Preparing Your Gerber Files for a Smooth China PCB Fabrication Process

Ordering printed circuit boards from China has become standard practice for engineers and businesses worldwide. The combination of competitive pricing, fast turnarounds, and advanced manufacturing capabilities makes Chinese PCB fabs an attractive choice. But none of that matters if your Gerber files are a mess. The Gerber format is the universal language between your design and the factory floor, and preparing it correctly is the single most important step to avoid delays, defects, and frustrating back-and-forth with your manufacturer.

In this guide, we walk through every layer, every file, and every common pitfall you need to know before uploading your Gerber package to a Chinese PCB Fabrication partner.

What Are Gerber Files and Why Do They Matter?

Gerber files are open-standard vector image files that describe each physical layer of a PCB. Originally developed by Gerber Scientific, the format (now officially RS-274X) uses aperture definitions and draw/flash commands to represent copper traces, solder masks, silkscreen legends, drill hits, and more.

When you send a PCB order to a factory in Shenzhen, Dongguan, or anywhere else in China, the first thing their CAM engineer does is load your Gerber files into their pre-production software. If the files are incomplete, inconsistent, or use outdated formats, the entire process stalls before it even starts.

Think of Gerber files as the construction blueprint for your board. A missing layer is like a missing page in that blueprint — the builder has to guess, and guessing on a PCB is expensive.

The Essential Gerber Layers Every Factory Expects

A complete Gerber package for a standard double-sided PCB includes at minimum the following layers. Each one must be a separate file with a clear, conventional name:

Copper Layers

• Top Copper (GTL or F.Cu) — The component-side copper pattern: traces, pads, and planes.
• Bottom Copper (GBL or B.Cu) — The solder-side copper pattern. For single-sided boards, this layer is typically empty or omitted.
• Inner Copper Layers (G1, G2, etc.) — For multilayer boards (4-layer, 6-layer, and up), each internal signal or plane layer needs its own Gerber file.

Solder Mask Layers

• Top Solder Mask (GTS or F.Mask) — Defines the openings in the green (or other color) solder resist on the component side.
• Bottom Solder Mask (GBS or B.Mask) — Same as above for the solder side.

Silkscreen Layers

• Top Silkscreen (GTO or F.SilkS) — Reference designators, component outlines, logos, and polarity marks on the top side.
• Bottom Silkscreen (GBO or B.SilkS) — Silkscreen on the bottom side, if applicable.

Solder Paste Layers

• Top Paste (GTP or F.Paste) — Used for stencil fabrication in Smt Assembly. Required if you are also ordering assembly.
• Bottom Paste (GBP or B.Paste) — Same for the bottom side.

Board Outline and Drill Data

• Board Outline (GKO or Edge.Cuts) — The physical shape of the board. This is critical. Without it, the factory cannot define the routing path.
• Drill File (TXT or .drl) — Excellon-format file specifying the locations and sizes of all plated and non-plated through-holes.
• Drill Map (optional but recommended) — A visual reference showing drill symbols and their corresponding sizes.

Missing even one of these layers can delay your order by days while the factory emails you asking for clarification. Chinese fabs run on tight schedules — a missing file on Friday might push your delivery to the following week.

File Naming Conventions: Speak the Factory's Language

Chinese PCB manufacturers deal with thousands of orders daily. Consistent, human-readable file names help their CAM team identify each layer at a glance. While most modern factories auto-detect layers, using standard naming conventions eliminates ambiguity.

Here is a widely accepted naming pattern:

Notice the pattern: the same base name followed by a three-letter extension that describes the layer. Avoid creative names like myboard_final_v3_top_copper_really_final.gbr — they only slow down the CAM review.

Common Gerber Preparation Mistakes and How to Avoid Them

After years of working with Chinese PCB fabs, certain errors show up again and again. Here are the top offenders and how to fix them before you upload.

1. Using Extended Gerber (RS-274X) vs. Standard Gerber (RS-274D)

Always export in RS-274X (Extended Gerber) format. The older RS-274D format requires a separate aperture list file, and many modern CAM systems do not support it. If your EDA tool still defaults to the old format, change it. Every major Chinese fab expects RS-274X.

2. Missing or Unclear Board Outline

This is the number-one cause of production delays. Your board outline must be a closed contour on a dedicated layer. Do not rely on the copper layer or solder mask to define the edge — the routing machine needs explicit edge cuts.

If your outline has gaps or overlapping segments, the CAM software may interpret the shape incorrectly, resulting in boards that are routed to the wrong dimensions.

3. Drill File Format Inconsistencies

Drill files must match the coordinate format of your Gerber files. The most common issue is a unit mismatch — Gerber files in millimeters but the drill file in inches, or vice versa. Always verify:

• Units (mm or inch) match across all files
• Coordinate format (e.g., 3:3 or 4:4) is consistent
• Zero suppression (leading or trailing) is set correctly
• Plated and non-plated holes are distinguished (some fabs require separate drill files for each type)

4. Silkscreen Over Solder Mask Openings

When silkscreen legend overlaps bare copper pads, the ink can interfere with solderability. Most CAM tools clip silkscreen automatically, but not always. Check for silkscreen text or outlines that extend onto exposed pad areas. This is especially common with component reference designators placed too close to pads.

5. No Aperture List Embedded

RS-274X embeds aperture definitions directly in the file header. If your export produces separate aperture list files (.apr), make sure they are included in your ZIP package. Better yet, ensure your EDA tool embeds them — this is the default in KiCad, Altium, and recent versions of Eagle.

6. Origin Point Far From the Board

If your design origin (0,0 coordinate) is far away from the actual board geometry, some CAM systems have trouble fitting the data into their workspace. Center the board near the origin before exporting. It takes five seconds and saves potential headaches.

Step-by-Step: Exporting Gerber Files From Popular EDA Tools

KiCad (Version 8+)

1. Open your PCB layout and click File → Fabrication Outputs → Gerbers.
2. Select the output directory.
3. Ensure "Use Protel filename extensions" is checked for maximum compatibility with Chinese fabs.
4. Set coordinate format to 4:6 absolute.
5. Check "Generate Gerber file for each layer" and include all relevant layers.
6. Click Plot, then click Generate Drill Files.
7. Verify the output folder contains all expected .gbr and .drl files.

Altium Designer

1. Open the PCB document and go to File → Fabrication Outputs → Gerber Files.
2. In the Gerber Setup dialog, under the Layers tab, select all required layers.
3. Under Format, set units to Millimeters and format to 4:4.
4. Under Advanced, uncheck "Use alternate aperture naming".
5. Click OK to generate. Altium will create a Project Outputs folder with all Gerber files.
6. Generate drill files separately via File → Fabrication Outputs → NC Drill Files.

Eagle (Autodesk)

1. Open the board layout and run the ULP script cam2gerber.ulp or use the built-in CAM processor.
2. Make sure all layers are selected and output format is RS-274X.
3. Set coordinate format and units to match your design grid.
4. Run the job to generate files in your chosen directory.

Verifying Your Gerber Package Before Upload

Never send Gerber files to a factory without reviewing them first. A free Gerber viewer is your best insurance policy. Here are the most reliable options:

• GerbView (online) — Upload your ZIP and instantly see every layer. Fast, no installation required.
• ViewMate (Druid CAM) — Professional-grade viewer that can also run DRC checks on Gerber data.
• Gerbv (open source) — Linux-native viewer, solid for quick layer-by-layer inspection.

During your review, check the following:

• Layer alignment: Do all layers register correctly? Misaligned layers indicate coordinate origin problems.
• Board outline completeness: Is the edge a single, closed contour with no stray lines?
• Drill hits: Do via and pad holes appear in the correct locations? Are sizes accurate?
• Copper clearance: Are traces and pours maintaining minimum spacing from the board edge?
• Silkscreen legibility: Can you read reference designators? Are they clipped at pad boundaries?

Catching a misaligned drill file on your own screen is far cheaper than receiving 500 boards where nothing lines up.

Special Considerations for Chinese PCB Factories

Working with China-based manufacturers introduces a few additional requirements that may differ from Western fabs.

Panelization Preferences

Many Chinese fabs prefer to handle Panelization themselves using their in-house tooling. If you send pre-panelized Gerber files, it can complicate their process — especially V-cut scoring and fiducial placement. Unless you have very specific Panelization needs, provide single-board Gerber files and let the factory panelize according to their standard guidelines.

Impedance Control Files

If your design requires Controlled Impedance (50Ω, 100Ω differential, etc.), most Chinese fabs will ask for a separate impedance control document or stackup specification. Include this information in your order notes, not embedded in the Gerber files themselves. The Gerber format has no native way to express impedance requirements.

Quality Standard Compliance

Specify your acceptance criteria upfront. The default for most Chinese fabs is IPC-A-600 Class 2. If your application requires Class 3 (medical, aerospace, automotive), state this clearly when placing the order — it affects their inspection procedures and, accordingly, the price.

Communication About Design Intent

Chinese CAM engineers are skilled, but they cannot read your mind. If a particular feature is intentional (for example, a copper pour with unusual spacing, or a non-standard pad shape), add a readme.txt to your Gerber ZIP package explaining it. This prevents the factory from "correcting" something you deliberately designed.

Packaging and Sending Your Files

The final step is packaging everything into a single ZIP archive. Here is what it should contain:

• All Gerber layer files (.gbr, .gtl, .gbl, etc.)
• Drill file(s) (.txt, .drl)
• Board outline file (if not already included as a Gerber layer)
• A readme.txt with any special instructions or design notes

Do not nest files in subdirectories. Place everything in the root of the ZIP. Do not include your native EDA project files (.kicad_pcb, .SchDoc, .brd) unless the factory specifically requests them — Gerber files alone are sufficient for fabrication.

Most Chinese fabs accept uploads through their web portal, email, or cloud storage links. File size is rarely an issue — even complex multilayer designs typically produce ZIP packages under 1 MB.

What Happens After You Upload

Once your files reach the factory, here is the typical flow:

1. CAM Review: An engineer loads your Gerber files into CAM350 or Genesis2000 and checks for manufacturability. This typically takes 4–24 hours depending on order volume.
2. Dfm Feedback: If any issues are found, the factory will email you with screenshots and suggested corrections. Respond quickly to avoid delays.
3. Engineering Approval: Once everything checks out, the CAM data is released to production. You may receive a Gerber review confirmation email — review it carefully.
4. Production: Film plotting, etching, drilling, lamination, and surface finish processes begin according to your specifications.

The CAM review step is where most problems surface. Submitting clean, well-organized Gerber files dramatically reduces the chance of pushback at this stage, which translates directly to faster delivery.

Conclusion

Preparing Gerber files is not the most exciting part of Pcb Design, but it is arguably the most consequential step in the manufacturing pipeline. A well-prepared Gerber package — complete layers, consistent formats, clear naming, and a verified board outline — is the difference between a smooth production run and a week of email ping-pong with your factory.

Chinese PCB manufacturers have invested heavily in advanced CAM systems and skilled engineers. They are ready to build your board. Your job is to give them a blueprint that leaves nothing to interpretation. Follow the guidelines in this article, verify your output before uploading, and you will find that the fabrication process runs exactly as it should — smoothly, predictably, and on schedule.

Frequently Asked Questions

Do I need to include my original EDA design files when ordering from a Chinese PCB factory?

No. Gerber files are the industry-standard manufacturing format. Chinese fabs do not need your native KiCad, Altium, or Eagle files. Gerber files contain everything required for fabrication. Only send native files if the factory explicitly requests them for design review or assembly purposes.

What if my Gerber files use inches instead of millimeters?

Most Chinese fabs accept both units, but you must ensure consistency across all files in your package. If your copper layers are in millimeters but your drill file is in inches, the CAM software will misinterpret hole positions. Pick one unit system and stick with it throughout.

How do I know if my board outline is correct?

Open your Gerber files in a viewer and check the outline layer independently. It should show a single, closed shape with no gaps, overlapping segments, or stray lines. The outline should exactly match the intended board dimensions with no extra geometry.

Should I panelize my boards before sending Gerber files to China?

In most cases, no. Chinese fabs typically prefer single-board files and handle panelization in-house using their own tooling. Pre-panelized files can complicate V-scoring, tab routing, and fiducial placement. Provide single-board Gerber data and specify your panelization requirements in the order notes instead.

What coordinate format should I use for Gerber files?

The safest choice is 3:3 or 4:4 absolute coordinates in millimeters. This is the most widely supported format across Chinese CAM systems. Avoid incremental (relative) coordinates — they are technically valid but less commonly used and more error-prone during CAM processing.