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PCB and IC Package substrates these days are complex. Multiple layers, hundreds to thousands of components and pins, degassed and cross-hatched shapes, routing, and everything in between can make the visual depiction of your layout imposing, to put it mildly.
How, then, do you reclaim control? Focus on exactly what you need to see and when you need to see it? Are there ways to simplify determining whether the via you are about to connect to is a stacked set of vias, a single micro via, or a through-hole? Maybe you need to differentiate a critical differential pair or bus from the surrounding objects to keep an eye on anything that impacts these paths when doing push and shove.
All of these are, I’m happy to say, very doable within the Allegro back-end tool environment. Whether you’re using the Allegro PCB Editor, Allegro Package Designer, or the SiP Layout tool, you have the same comprehensive suite of visualization aides at your fingertips. Today, we’re going to walk through a few of these and talk about when you can use them to streamline an otherwise chaotic information overdose in your canvas.
Any discussion of visibility must begin here with the Allegro tools. This form, shown below, allows you to toggle the visibility of any or all the layers in the design, set colors for them, or apply stippling patterns. This form is the basis for differentiating elements.
As you add or remove layers to the substrate or the companion classes, they show up here immediately. Use the Highlight unused colors option when assigning colors to different layers so that you can know right away that the color you’re assigning hasn’t been used anywhere else (You CAN use the same color on multiple layers, of course, and frequently you will on non-etch layers; many people also color all their dielectrics a common color if they are named). If your design team uses a common color palette for layers, you can import this from an external file. More on that later.
Once layers are set up, next comes nets. We don’t typically advise trying to set a unique color on every net. That would take a long time and probably be harder to try and remember than it would be helpful. However, any critical signals and your power/ground nets make sense to color. In this way, you can see where your ground planes are as you move through the design. A consistent color gives you that immediate recognition. Otherwise, you can color differential pairs, net groups, or entire bus structures with a common color.
That covers the basics of colors in your design. But, color alone isn’t enough to tame the complexity of today’s substrates.
If you have 100,000 vias on a layer, when you zoom out to see the whole design, they can look like a solid mass. It’s impossible to distinguish one from the next. At this point, is there much point in seeing them? Probably not unless you like watching your computer draw each via as an individual pixel on the screen. Consider removing these objects from the screen when you’re zoomed out. When you zoom in to do detail routing, you want to see them. But, at a high level, they are not useful.
Back in the Color dialog, on the Display tab, you’ll find Object filter. Size-based object filtering is not a new concept in IC layout tools, where you have billions of elements. It is, however, relatively new to PCB and package design. Smaller geometries have made it important, though.
Configure the minimum width/height in pixels for an object before it is drawn. You can, of course, filter only specific types of objects by size. Perhaps you always want to see pins, even at the highest level. Turn off those that aren’t critical elements here.
Finally, shadow mode coupled with global and shape transparency affords you the flexibility to see through a layer to those below. These are recommended, particularly during routing, so that you can keep the layers above and below the active routing layer as plane references. You don’t want these layers to overwhelm your senses, just to know they are there for decision making.
We’ve covered the color form. This is where you set things up, but it isn’t your day-to-day access while you’re working on your layout. It’s a large form and has a lot of one-time information or layers you don’t often need. The visibility tab, by default docked to the right of the main canvas, shows you the stackup layers.
It’s possible that, depending on your role, you need to see different classes in the visibility tab. Use the Visibility Pane tab in the color form to add or remove classes you don’t want to see. You can completely remove things like the plane and mask layers if you’re not interested in them or add the dynamic shape boundary class to quickly work on them when in the shape editing mode.
If you frequently access specific non-stackup layers (place bound top/bottom, silkscreen, soldermask, etc.), add these as additional layers to the visibility tab. Don’t keep the big color form open. In the color form, you can right-click on any layer and add it to the visibility tab. This will be remembered with the design, so there is no need to configure things as you move between designs.
Join us again next time, and we’ll cover how to distinguish between nets on screen by labeling them, how to see the layers a via (stack) spans.