A Complete Checklist for Ordering Prototype PCB Assembly

Ordering a Prototype PCB Assembly for the first time—or from a new vendor—can feel overwhelming. There are dozens of details to specify, files to prepare, and decisions to make, and missing any one of them can delay your build by days or result in boards that do not match your intent. This checklist distills the entire process into a structured, sequential guide so you can submit your order with confidence and get working hardware back on schedule.

Phase 1: Design Data Preparation

Before you contact any assembler, your design data must be complete, consistent, and exportable in the formats the vendor requires. Incomplete or ambiguous data is the single largest cause of prototype delays.

1.1 Gerber Files

• ☐ Export one Gerber file per layer: top copper, bottom copper, inner copper layers (each separately), top solder mask, bottom solder mask, top silkscreen, bottom silkscreen, board outline, drill files
• ☐ Use RS-274X (extended Gerber) format—never RS-274D (standard Gerber), which requires a separate aperture list that vendors may not parse correctly
• ☐ Verify coordinate units (metric or imperial) are consistent across all files
• ☐ Confirm all files reference the same origin point (typically the lower-left corner of the board outline)
• ☐ Include a board outline Gerber on a dedicated layer—do not rely on the copper layer to define the board shape
• ☐ Run a Gerber viewer (such as GerbView or ViewMate) to verify the output matches your CAD layout before sending

1.2 Drill Files

• ☐ Export Excellon-format drill files for plated through-holes and non-plated holes separately
• ☐ Verify drill sizes are in the same units as your Gerber Files
• ☐ Confirm plated vs. non-plated hole designation is correct—this cannot be inferred from the drill file alone and must match your design intent
• ☐ Include any slot drills or routed features as separate drill or rout files

1.3 Netlist

• ☐ Export an IPC-D-356A netlist for electrical test comparison
• ☐ The netlist allows the vendor to generate a flying-probe or fixture test that verifies connectivity against your schematic—catching open and short circuits that Visual Inspection misses

1.4 Assembly Data

• ☐ Export centroid/pick-and-place file (X-Y coordinates, rotation, and reference designator for every surface-mount component)
• ☐ Verify coordinates are in the same origin and units as the Gerber Files
• ☐ Confirm rotation convention matches the vendor's expectation (0° = up, rotation clockwise or counter-clockwise)—this is a common source of placement errors

Phase 2: Bill of Materials (BOM) Preparation

The BOM is the most error-prone document in any assembly order. A well-prepared BOM prevents substitutions you did not approve, eliminates ambiguity, and enables the vendor to source components efficiently.

2.1 Essential BOM Fields

Every line item must include:

• ☐ Reference designator(s)—matching the schematic and Pcb layout exactly (e.g., R1, R2, C3, U4)
• ☐ Component value or description (e.g., 10kΩ, 100nF, STM32F407VGT6)
• ☐ Manufacturer name
• ☐ Manufacturer part number (Mpn)—this is the single most important field for sourcing accuracy
• ☐ Package footprint (e.g., 0402, SOIC-8, Bga-256) as a cross-check against the Pcb land pattern
• ☐ Quantity per board

2.2 Optional but Recommended BOM Fields

• ☐ Distributor part number (Digi-Key, Mouser, etc.)—accelerates sourcing for common parts
• ☐ Acceptable substitute part numbers—prevents delays when the primary Mpn is out of stock; specify whether substitutes require your approval or are pre-authorized
• ☐ Component type classification (resistor, capacitor, IC, connector, etc.)—helps the vendor's procurement team organize sourcing
• ☐ Mounting type (SMT or through-hole)—prevents confusion for components available in both packages
• ☐ Side (top or bottom)—critical for double-sided assembly

2.3 BOM Quality Checks

• ☐ No duplicate reference designators
• ☐ No reference designators in the BOM that are not on the PCB (and vice versa)
• ☐ Every component has a valid MPN—not "TBD," "any," or internal abbreviations that the vendor cannot decode
• ☐ Values match the schematic (a 10k resistor listed as 100k in the BOM will be sourced and placed incorrectly)
• ☐ No obsolete or end-of-life (EOL) parts without a documented substitution plan
• ☐ Check for long-lead-time components (12+ weeks) and flag them to the vendor early

Phase 3: Board Specifications

These parameters define the physical and electrical characteristics of the Bare Board. Many can be inferred from the Gerber files, but explicit specification eliminates ambiguity and ensures the vendor quotes against your actual requirements.

3.1 Base Material and Stack-Up

• ☐ Number of copper layers
• ☐ Base material (FR-4 standard, FR-4 high-Tg, Rogers RO4003C, IS410, etc.)
• ☞ If using a non-standard material, confirm the vendor stocks it or can procure it within your timeline
• ☐ Finished board thickness (e.g., 1.6 mm ± 10%)
• ☐ Copper weight per layer (1 oz, 2 oz, etc.)—specify if different layers use different weights
• ☐ Stack-up diagram showing layer assignment (signal, ground, power) and dielectric thickness between each layer—critical for impedance-controlled designs

3.2 Surface Finish

• ☐ Select surface finish: HASL (lead-free), ENIG, OSP, immersion tin, or immersion silver
• ☞ ENIG is the most common choice for prototype assembly because it provides a flat, solderable surface compatible with fine-pitch components and Bga
• ☞ HASL is the lowest cost but has uneven surface topography that can cause issues with fine-pitch placement

3.3 Solder Mask and Silkscreen

• ☐ Solder mask color (green, red, blue, black, yellow, white)
• ☐ Solder mask coverage—define whether pads on unused I/O pins should be covered or left exposed
• ☐ Silkscreen color (white is standard on green/blue solder mask; black on red/yellow)
• ☐ Silkscreen content: reference designators, component values, polarity markers, pin 1 indicators, test point labels, company logo

3.4 Via Processing

• ☐ Specify via tenting (solder mask over vias), plugging (epoxy fill), or filling (copper fill and planarization)
• ☞ Via-in-pad designs require filled and capped vias—specify this explicitly, as it is a premium process

3.5 Impedance Control

• ☐ Identify traces requiring controlled impedance (e.g., 50 Ω single-ended, 100 Ω differential)
• ☐ Specify target impedance and tolerance (e.g., 50 Ω ± 10%)
• ☞ Provide a stack-up diagram with dielectric thicknesses and material Dk values so the vendor can adjust trace widths to hit the target impedance
• ☐ Request impedance test coupon on the production panel for verification

Phase 4: Assembly Specifications

4.1 Assembly Type

• ☐ Specify assembly type: surface-mount only (SMT), through-hole only (THT), or mixed (SMT + THT)
• ☐ For double-sided boards: specify which side is primary (reflowed first) and which is secondary
• ☐ Identify any components requiring manual or hand soldering (odd-form parts, press-fit connectors)

4.2 Component Sourcing

• ☐ Turnkey (vendor sources all components): provide complete BOM with MPNs and acceptable substitutes
• ☐ Partial turnkey (you supply some components, vendor sources the rest): clearly designate which line items are customer-furnished and which are vendor-sourced
• ☐ Consigned (you supply all components): coordinate delivery schedule to ensure all parts arrive before the assembly start date; include incoming inspection data for critical components
• ☞ For consigned builds, label every component bag/reel with the MPN, quantity, and reference designators—unlabeled parts cause delays and errors

4.3 Solder Type

• ☐ Specify solder alloy: SAC305 (standard lead-free), Sn63Pb37 (leaded, if exempt under RoHS), or other
• ☐ Specify Solder Paste type if you have a preference (no-clean, water-soluble, ROLMA)—otherwise the vendor will select based on their standard process

4.4 Special Assembly Requirements

• ☐ Identify BGA and Qfn components that require X-ray inspection after reflow
• ☐ Specify any components requiring adhesive staking (for double-sided assembly)
• ☐ List any moisture-sensitive devices (Msl rating ≥ 3) that require bake-out before reflow
• ☐ Identify components requiring specific placement accuracy (e.g., 0.4mm pitch Qfn, 01005 passives)
• ☐ Specify any press-fit, swaged, or snap-in hardware that requires special tooling

Phase 5: Testing and Inspection

The level of testing you specify for a prototype depends on your goals. A proof-of-concept build may need only Visual Inspection, while a design-validation build should include comprehensive electrical testing.

5.1 Bare Board Testing

• ☐ Electrical test: flying probe (preferred for prototypes—no fixture cost, 100% net coverage) or fixture-based (faster for volume, but NRE cost)
• ☐ Visual inspection per IPC-A-600 (class 1, 2, or 3)
• ☞ Request a cross-section sample if this is your first build with a new vendor—it validates plating quality, lamination integrity, and via construction

5.2 Assembly Inspection

• ☐ AOI (Automated Optical Inspection): standard for most prototype builds—catches placement errors, solder bridges, tombstones, and Missing Components
• ☐ X-ray inspection: required for BGA, QFN, and any area-array package—verify solder joint formation and check for voids, shorts, or head-in-pillow defects
• ☞ For first-article prototypes, request 100% X-ray on all BGA devices, not just a sample
• ☐ Manual visual inspection: as a supplement to AOI, particularly for through-hole solder joints and connector pin soldering

5.3 Electrical and Functional Test

• ☐ ICT (in-circuit test): verifies component values and connectivity—requires a test fixture for fixture-based ICT, or use flying-probe ICT for prototype quantities
• ☐ Functional test: provide a test procedure and any required test fixtures or jigs to the vendor
• ☞ For prototypes, many teams prefer to do functional testing in-house—specify whether you want the vendor to perform functional test or ship untested assemblies

Phase 6: Mechanical and Packaging Details

6.1 Panelization

• ☐ Specify whether the board should be delivered as single boards or in a panel array
• ☐ If panelized: specify panel size, array configuration (X × Y), fiducial locations, tooling hole locations, and breakaway tab or V-score method
• ☞ For prototype assembly, panelization may be required by the vendor's pick-and-place equipment—check their minimum panel size requirements

6.2 Electrical Test Coupon

• ☐ Include impedance test coupon on the panel if impedance control is specified
• ☐ Include copper plating thickness test coupon if required for verification

6.3 Packaging and Shipping

• ☐ ESD-safe packaging (required for all assembled boards)
• ☐ Moisture barrier bagging for boards with moisture-sensitive components
• ☐ Specify shipping method and any delivery date requirements
• ☐ International shipments: provide correct HS code (typically 853400 for printed circuits) and declared value for customs

Phase 7: Documentation and Communication

7.1 Design Intent Documentation

• ☐ Assembly drawing showing component placement, polarity/orientation markers, and any special instructions
• ☐ Schematic (PDF)—enables the vendor to verify BOM completeness and troubleshoot if issues arise
• ☐ Mechanical drawing showing board dimensions, critical tolerances, and mounting hole locations
• ☐ Stack-up diagram (if impedance controlled or multi-layer with specific dielectric requirements)

7.2 Special Instructions

• ☐ Any components that must not be substituted without your written approval
• ☐ Specific reflow profile requirements (if your components have unusual thermal limits)
• ☐ Firmware or programming requirements (if boards should be programmed before shipping)
• ☐ Conformal Coating type and areas to be coated or masked
• ☐ Any NDA or confidentiality requirements for your design data

7.3 Order Information

• ☐ Quantity of assembled boards
• ☐ Required delivery date (be realistic—overly aggressive dates lead to rushed processes and quality compromises)
• ☐ Shipping address and contact information
• ☐ Billing address and purchase order number

Phase 8: Pre-Order Review

Before you hit send on the order package, run through this final review:

8.1 Data Package Completeness

• ☐ All Gerber files present and verified in a viewer
• ☐ Drill files included with correct plated/non-plated designation
• ☐ BOM complete with MPNs for every component
• ☐ Pick-and-place file matches BOM and Gerber coordinates
• ☐ Netlist file included for electrical test

8.2 Consistency Checks

• ☐ BOM reference designators match PCB silkscreen
• ☐ BOM component count matches pick-and-place file
• ☐ Board outline in Gerber matches mechanical drawing dimensions
• ☐ Copper weights in stack-up diagram match fabrication notes
• ☐ Surface finish specified consistently in all documentation

8.3 Risk Assessment

• ☐ Identify long-lead-time components and confirm availability with the vendor
• ☐ Flag any first-time design elements (new component package, new material, new stack-up) for extra attention during Dfm Review
• ☐ Confirm the vendor's capability for any non-standard requirements (flex regions, heavy copper, buried vias, via-in-pad)
• ☐ Verify moisture-sensitive device handling plan (bake-out before reflow)

Common Mistakes That Delay Prototype Orders

After reviewing thousands of prototype orders, these are the most frequent errors that push delivery dates:

Vague or Missing MPNs

Listing "100nF cap" without a part number forces the vendor to guess which specific capacitor—there are hundreds of 100nF capacitors in different packages, voltage ratings, and temperature coefficients. The wrong guess means a capacitor with the wrong footprint or inadequate voltage rating on your board. Always provide the exact MPN.

Gerber File Format Errors

Missing layers, incorrect apertures, or mixed coordinate units cause CAM delays while the vendor requests corrections. The five minutes spent verifying Gerber output in a viewer saves days of back-and-forth after order submission.

Unapproved Substitutions

If you do not specify acceptable substitutes and the primary MPN is out of stock, the vendor will either wait (delaying your build) or substitute without your knowledge (risking a footprint or electrical mismatch). Defining pre-approved substitutes in the BOM eliminates this bottleneck.

Missing Assembly Instructions for Polarity-Sensitive Components

Diodes, electrolytic capacitors, ICs, and connectors have orientation requirements that must be unambiguous in your data. If pin 1 markers are missing from the silkscreen or the pick-and-place rotation is wrong, components will be placed backwards—and the board will not work.

Ignoring DFM Feedback

When the vendor flags a design issue in their Dfm Review, address it. Prototype schedules are tight, and the temptation to "build it as-is and fix it later" is strong—but a DFM issue that causes a 0% first-pass yield wastes more time than a one-day revision cycle.

What to Expect After Submission

A well-prepared order package enables a smooth process flow:

1. DFM review (1–2 days): The vendor's engineering team reviews your design for manufacturability issues. They may request clarification or suggest changes. Respond promptly to avoid delays.
2. Component Sourcing (3–10 days): For turnkey orders, the vendor procures all components. Long-lead parts may require alternative sourcing or timeline adjustment. This runs in parallel with Bare Board fabrication.
3. Bare board fabrication (3–7 days): Standard prototype lead time. Impedance-controlled builds or non-standard materials may add 2–3 days.
4. Assembly (2–5 days): Solder Paste Printing, component placement, reflow, inspection. Double-sided boards add 1–2 days.
5. Testing (1–2 days): AOI, X-ray, and any specified electrical or functional testing.
6. Shipping: Per your specified method and destination.

Total typical lead time for a turnkey prototype order: 10–20 business days from complete data package submission to delivered assemblies. Quick-turn options (5–7 days) are available at premium pricing from many vendors.

Conclusion

Ordering Prototype PCB Assembly does not have to be a leap of faith. A thorough, well-organized order package—complete Gerber data, an unambiguous BOM with MPNs and approved substitutes, explicit board and assembly specifications, and clear testing requirements—sets the foundation for a successful build. The checklist in this article covers every detail that matters, from the first Gerber export to the final pre-order review. Work through it methodically, and you will eliminate the ambiguity and missing information that cause the vast majority of prototype delays. The result is not just faster delivery—it is boards that work the first time, because every specification was correct before production started.

Contact us to discuss your requirements.