SMT assembly down to 01005 and 0.35 mm pitch
Six lines print, place and reflow surface-mount assemblies from a single 20 × 20 mm sensor board to a 610 × 510 mm backplane. The line is qualified chip-by-chip: 0.35 mm pitch BGA, 0.4 mm QFN and 0.3 mm CSP all run on the same process of record, gated at print by 3D SPI and after reflow by inline 3D AOI.
- SMT lines
- 6 · 4 CA · 2 MY
- Placement rate
- 30,000 pcs/hour
- Smallest chip
- 01005 · 0.4 × 0.2 mm
- Fine-pitch accuracy
- ±25 µm @ 3σ
The print step decides the joint before a part is placed
Every surface-mount defect you can name — tombstoning, bridging, voids, insufficient fillet — is either created or prevented in the 200 ms the squeegee takes to cross the stencil. We treat print as the controlled step and everything downstream as verification of it.
Stencils are laser-cut stainless steel between 0.10 mm and 0.20 mm, nano-coated on both faces, and released 4 hours after the Gerber set is frozen. Foil thickness is chosen per board: 0.10 mm for 0.35 mm pitch and 01005 work where the paste release is the limiting factor, 0.15 mm for general mixed SMD, 0.20 mm where through-hole connectors are pin-in-paste and need the extra volume.
Print parameters are set from the area ratio of the smallest aperture on the panel, not from a house default: squeegee speed 30–60 mm/s, 60° metal blade, 3–8 mm/s stencil separation, dry wipe every 5 prints and vacuum wipe every 20. Paste is Type 4 (20–38 µm particle) for 0.35–0.5 mm pitch and Type 5 (10–25 µm) below that.
3D SPI runs on 100 % of boards. Volume, area and height are measured against the paste file, and the line stops when the process capability index for any aperture group falls under 1.67. The printer then corrects its own offset from the last 5 boards — an operator does not adjust a print by eye here.
Placement spec, from 01005 to a 55 mm connector
The table below is the window our programmes are written against. Nozzle, feeder and vision set change per build; the accuracy figures do not.
| Parameter | Window | Verification |
|---|---|---|
| Component range | 01005 (0.4 × 0.2 mm) to 55 mm connectors | Nozzle and feeder set per programme |
| Pitch floor | 0.35 mm BGA · 0.4 mm QFN · 0.3 mm CSP | 3D AOI plus 3D CT X-ray |
| Chip placement accuracy | ±35 µm @ 3σ | Daily glass-plate check |
| Fine-pitch accuracy | ±25 µm @ 3σ | Glass-plate check before each new programme |
| Panel size | 20 × 20 mm to 610 × 510 mm | Vacuum tooling and edge support |
| Board thickness | 0.4 mm – 6.4 mm | Rail and pin support per panel |
| Placement rate | 30,000 pcs/hour per line | MES counter, reviewed monthly |
| Changeover | Feeder and nozzle set rebuilt from the CAD centroid export | First-article placement check before release |
| Paste deposit | 3D SPI on 100 % of boards, CpK ≥ 1.67 | Automatic printer offset correction |
Ask for a panel review before you release artwork. Rail width, fiducial placement, bad-board marking and array spacing decide whether a 01005 design runs at 30,000 pcs/hour or at half that with an operator watching every board. We return a panel drawing with the DFM report in 24 hours. Components for the build come from our own sourcing desk or from your consigned stock, kitted in the same ESD store.
Twelve-zone nitrogen reflow with a profiled window
Reflow is where the paste that printed correctly either forms a proper intermetallic joint or oxidises into a weak one. The profile is developed per board, not selected from a menu.
Profile window for SAC305
Soak 150–180 °C for 60–120 s, ramp 1–3 °C/s from ambient to soak, peak 235–245 °C with 30–60 s above the 217 °C liquidus, and cooling at no more than 4 °C/s down to 150 °C. The twelve convection zones hold ±1.5 °C repeatability across the soak band, which is what keeps a heavy connector and a 01005 pad on the same panel inside the same window.
Nitrogen inerting is used on every reflow pass. Lower residual oxygen keeps the OSP or ENIG finish from oxidising during the soak, widens the wetting window on fine-pitch pads and cuts solder-ball formation — the most common cosmetic reject on 0.35 mm pitch assemblies.
How the profile is proven
Six thermocouples are attached per panel on a new design: panel entry edge, panel exit edge, board centre, the heaviest thermal mass (usually a through-hole connector or a shielded inductor), the finest-pitch device, and the ground-plane area under a large area array. Profiles are re-run after any stencil thickness change, paste lot change, or when a panel revision moves copper area by more than a few percent.
The profiled panel is kept as the reference for the programme. Every subsequent run is checked against the oven's logged zone temperatures, and the oven is profiled again on a fixed cadence and after any element replacement.
Optical and X-ray gates, and what each one rejects
Inline 3D AOI is installed at three points on the line, and X-ray closes the fourth gate on area arrays. Each one is programmed from the CAD centroid and paste file, so it inspects the design you released rather than a hand-picked golden board.
- A13D SPI after printRejects low or missing paste volume, slump, bridging between adjacent apertures and stencil-clog smear. Feeds the printer's automatic offset correction.CpK ≥ 1.67
- A23D AOI after reflowRejects tombstoning, billboarding, side and end overhang, lifted leads, insufficient or excess solder, missing and wrong-polarity parts, and stray solder balls down to 01005.100 %
- A3AOI after depanelAdded because routing and V-score are mechanical operations: this gate looks for chipped ceramic capacitors, cracked MLCC terminations, lifted pads and solder-mask damage introduced after electrical test would normally have run.100 %
- A4X-ray on area arrays2D and 3D CT on BGA, CSP, LGA and QFN. Void area is held at or below 25 % per IPC-A-610, with ball-diameter and bridging checks on the same scan.≤ 25 %
What changes between Class 2 and Class 3 on the same board
The assembly does not change. The acceptance criteria, the inspection coverage and the paperwork do — and that difference is priced at quote stage, not discovered at final inspection.
| Criterion | Class 2 default | Class 3 build |
|---|---|---|
| Fillet condition | Blowholes and pinholes accepted within IPC limits | Blowholes and pinholes not accepted in the fillet |
| Wetting | Wetting evident on the accessible side | Wetting required on both sides where visible, with a continuous fillet |
| Area arrays | Sampled X-ray under the control plan | 100 % X-ray on BGA, CSP, LGA and QFN |
| Component alignment | Overhang within the Class 2 table | Tighter alignment limits; overhanging terminations are reworked, not accepted |
| Conductor and laminate damage | Minor damage accepted with limits | No nicked conductors; laminate damage is a reject |
| Traceability | Board-level serialisation and MES record | Board-level serialisation, MES record and FAI package per revision |
Class 3 is the standing default for medical, aerospace and safety hardware. If your drawing calls it out only for the through-hole joints, say so — the criteria are applied per joint type, and that distinction affects the inspection time in the quote.
How a 24-up industrial controller panel reached 98.5 % first-pass yield
An industrial automation customer transferred a 24-up controller panel with 412 placements per board, including two 0.4 mm pitch QFNs and a 0.5 mm pitch connector, plus 14 through-hole parts inserted after reflow. The first build ran at 94 % first-pass yield with two repeat failure modes: insufficient paste on the QFN thermal pad and solder balls along the connector edge.
Three changes fixed it. First, the QFN thermal pad aperture was split into a windowpane pattern at 0.15 mm foil instead of a single opening at 0.12 mm, which raised paste volume without exceeding the 25 % void limit on the thermal pad. Second, the soak band was widened to 165–180 °C and the ramp lowered to under 2 °C/s, which removed the solder-ball spatter created by outgassing flux at the connector edge. Third, a support block was added under the connector footprint so the board could not flex during placement of the 55 mm part.
Yield moved to 98.5 % on the third build and held there across the following 6 production lots. The stencil and the support tooling belong to the customer under our standard tooling term, and both transferred with the program when it moved to a volume line. Read more about that side of the work on the test and inspection page.
SMT questions we get at the RFQ stage
You do. Stencils, test fixtures and programming become customer property after first article acceptance, and we release them on request with the laser-cut artwork data. Stencils are cut in 4 hours from a released Gerber set, and most programs keep two identical foils in the rack so a damaged stencil does not stop a run. Nano-coating is re-applied on our cadence, and the foil is retired when aperture wear reaches the point where paste volume drifts outside the CpK window.
At volume, but only with the right board support and panel design. A 01005 chip is 0.4 × 0.2 mm; at that size placement accuracy is not the limit — paste release and board support are. We ask for a 0.10 mm foil, Type 5 paste in the fine-pitch region, vacuum support under the array and fiducials on every panel break. Where a design puts 01005 parts next to a heavy connector with no support, the yield conversation is about panel design, and we will say so at DFM rather than absorb it at final test.
It adds gas and maintenance cost to every pass, so we do not sell it as free. On 0.35 mm pitch and finer assemblies it usually pays for itself in reduced solder-ball and non-wetting rework. On a coarse single-sided board with generous pads it changes very little, so it becomes a choice rather than a default. Tell us the pitch floor and the finish on your board and we will quote both ways if the difference is material.
Send the artwork and we will check the print window
Stencil thickness, aperture area ratio, panel support and fine-pitch placement are all in the 24-hour DFM report. Nothing is firm-quoted until you have seen it.