What files are in a Gerber package?

A complete Gerber fabrication package includes one file per physical layer and process step. Top copper (.GTL): the component-side copper pattern including traces, pads, and pour areas. Bottom copper (.GBL): the solder-side copper pattern. Inner layers (.G2, .G3, etc.): internal copper layers for power planes, ground planes, and internal signal routing. Top solder mask (.GTS): defines openings in the solder mask on the component side (negative image: the file shows where mask is removed). Bottom solder mask (.GBS): same for solder side. Top silkscreen (.GTO): component outlines, reference designators, polarity marks. Bottom silkscreen (.GBO): solder-side markings. Top paste (.GTP): stencil openings for solder paste application. Bottom paste (.GBP): same for bottom side. Drill file (.DRL or .XLN, Excellon format): defines all drill holes with XY coordinates and tool sizes. Separate files for plated and non-plated holes. Board outline (.GKO or .GM1): defines the PCB boundary and any internal cutouts. Fabrication notes: a separate document (PDF or Gerber layer) specifying stackup, material, impedance requirements, copper weight, surface finish, and special instructions. For RF boards, this document is critical.

What is special about RF PCB Gerber files?

RF PCB fabrication requires additional specifications beyond standard digital boards. Impedance control: the fabrication notes must specify target impedances (50 ohm microstrip, 50 ohm stripline, 100 ohm differential) with tolerances (typically plus or minus 10 percent). The fab house adjusts trace widths during manufacturing to hit the target impedance based on actual dielectric thickness and Er measurements. Stackup specification: exact layer order, dielectric materials (Rogers 4350B, Megtron 6, standard FR4), copper weights (0.5 oz, 1 oz, 2 oz), and prepreg/core thicknesses must be explicitly defined. RF boards often use mixed dielectric stackups (Rogers on signal layers, FR4 on power/ground) to balance performance and cost. Via specifications: for RF, via drill size, pad size, and anti-pad size in ground planes affect impedance and parasitic capacitance. Blind and buried vias (HDI) require separate drill files. Back-drilled vias (stub removal) require additional drill files with controlled depth. Surface finish: ENIG (Electroless Nickel Immersion Gold) is standard for RF due to consistent impedance and solderability. OSP degrades with reflow cycles, and HASL is too rough for fine-pitch RF components.

What is Gerber X2 vs RS-274X?

RS-274X (Extended Gerber): the long-standing industry standard since 1998. Self-contained files with embedded aperture definitions (no separate aperture list needed). Describes geometry only: the fab house must determine which file is which layer based on file naming conventions or a readme file. This is a frequent source of errors: mislabeled files lead to swapped layers, inverted masks, or missing drill data. Gerber X2: introduced in 2014, adds machine-readable metadata attributes to each file. Each file contains attributes that identify: file function (copper, solder mask, silkscreen, drill), layer polarity (positive/negative), layer position (top, bottom, inner), and other properties. This eliminates the layer-identification problem. The fab house CAM software automatically recognizes each file's purpose. Gerber X3 (in development): will add component placement data and BOM information, making the Gerber package a complete manufacturing dataset. IPC-2581: an alternative to Gerber that combines all manufacturing data into a single XML file. Includes stackup, materials, netlist, and component data. Gaining adoption but Gerber remains dominant for fabrication.

PCB Manufacturing

Gerber

/ger-ber/

PCB fabrication file standard. RS-274X: self-contained, embedded apertures. One file/layer: .GTL (top Cu), .GBL (bot Cu), .GTS/.GBS (mask), .GTO/.GBO (silk), .DRL (drill, Excellon). Gerber X2: adds layer-type metadata (auto-recognition). RF-critical: impedance control notes, mixed-dielectric stackup, via specs, ENIG finish. Fabrication notes document = lifeline for RF boards.

Standard: RS-274X

Current: X2

Drill: Excellon

Understanding Gerber Files

Gerber files are the universal language between PCB designers and fabricators. Every PCB ever manufactured started as a set of Gerber files. For RF engineers, the Gerber package and its accompanying fabrication notes are critical: errors in layer assignment, stackup specification, or impedance callouts result in boards that don't work at microwave frequencies.

The transition from RS-274X to Gerber X2 addresses the most common source of fabrication errors: mislabeled or misidentified layers. X2's machine-readable metadata eliminates guesswork at the fab house.

Gerber File Types

Copper layers:
.GTL (top), .GBL (bottom), .G2-.Gn (inner)

Mask/silk:
.GTS/.GBS (solder mask, negative)
.GTO/.GBO (silkscreen, positive)
.GTP/.GBP (paste stencil)

Mechanical:
.GKO/.GM1 (board outline)
.DRL/.XLN (drill, Excellon format)
Separate: plated vs non-plated holes

Gerber Format Evolution

Format	Year	Key Feature	Limitation	Status
RS-274D	1980s	Basic vectors	External apertures	Obsolete
RS-274X	1998	Embedded apertures	No layer metadata	Dominant
Gerber X2	2014	Layer attributes	No BOM/placement	Adopted
Gerber X3	WIP	Components+BOM	In development	Future
IPC-2581	2004	Single XML file	Adoption lag	Growing

Common Questions

Frequently Asked Questions

What files?

One per layer: .GTL/.GBL (copper), .GTS/.GBS (mask, negative), .GTO/.GBO (silk), .GTP/.GBP (paste), .DRL (drill, Excellon), .GKO (outline). Separate plated/non-plated drill. Fab notes PDF: stackup, materials, impedance, finish. RF boards: fab notes = most critical document.

RF specifics?

Impedance control: ±10% tolerance callout. Mixed dielectric: Rogers signal + FR4 power. Via specs: drill/pad/anti-pad sizes. Back-drill for stub removal. ENIG finish (consistent Z₀). Stackup drawing with exact thicknesses. Without these: board won't hit impedance targets at microwave.

X2 vs 274X?

RS-274X: geometry only, layer ID by filename convention (error-prone, swapped layers = scrapped boards). X2: machine-readable attributes per file (auto layer recognition). Eliminates mislabeling. X3 (WIP): adds component + BOM data. IPC-2581: single XML, all data, growing adoption.

Related Terms

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