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A few thousandths of an inch. That's all it takes.

Here's something most designers don't think twice about: the ring of copper around a via.

It's small. It's routine. It's the kind of thing you place and move on from.

But get it wrong, and it's one of the fastest ways to stall a quote, or worse, get flagged after your board's already in fab or assembly review. We see it happen more than you'd think, and it usually comes down to one of four scenarios. Small layout decisions can create downstream challenges for both fabrication and PCB assembly, resulting in engineering questions, delays, or redesigns. If you are ever in doubt, contact our support team early to discuss your design before placing your order

From Fab to Assembly: Four Via Scenarios 
Every Designer Should Know

1

THE GOOD SCENARIO (SO YOU KNOW WHAT RIGHT LOOKS LIKE)
Give your via enough ring area, and even if the drill lands slightly off-center, you're fine. A little imperfection in placement won't hurt your connectivity as long as there's enough copper to work with.

From an assembly perspective, robust annular rings also improve long-term solder joint reliability by ensuring plated through-holes maintain strong electrical and mechanical integrity throughout the assembly process.

2

THE ZERO-WIDTH RING

Not enough ring area, and the hole can creep right up to the edge of the pad, sometimes touching it. That's a zero-width annular ring, and when the drilled hole becomes tangent with the outer rim, you've got a connection problem between the via and the copper traces. It also violates Class 3 requirements outright, which means it won't pass review as-is.

For assembly, insufficient annular rings can also reduce process margins, making the board more susceptible to defects that impact reliability during soldering and inspection.

3

THE BREAKOUT
Sometimes the drill bit deviates outside the pad during drilling. That's called an annular breakout, and it causes more than one headache: connection problems between the via and the layers, complications with component placement and solderability, and in the worst case, a direct short if the breakout is severe enough. The fix is straightforward, maintain an 8-mil drill-to-copper distance, but it has to be built into the design from the start, not caught after the fact.

Breakouts can also complicate automated optical inspection (AOI) and make troubleshooting more difficult during assembly, increasing engineering review time before production can begin.

4

THE TOO-CLOSE CALL
Place two vias too close together, and the current running through them can get high enough to short the two together. This is conductive anodic filament (CAF) formation, and it's one of those failures that doesn't show up until the board's already stressed in the field.

None of these look like mistakes on screen. A ring that's a hair too thin. A via placed just a little too close to its neighbor. But they're some of the most common reasons a design gets sent back, and they're all avoidable with the right spacing built in up front.

Tight via spacing can also restrict component placement flexibility and make routing around dense BGAs or fine-pitch devices more challenging, often requiring additional design review before assembly.

None of these look like mistakes on screen, a ring that's a hair too thin, a via placed just a little too close to its neighbor. But they're some of the most common reasons a design gets sent back, and they're all avoidable with the right spacing built in up front.

The best PCB designs are optimized for fabrication, assembly, and long-term reliability, not just manufacturable. Catching these details early means fewer engineering questions, faster quote turnaround, and a smoother path to production.

That's where the ASC Sunstone and Screaming Circuits partnership helps:  Two companies aligned on fabrication and assembly, catching issues before they become delays.

Contact Sunstone Support
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