6.2 Maintenance & Calibration
While Book 08 covers facility-wide operational strategies, this section touches on the specific maintenance actions helpful for
Solder Paste Printer Hygiene
Section titled “Solder Paste Printer Hygiene”The printer is a primary variable in process defects. Maintenance typically focuses heavily on the cleanliness of the transfer mechanism.
- Squeegee Blades:
- Inspection: Blades should be inspected daily for nicks or dents. A physical imperfection of > 0.1 mm on the blade edge can cause paste “streaking” or uneven scooping.
- Cleaning:
Solder paste is removed from the blade holder and side dams routinely at the end of a shift. Dried paste can act as a contaminant if it falls back onto the stencil.
- Stencil Cleaning:
- Underside Wipe: Verifying automatic solvent tank levels and the paper roll supply at the start of every shift ensures stable wiping.
- Aperture Wash: Stencils respond best when cleaned in an automated ultrasonic or spray-under-immersion system after use. Hand wiping is generally avoided, as it can inadvertently pack solder balls into fine-pitch apertures.
- Clamping Rails: Conveyor rails and the support table are cleaned daily. Hardened paste buildup alters the effective board height (Z-axis), which can affect the gasket seal between the board and the stencil.
Pick-and-Place Head & Nozzle Maintenance
Section titled “Pick-and-Place Head & Nozzle Maintenance”The placement head is a central, sensitive component on the line. Vacuum integrity is functionally paramount for accurate component handling.
- Nozzle Conditioning:
- Cleaning Cycle: Nozzles are best processed in an automated nozzle cleaner (typically utilizing mist and drying cycles) at regular intervals, such as every 24 hours or 100,000 picks. Manual wiping with alcohol is often insufficient for clearing flux buildup inside the fine shaft.
- Inspection: Using a microscope to check for tip wear or deformation weekly is a good practice. Worn tips can contribute to component “
tombstoning ” or dropping due to an uneven vacuum hold.
- Vacuum Filters:
- Paper Dust: Paper tape naturally generates fibrous dust. Vacuum filters on the placement head are inspected weekly and replaced if clogged or darkened to help prevent suction loss.
- Vision System:
- Lens Cleaning: The upward-looking camera lens should be cleaned with optical-grade tissues daily. Dust on the lens can lead to component recognition errors and an increased rate of false rejections.
Feeder Maintenance & Verification
Section titled “Feeder Maintenance & Verification”Feeders are highly active mechanical assets and operate best when treated as precision instruments.
- Debris Removal: Operators can use a localized vacuum to remove paper dust and loose components from the feeder bank area during reel changes. Compressed air blow-offs are generally avoided, as they can force debris deeper into the machine’s linear guides.
- Offline Calibration:
- Frequency: Feeders benefit from cycling through an offline Calibration Jig periodically (e.g., every 6 months) or after experiencing a major jam.
- Test: The jig helps verify the “Advance Pitch” accuracy and the “Take-Up” tension.
- Tagging: Feeders passing calibration are typically tagged with a sticker indicating the next due date, ensuring tools remain within specification on the machine.
Reflow Oven Maintenance
Section titled “Reflow Oven Maintenance”The
- Flux Management Systems:
- Cooling Zone: Flux naturally condenses on the heat exchangers in the cooling zone. These radiators should be removed and chemically cleaned monthly to prevent accumulated flux from dripping onto processed boards.
- Extraction Tubes: Flexible exhaust hoses are inspected weekly for restrictions. Reduced airflow alters the thermal profile and can allow volatile organic compounds (VOCs) to seep into the factory environment.
- Conveyor Chains:
- Lubrication: Automated chain oilers are checked weekly. Dry chains can cause vibrations that may shift components while the solder is in a delicate liquidus state.
- Parallelism: Width consistency between the entrance, center, and exit of the oven is measured monthly to prevent PCBs from dropping or jamming mid-process.
Calibration Verification (The “Glass Board”)
Section titled “Calibration Verification (The “Glass Board”)”Machine positioning accuracy is typically verified empirically using a certified artifact.
- Machine Capability (Cₚₖ) Check:
- Method: A “Glass Board” or “Verification Plate” (a precise artifact with measured fiducials) is run through the machine periodically, such as monthly.
- Metric: The machine places test components or measures the fiducials, and the positioning offset is calculated.
- Limit: If the Cₚₖ drops below an established threshold (e.g., 1.33), the machine axes (X/Y gantries) are mechanically re-calibrated by a certified engineer to restore baseline capability.
Final Checkout: Maintenance & calibration
Section titled “Final Checkout: Maintenance & calibration”| Asset | Task | Frequency | Standard Practice |
|---|---|---|---|
| Printer | Squeegee edge must be inspected | Daily | Must be replaced if nicked |
| Printer | Conveyor rails must be cleaned | Daily | |
| Mounter | Nozzles must be auto-cleaned | Daily | Automated machine cleaning |
| Mounter | Vision lens must be cleaned | Daily | Only optical tissue must be used |
| Feeders | Tape debris must be cleaned | Per Shift | Vacuum only (no air blow-off) |
| Feeders | Calibration Jig | 6 Months | Pitch and tension must be verified |
| Flux traps must be cleaned | Monthly | Chemical wash | |
| System | Cₚₖ Verification | Monthly | Glass board run |