Scrap and NG (Non-Good) in a PCB/PCBA factory don’t come from one single issue—they’re usually a combination of design gaps, process variation, material defects, and handling problems.
1. Soldering Defects (Top Contributor)
This is usually the #1 scrap driver in SMT lines.
Common issues:
- Solder bridges (short circuits)
- Insufficient solder / open joints
- Cold solder joints
- Tombstoning (chip components lifting)
- Voids in BGA/QFN packages
Root causes:
- Poor stencil design or aperture size
- Incorrect solder paste printing parameters
- Reflow profile not optimized
- PCB pad design issues (DFM problem)
2. Component Placement Defects
Errors during pick-and-place process.
Typical NGs:
- Misalignment
- Missing components
- Wrong polarity (e.g., diodes, ICs)
- Wrong component loaded
Root causes:
- Feeder setup errors
- Vision system miscalibration
- Program errors in placement machine
- Operator mistakes
3. PCB Fabrication Defects
Incoming PCB quality has a big impact.
Common defects:
- Open/short circuits in traces
- Delamination
- Solder mask misalignment
- Warpage / bow & twist
- Pad lifting
Root causes:
- Supplier process issues
- Poor material quality
- Improper storage (moisture absorption)
4. ESD (Electrostatic Discharge) Damage
Silent but very critical—often leads to latent failures.
Effects:
- IC damage (immediate or latent)
- Reduced product reliability
Root causes:
- Lack of ESD controls (grounding, wrist straps)
- Poor handling practices
- Inadequate EPA (ESD Protected Area)
5. Reflow / Thermal Process Issues
Improper heating profile causes multiple defects.
Typical NGs:
- Component damage
- Solder cracks
- PCB warpage
- Head-in-pillow (BGA)
Root causes:
- Incorrect temperature profile
- Uneven heating
- Poor oven calibration
6. Contamination & Cleanliness Issues
Often overlooked but critical in high-reliability products.
ตัวอย่าง:
- Flux residue
- Dust or foreign particles
- Ionic contamination
Impact:
- Corrosion
- Leakage current
- Field failures
7. Mechanical Damage / Handling Issues
Occurs during manual or automated handling.
Common NGs:
- Scratches on PCB
- Broken components
- Connector damage
- Bent pins
Root causes:
- Poor packaging
- Improper handling
- Lack of fixtures or protection
8. Testing Failures (ICT / FCT / Functional)
Final stage where hidden defects appear.
Failures include:
- No power / dead board
- Signal failure
- Communication issues
- Intermittent faults
Root causes:
- Upstream process defects
- Design issues
- Poor solder joints or components
9. Moisture Sensitivity (MSL Issues)
Critical for IC packages.
Defects:
- Popcorn effect during reflow
- Internal cracking of ICs
Root causes:
- Improper storage (humidity exposure)
- Not following bake-out procedures
10. Design-Related Issues (DFM / DFT Gaps)
Sometimes the process is fine—but design causes scrap.
ตัวอย่าง:
- Poor pad design
- Inadequate spacing → solder bridging
- Difficult test access
- Thermal imbalance