BoardSurfers: Look Before You Leap - Verifying Footprints in the Design Capture Phase

Look before you leap and seeing is believing - two very apt universal truths, and this post is about these truths in a way; about how these truths are related to viewing footprints early in the design entry phase to prevent board and fab issues later. You can also add a penny saved is a penny earned and a stitch in time saves nine. Well, you are in the design entry phase, capturing the logic using a schematic editor, maybe Capture, and the PCB layout and the fab house is a faraway thought, a wisp of cloud in the distant horizon. But what if you could look before you took the leap? What if you could see the footprints of the symbols you are placing because seeing is believing? You end up stitching in time: verifying the footprint and land pattern dimensions before exporting your design to a board layout tool, maybe PCB Editor. Yes, you end up saving pennies; dollars, actually. 

I always like to do that; view the footprint - verify that it is exactly what I want, cross-probe the pins, view information about the footprint and the pins. It is a best practice of course, and a best practice with lots of practical implications in terms of time to market and saving money. What do I verify? At the least, I ensure that the footprint has the same or greater number of pins than the symbol and that the pin types are valid.  And, with the fast shrinking and flexible devices, size of components and placement is a matter of utmost importance. It’s definitely better to keep in mind board layout and placement from the initial stages. I will like to know the dimension of the footprint and the placement of pins early on, especially so if it’s a rigid or rigid-flex design or a dense DDR4 design.

So, when I design in Capture, I simply right-click the components and choose Show Footprints to open the footprint viewer and see the footprint. I click a symbol pin to cross-probe; highlight the equivalent pin in the footprint. Or, use the footprint viewer menu to see additional information, such as dimensions, pin numbers, and pin names. 

By the way, update the Capture.ini file to be able to open Footprint Viewer and see footprints. Simply add two sections, [Footprint Viewer Type] and [Allegro Footprints] to the file. The [Footprint Viewer Type] section contains only one line, Type=Allegro. Specify the path of the footprint files in the [Allegro Footprints] section. I usually have a few paths; for example, Dir0 points to the files that are installed with the software and Dir1 and Dir2 and so on point to other footprints, created by me or acquired from other sources.

If Show Footprint does not work although your INI file is correctly configured, check if you have the capFootprintViewer.tcl file in the tools\capture\tclscripts\capAutoLoad folder of your installation. Rename the Tcl file and restart Capture.

So, if you are designing a smartphone or maybe a smartwatch and the schedule is as tight as all project schedules usually are (not to mention costs involved); a simple, early step to verify footprints is something you can do to minimize rework and ensure a perfect board. Happy exploring footprints and yes, a journey of a thousand miles begins with a single step (and leaves a footprint, quite often)!