6.2 Maintenance & Calibration

Solder Paste Printer Hygiene

The printer is the single largest source of process defects. Maintenance focuses on the purity of the transfer mechanism.

Squeegee Blades:
- Inspection: Inspect blades daily for nicks or dents. A physical imperfection of > 0.1 mm on the blade edge will cause paste "streaking" or uneven scooping.
- Cleaning: Solder paste must be removed from the blade holder and side dams at the end of every shift. Dried paste acts as a contaminant if it falls back onto the stencil.
Stencil Cleaning:
- Underside Wipe: Verify the automatic solvent tank levels and paper roll supply at the start of every shift.
- Aperture Wash: Stencils must be cleaned in an automated ultrasonic or spray-under-immersion system after use. Hand wiping is prohibited as it packs solder balls into fine-pitch apertures.
Clamping Rails: Clean the conveyor rails and support table daily. Hardened paste buildup here changes the effective board height (Z-axis), affecting the seal between board and stencil.

The placement head is the most expensive component on the line. Vacuum integrity is paramount.

Nozzle Conditioning:
- Cleaning Cycle: Nozzles must be processed in an automated nozzle cleaner (mist/drying) every 24 hours or 100,000 picks. Manual wiping with alcohol is insufficient for removing flux buildup inside the shaft.
- Inspection: Use a microscope to check for tip wear or deformation weekly. Worn tips cause component "tombstoning" due to uneven vacuum hold.
Vacuum Filters:
- Paper Dust: Paper tape generates significant fibrous dust. Vacuum filters on the placement head must be inspected weekly and replaced if grey/clogged to prevent suction loss.
Vision System:
- Lens Cleaning: The upward-looking camera lens must be cleaned with optical-grade tissues daily. Dust on the lens leads to component recognition errors and high false rejection rates.

Feeders are mechanical assets subject to high wear. They must be treated as calibrated tools, not passive holders.

Debris Removal: Operators must use a localized vacuum to remove paper dust and loose components from the feeder bank area at every reel change. Compressed air blow-off is strictly prohibited as it forces debris into the machine's linear guides.
Offline Calibration:
- Frequency: Every feeder must be cycled through an offline Calibration Jig every 6 months or after a major jam.
- Test: The jig verifies the "Advance Pitch" accuracy and the "Take-Up" tension.
- Tagging: Feeders passing calibration must be tagged with a color-coded sticker indicating the next due date. Untagged feeders are not permitted on the machine.

The reflow oven is a collection point for flux volatiles (fumes).

Flux Management Systems:
- Cooling Zone: Flux condenses on the heat exchangers in the cooling zone. These radiators must be removed and chemically cleaned monthly to prevent flux dripping onto processed boards.
- Extraction Tubes: Inspect flexible exhaust hoses weekly for restrictions. Reduced airflow alters the thermal profile and allows volatile organic compounds (VOCs) to leak into the factory air.
Conveyor Chains:
- Lubrication: Automated chain oilers must be checked weekly. Dry chains cause vibration that can shift components while the solder is liquidus.
- Parallelism: Measure the width consistency between the entrance, center, and exit of the oven monthly to prevent boards from dropping or jamming.

Machine positioning accuracy must be empirically verified using a certified artifact.

Machine Capability (Cpk) Check:
- Method: Run a "Glass Board" or "Verification Plate" (a precise artifact with fiducials) through the machine monthly.
- Metric: The machine places test components (or measures fiducials), and the offset is calculated.
- Limit: If Cpk drops below 1.33, the machine axes (X/Y gantries) must be mechanically re-calibrated by a manufacturer-certified engineer.