Vertical Conductive Structures (VeCS) for PCB HD Trace Routing
What are Vertical Conductive Structures (VeCS), and how do they work?
Some of the benefits that your PCB design can realize with VeCS.
The next steps in designing a board using VeCS technology.
A high-speed high-density printed circuit board.
If you step back from the overall purpose of the circuit board that you are designing and just look at the board, it is actually a really cool thing. Think about it--we’re putting different types of electronic components on this board so that it can process the various types of signal and power inputs coming into it in order to do what we want it to do. In times past, they would describe this as the work of wizards and sorcerers.
To continually improve on this magic, however, we work to enhance how we design and build circuit boards. We’ve already gone from thru-hole to surface mount parts, from double layer to multilayer boards, and from regular trace routing to high-density routing. It would almost seem at this point as if there is nothing else to try. Well, that kind of thinking would be a mistake.
In an attempt to use the available board space as effectively as possible, there is a new method of routing traces that is being introduced. This method uses Vertical Conductive Structures (VeCS), which allow for the routing of traces vertically through the board layer stackup instead of using traditional vias. As you can imagine, there is quite a bit of space that can be saved by doing this, plus, it yields many other benefits as well. Let me describe to you what I’ve learned.
What Are Vertical Conductive Structures (VeCS), and How Are They Created?
One of the challenges of routing high-density circuit boards with high pin-count fine-pitch parts is finding enough routing channels for all of the traces. Even with microvias and BGA via-in-pad technologies for escape routing, the usable space for routing can get consumed very quickly. The other problem is that in order to plate deeper holes that span more layers, the holes have to be drilled at a larger diameter, which also takes up more room. Here is where Vertical Conductive Structures (VeCS) can help.
VeCS technology allows for traces to run vertically through the layer stack of the circuit board instead of using a drilled hole for the same function. This doesn’t require any specialized equipment other than what is already in place for conventional thru-hole circuit manufacturing, yet it will increase the routing density of a PCB to almost HDI levels. Here are the basic steps of how a VeCS is manufactured in a circuit board, as shown in the picture below:
Looking from the top, a slot is created by drilling and/or routing out the board material.
The slot is metalized and plated according to standard PCB fabrication techniques.
Larger drill holes are positioned next to each other to drill out the unwanted metal.
What’s left is small, vertical traces running through the layer stackup of the board.
The basic manufacturing process of a VeCS.
This is a very basic example, of course, and the process will vary depending on what is required for each application. But as you can see at the bottom of the picture above, those small areas of red are the metal left running vertically through the board. These vertical conductors can then be accessed by regular horizontal traces on the inner layers of the board.
There are two types of slot technologies that are in use with Vertical Conductive Structures: VeCS-1 and VeCS-2. The first type has slots that go through the entire stack of the board, while the second type is used for multi-level blind connections. Since VeCS are manufactured using standard processes, they can also be combined with thru-hole, blind, and buried vias as well as microvia technologies. This gives you a wealth of advantages which we will discuss next.
The Benefits of Using Vertical Conductive Structures
From the picture above, you can see how the smaller vertical conductors have a cross-section that more closely resembles a standard trace than a drilled hole would. This conductor profile ultimately results in less inductance for the net than if it were to go through a hole instead. At the same time, the vertical traces will have a better signal to plane reference, and all of this can help to improve the overall signal integrity of the board.
Perhaps the main advantage, though, is in the added routing channels that VeCS will create for trace routing. When you consider a BGA part with 0.5 mm pitch pins with via-in-pads being used for its escape routing, there is only enough room for one trace between the holes on the inner layer routing channels. By using VeCS, however, the number of routing channels goes up to five. In the picture below, you can see the difference between the two with a standard via-in-pad escape pattern on the left and VeCS on the right.
The blue represents the drilled or routed areas, while the red is the traces that can be routed through the channels on the inner layers. You can see the vertical connections represented in yellow connecting to the BGA pads in black and then extending down through the board layer stackup. Again, this is just a basic example, but it will give you an idea of some of the space benefits that VeCS can provide.
A comparison between routing with via-in-pads and VeCS.
With the ability to increase the routing density, the size and/or layer count of the board can be reduced; this will result in reduced manufacturing costs as well. The next question is, what does it take to design VeCS into a PCB?
What Is the Next Step?
Fortunately, the technology for both the manufacturing and design of Vertical Conductive Structures (VeCS) is already available. PCB design CAD tools can be made to work with this technology with the right settings, and advanced systems, such as Cadence’s Allegro PCB Designer, are already set up to work with VeCS right out of the box. You will also want to make sure that the PCB fabricator you are working with is licensed and able to produce this technology as well. Once you have confirmed this, you will be able to start exploring this new technology.
There will be many more new circuit board design and manufacturing technologies developed in our industry, and to stay ahead of the curve, we should be ready to explore these new ideas as they come along. To do this, it is important to have a PCB design system that is capable of supporting these new technologies as the foundation of our design process. As we have already seen, Allegro PCB Designer is set up to support VeCS and many other new technologies.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.