What Actually Happens Between "Export Gerbers" and a Physical PCB Showing Up at Your Door

If you’ve ever designed a board in KiCad, EasyEDA, or Altium, clicked “Export Gerbers,” uploaded a zip file to a fab house, and then a couple weeks later a small padded envelope showed up with actual copper-and-fiberglass boards inside — you’ve probably wondered, at least once, what happens in between. What does a design file actually turn into on a factory floor, and why does it take days instead of minutes?

I went down this rabbit hole recently while debugging why a batch of boards came back with a slightly different impedance than I’d simulated. Understanding the fabrication pipeline turned out to be useful for more than just satisfying curiosity — it changed how I write my design rule checks. Here’s the short version, from a developer’s point of view rather than a process engineer’s.

Your Gerbers are a set of 2D stencils, not a 3D model

This is the part that took me longest to internalize: a PCB isn’t fabricated the way you’d picture a 3D print. There’s no printer that magically deposits copper in the right places layer by layer. Instead, each layer of your board starts as full-sheet copper, and the fab removes copper according to your Gerber file for that layer — closer to subtractive manufacturing than additive.

Roughly, the pipeline looks like:

1. Inner layers first. For a multilayer board, the internal copper layers get imaged and etched before anything is stacked. Whatever routing you buried on an inner layer is committed at this stage — no going back and rerouting after this point.
2. Lamination. The imaged inner layers get pressed together under heat with a bonding material (prepreg) sandwiched between them, along with the outer copper foils. This is where your stackup — the thing you probably just picked from a dropdown in your CAD tool — actually becomes physical.
3. Drilling. Every via and through-hole gets drilled through the stack. Small vias are usually laser-drilled; larger through-holes are mechanically drilled. This step is also why minimum via size and aspect ratio limits exist — a hole that’s too deep relative to its diameter is genuinely hard to plate reliably.
4. Plating. Copper is deposited onto the drilled hole walls so that a via actually connects the layers it’s supposed to connect, rather than just being an empty hole through fiberglass.
5. Outer layer imaging and etching. Same process as step 1, but for the top and bottom copper.
6. Solder mask, silkscreen, surface finish. The green (or whatever color) coating goes on, your reference designators get printed, and a finish like ENIG, HASL, or OSP is applied to the exposed copper pads so they don’t oxidize before you can solder to them.
7. Electrical test. Every board gets tested for opens and shorts — usually with a flying probe tester for small batches, or a fixed test fixture for high volume — before it ships.

None of this is exotic if you already know it, but it explains a lot of the DRC rules your CAD tool nags you about: minimum trace/space isn’t arbitrary, it’s a function of what the etching process can actually resolve; minimum drill size and annular ring aren’t arbitrary either, they’re tied to what can reliably be laser- or mechanically-drilled and then plated.

Why aspect ratio and via size actually matter to you

This is the part that bit me. I’d routed a design with some tight vias to save space, satisfied my CAD tool’s default DRC, and sent it off — only to have the fab flag a manufacturability issue on a couple of the smaller vias in a thicker section of the board. The default DRC rules in most CAD tools are conservative-but-generic; they don’t necessarily match a specific fab’s actual capability for your specific board thickness.

The practical fix, and the thing I do now on every board before ordering:

• Run your Gerbers through an actual DFM (design-for-manufacturability) check, not just a viewer. A viewer shows you what the board looks like; a DFM tool checks things like clearance violations, drill-to-copper spacing, and acid trap geometry against a real process capability, not just your CAD tool’s generic default rules.
• If you’re doing anything with buried or blind vias (common on denser HDI-style boards), ask explicitly about aspect ratio limits and whether laser drilling for microvias is done in-house — this varies a lot between fabs and directly affects whether your stackup is even manufacturable as drawn.
• Double-check your surface finish choice against your components. ENIG is the safer default for fine-pitch parts; OSP is cheaper but has a shorter shelf life before you need to solder; HASL is fine for through-hole-heavy boards but can be uneven under very fine-pitch SMD pads.

Prototype vs. production is a different optimization, not just a quantity slider

One thing that surprised me: a fab that’s great for 10-piece prototype turnarounds isn’t automatically the right choice once you’re ordering 5,000 units. Quick-turn prototyping is optimized for speed on a small batch — getting a handful of boards back in a day or two so you can validate a design. Volume production is optimized for consistency and cost per unit across much larger panel runs, with more incoming-material inspection and statistical process control layered in. Some shops do both well in-house; others quietly subcontract one side of it. If you expect to go from prototype to production with the same vendor, it’s worth asking directly whether both stages actually happen on their own floor.

Further reading

If you want the deeper version of this — the certification landscape (IATF 16949, ISO 13485, UL, and why AS9100 specifically is not universal across Chinese fabs even though the others often are), how flex and HDI fabrication differ from standard rigid boards, and a checklist for evaluating a fab before committing a production run — I found this write-up useful: How PCB Fabrication Works, What to Check, and How to Choose a Manufacturer. It also covers a 2026 EU customs change that affects anyone ordering boards for delivery into the EU, which is easy to miss until an order gets held up.

If you’ve hit your own manufacturability surprises going from CAD to fabricated board, I’d genuinely like to hear about them in the comments — the gap between “DRC passed” and “the fab can actually build this cleanly” seems to be where most of the non-obvious lessons live.