How Blind, Buried and Through-Hole Vias Can Impact Your PCB Design
Growing up, I was obsessed with all things Super Mario, but honestly, who wasn’t. Specifically, I was a sucker for the Super Nintendo, old school version. Bounding from platform to platform, tossing pixelated turtle shells, saving princesses… what a life. One of the best, albeit strangest, of the game, no doubt, was jetting in and out of those little green tubes that were seemingly all over the place. Who made them? Why were they even there?
Strangely enough, and nearly a whole childhood later, I found myself staring at a circuit board asking myself the exact same questions. Small holes seemly leading to nowhere were quite literally littered all over the board. Enter blind, buried, and through-hole vias.
As we continue our road to discussing that fact that the world is forcing our designs into smaller and smaller spaces (same story, different day), we continue to learn of new and exciting technological and manufacturing advancements that allow us to meet these worldly demands. From multilayered board stacking to changes in form factors, we’ll push the envelope further by introducing blind, buried, and through-hole vias.
Blind and Buried Vias: One-Up or Poisoned Mushroom?
Setting out to discover where each green tube went and not knowing which secret room you’d end up in was half the fun, wasn’t it? Fear not, although the point of Super Mario was to keep you guessing from green tube to green tube, designing your PCB is (hopefully) exactly the opposite. We should know exactly where and why you place holes all over your PCB without having to look in a thick strategy book.
Vias are holes that are drilled through the traces of PCB layers with the sole purpose of connecting to another trace on another layer. They are often present in multi-layered PCBs which require each layer to be connected in one way or another.
There are three distinct versions of vias that can be incorporated into any multi-layered PCB:
- Blind Vias: They connect an outer layer of the PCB to an internal layer of the PCB but do not go any further. So if we have a four-layered PCB, the first two layers will have holes drilled through the traces, but not the third or fourth.
- Buried vias: These connect two or more internal layers to one another. Again, in our four layered PCB, the second and third layers will be drilled and connected, while the outer layers, the first and fourth, won’t show any holes and will simply look like a blank spot on the board.
- Through-hole vias: As you may now have deciphered, these are drilled literally ‘through’ the entire board connecting the outer first and fourth layers together (or other combinations of connecting the four layers together).
Proper Via Understanding Encourages Your Design Growth
Seemly unimportant to the overarching mission to save the princess, there seemed to be no benefit to these green tubes other than the fact it was oh so satisfying to hop in and out of. Vias, on the other hand, play crucial roles in multi-layered PCBs.
Often times, and again in this day and age of smaller is better, we are left with the task of saving as much real estate as possible. With vias, we are in theory now able to bypass all the space stealing trace routing on the top layers (where all our components are sitting as well) and route all that is needed within our second, third, or even fourth layers. This can be a godsend for some designers out there looking for techniques to save space.
Another added benefit you’ll receive when implementing blind, buried, or through-hole vias into your board is a lowered parasitic capacitance between traces which could otherwise wreak havoc on your design. This lowered parasitic capacitance is due to realized improvements in shortening trace leads. Although not necessarily a primary reason, if designed correctly, you’ll certainly benefit from adding vias to the design.
Other Considerations Before Via Application
Although you may be jumping out of your seat looking for where to sign, hold your horses, as there are a few drawbacks to incorporating vias into your design (why do there always have to be drawbacks?!).
Vias and multi-layered boards go together hand-in-hand, and when doing anything to more than one board cost considerations must come into play. This includes the drilling of the via’s holes through not just one, but two, three, even four boards at precisely the same location. If there are even slight tolerance errors in the drilling and stacking process, the board might as well be trash.
To alleviate this, manufacturers must have their machines and tolerances down to fractions of millimeters, which of course, will add considerable costs to the manufacturing and assembly process. As always, be sure to contact your manufacturer(s) as far in advance as possible in order to gain their limitations and capabilities before you travel too far down the via rabbit hole (or green tube, whichever you prefer).
Are Vias Right for Your Design?
This advancement in PCB design isn’t cutting edge, nor is it rocket science, but careful consideration should be made if you are to embark down this path. The complexity that they can add, cost, and overall implementation challenges might send some running for hills. If implemented correctly, however, you will reap an innumerable amount of space saved, lowered parasitic capacitance and a generally awesome looking Super Mario inspired board.
With a new understanding of what vias are, how they can assist in designs, and the natural drawbacks of them, have you determined if they might be correct for you? If not, there’s always something which will be correct for you: strong PCB design software. Your design methodology should be as smooth as Super Mario Odyssey feels compared to Super Mario World, and Altium Designer® can keep you moving forward with an intuitive, unified design environment.
If you’d like to see what Altium design software can do for your multi-layered PCB with vias incorporated, talk to an Altium expert today.