Use this buyer-friendly guide at incoming inspection or supplier audits. Each topic shows what to ask, typical risks, how to prevent/fix, and what evidence to request.
Quick overview (one-page matrix)
| Topic | Typical risks if uncontrolled | What good looks like | Evidence to request |
|---|
| Per-pass wet film (limit & target) | Trapped solvent → peeling/bubbles; high resistance; lot variability | Clear wet-film limit per recipe; comb gauge check online; gravimetric delta-mass per pass | Per-part weight distribution with g/m² conversion (L = Δm/A); per-pass weighing logs; comb-gauge records |
| Operator & fixtures consistency | Edge/holes thickness scatter; runs | Trained operators, cross-checks, repeatable fixtures & paths | Training/qualification records; first-article comparisons; cross-shift consistency data; fixture drawings |
| Defects (runs, pinholes, fisheyes, bubbles, orange-peel) | Early failure points; high leakage | Viscosity window, clean air, edge back-brushing, full drying 100–200 °C | Defect atlas, rework SOP + window (e.g., strip-and-recoat within last 2–3 passes), re-inspection results |
| Atmosphere & O₂ control | Under-oxidation (unstable phase) or over-burn (grain growth) | Defined air/O₂ setting; verified flow/refresh; calibrated sensors | Gas setpoints & calibration logs; periodic checks; exception curves |
| Furnace loading & uniformity | Door-zone cool-down, shadowing, local overheat | Proper vertical/horizontal/suspended loading, min spacing, door-zone compensation | Loading photos/diagram; multi-point temp comparison; heat–soak–cool curves (≥ 400 °C, 10–15 min/pass) |
| System segregation (Ru-Ir / Ir-Ta / Pt) | Cross-contamination → life scatter | Separated furnaces/batches or strict clean-down | Chamber clean SOP, isolation batch records, fixture segregation list |
| Sintering window & inter-pass cooling | Under/over-temp; poor interlayer bond | Soak ≥ 400 °C, 10–15 min/pass; forced cool to room temp every pass | Per-pass temp/time logs, cooling start/end temps, TC map, representative furnace cycle |
A) Per-pass wet film: limits, targets, and measurement
Ask: What is your per-pass wet-film limit/target? How do you measure it (comb gauge / weighing)?
Risks: No limit or too thick → incomplete drying, peel/bubble, high resistance.
Prevent: Define wet-film limit per recipe; control viscosity, brush load, overlap 30–50%; comb-gauge online, Δmass per pass offline.
Fix (this lot): Local light sand → thin touch-up → re-fire; if peel/black-wipe appears, follow strip-and-recoat SOP.
Evidence: Weight distribution per part + g/m² conversion (L = Δm/A) and per-pass weight logs (with photos of comb-gauge checks).
B) Operator qualification & fixture repeatability
Ask: How do you ensure operator consistency, cross-checks, and fixture location accuracy?
Risks: Human variation → edge/hole scatter or runs.
Prevent: Training & test-out, first-article side-by-side, visual path arrows/takt on fixtures.
Fix: Local light sand + directional touch-up; if lot scatter is high, add one uniform thin pass then re-fire.
Evidence: Training files, first-article reports, cross-shift data, fixture drawings.
C) Defects: runs / pinholes / fisheyes / bubbles / orange-peel
Ask: How do you prevent these? What is the rework standard if they appear?
Risks: Leak paths, early failure.
Prevent: Hold viscosity & wet-film limits, clean airflow, edge back-brush & fan path at holes, complete drying at 100–200 °C.
Fix:
Minor: local light sand → thin recoat → re-fire.
Multiple areas: overall light sand → uniform thin pass → re-fire.
Black-wipe/bubbles: strip-and-recoat within the defined rework window (e.g., within last 2–3 passes).
Evidence: Defect atlas, rework SOP + window, post-rework inspection.
D) Atmosphere & oxygen control
Ask: Air or oxygen-enriched? How do you verify refresh rate/flow and O₂ partial pressure?
Risks: Low O₂ → under-oxidation; too high + over-soak → grain growth, de-chlorination, higher resistance.
Prevent: Fixed gas setpoints, measured flow/refresh, calibrated sensors.
Fix: If under-oxidized, extend/redo soak; if over-burn (bluish tint, high R), dial back next lot, optionally redo last 1–2 passes.
Evidence: Gas setpoints, calibration logs, periodic check sheets, exception curves.
E) Furnace loading: orientation, spacing, and door-zone compensation
Ask: Vertical/horizontal/suspended? What spacing/orientation avoids shadowing?
Risks: Door-zone cool-down, stacked parts, hot spots → non-uniform temperature.
Prevent: Choose loading mode by geometry; keep minimum spacing; apply door-zone temperature compensation; multi-point thermocouples.
Fix: For suspect lots, re-fire reference coupons or add a uniform thin pass and re-fire.
Evidence: Loading diagram/photos; multi-point temperature comparison; zone setpoints & door compensation; furnace curves (≥ 400 °C, 10–15 min/pass).
F) System segregation & cross-contamination
Ask: Are Ru-Ir / Ir-Ta / Pt run in separate furnaces/batches? What’s the anti-cross-contamination plan?
Risks: Mixed residues → surface contamination, phase shift, lifetime scatter.
Prevent: Separate or strict clean-down; fixture segregation.
Fix: If contamination is found: strip-and-recoat; audit clean-down.
Evidence: Chamber clean SOP, isolation batch records, fixture logs, trace-back reports.
G) Sintering window & inter-pass cooling (critical checks)
Ask: Do you force-cool to room temp between passes? Is the temperature window fully achieved?
Risks: Warm recoating → weak interlayer bond; over/under-temp → resistance up / unstable phase.
Prevent: Soak ≥ 400 °C, 10–15 min per pass; forced cool to room temp every pass.
Fix: Under-temp → complete soak or add uniform thin pass; over-temp (bluish/high R) → retune zones & door compensation, possibly redo last 1–2 passes.
Evidence: Per-pass temp/time logs, cooling start/end temps & durations, TC map, representative furnace cycle.
Defect cheatsheet (symptom → likely cause → quick fix → prevent next lot)
| Symptom | Likely cause | Quick fix (this lot) | Prevent next lot |
|---|
| Black wipe mark | Under-temp; too-thick pass; recoated warm | Strip-and-recoat; or light sand + thin pass + re-fire if minor | Enforce wet-film limit; full dry; force-cool to room temp |
| Bluish tint | Over-temp / over-soak; door-zone over-comp | Redo last 1–2 passes at correct window | Map furnace; tune zoned control & door compensation |
| Runs / sags | Low viscosity; too thick; vertical pooling | Local sand → thin touch-up → re-fire | Hold viscosity; edge back-brush; fan path at holes |
| Pinholes / fisheyes | Dust/oil; incomplete drying | Local recoat or strip/recoat within window | Clean air; 100–200 °C full drying; fixture hygiene |
| High resistance scatter | Non-uniform thickness; over-burn; under-dry | Add uniform thin pass + correct soak | Per-pass weighing; soak window control; inter-pass cooling |
Buyer action list (fast)
At receiving: filter-paper wipe, low-angle light check, color scan.
Ask for the evidence pack: zoned setpoints + door compensation, TC map, furnace curve, inter-pass cooling logs.
Quantify: per-part weight distribution + g/m², per-pass weighing logs, comb-gauge checks.
For defects, follow the rework window; beyond window → scrap to protect schedule.
For different systems, require separate furnaces or clean-down records to avoid cross-contamination.