Fabrication
Gerber X2 / X3 (RS-274X)
One file per copper layer, plus solder mask, silkscreen and drill layers, with units and number format stated explicitly. X2 and X3 carry the layer and net context that plain RS-274X loses.
DESIGN & DFM GUIDES
Send files we can build from the first time.
Accepted data packages, a 14-row design rule table and the six DFM errors we return most often. No automatic part substitution, ever.
WHAT TO SEND
Six file types, and what each one has to contain
A fabrication package without a centroid file or a BOM with manufacturer part numbers cannot be quoted accurately. Each card below lists the minimum content for that file.
CAD exchange
ODB++
A complete CAD exchange package with layer structure and netlist intact. Preferred when the design has impedance-controlled nets, because the stackup and net data arrive together.
Single file
IPC-2581
One XML file carrying stackup, netlist and component data. Useful when you do not want to transmit a directory tree, and it is read without conversion loss.
Drilling
Excellon drill files
Include the tool table and separate plated from non-plated holes. A merged drill file is the most common reason a first article stalls at the bare-board stage.
Placement
Pick-and-place / Centroid
Reference designator, X and Y coordinates, rotation and side (top or bottom) for every placed part. Missing rotation data is corrected by hand in the placement programme, which costs a day.
Bill of materials
BOM with MPN, manufacturer and reference designators
Every line needs the manufacturer, the manufacturer part number and the reference designators it covers. Approved alternates, if you have them, go on the same line. An assembly drawing should travel with it, showing polarity, connector orientation and keep-out areas.
Not sure your package is complete?
Send what you have. A process engineer reads it, tells you the two or three files that are missing, and the DFM checklist goes back with the answer.
BEYOND THE GERBERS
Five things that are recommended, not required
None of these are mandatory to start a build. Each one removes a question that would otherwise come back to you mid-build.
Stackup drawing
Layer count, dielectric thickness, copper weight and material, including the glass transition temperature and the flammability rating. Without a stackup there is no route to an impedance commitment.
Impedance requirements
Name the target impedance per net class and supply the stackup that produces it. Tolerance is ±10% single-ended and ±10% differential, and that figure cannot be quoted from a net name alone.
Stencil aperture requirements
Special aperture strategies for specific parts: a window-pane aperture on a QFN thermal pad, a home-plate narrowing on an 01005 land. Saying so up front is faster than a stencil revision.
Test point list
Which nets need probe access for flying probe, bed-of-nails ICT or boundary scan. Test access designed in is free; test access retrofitted is a layout revision.
IPC-A-610 acceptance class
Class 2 or Class 3. The class determines inspection configuration, cost and the traceability package, and it has to be settled before the stencil is cut. See testing and inspection for how the class changes the test plan.
RECOMMENDED PARAMETERS
Fourteen numbers to design against
| Parameter | Value | Source |
|---|---|---|
| Smallest chip component | 01005 imperial / 03015 metric | Line capability |
| Minimum QFP lead pitch | 0.4 mm | Line capability |
| Minimum BGA ball pitch | 0.4 mm | Line capability |
| Largest component | 100 × 90 mm, up to 28 mm tall | Line capability |
| Board thickness for assembly | 0.4 – 4.0 mm | Line capability |
| Stencil area ratio | ≥0.66 | IPC-7525B |
| Stencil aspect ratio | ≥1.5 | IPC-7525B |
| Panel breakaway rail | ≥5 mm | Panel rules |
| V-CUT minimum board thickness | ≥0.8 mm | Panel rules |
| Perforated tab spacing | 0.5 – 1.0 mm | Panel rules |
| Single-ended impedance tolerance | ±10% | Impedance rules |
| Differential impedance tolerance | ±10% | Impedance rules |
| Component spacing | Must leave room for the placement nozzle envelope | Common DFM issue |
| Heavy components | Need a mechanical support point | Common DFM issue |
The impedance figures are design tolerances and say nothing about finished electrical performance. A stackup and a target impedance have to be on the table before either ±10% can be quoted. Designs that fall outside this window are returned at the DFM stage with a proposed change, not silently built.
WHAT COMES BACK
The six DFM errors we return most often
Each of these is flagged with the specific pads, vias or components involved, and a proposed fix. None of them is a rejection of the design.
01 · Land pattern
Footprint does not match the component
Library footprints drift from the datasheet. The datasheet land pattern wins, and the pads are redrawn to match it. This is the leading cause of tombstoning, bridging and head-in-pillow on a first build.
02 · Solder mask
Solder mask dam too narrow
When the dam between adjacent pads is too thin it collapses during reflow and the pads bridge. Fixed by widening the pad gap or by adjusting the mask opening, not by adding flux.
03 · Vias
Vias neither tented nor plugged
An open via in a land or beside a pad wicks paste and leaves flux residue on the surface. State whether each via class is tented or plugged, and the assembly recipe stops guessing.
04 · Panel
Breakaway rail under 5 mm
A rail narrower than 5 mm does not carry the panel through the conveyor or hold it flat under the placement head. Rails are at least 5 mm, and V-CUT needs at least 0.8 mm of board thickness.
05 · Fiducials
Fiducials missing or asymmetric
Global fiducials are needed on the panel, local fiducials on fine-pitch parts, and the pattern has to be non-symmetric so the machine can resolve rotation. Two fiducials on a diagonal is the usual answer.
06 · Access
Placement access and unsupported mass
Tall parts placed closer than the nozzle envelope cannot be placed reliably, and a heavy component with no support point can fall off during the second reflow pass. Both are returned with a minimum spacing.
HARD RULES
Panelisation, impedance and substitution
Breakaway rail≥5 mm
V-CUT minimum board thickness≥0.8 mm
Perforated tab spacing0.5 – 1.0 mm
Single-ended impedance±10%
Differential impedance±10%
Automatic part substitutionNever
These four panelisation and impedance figures are the ones that cost the most to get wrong, because a mistake re-opens the stencil and the panel at the same time. Mirror-image (front-and-back) panels have to be labelled explicitly; an unlabelled mirrored panel is built upside down.
Substitution is a separate rule. Components are never swapped automatically, however close the second source looks on paper. A substitution needs a parameter comparison from the datasheets and your written confirmation, and approved vendor list parts are considered first. If a part is unobtainable, the question goes to you before anything is ordered.
FILE SECURITY & NDA
Six questions about your data, answered
Do you sign an NDA?
Yes, an NDA is standard practice here. Send yours or ask for ours; either is signed before files are transferred if you prefer.
Where do the Gerbers and the BOM sit?
In an access-restricted directory. Files are not disclosed to third parties, and the bare boards are sourced from audited partner fabs that receive only the fabrication data they need.
Will you substitute a part without telling me?
No. Substitution is never automatic. A proposed alternate comes to you with a datasheet parameter comparison, approved vendor list parts are preferred, and nothing is ordered until you confirm in writing.
How fast is the DFM report?
Within 24 hours for prototype boards, covering the returned items and the proposed fixes. The quotation follows the review rather than preceding it, so the price matches what will actually be built.
Can I choose the acceptance class?
You choose Class 2 or Class 3, and it has to be fixed before the stencil is cut, because the class sets inspection configuration, cost and the traceability package. Changing it later means re-cutting parameters and re-configuring inspection.
Who decides how the board is panelised?
We propose it against the line rules — array, V-CUT or perforated tabs — and you confirm the panel drawing. Nothing is cut until the confirmed drawing is on the work order.
REQUEST THE DFM CHECKLIST
Get the checklist before you send the files
The checklist lists every accepted file type, the fields each one needs, and the six design errors above with the fix for each. Ask for it and it comes back with your first quotation.
Reply within one business day
Rules are quoted from your stackup and target impedance, or returned with a proposed change.