these numbers yourself with the measure or constraint tool would be a tedious nightmare. Writing your own skill code can do the job if you have the right SKILL skills. Having a tool available, right there, ready at a moment’s notice, is invaluable!