Gerber, BOM, CPL, and stackup files tell a PCB manufacturer four different things. Gerber files define the board layers. The BOM defines components. The CPL defines placement. The stackup defines layer construction, materials, copper, dielectric thickness, and impedance assumptions.
Many PCBA quote delays happen before production starts. Why? The factory may have board data, but not component data. Or it may have a BOM, but no placement file. Sometimes the Gerber, BOM, and CPL were exported from different design revisions.
For a broader RFQ checklist, see our PCBA quote files checklist. This article explains what each file means and how to check the package before sending it to a supplier.
Key Takeaways
- Gerber answers what to fabricate, BOM answers what to buy, CPL answers where to place, and stackup answers how the board is built.
- BOM/CPL designator matching and same-revision exports are the fastest ways to avoid RFQ clarification loops.
What Are Gerber, BOM, CPL, and Stackup Files?
IPC releases electronics assembly benchmark studies that cover yields, defect rates, DPMO, rework/scrap, customer returns, supplier performance, and inspection/test methods (IPC, Quality Benchmark Study for Electronics Assembly). File clarity is not admin work. It is production control.
Gerber, BOM, CPL, and stackup files are the core data package behind most PCB and PCBA quote reviews. They are not four names for the same thing. They describe different parts of the job.
| File | Main question answered | Used by |
|---|---|---|
| Gerber + drill | What PCB should be fabricated? | PCB fabrication engineering |
| BOM | What components should be sourced and assembled? | Sourcing and PCBA engineering |
| CPL / pick-and-place | Where and how should parts be placed? | SMT programming and assembly |
| Stackup | How are layers, materials, and copper built? | Fabrication and impedance review |
Think of the PCBA file package as a four-question system. Gerber answers what to fabricate. BOM answers what to buy. CPL answers where to place. Stackup answers how the board is constructed. If one answer is missing, the supplier has to guess or stop and ask.
A complete package also needs revision alignment. The Gerber, BOM, CPL, and stackup should describe the same release of the board. If they don’t, the quote may be based on the wrong components, footprint count, board thickness, or test scope.
Gerber, BOM, CPL, and stackup data should describe one board revision before fabrication, sourcing, placement, and construction assumptions are quoted. IPC quality benchmark releases cover assembly outcomes such as yields, defects, DPMO, rework, returns, supplier performance, and inspection methods, which depend on clear manufacturing inputs.
For a deeper RFQ checklist, use our PCBA quote files checklist.
Gerber Files in PCB Manufacturing
In current PCB assembly process guides, file or order review appears before solder paste printing, pick-and-place, reflow, and inspection. Gerber files are the board-fabrication data reviewed at that first step.
Gerber files describe the physical PCB layers. They usually include copper layers, solder mask, silkscreen, paste, board outline, and mechanical layers. Drill files are closely related, but separate. They define plated holes, non-plated holes, vias, and slots.
Gerber does not tell the assembler which exact components to buy. It also does not reliably tell the SMT line how every part should be placed. That information comes from the BOM and CPL.
Common Gerber layers and what they control
| Gerber or drill item | What it controls | Common mistake |
|---|---|---|
| Copper layers | Traces, pads, planes | Missing inner layer or wrong revision |
| Solder mask | Mask openings and protected copper | Mask opening mismatch around fine-pitch pads |
| Silkscreen | Designators, polarity marks, logos | Polarity mark hidden or inconsistent |
| Paste layer | Stencil aperture reference | Paste layer missing for SMT pads |
| Board outline | Shape, cutouts, slots | Outline exported on unclear mechanical layer |
| Drill file | Holes and vias | Drill file missing or not matching Gerber revision |
Gerber X2 and RS-274X exports are common formats. For most buyers, the format name matters less than completeness. Can the fabricator identify every layer, board outline, hole, surface feature, and revision? If yes, the review starts well.
File or order review comes before SMT production in common PCB assembly workflows. That review depends on complete Gerber and drill data because copper, mask, silkscreen, paste, board outline, and hole information define the bare PCB before assembly begins.
See how file review fits into the printed circuit board assembly process.
What Is a BOM in PCB Assembly?
IPC’s 2022 electronics assembly benchmark release lists metrics such as yields, defect rates, DPMO, rework/scrap, customer returns, supplier performance, and inspection/test methods (IPC, Quality Benchmark Study for Electronics Assembly). A BOM affects several of those risks because it controls what parts enter the build.
A BOM, or bill of materials, is the component list for the assembly. It tells the PCBA supplier which resistors, capacitors, ICs, connectors, modules, and mechanical items to source and populate.
A clean BOM includes reference designators, quantities, manufacturer names, MPNs, packages, values, descriptions, and DNP/DNI status. Better BOMs also include approved alternates, lifecycle notes, tolerance, voltage ratings, and preferred suppliers.
Minimum BOM fields for a clean PCBA quote
| BOM field | Example | Why it matters |
|---|---|---|
| Reference designator | R1, C5, U2, J1 | Connects the part to the schematic and CPL |
| Quantity | 12 | Supports sourcing and assembly count checks |
| Manufacturer | Texas Instruments | Reduces ambiguity |
| MPN | Exact part number | Controls sourcing, cost, and alternates |
| Package / footprint | 0603, QFN-32, SOIC-8 | Helps compare BOM and placement data |
| Value / rating | 10 kΩ, 16 V, 1% | Prevents wrong generic substitutions |
| DNP / DNI | Do not populate | Prevents optional parts from being assembled |
LEADHUI PCB engineering reviews move faster when the BOM uses exact MPNs and clear DNP markings. A line that says “10k resistor” may be enough for a prototype discussion, but it is not enough for controlled sourcing.
Approved alternates help, too. If one MPN is unavailable, the supplier can quote an approved substitute instead of stopping the RFQ. The key is control. Alternates should be engineering-approved, not chosen blindly.
BOM quality affects production controls because ambiguous MPNs, missing DNP status, and uncontrolled alternates can change what parts are sourced and assembled. IPC benchmark releases track quality measures such as yields, defects, DPMO, rework, returns, supplier performance, and inspection/test methods.
If you are preparing a turnkey build, compare your BOM against the broader PCBA quote files checklist.
What Is a CPL File in PCB Assembly?
Current assembly guides describe pick-and-place as a core SMT step between solder paste printing and reflow (JLCPCB, Printed Circuit Board Assembly Guide; PCB Assembly Express, PCB Assembly Process). A CPL file supplies the placement data behind that step.
A CPL file is a component placement list. It may also be called a pick-and-place file, centroid file, XY file, or placement file. It tells SMT programming where each component sits on the board.
Typical CPL fields include designator, X coordinate, Y coordinate, rotation, board side, and package. The designator is the bridge between the BOM and the CPL. If the BOM says U3 and the CPL says U4 for the same part, someone has to resolve the conflict.
Why rotation and polarity review matters
Rotation conventions can vary between CAD exports and SMT programming. That does not mean CPL rotation is useless. It means the assembler should verify rotation-sensitive parts before production.
Check LEDs, diodes, IC pin 1, electrolytic capacitors, connectors, modules, and asymmetric packages. Silkscreen markings and assembly drawings help resolve unclear orientation. Would you rather catch that in review, or after reflow?
A CPL, centroid, XY, or pick-and-place file supports SMT setup by listing each component’s designator, X/Y location, rotation, side, and package. That placement data lets the SMT program be checked against the BOM and assembly drawing before build.
For quote preparation, include the CPL with the files listed in the PCBA quote files checklist.
PCB Stackup Requirements for PCBA Quotes
IPC-2221 describes generic PCB design principles, including material, mechanical, and electrical design considerations (IPC, IPC-2221). Stackup belongs to that bare-board construction discipline because layer order, dielectric thickness, copper, material, and impedance assumptions affect fabrication review.
A PCB stackup defines the physical layer construction of the board. It lists layer order, copper thickness, dielectric thickness, core and prepreg structure, material, Tg, finished thickness, and controlled-impedance targets where needed.
Simple 2-layer prototypes may use a manufacturer’s standard stackup. But multilayer, high-speed, RF, high-current, HDI, or controlled-impedance boards need clearer stackup data. Otherwise, the fabricator must infer construction details that affect cost and performance.
When stackup is usually required
Send stackup data for 4-layer and higher PCBs, controlled-impedance designs, high-speed digital boards, RF boards, antenna designs, high-current boards, and production builds that must be repeatable. Include target impedance, material, copper weight, layer order, and finished thickness.
When stackup may be less critical
For simple 2-layer prototypes, a supplier’s standard material and thickness may be acceptable. Still, state any constraints. If board thickness, copper weight, finish, material, or impedance matters, don’t assume the supplier knows.
Stackup data defines layer order, dielectric thickness, copper, material, finished thickness, and impedance assumptions before the PCB is fabricated and assembled. IPC-2221 covers generic PCB design principles, so stackup details should be treated as design-control data, not as an optional note for complex boards.
If stackup is part of the quote scope, include it alongside the files in the PCBA quote files checklist.
How Do These Files Work Together in a PCBA Quote?
IPC’s quality benchmark releases track 7 categories of assembly performance data, including yields, defect rates, DPMO, rework/scrap, returns, supplier performance, and inspection/test methods (IPC, Quality Benchmark Study for Electronics Assembly). A quote should define the inputs that affect those outcomes.
The files work together when they describe the same board revision and the same manufacturing scope. Gerber and drill files support PCB fabrication. BOM supports component sourcing. CPL supports SMT placement. Stackup supports construction review. Assembly drawings and test plans close the loop.
One missing file can change the quote. Missing CPL data can make SMT setup unclear. Missing stackup data can affect PCB cost and impedance review. Missing test requirements can make two suppliers quote different scopes.
Quantity, lead time, surface finish, panelization, programming, coating, packaging, and compliance requirements can also affect pricing. The more clearly you define the scope, the easier it is to compare quotes fairly.
A complete PCBA file package should define the manufacturing inputs that affect assembly outcomes before the supplier prices the build. IPC quality benchmark releases cover 7 performance areas, including yields, defects, DPMO, rework/scrap, returns, supplier performance, and inspection/test methods.
For a full-service view, see how files move through PCBA quote files checklist.
Additional PCBA Package Files to Send
The EU RoHS Directive restricts hazardous substances in electrical and electronic equipment, while REACH governs chemical registration, evaluation, authorization, and restriction in the EU (European Commission, RoHS Directive; ECHA, Understanding REACH). Compliance needs should be part of the package when they apply.
Gerber, BOM, CPL, and stackup are central files, but they are not always enough. A practical PCBA package may also need drill files, assembly drawings, fabrication drawings, test requirements, programming files, labels, packaging notes, and compliance requirements.
| File or requirement | When to include it | Why it matters |
|---|---|---|
| Drill files | Always with Gerber | Defines holes, vias, and slots |
| Assembly drawing | SMT or mixed assembly | Clarifies polarity, pin 1, DNP, connectors |
| Fabrication drawing | Controlled build | Defines tolerances, finish, material, notes |
| Test plan | Tested PCBA | Defines AOI, X-ray, ICT, functional test |
| Programming file | Firmware-loaded boards | Controls MCU or module programming |
| Compliance notes | Regulated markets | Defines RoHS, REACH, UL, or customer requirements |
| Packaging notes | Production delivery | Controls labels, trays, ESD bags, cartons |
A minimum RFQ package may be enough for a rough quote. A production-ready package should be more complete. Do you need serialized labels, conformal coating, functional testing, or firmware loading? Say so before the supplier quotes.
RoHS restricts hazardous substances in electrical and electronic equipment in the EU, while REACH governs chemical registration and restrictions. When those requirements apply, they belong in the PCBA file package beside Gerber, BOM, CPL, stackup, drawings, test plans, programming notes, and packaging instructions.
Testing scope also affects quote accuracy; start with the PCBA quote files checklist if you need a minimum package.
What File Mismatches Should You Check Before Sending an RFQ?
IPC’s 2019 quality benchmark release included electronics assembly data categories such as yields, defect rates, DPMO, rework/scrap, returns, supplier performance, and inspection/test methods (IPC, 2019 Quality Benchmark Study for Electronics Assembly). Pre-RFQ checks help prevent avoidable causes of rework and clarification.
The most important checks are revision alignment, BOM/CPL designator matching, CPL rotation, polarity notes, stackup completeness, and defined test requirements. These checks are simple, but they catch many quote problems.
LEADHUI PCB engineering teams usually review RFQs faster when Gerber, BOM, and CPL are exported from the same CAD release. The files don’t need to be fancy. They need to agree.
| File mismatch | Consequence | Fix before sending |
|---|---|---|
| Gerber revision differs from BOM | Wrong footprint or part count | Export all files from the same release |
| BOM designator missing from CPL | Part may be sourced but not placed | Sort both files by designator |
| CPL has bottom-side parts missing | SMT program may be incomplete | Check top/bottom side column |
| Rotation or polarity unclear | LEDs, ICs, diodes may be oriented wrong | Add assembly drawing and pin-1 notes |
| MPNs are generic or obsolete | Sourcing delay or wrong substitution | Add exact MPNs and approved alternates |
| Stackup missing for multilayer PCB | Cost or impedance assumptions unclear | Add layer order, material, copper, thickness |
| Test requirements undefined | Suppliers quote different scopes | Attach acceptance criteria and test notes |
Fast pre-send checklist
Before sending an RFQ, export Gerber, BOM, and CPL from the same CAD release. Confirm revision names and dates match. Sort BOM and CPL by designator. Check top and bottom side placement. Verify pin 1 and polarity-sensitive parts.
Then include stackup for multilayer or impedance-sensitive boards. Attach test requirements and production notes. If you’re unsure, ask the supplier to review the package before final pricing.
Not sure whether your BOM and CPL match? Send LEADHUI PCB your Gerber, BOM, CPL, stackup, quantity, and test requirements for engineering review before assembly.
Pre-RFQ checks for revision alignment, BOM/CPL matching, polarity, stackup, and test scope reduce avoidable clarification before production. IPC’s 2019 quality benchmark release tracked 7 assembly quality categories, including yields, defects, DPMO, rework, returns, supplier performance, and inspection/test methods.
These checks help suppliers quote the same scope; they also connect to the broader PCBA quote files checklist workflow.
Frequently Asked Questions
What is the difference between Gerber and BOM?
Gerber files define PCB fabrication layers such as copper, mask, silkscreen, paste, and outline. The BOM defines the components to source and assemble. IPC benchmark releases track assembly quality categories such as yields, defects, DPMO, rework, returns, supplier performance, and inspection/test methods, so both board data and part data matter.
What is the difference between BOM and CPL?
A BOM identifies parts, while a CPL places parts. Current SMT process guides list pick-and-place as a core assembly step, and CPL data supports that step. The reference designator links the 2 files: the BOM says what U3 is; the CPL says where U3 goes.
Do I need stackup for a PCBA quote?
You need stackup data when layer construction affects price, performance, or repeatability. IPC names 2 major assembly references, IPC-A-610 and J-STD-001, but stackup handles the PCB construction side. Send it for multilayer, controlled-impedance, RF, high-speed, high-current, or production-critical boards.
Can a manufacturer quote without a CPL file?
Sometimes a rough quote is possible without CPL, especially for simple boards. But pick-and-place is a standard SMT step in assembly guides, and accurate setup needs placement data. Without CPL, the supplier may need to estimate placement work or request more files.
What files should I check before sending a PCB assembly RFQ?
Check at least 7 inputs: Gerber, drill, BOM, CPL, stackup when needed, assembly drawing, and test requirements. Also confirm quantity, lead time, revision names, polarity notes, DNP markings, approved alternates, and compliance needs such as RoHS or REACH when applicable.
For the shortest RFQ path, start with the PCBA quote files checklist and then review the printed circuit board assembly process.
Conclusion
Gerber, BOM, CPL, and stackup files each answer a different factory question. Gerber defines the PCB. BOM defines the parts. CPL defines placement. Stackup defines construction.
A clean PCBA quote package does more than upload files. It aligns revisions, connects BOM and CPL designators, clarifies polarity, defines stackup needs, and states test scope. That gives the supplier fewer assumptions to make.
Send LEADHUI PCB your Gerber, BOM, CPL, stackup, quantity, and test requirements for a practical engineering review and accurate PCBA quote.
Next, compare how these files support PCBA quote files checklist from fabrication through testing.
