Hey there, it’s Mia from your go-to PCB supplier—let’s cut the corporate jargon for a sec, because I know choosing the right via size for your board can feel like picking a random number out of a hat when you’re knee-deep in design. I’ve seen it all over the years: a designer grabs a standard 0.2mm via because “that’s what I always use,” only to hit soldering issues, signal loss, or even board costs blowing out way more than they needed to. Today we’re breaking this down like we’re chatting over coffee, no stuffy textbooks required—just real, tested tips from folks who’ve built thousands of boards for everything from smart watches to industrial power systems. PCB
First, let’s make sure we’re on the same page: a via is just that little hole in your PCB that connects copper layers together, right? Some are through-hole (go all the way through the board), blind (connect top layer to an inner layer), or buried (only inner layers). But size—when we talk about via size, we’re not just talking the hole diameter. It’s the drill size, the finished hole size, the annular ring (the copper around the hole), and even the land pad size. I can’t tell you how many times a designer will pick a drill size and forget the annular ring is too small, leading to copper peeling off when the board gets assembled. Annular ring is non-negotiable here—you need at least 0.1mm of copper around the whole hole, no exceptions. If your drill is 0.2mm, the finished hole is basically that minus a tiny margin for plating, so let’s say 0.18mm. Then your annular ring needs 0.1mm on every side, so total pad size is 0.18mm + 0.1mm + 0.1mm = 0.38mm. A lot of cheap EDA tools won’t call that out, but trust me, we’ve rejected tons of boards over that small detail.
Let’s start with the most common constraint everybody faces: board size and layer count. If you’re building a tiny board for a fitness tracker, your overall real estate is limited—you can’t use a big 0.8mm via because there’s no space. That’s when you go micro-vias, right? Micro-vias are under 0.15mm drill size, and they’re drilled with laser, not mechanical bits. But wait—micro-vias aren’t free. They cost way more to make, and they only connect one layer to an adjacent one (blind vias), so if you need to jump three layers, you might need multiple micro-vias. On the flip side, if you’re doing a big industrial control board with 10 layers, you’ve got room to breathe, so using a 0.4mm or 0.5mm via is totally fine. Bigger vias are more robust, easier to solder, and cheaper to manufacture because mechanical drilling of larger holes is faster than tiny ones. Pro tip: if your board is over 2 layers, count how many vias you have total. More small vias = more drill bits changing = longer lead time = higher cost. I’ve had a designer trim 50 micro-vias off their 10-layer board, and their quote dropped by 15% immediately. That’s the kind of win we love.
Next up: electrical performance, because vias are a pain in the butt for signals—they cause what’s called “via stub” and impedance mismatch. Stub is the extra length of the via that’s not connected to the top or bottom layer, right? If you have a through-hole via that goes from top layer to layer 2, the stub from layer 2 to the bottom layer is just hanging there, creating a little antenna that messes with high-frequency signals. So for high-speed boards (anything over 1GHz, like RF gear, 5G modules, or gaming motherboards), you need smaller vias, or better yet, back-drilled vias. Back-drilling is when we drill out the extra stub from the bottom, but that only works with through-hole vias, and it’s an extra step. Smaller vias have shorter stubs, so less signal degradation. I had a client a few months back who was having signal loss in their 2.4GHz router board—they were using 0.6mm vias, switched to 0.3mm, and their signal strength jumped 12% without changing anything else. Game changer. Also, impedance: the via’s impedance depends on its size, the surrounding copper, and the dielectric material between layers. If you’re designing for 50-ohm or 75-ohm signals, a too-big via will lower the impedance too much, and a too-small one will make it too high. Most EDA tools have via impedance calculators now, but don’t rely solely on that—send your design to your PCB supplier, and we can run a quick check for free. We do that all the time, because a small adjustment to via size can save you from a whole spin of boards.
Then there’s thermal considerations, especially for power boards. If you’re running high current (like 5A or more), you need vias that can handle that heat without melting or causing voltage drop. The current capacity of a via is directly tied to its size—bigger via = more copper, so more current it can carry. Let’s say you have a 0.5mm via, that can handle about 1A. A 0.8mm via? That’s around 2.5A. If you’re putting 3A through a 0.5mm via, it’ll get hot enough to lift the copper pad, and that’s a board failure waiting to happen. For power-heavy designs, we also recommend multiple smaller vias in parallel instead of one big one, because that spreads the current and heat better. I had a client who was designing a solar charge controller, they were using four 0.4mm vias for their power rail, we suggested swapping to six 0.3mm vias, and their operating temp dropped 8°C. That might not sound like much, but it doubles the lifespan of the board in outdoor conditions.
Soldering and assembly is another big one, and this is where a lot of new designers mess up. If you’re doing hand-soldering, you can’t use a 0.1mm via—way too tiny to get a soldering iron tip in there. Even for automated SMT assembly, your stencil size matters. The stencil aperture for a via pad needs to be big enough to let solder flow, but not so big that it wicks away from the component pads. For through-hole components, the via size has to match the lead size—if your component lead is 0.3mm, your via should be at least 0.05mm bigger than that to make soldering easy. Too small, and you’ll have cold joints or leads that don’t fit. Also, plated through-holes (PTH) vs. non-plated vias: PTH is standard for most boards, but non-plated are for things like test points. If you’re using a test point via, a 0.25mm drill is standard, but if you’re going to probe it, don’t make it smaller than 0.2mm or you’ll damage the pad when probing. I’ve seen so many boards with tiny test point vias that the assembly team can’t probe, so they have to add extra test points, which adds cost. Rule of thumb: if the via is going to be handled during assembly or testing, err on the side of slightly bigger, within reason.
Wait, let’s talk about common mistakes I see all the time. First, using the same via size for the entire board. That’s lazy! Your high-speed signals need small vias, your power rails need bigger ones, your test points can be medium size. Second, ignoring the minimum annular ring. Some designers set their annular ring to 0.05mm, which is technically what their EDA tool allows, but it’s impossible to manufacture reliably. Our minimum recommended annular ring is 0.1mm, and we can do 0.07mm if it’s a super tight design, but at your own risk—we don’t warranty boards with that. Third, not accounting for plating. When you drill a hole, we plate the inside with copper, so the finished hole is a tiny bit smaller than the drill size. So if you set your finished hole size to 0.2mm, you need to use a 0.22mm drill to get that 0.2mm finished hole. That’s a detail that trips up so many people. Fourth, forgetting about the board’s minimum trace width. If your board has 0.1mm traces, you can’t put a 0.3mm via next to them, because they’ll overlap during manufacturing. Always check the clearance between vias and traces—at least 0.1mm, more if you can.
Let’s do a quick example to make this real. Say you’re designing a 4-layer board for a Bluetooth speaker, with low-speed signals (less than 100MHz), a 2A power rail, and hand-soldered components. What via size makes sense? Let’s break it down: total board size is 50x50mm, so space is tight, not tiny like a watch. No super high-speed signals, so stub isn’t a big deal. 2A power rail, so we need a via that can handle at least 2.5A (for safety). Hand-soldered, so hole can’t be too tiny. Let’s pick a 0.3mm drill size. Finished hole will be ~0.28mm. Annular ring is 0.1mm, so pad size is 0.28 + 0.1 + 0.1 = 0.48mm. Clearance: 0.1mm from traces, so that works. Current: a 0.3mm via can handle ~1.2A, so we’ll put two parallel vias for the power rail—perfect, that’s enough for 2A, spreads heat, and still fits on the board. Signals can use the same 0.3mm via, no need for smaller ones. That’s simple, works, and won’t cost you an arm and a leg.
If you’re working on a different design: 10-layer 5G module (high-speed, tiny, 0.5A total current). Here, micro-vias are the way to go. 0.1mm drill size, finished hole ~0.09mm, annular ring 0.08mm (we can squeeze that for micro-vias, since space is non-negotiable). Back-drill the stubs to eliminate signal loss. That gives you tiny vias that don’t take up much space, keep signals clean, and handle the low current fine. The extra cost for micro-vias is worth it here, because if you used standard vias, the board would be too big for your design.
One last thing: always talk to your PCB supplier before finalizing your via sizes. We’ve seen every trick in the book, and we can spot issues you’d never catch in your EDA tool. For example, a designer once used 0.2mm vias for a 12-layer board, and we noticed that the drill bit would break halfway through because the stackup was too thick for such a small drill. We suggested switching to 0.25mm, which was still small enough for their space constraints, and saved them from a whole batch of defective boards. We don’t charge extra for that feedback—it’s part of the service, because we want you to come back.
If you’re in the middle of a design right now, or you’re starting a new project and want to avoid the headache of via size missteps, hit us up. No pushy sales talk, just honest advice to get your boards right the first time. We’ve got engineers on staff who can run impedance checks, current calculations, and even mock up different via size options for your design. Let’s get your board built without the surprises.
PCB References
IPC-2221: Printed Board Design Standard
IPC-7351: Generic Requirements for Surface Mount Design and Land Pattern Standard
High-Speed Signal Propagation: Advanced Black Magic, Howard Johnson
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