Understanding Gerber Files and Ordering PCBs from a Fab House

1. Introduction

Gerber is the industry-standard file format that virtually every PCB fab in the world can read — it describes the geometry of each layer on the board (copper, soldermask, silkscreen, board outline, etc.) as 2D vectors, along with a separate drill file for pad/via holes. Understanding what each Gerber layer means lets you check your own design before sending it out, avoiding a botched order from a missing layer or a wrong hole size. This guide explains the common Gerber layers, how to review them with a Gerber viewer, and the general PCB fab ordering process — using the Gerber set exported from an ESP32 DevKit V4 + DHT22 circuit as the running example throughout.

2. Components Needed (the circuit used to export the example Gerbers)

Component	Qty	Notes
ESP32 DevKit V4	1	The main control board
DHT22 (AM2302)	1	The example sensor, shown on the PCB layout

3. Wiring Diagram

DHT22	ESP32 DevKit V4
VCC	3V3
GND	GND
DATA	GPIO4

4. Gerber Layers You Should Know

Layer	Meaning
F.Cu / B.Cu	The front copper (F.Cu) and back copper (B.Cu) layers — where the actual conductive traces and pads live
F.Mask / B.Mask	The soldermask layer — areas NOT covered by insulating paint, exposing bare copper for soldering; everywhere else is coated (usually green) to protect the copper from oxidation/shorts
F.SilkS / B.SilkS	The silkscreen layer — text, symbols, and component outlines printed on the board surface to help whoever assembles it identify component placement and pinout
F.Paste / B.Paste	The solder paste layer — only needed when making a stencil for SMD reflow soldering, not required for a simple hand-soldered board
Edge.Cuts	The board outline — defines the PCB's final physical shape and dimensions
Drill File (Excellon)	Not strictly a Gerber file, but always included — a list of coordinates and diameters for every drilled hole (through-hole pads, vias, mounting holes)

For the ESP32 + DHT22 circuit in this guide, the PCB needs at minimum: F.Cu (copper connecting the VCC/GND/DATA signals), F.Mask, F.SilkS (printing component names/pins), Edge.Cuts, and a drill file for the through-hole pads on the ESP32 header and the DHT22.

5. Checking Gerbers with a Viewer Before Sending Them Out

After exporting Gerbers from KiCad (File → Fabrication Outputs → Gerbers, along with Generate Drill Files), always reopen the full set in a Gerber viewer (built into KiCad, or your fab's online viewer) to cross-check before sending:

• Toggle each layer on and off individually to make sure nothing is missing (especially Edge.Cuts — without it, the fab has no idea what shape to cut the board into).
• Check that traces and pads appear in the same positions as in the PCB Editor — a mismatch usually means the wrong unit (mm/inch) or the wrong coordinate origin was used on export.
• Check that the silkscreen doesn't overlap bare copper pads — this causes printed text to disappear or pads to get obscured, making soldering harder.
• Cross-check the number of holes in the drill file against the actual number of through-hole pads — a missing hole means that component simply won't fit.

6. The General PCB Fab Ordering Process

Most PCB fabs follow a fairly similar ordering process:

1. Zip the files: bundle all the Gerber and drill files into a single .zip archive.
2. Upload to the ordering system: most fabs automatically parse the Gerbers and show a 2D/3D preview for you to confirm before ordering.
3. Choose manufacturing options: number of copper layers, board dimensions, board thickness (usually 1.6mm by default), soldermask color, surface finish (HASL, ENIG, etc.), and order quantity.
4. Confirm the preview and pay: fabs typically run their own internal DRC based on their manufacturing capabilities — if they spot a problem (too-thin traces, too-tight spacing), they'll flag it before production.
5. Production and shipping: standard (non-expedited) production usually takes a few business days, plus shipping time depending on your location.

Actual pricing depends on layer count, dimensions, quantity, and the fab itself — this guide only describes the general process and doesn't name a specific price or vendor, since the market changes constantly.

7. ESP32 + DHT22 Sample Code (the circuit used to export the example Gerbers)

#include <DHT.h>

#define DHTPIN 4
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);

const unsigned long TELEMETRY_INTERVAL_MS = 2000;
unsigned long lastTelemetryAt = 0;

void setup() {
  Serial.begin(115200);
  delay(200);
  Serial.println();
  Serial.println(F("=== ESP32 + DHT22 - Vi du minh hoa cho bai viet KiCad/PCB ==="));
  Serial.println(F("Boot OK. Khoi tao cam bien DHT22..."));

  dht.begin();

  Serial.println(F("San sang doc du lieu."));
}

void loop() {
  unsigned long now = millis();
  if (now - lastTelemetryAt >= TELEMETRY_INTERVAL_MS) {
    lastTelemetryAt = now;

    float humidity = dht.readHumidity();
    float temperatureC = dht.readTemperature();

    Serial.print(F("{\"temperature_c\":"));
    if (isnan(temperatureC)) {
      Serial.print(F("null"));
    } else {
      Serial.print(temperatureC, 1);
    }
    Serial.print(F(",\"humidity_pct\":"));
    if (isnan(humidity)) {
      Serial.print(F("null"));
    } else {
      Serial.print(humidity, 1);
    }
    Serial.print(F(",\"uptime_ms\":"));
    Serial.print(now);
    Serial.println(F("}"));

    if (isnan(humidity) || isnan(temperatureC)) {
      Serial.println(F("[WARN] Doc cam bien DHT22 that bai - kiem tra day noi hoac dien tro keo len DATA."));
    }
  }
}

8. Common Issues

Issue	Cause	Fix
Fab reports "missing outline layer"	Forgot to enable Edge.Cuts when exporting Fabrication Outputs	Re-export the Gerbers, making sure Edge.Cuts is selected in the layer list
The board arrives at the wrong size	Wrong unit or scale used in the Plot dialog when exporting Gerbers	Double-check the unit (mm) and confirm via a Gerber viewer before sending, comparing the displayed dimensions against the original design
Holes are missing or misplaced	Forgot to check "Generate Drill Files", or used a drill format the fab doesn't support	Re-export the drill file in Excellon format, and check that the hole count matches the number of through-hole pads
Silkscreen text is faint or missing on the physical board	Silkscreen overlapped a bare copper pad and got automatically trimmed by the fab to prevent solder bridging	Check it in a Gerber viewer and move the silkscreen text off the pad area before re-exporting

9. Summary

A complete Gerber set includes the copper layers (F.Cu/B.Cu), soldermask (Mask), silkscreen (SilkS), board outline (Edge.Cuts), and an accompanying drill file. Before sending it to a fab, always reopen it in a Gerber viewer to check that every layer is present, dimensions are correct, and there's nothing rendering unexpectedly. Most fabs follow the same ordering flow: zip the files → upload → confirm the preview → pay → manufacture → ship. Understanding this flow lets you confidently order your first PCB without depending on any one specific vendor.