Scrap and NG (non-good) are usually not random—they concentrate in a few high-risk processes where variation, material sensitivity, and process control gaps exist
🔷 1. Bare PCB Manufacturing – High Scrap Areas
🟠 a) Lamination Process
Common NG:
- Delamination
- Voids / air bubbles
- Resin starvation
Why it happens:
- Improper temperature/pressure profile
- Moisture in prepreg
- Incorrect lay-up alignment
👉 Impact: Internal defects → cannot rework → 100% scrap
🟠 b) Drilling Process
Common NG:
- Misregistration (hole shift)
- Broken drill bits → rough holes
- Nail-heading
Root causes:
- Worn-out drill bits
- Stack height variation
- Poor machine calibration
👉 Critical for multilayer PCB → affects connectivity
🟠 c) Plating (PTH / Copper Plating)
Common NG:
- Void in via (open circuit risk)
- Thin copper plating
- Overplating / nodules
Root causes:
- Poor bath chemistry control
- Agitation issues
- Contamination
👉 One of the highest scrap contributors because defects are internal and hidden
🟠 d) Etching Process
Common NG:
- Over-etch → open circuit
- Under-etch → short circuit
- Line width variation
Root causes:
- Etchant concentration variation
- Conveyor speed mismatch
- Resist issues
🟠 e) Solder Mask Application
Common NG:
- Misalignment
- Pinholes
- Poor adhesion
Root causes:
- Exposure issues
- Contamination
- Improper curing
🔷 2. PCBA (Assembly Process) – Major NG & Scrap Drivers
🔴 a) Solder Paste Printing (MOST CRITICAL)
~60–70% of defects originate here
Common NG:
- Insufficient solder
- Excess solder
- Solder bridging
- Misalignment
Root causes:
- Stencil design issues
- Printer setup (pressure/speed)
- Paste quality / viscosity
👉 This is your #1 yield driver
🔴 b) Pick & Place Process
Common NG:
- Missing components
- Wrong placement
- Misalignment
Root causes:
- Feeder issues
- Vision alignment error
- Program mistakes
🔴 c) Reflow Soldering
Common NG:
- Tombstoning
- Cold solder joints
- Voids in solder
- Component damage
Root causes:
- Incorrect reflow profile
- Thermal imbalance
- PCB design issues
🔴 d) Wave Soldering (for THT)
Common NG:
- Solder bridges
- Insufficient fill
- Icicles
Root causes:
- Flux inconsistency
- Wave height variation
- Conveyor speed
🔴 e) Manual Soldering / Repair
Common NG:
- Overheating damage
- Poor solder joints
- Lifted pads
👉 High variation due to human factor
🔷 3. Component & Material Related Issues
🟡 a) Incoming Material Defects
Examples:
- Warped PCB
- Oxidized pads
- Component lead issues
👉 Weak IQC = downstream scrap explosion
🟡 b) Moisture Sensitivity (MSL Components)
Common NG:
- Popcorning
- Cracked ICs
👉 Especially critical for BGA/QFN packages
🔷 4. Inspection & Test Escape (Hidden Scrap Drivers)
🟣 a) AOI / SPI / AXI Inefficiency
Issues:
- False calls → rework cost
- Missed defects → field failure
🟣 b) ICT / Functional Test Failures
Common NG:
- Open/short circuits
- Programming failure
👉 Late-stage failures = highest cost scrap
🔷 5. High Scrap Zones Summary (Priority Ranking)
From industry experience + yield impact:
- Solder Paste Printing (SPI control failure)
- Reflow Profile Issues
- Plating (via defects – hidden scrap)
- Etching (open/short circuits)
- Material Quality (PCB + components)
- Manual handling & rework damage
🔷 6. Key Quality Engineer Focus Areas (Your Interview Edge)
You can frame this like a pro:
👉 Focus on 3 control pillars:
1. Prevention (Best ROI)
- SPI control (Cp/Cpk > 1.33)
- Reflow profile validation
- Supplier quality control
2. Detection
- AOI + AXI optimization
- ICT coverage improvement
3. Reaction
- 8D for top defects
- Pareto analysis for scrap