1.5 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.

1.5.1 The Troubleshooting Protocol: Triage and Fix

Most THT soldering defects stem not from mystery but from a handful of predictable missteps in preparation,fluxing, heat,preheating, or exit.wave Bridges,dynamics. icicles,Effective troubleshooting requires a disciplined, sequential approach: verify preparation first, change one variable, and skips all trace back to flux coverage, top-side activation, wave balance, or nozzle control—and each has a small, reliable correction. By treating symptoms with the lightest adjustment and confirming resultsre-check on a single panel,panel. Do not adjust multiple machine settings simultaneously, as this obscures the processroot stays both stable and teachable.

1.5.1 Triage first (don’t turn five knobs)

cause.

1. PrepPreparation checkCheck (Mandatory First Step): (always first): fluxVerify flux coverage/dose and top-side temptemperature at wave entry (Chapter 1.2).
2. MechanicsMechanical Check:: Verify pallet seals/clearances,sealing and clearances; check conveyor finger cleanliness/cleanliness and angle (Chapter 1.4.4), nozzle Z/height (1.3.6).
3. Process knobAdjustment:: changeChange one— parameter only (e.g., speed/dwell, fountain height, chip↔mainchip balance—wave balance), then recheck the result on a onesingle panelsample board.
   

---

1.5.2 Quick mapDefect (symptomMap: →Symptom, likelyCause, and Correction

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

Symptom	Likely cause(Cause(s)	First fixCorrective (fastest that sticks)Action
Bridging (betweenFine pins/rows)Rows)	Flooded fluxflux; film;poor colddrain entry;angle; chip wave too low/short; parallel long rows; fountain too tallshort.	TrimRaise flux dose; add/extend chip wave dwell +0.3 s; raise top-side 5–10 °C; lower fountain 0.2–0.5 mm; rotate layout vs wavemm or addincrease dwell thief+0.3 seconds (13.1/13.4).
Bridging at rowRow endEnd	Lazy exit; no tailsolder dam/thief (DFM issue).	Add end-dwell 0.3–0.5 s then+ quick kick-out;out; program aenforce solder thief tail pastin lastnext pad;design sharpen(Chapter pallet exit edge1.1).
Icicles / spearsSpears	Over-dwell with cool exit; low pot; long lead protrusion (Chapter 1.1).	Faster exit;exit (increase conveyor speed); apply light air/N2 knife; +5 °C pot;pot trimtemperature.
Poor dwellTop-Side −0.2Fill	Inadequate s;preheat/flux enforcein holes; hole clearance too tight; heavy copper sink.	Raise 0.5–1.5top-side mmtemperature protrusion5–10 °C; slow conveyor speed (12.1)longer contact time).
Skips / non-wet / de-wetNon-Wet	Oxide/aged finish; flux starved; short contact;contact thermals to planestime.	Add light extra spray pass; slow belt (longer contact);a 4-spokesecond thermalslight in next rev; try N₂ on wave
Poor top-side barrel fill	Inadequate preheat/flux in holes; drag too fast; hungry copper/planes	Raise top-side temp 5–10 °C; second lightspray pass; reduceslow speed 2–3 mm/s or +0.3 s spot-dwell; bump pot +5 °Cbelt; if stillpersistent, shortconsider N2 over the wave.
Solder ballsBalls / spittingSpitting	Wet solvent at entry;entry (preheat failure); fountain turbulence; dirty fingersturbulence.	Increase preheat dry timeDry earlier (samelonger totalramp, heat,not smoother ramp)hotter); lower fountain 0.5–1.0 mm; clean/degunk fingers & railsmm.
Blowholes / voids in barrelsVoids	Moist PCB; volatile flux boils in hole; tight mask dams gasannulus.	Bake boards;boards gentler,before longerassembly; longer, gentler preheat; relieve mask annulus 0.10–0.15(Chapter mm (13.1.1).
Dull/grainy joints	Cold joint; over-baked flux	+5 °C pot or +0.2 s main dwell; even preheat (no burnt zones); consider N₂
SMT splash / contamination	Overspray; fountain too tall; masking gaps	Tighten spray window; lower fountain; improve pallet seal and add clip-on fences
Selective: randomRandom non-fillNon-Fill	Nozzle Z too high (no engulf)full engulfment); path outrunsspeed cuptoo fast.	Touch-off Z-zero; slow down path to 5–8 mm/s on that segment;second; add quick-wet + targeted slow second pass
Selective: persistent bridges in 2.00 mm rows	Cup overfills trench; end dwell missing	Smaller non-wettable nozzle; add end-dwell + kick; 5–10° approach anglepass.

---

1.5.3 Root causesCauses youto canDesign design outOut (DFM Feedback)

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

• Hole/Pad Geometry: Holes too tight /or thintiny annular rings →guarantee undersizednon-fills barrelsand neverpad fill.lift during rework.
  • Fix: Mandate lead Ødiameter +0.20–0.45 mm (byclearance thickness/copper),and annular rings ≥greater than 0.25–0.3025 mm, teardropsradial copper (Chapter 1.1).
• Heat Sinks: No thermal reliefs on THT pins connected to planes →will always cause cold joints.
  • Fix: Fix:Mandate 4 spokes, 0.25–0.40 mm wide thermal reliefs (Chapter 1.1).
• RowsLayout: Pin rows parallel to the wave →and longSMT solder dams.components Fix:crowding the mini-wave zone rotateinvite orbridging addand splash.
  • Fix: Mandate robber pads/pallet thieves (1.1,thieves) 1.4).
  • SMTon crowdingfine-pitch miniwaverows →and splash/bridges.maintain Fix:a 3–4 mm keepout orfrom pallet maskingSMT (1.1,Chapter 1.3)1).

1.5.4 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).
• LeadsTo toofix longEarly Bridges / Solder Splash: →Control icicles.is Fix: plan protrusion 0.5–1.5 mm after solder (1.1).
  

---

1.5.4 Knob guide (change the right thing)

• Looks flooded / bridges early? →mainly Flux &/ preheatPreheat first,(must be dry at entry), then chipChip waveWave height/dwell.
• LooksTo starvedfix Exit Stringiness / no top-fill?Icicles: →Control is mainly ConveyorPeel speedAngle &/ dwellAir Knife / End-Dwell, not raw pot temperature.

1.5.5 Selective vs. Wave: What is Different

The philosophy of fixing selective defects is local and targeted, thenwhile pot +5 °C.

Exit looks stringy? → End-dwell + quick lift, small air/N₂ knife; don’t just raise temperature.

Selective only on a few pins failing? → Local pass (spot dwell) and smaller nozzle, not global changes.

---

1.5.5 Mini playbooks (by defect)

A) Bridging (fine rows)

1. Verify UV flux carpet and top-side in band (1.2).
2. Raise chip 0.2–0.5 mm or +0.3 s dwell; keep main calm.
3. Add end-dwell + kick; if still there → lower main 0.2 mm and add thief.
4. Next rev: robber pad or pallet tail.
   

B) Poor top-side fill

1. +5–10 °C top-side via preheat; slow belt or +0.3 s spot-dwell.
2. Second light pass (drag or selective).
3. If still low → +5 °C pot; check hole clearance/thermals for next spin.
   

C) Icicles on tabs/posts

1. Faster exit; small knife.
2. +5 °C pot; shorten dwell; confirm lead protrusion.
3. For huge tabs: mini-dip or local spot dwell, not whole-board heat.
   

---

1.5.6 Selective vs wave: what’s different

• Selective fixes are local: nozzle Ø, Z touch-off, path speed/dwell, fountain height. Prefer two-stage passes (quick wet → slow finish).
• Wavewave fixes are global and balance-dependent.
  • Selective Fixes:: chip↔mainFocus balance,on conveyorlocal angle,parameters. peel/knife.Adjust Don’tnozzle 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 mainthe waveMain Wave do chip’the Chip Wave's job.job; this only leads to excessive turbulence and bridges.
    

  Final Checklist: THT Defect Containment

  Checkpoint	Immediate 1.5.7 “Do not” listAction (savesContainment)	Next days)Rev Action (Prevention)
  Prep State	Don’t raiseVerify potTop-Side tempTemp tois fixin flux/preheatthe mistakes—spatterflux andvendor’s oxidationband follow.(Chapter 1.2).	Don’tReview widenDFM for AOIthermal limits for bridges; fix chip wave / exit. Don’t drown boards in flux; dry, even films beat puddles. Don’t tweak three settings at once—you lose the cause. Don’t accept “random non-fill” until you’ve checked hole size vs lead. 1.5.8 Tiny DOE when you’re stuck (3× panels) Factor A: Speed (−2 mm/s / nominal / +2 mm/s) Factor B: Fountain (−0.3 mm / nominal / +0.3 mm) Factor C: End-dwell (0 / +0.3 s)  Measure bridges/row, top-fill %, icicles. Keep the combo that improves the Pareto with the smallest heat. 1.5.9 Inspect what proves the fix Top-side barrel photosrelief on thepersistent worstcold header (same pads each run).joints.
  Bridging	CountAdjust bridgesChip per rowWave, (height/dwell) or enable icicleAir/N2 lengthKnife,.	Mandate skipSolder rateThief Pads on 3 panels before/after. Save settings in recipe comments (what you changed and why). 1.5.10 Pocket checklists Before first article Flux pattern even; dose logged; no overspray Top-side temp at entry in band (per flux family) Chip and main heights set; angle 6–8°; finger path clean Selective: Z-zero taught; nozzle Ø sized to pad +1–2 mm If bridging Add/extend chip; lower main a touch; end-dwell + kick Thief tail or pallet insert;modification re-photo(Chapter same row1.4).
  If non-fillNon-Fill / skipsSkips	Slow beltConveyor Speed or +0.3 s spot dwell; raise top-side 5–10 °C Second light pass; check hole/thermal design for next rev If icicles Faster exit; light knife; +5 °C potPot onlyTemp; ifrun neededsecond light flux pass.	VerifyCheck hole clearance (too tight) against lead protrusion;diameter shorten(Chapter dwell1.1).
  Solder onBalls	Increase tabsPreheat Time (dryer entry); check for flux system clogs.	Ensure mask annulus is Theopen pathgreater than 0.10 mm around pads to fewervent defectsgas.
  Troubleshooting	Change is disciplined troubleshooting: verify flux and preheat first, changeonly one knobprocess variable at a time, andtime; log whatthe works.change Thisin approachthe eliminatesrecipe recurringnotes.	Update issues,the strengthensGolden recipes,Recipe andonly ensuresafter thatthe qualityfix is sustainedproven insteadeffective ofon rediscovered.three consecutive panels.