How to Check Gerber Files for Manufacturing Problems

Introduction

When working on a complex PCB layout, designers tend to rely heavily on the DRC (Design Rule Check) engine within their CAD software to spot errors that could reduce manufacturing yield. However, reliance on DRC alone is not always sufficient. Some electrically correct design choices will create DFM (Design for Manufacturing) problems that need to be identified and rectified before sending a PCB out for manufacturing.

PCB designers typically perform these checks in their layout file before it is exported to Gerber files, but the Gerber files themselves should always be reviewed independently before a board is sent to the fabrication house.

1. Table of Contents
2. Design Problems You Can Find in Your Gerber Files
3. Problems with Manual Gerber Checks
4. Why Use Gerber File Checker Software
5. HQDFM: Free Online Gerber Viewer and DFM Analysis
6. Frequently Asked Questions (FAQ)

Design Problems You Can Find in Your Gerber Files

The list of design and DFM problems below is not exhaustive, but these are critical areas that any designer should verify before releasing their data to a manufacturer. There are 6 common DFM problems found in many PCB designs:

• Incorrect solder mask opening on SMD pads: If there is no opening or the opening is too large, a solder ball may flow during reflow and bridge two leads on an SMD component, causing a short circuit.
• Vias in SMD pads: This is often a mistake in the component footprint. You might not see this in your CAD tools if the view configuration is not set to show drill hits on top of pads. This can cause solder wicking and poor connections.
• Acid traps: Manufacturers have specific corner angle requirements to prevent acid traps from occurring during the etching process. Acute angles can trap etchant, leading to over-etching and open circuits.
• Incorrectly sized vias: In multilayer boards, vias might be defined as too small for standard mechanical drilling, or their aspect ratio (board thickness vs. hole diameter) might be too large (typically greater than 10:1), requiring expensive laser drilling or resulting in plating failures.
• Clearances: Common clearance mistakes include conductors placed too close together (risking arcing in high-voltage boards), 1 mil spacing between grounded vias and copper pours (clearance conflicts), and overlapping drill hits which can break drill bits.
• Trace widths for controlled impedance: Some CAD tools do not enforce an impedance profile during routing. It is often up to the designer to manually set the correct width on all impedance-controlled nets based on the stack-up.

In the example above, thin copper can be identified in the top layer, and there may be a clearance problem between traces and vias on the inner layer.

It is important to note that these design problems might not trigger an electrical DRC error unless you have specifically configured complex design rules for these DFM points in your PCB design software. Therefore, designers need to check their Gerber files for these DFM problems either manually or, preferably, with automated Gerber file checker software.

Problems with Manual Gerber Checks

Designers need to review these potential issues before starting their fab run. However, not all designers have access to the enterprise-level CAM engineering software used by professional manufacturers. This usually leaves designers relying on the native DRC engine in their CAD tools or manually scrolling through layers in a basic viewer. Here are the risks associated with manual checks:

• Shorts and opens are not always obvious: Since manual Gerber file checks often happen on each layer individually, it is difficult to spot opens and shorts that involve complex layer transitions (blind/buried vias). These problems may slip past a CAD DRC, and basic viewers will not highlight net logic connectivity.
• Easy to miss DFM mistakes without measuring: Simple design mistakes like small vias, insufficient solder mask slivers, excessive gaps, and length mismatches require precise measurements. Inspecting every aspect of the layout manually is prone to human error.
• Checking complex layouts takes too long: While Gerbers for simple 2-layer designs can be reviewed manually, complex multilayer PCB layouts with thousands of tracks simply take too long to review thoroughly by eye.

With so many potential risks before fabrication, PCB designers need an automated solution to ensure efficiency and accuracy.

Use a Gerber File Checker Software

The fastest way to spot manufacturability problems in your Gerber files is to use dedicated software. Most applications accept Gerber files in RS-274X and X2 formats, while others support IPC-2581, ODB++, or native CAD files.

These applications are designed to simulate the manufacturing process and spot problems that will reduce fabrication or assembly yield. The best Gerber checking programs provide specific benefits beyond simple viewing:

• Optimized analysis: High-quality DFM tools optimize the process of loading, rendering, and analyzing files. While older programs might struggle with complex data, modern cloud-based tools can process designs in minutes.
• Cost analysis: When reviewing a design, seeing how geometry changes affect the production price allows designers to value-engineer their boards to save time and money.
• Automated calculations: As long as nets can be identified, DFM tools use the geometry of interconnects to calculate impedance, routing length, utilization rate, and pad/silkscreen overlap automatically.
• Gerber compare feature: Advanced applications allow you to overlay and compare two sets of Gerber files (e.g., Revision A vs. Revision B) to quickly verify changes before production.

Example: CAD tools often apply 1 mil clearances by mistake when grounding a net to a plane or polygon. These vias are supposed to be connected to the surrounding plane, and this clearance mistake can be instantly flagged by an automated checker.

With these capabilities, you can identify design problems before the data reaches the factory floor. Unless you utilize a turnkey service with enhanced inspection, a budget fabricator might not pause production to warn you of these errors, leading to a failed run (scrap).

HQDFM Free Online Gerber Viewer and DFM Analysis Tool

No download, no sign-up required for basic viewing, no obligation.

NextPCB Online Gerber Viewer is a free, advanced PCB visualizer with in-depth Design for Manufacture (DFM) analysis capabilities. It supports RS-274x and Extended (X2) Gerber files from a broad range of PCB CAD software, including Altium Designer, OrCad/Allegro, Eagle, KiCad, DipTrace, DesignSpark, and EasyEDA.

Developed by HQ Electronics, HQDFM leverages over 15 years of industry expertise to provide advanced manufacturing insights directly in your web browser.

>> Try Best Free Online Gerber Viewer

Once you have checked your PCB layout in HQDFM, you can seamlessly transition your design into fabrication with NextPCB, one of China’s most experienced and reliable PCB manufacturers. The pricing analysis provided by HQDFM is accurate, ensuring your design passes NextPCB’s engineering review process smoothly.

Frequently Asked Questions (FAQ)

What is the difference between DRC and DFM?

DRC (Design Rule Check) is performed within your CAD software to ensure the layout meets specific electrical constraints (like trace width and spacing) defined by the designer. DFM (Design for Manufacturing) analyzes the design to ensure it can actually be built by the factory equipment. DFM checks for issues like acid traps, solder mask slivers, and drill aspect ratios that DRC often misses.

Can I edit Gerber files after exporting them?

Yes, Gerber files can be edited using CAM software (Computer-Aided Manufacturing) or advanced Gerber editors. However, it is generally recommended to make changes in the original CAD source files and re-export the Gerbers to ensure data consistency between your schematic and the final layout.

Why are my vias covered by solder mask?

If your vias are covered, it usually means the "tented vias" option was selected during Gerber generation, or the solder mask expansion was set to zero or a negative value. If you need exposed vias for testing, ensure your solder mask expansion is set correctly in your CAD tool.

What files do I need to send for PCB assembly?

For full turnkey PCB assembly, you typically need to provide:

1. - Gerber Files (for the bare board fabrication)
2. - Centroid File / Pick and Place File (XY coordinates for components)
3. - BOM (Bill of Materials)
4. - Assembly Drawings (optional but recommended)

How do I check if my PCB is manufacturable?

The most reliable method is to use a dedicated DFM tool like the HQDFM Viewer. This software simulates the manufacturing process and highlights areas that violate standard production capabilities, preventing costly delays.

About the Author

Arya Li, Project Manager at NextPCB.com

With extensive experience in manufacturing and international client management, Arya has guided factory visits for over 200 overseas clients, providing bilingual (English & Chinese) presentations on production processes, quality control systems, and advanced manufacturing capabilities. Her deep understanding of both the factory side and client requirements allows her to deliver professional, reliable PCB solutions efficiently. Detail-oriented and service-driven, Arya is committed to being a trusted partner for clients and showcasing the strength and expertise of the factory in the global PCB and PCBA market.

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