PCB design file output is the final stage of the PCB design process, where the digital design (created in CAD software like Altium Designer, KiCad, or Eagle) is converted into a set of standardized, manufacturing-ready files that PCB fabricators and assemblers use to produce the physical board. Unlike intermediate design files (e.g., schematic PDFs), output files contain precise, machine-readable data—including trace layouts, component footprints, drill locations, and material specifications—ensuring the fabricated PCB matches the designer’s intent. A complete PCB design file package must be accurate, comprehensive, and compliant with manufacturing standards (e.g., IPC-2221), as errors or missing data can lead to costly reworks, delays, or non-functional boards.

Key types of PCB design output files and their purposes include:

Gerber Files: Gerber files (the most critical output) are a standard format (defined by Ucamco) that describes the geometry of each PCB layer—copper layers (top, bottom, inner), solder mask (top/bottom), silkscreen (top/bottom), and solder paste (top/bottom). Each layer is saved as a separate Gerber file with a specific extension: .GTL (Top Copper), .GBL (Bottom Copper), .GTS (Top Solder Mask), .GBS (Bottom Solder Mask), .GTO (Top Silkscreen), .GBO (Bottom Silkscreen), .GTP (Top Solder Paste), .GBP (Bottom Solder Paste). Gerber files include detailed information like trace width (minimum 0.1mm for most boards), pad size (minimum 0.2mm for 0402 components), and via dimensions (drill size + annular ring—e.g., 0.3mm drill + 0.6mm annular ring). Designers must ensure Gerber files are generated with the correct units (millimeters, not inches) and resolution (2000 dpi or higher) to avoid fabrication errors.

Drill Files: Drill files specify the location, size, and type of holes (through-hole, blind, buried) to be drilled in the PCB. The most common format is Excellon Drill File (extension .DRL), which includes: hole coordinates (X/Y positions relative to the board origin), drill diameter (e.g., 0.3mm for signal vias, 1.0mm for through-hole components like resistors), and hole type (P for plated, N for non-plated). A companion Drill Tool List (extension .TXT) lists all drill sizes used, their quantities, and tool numbers—critical for fabricators to set up drilling machines. For PCBs with blind/buried vias, additional drill files (e.g., .BDL for blind holes) are required to specify the depth of each hole (e.g., 0.5mm depth for a blind via from top to inner layer 2).

Bill of Materials (BOM): The BOM is a spreadsheet (typically Excel or CSV) that lists all components required for PCB assembly, including: component reference designator (e.g., R1, C2, U1), part number (e.g., 0402 10kΩ 5% resistor: RC0402JR-0710KL), description (e.g., “Chip Resistor, 0402, 10kΩ, 5%, 1/16W”), quantity, manufacturer, and supplier (e.g., Digikey, Mouser). The BOM must be accurate and up-to-date—missing or incorrect part numbers can lead to wrong components being soldered (e.g., a 10Ω resistor instead of 10kΩ, causing circuit failure). Advanced BOMs include lifecycle status (e.g., “Active” or “Obsolete”) and alternative part numbers to mitigate supply chain risks.

Assembly Drawings: Assembly drawings (PDF or DXF format) provide visual guidance for PCB assemblers, showing: component placement (with reference designators), polarity markers (for diodes, capacitors, and ICs), solder paste requirements (e.g., “0.2mm paste deposit for QFP-64 package”), and inspection criteria (e.g., “IPC-A-610 Class 2 for consumer electronics”). They include dimensions (board size, component clearance), notes on special assembly processes (e.g., “Hand-solder U1 due to heat sensitivity”), and a revision history (to track design changes). For high-volume assembly, 2D or 3D STEP files may be included to help program pick-and-place machines.

Design Rule Check (DRC) Report: The DRC report (generated by the CAD software) verifies that the design complies with manufacturing constraints (e.g., minimum trace width, clearance, and hole size) and safety standards. It lists any violations (e.g., “Trace width 0.08mm < minimum 0.1mm”) and their locations, allowing designers to fix issues before file output. A clean DRC report (no critical violations) is required by most fabricators to accept the design.

Best practices for PCB design file output:

Zip all files into a single package (labeled with project name and revision, e.g., “PCB_Project_Rev1.0.zip”) for easy sharing.

Include a readme file with instructions for fabricators: board thickness (e.g., 1.6mm), material type (e.g., FR-4), copper weight (e.g., 1oz), and surface finish (e.g., HASL, ENIG).

Verify files with a Gerber viewer (e.g., GerbView) to ensure layers align correctly, no traces are missing, and drill holes match pad locations.

By providing a complete, accurate set of output files, PCB designers streamline the manufacturing process, reduce errors, and ensure the final product meets design specifications.