How to Prepare Perfect PCB Manufacturing Files: BOM, Centroid, and Stackup Documentation

Most PCB delays and assembly mistakes are not caused by bad layouts; they happen because the handoff package is incomplete or inconsistent. The three documents that cause the most trouble are the Bill of Materials (BOM), the centroid / XYRS file, and stackup documentation.

If your BOM does not match the centroid, or your stackup notes do not match your impedance needs, your manufacturer has to stop, ask questions, or guess. By treating these files as part of your design—not as an afterthought—you can make your boards cheaper, faster, and more reliable to build.

Step 1: Build a Clean, Production‑Ready BOM

Your BOM tells the factory exactly what to buy and place on the board. A messy BOM leads to wrong parts, line stops, and manual email ping‑pong.

A solid manufacturing BOM should include at least:

• Line number
• Reference designators (R1, C5, U3, etc.)
• Quantity per board
• Manufacturer part number (MPN)
• Description (value, tolerance, voltage, type)
• Package / footprint (0603, SOT‑223, QFN‑32, etc.)
• Mount type (SMT, THT, or DNP for “do not populate,” if applicable)

Best practices:

• Use one line per unique part and list all reference designators in a single field, not separate lines for each refdes.
• Ensure reference designators exactly match those in your PCB layout and silkscreen.
• Clearly mark any optional or “do not populate” components so the assembler does not order or place them.
• Include preferred alternates for critical parts to reduce supply‑chain risk.

MorePCB’s turnkey PCB assembly and small‑batch services rely on a clean BOM with correct MPNs and alternates, and their engineers can help you refine your template so every future project is easier to quote and build.

Step 2: Generate a Correct Centroid / Pick‑and‑Place (XYRS) File

The centroid (also called pick‑and‑place, XY, or XYRS file) tells SMT machines exactly where to place each component and how to orient it. If this file is wrong or incomplete, the line stops until someone fixes it.

A valid centroid file must include at least these fields for each SMT component:

• Reference designator (must match the BOM exactly)
• X coordinate
• Y coordinate
• Rotation (0–360 degrees)
• Side / layer (Top or Bottom)

Key tips:

• State in the header: units (mm or mil/inch), origin location (lower‑left of outline, board center, or another datum), and rotation convention (for example, 0° with pin 1 at a specific corner, CCW positive rotation).
• Include only placed SMT parts; through‑hole components are usually set by assembly drawings and silkscreen.
• After export, sanity‑check that the number of centroid rows equals the number of placed SMT parts in your BOM and that all coordinates are within the PCB outline.
• Do not manually “tweak” coordinates in a spreadsheet without re‑exporting from your CAD; any mismatch between layout and XY file can create hidden placement errors.

Manufacturers like MorePCB program SMT lines directly from your centroid and BOM, so accurate XYRS data lets them build boards quickly—with fewer manual checks and lower cost.

Step 3: Document Your Stackup and Layer Specs

Stackup documentation explains how the board is built: layers, materials, thicknesses, copper weights, and any impedance or high‑speed constraints. For 4‑layer and above, or any design with controlled impedance, this is essential for predictable performance.

Useful stackup information includes:

• Number of layers and layer order (for example, Top – GND – PWR – Bottom for 4‑layer)
• Dielectric materials and thickness between layers
• Copper weight per layer (1 oz, 2 oz, etc.)
• Target impedances (for example, 50 Ω single‑ended, 90 Ω differential) and which nets need them
• Surface finish (HASL, ENIG, OSP) and any special requirements (gold fingers, edge plating, buried vias, HDI stack details)

Best practices:

• Keep your CAD layer stack‑up and your fabrication notes in sync; do not change one without updating the other.
• If you rely on impedance control, state whether impedance is “for reference” or must be guaranteed and tested.
• Attach stackup diagrams or text notes in your fabrication drawing so your manufacturer does not have to guess from Gerbers alone.

MorePCB’s fabrication capabilities include FR‑4, aluminum, PTFE/Rogers, ceramic, multilayer, rigid‑flex, and HDI, and their team can suggest standard stack‑ups that meet your electrical goals while staying cost‑effective and repeatable.

Step 4: Make All Files Consistent and Version‑Locked

Even “perfect” individual files cause problems if they do not match each other. Misaligned revisions are one of the top reasons for manufacturing holds.

Before zipping and uploading your package:

• Confirm that board revision identifiers match across Gerbers, BOM, centroid, and drawings.
• Ensure every reference designator in the centroid exists in the BOM and on the silkscreen.
• Verify that coordinates in the centroid file sit within the outline defined by your Gerbers.
• Run a quick internal checklist: do you have Gerber + drill, BOM, centroid, stackup/fab notes, and assembly drawings?

Engineers at MorePCB regularly help customers refine this “zero‑defect handoff” so every new project starts from a known‑good template instead of reinventing the process.

Why Manufacturer Selection Matters for File Preparation

Preparing good files is easier when you know exactly what your manufacturer expects. Generic templates often miss manufacturer‑specific details like preferred coordinate origin, naming conventions, and minimum stackup data.

A strong manufacturing partner will:

• Publish clear assembly file requirements for BOM and centroid, including required columns and acceptable formats.
• Provide example stackup diagrams and suggest standard builds that fit most designs.
• Offer engineering review so they can warn you early about missing or inconsistent information.

This is where a full‑service provider like MorePCB gives you a smoother path from design to global shipment.

How MorePCB Helps You Hand Off Manufacturing Files the Right Way

MorePCB is a leading PCB manufacturer and EMS provider with over 15 years of experience across design, fabrication, assembly, testing, and prototyping. Their capabilities are built around clean handoffs: clear Gerber/stackup requirements, BOM guidelines, and assembly file expectations.

From their capabilities and service offerings:

• PCB design support: MorePCB’s engineers help optimize PCB layout, component placement, routing, and signal integrity, and can advise on panelization, test points, and stackup choices that integrate smoothly into their production lines.
• PCB fabrication: They manufacture single‑, double‑, and multilayer PCBs on FR‑4, aluminum, PTFE/Rogers, and ceramic, with surface finishes like HASL, ENIG, and OSP, so your documented stackups can match real, proven builds.
• Turnkey PCB assembly: MorePCB offers SMT, through‑hole, and mixed‑technology assembly, handling BOM sourcing, centroid‑based placement, IC programming, and functional testing in one flow.
• Testing and prototyping: Their electrical, functional, and environmental tests plus fast prototyping services make it easy to validate that your documentation and board behaviour match before scaling up.

MorePCB works with international customers and ships PCB and PCBA orders globally, so once your documentation is solid, they can build and deliver boards to your team anywhere in the world.

FAQ

Q: What are the most important PCB manufacturing files after Gerbers?

A: After Gerbers and drill files, the most critical manufacturing files are a complete BOM, a correct centroid/pick‑and‑place file, and clear stackup documentation for multilayer or impedance‑controlled boards. When these three match each other, most production delays disappear.

Q: How do I know if my centroid file is correct?

A: Your centroid file is ready when it lists every SMT component with matching reference designators, X/Y coordinates, rotation, and side, uses clear units and origin definitions, and passes a quick sanity check against your BOM and board outline. If the row count, units, or coordinates do not match, fix them before sending to your manufacturer.

Q: Can MorePCB help me if my documentation is not perfect yet?

A: Yes. MorePCB’s engineering and DFM teams can review your BOM, centroid, and stackup documentation, suggest corrections, and help you build a standard file package template for future projects. They then use that package to fabricate, assemble, test, and ship your PCB and PCBA orders globally.