3.5 Common Defects & Corrections

Solder balls, non-fills, and bridging are often not defects of the solder wave itself, but failures of preparation. This chapter details the non-negotiable process of managing flux activation and the thermal ramp rate. Controlling these factors is the only way to drive off volatile solvents, stabilize the temperature differential (∆T), and maximize the throughput of the THT process by eliminating avoidable rework.

1.3.5.1 The Troubleshooting Protocol: Triage and Fix

Most THT soldering defects stem from a handful of predictable missteps in fluxing, preheating, or wave dynamics. Effective troubleshooting requires a disciplined, sequential approach: verify preparation first, change one variable, and re-check on a single panel. Do not adjust multiple machine settings simultaneously, as this obscures the root cause.

1. Preparation Check (Mandatory First Step): Verify flux coverage/dose and top-side temperature at wave entry (Chapter 1.2).entry.
2. Mechanical Check: Verify pallet sealing and clearances; check conveyor finger cleanliness and angle (Chapter 1.4).angle.
3. Process Adjustment: Change one parameter only (e.g., speed/dwell, fountain height, chip wave balance), then recheck the result on a single sample board.

1.3.5.2 Quick Defect Map: Symptom, Cause, and Correction

This table maps common THT defects to their probable cause and the smallest, most reliable fix required to contain the issue.

Symptom	Likely Cause(s)	First Corrective Action
Bridging (Fine Rows)	Flooded flux; poor drain angle; chip wave too low/short.	Raise chip wave 0.2–0.5 mm or increase dwell +0.3 seconds.
Bridging at Row End	Lazy exit; no solder dam/thief (DFM issue).	Add end-dwell + quick kick-out; enforce solder thief in next design (Chapter 1.1).design.
Icicles / Spears	Over-dwell with cool exit; long lead protrusion (Chapter 1.1).protrusion.	Faster exit (increase conveyor speed); apply light air/N2 knife; +5 °C pot temperature.
Poor Top-Side Fill	Inadequate preheat/flux in holes; hole clearance too tight; heavy copper sink.	Raise top-side temperature 5–10 °C; slow conveyor speed (longer contact time).
Skips / Non-Wet	Oxide/aged finish; flux starved; short contact time.	Add a second light flux spray pass; slow belt; if persistent, consider N2 over the wave.
Solder Balls / Spitting	Wet solvent at entry (preheat failure); fountain turbulence.	Increase preheat dry time (longer ramp, not hotter); lower fountain 0.5–1.0 mm.
Blowholes / Voids	Moist PCB; volatile flux boils in hole; tight mask annulus.	Bake boards before assembly; longer, gentler preheat; relieve mask annulus (Chapter 1.1).annulus.
Selective: Random Non-Fill	Nozzle Z too high (no full engulfment); path speed too fast.	Touch-off Z-zero; slow down path to 5–8 mm/second; add quick-wet + targeted slow second pass.

1.3.5.3 Root Causes to Design Out (DFM Feedback)

Systemic defects that persist across multiple runs are rooted in Design for Manufacturing (DFM) failures and must be addressed in the next PCB revision.

• Hole/Pad Geometry: Holes too tight or tiny annular rings guarantee non-fills and pad lift during rework.
  • Fix: Mandate lead diameter +0.20–0.45 mm clearance and annular rings greater than 0.25 mm radial copper (Chapter 1.1).copper.
• Heat Sinks: No thermal reliefs on THT pins connected to planes will always cause cold joints.
  • Fix: Mandate 4 spokes, 0.25–0.40 mm wide thermal reliefs (Chapter 1.1).reliefs.
• Layout: Pin rows parallel to the wave and SMT components crowding the mini-wave zone invite bridging and splash.
  • Fix: Mandate robber pads (thieves) on fine-pitch rows and maintain a 3–4 mm keepout from SMT (Chapter 1.1).SMT.

1.3.5.4 Process Adjustment Guide: Change the Right Knob

Troubleshooting requires knowing which process knob controls which defect mechanism.

• To fix Starvation / Poor Top-Fill: Control is mainly Conveyor Speed / Dwell (longer contact time), then Pot Temperature (plus 5 °C).
• To fix Early Bridges / Solder Splash: Control is mainly Flux / Preheat (must be dry at entry), then Chip Wave height/dwell.
• To fix Exit Stringiness / Icicles: Control is mainly Peel Angle / Air Knife / End-Dwell, not raw pot temperature.

1.3.5.5 Selective vs. Wave: What is Different

The philosophy of fixing selective defects is local and targeted, while wave fixes are global and balance-dependent.

• Selective Fixes: Focus on local parameters. Adjust nozzle diameter, Z-touch-off height, path speed, or spot dwell time. Prefer creating a two-stage pass (quick pre-wet followed by a slow final pass) for difficult joints rather than increasing global temperature.
• Wave Fixes: Focus on balance. The key is setting the Chip Wave to scrub and the Main Wave to drain. Do not try to make the Main Wave do the Chip Wave's job; this only leads to excessive turbulence and bridges.

Final Checklist: THT Defect Containment

Checkpoint	Immediate Action (Containment)	Next Rev Action (Prevention)
Prep State	Verify Top-Side Temp is in the flux vendor’s band (Chapter 1.2).band.	Review DFM for thermal relief on persistent cold joints.
Bridging	Adjust Chip Wave (height/dwell) or enable Air/N2 Knife.	Mandate Solder Thief Pads or pallet modification (Chapter 1.4).modification.
Non-Fill / Skips	Slow Conveyor Speed or +5 °C Pot Temp; run second light flux pass.	Check hole clearance (too tight) against lead diameter (Chapter 1.1).diameter.
Solder Balls	Increase Preheat Time (dryer entry); check for flux system clogs.	Ensure mask annulus is open greater than 0.10 mm around pads to vent gas.
Troubleshooting	Change only one process variable at a time; log the change in the recipe notes.	Update the Golden Recipe only after the fix is proven effective on three consecutive panels.