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2.4 Defect Atlas & Acceptance

Defect evaluation sits at the intersection of quality, speed, and fairness in electronics manufacturing. Instead of relying on personal judgment, inspectorsinspection personnel must use the established IPC standards as the common rulebook, ensuring every callacceptance or rejection decision is backed by shared definitions of “good”"good" and “"not good.”" VisualConsistent visual cues, imaging tools, and clear acceptance classes allow fast decisions that hold up under scrutiny, while repair standards define exactly how far fixes can go. With evidence logged and references at hand, defect calls become objective checkpoints that protectprotecting both the final product and the process.manufacturing process stability.

2.4.1 WhyAcceptance useMandate: theIPC standards (and how)Standards

  • The IPC-A-610 =standard, what’sAcceptability of Electronic Assemblies, is the mandatory reference that defines the visual criteria for acceptance or rejection of a soldered joint or assembly.

    • IPC-A-610: Defines what is visually acceptable on shipped hardware (visualacross acceptance).various product classes.
    • IPC-7711/77217721: =Defines howthe todetailed procedures for rework/rework and repair of defects safely and whenestablishes the limits for how far a repair isoperation evencan allowed.go without compromising reliability.

    YourThe factory addsmust augment these standards with limit samples (physical boards showing the acceptable borderline) and customer notes (cosmetics, specialspecific void limits)limits, cosmetic standards, etc.).

    Product Acceptance Classes

    The acceptance criteria are not universal; they depend on top.

Post the product's intended service life and consequence of failure. The class must be posted on the traveler (Classor 2work typical industrial, Class 3 high-reliability). Inspectors decide fast by comparing to limit examples (photos, golden boards) tied to the correct class.instruction.



2.4.2 Class quick reference (mindset, not legalese)

Topic

Class 2 (mostGeneral EMS builds)Industrial)

Class 3 (life/safety/high-rel)High Reliability/Life Support)

General Reliability

Functional reliability expected over service life.

Maximum reliability,reliability; tighteressential cosmetics

Cosmetics

Minorperformance benignand blemishesservice allowed

Stricter:life minimal residue/marksguaranteed.

Barrel fillFill (THT)

Adequate vertical fill per IPC (often ≥ ~75% when inspected from solder side; confirm by product spec)side).

HigherMaximum expectationvertical fill; required; must show clear evidence of full wetting throughon the barreltop and top-sidepad.

Solder ballsBalls

Trapped/immobileTrapped, immobile, or benign balls may be allowed if no riskelectrical risk.

Far fewerstricter; allowed;virtually no loose particles allowed; minimal acceptable residue.

Rework

Allowed per 7711/7721 procedures.

More restricted; trackrequires strict tracking of heat cycles and component limits.

(Use your customer’s spec sheet for exact numbers—they win any tie.)



2.4.32 Universal GO / NO-GO Cues

Inspection personnel must use these universal cues (worksfor rapid decision-making across parts)all component types:

Acceptance Status

Criteria

  • (GO)

GOCriteria (NO-GO)

    • Wetting

    : solderSolder thins out onto the pad/lead (concave fillet;fillet); wetting angle typically <~ 60°).

    • CoverageNon-wet/De-wet:: padSolder edgesbeads visible,up like a raindrop; grainy, matte, or matte islands.

    Geometry

    Clean separation; no exposedbridges base metal on leads.

  • Clean geometry: no bridges, no whiskers, noor unintended solder balls.
  • Identity: correct part, pin-1/polarity right, marking readable.
  • NO-GO
    • Non-wet/de-wet: beads sit like raindrops; grainy, matte islands.

    • Bridges/shortsShorts, tombstones/skewTombstones/Skew, Head-in-Pillow (HIP) seam.

    Damage

    No cracks, chipped component bodies, or lifted pads/traces.

    Damage: Cracked bodies, blistering, solder mask damage exposing copper.

    Identification

    Correct component; correct Pin-1/polarity; marking readable.

    Incorrect component placed (BOM mismatch) or reverse polarity.

    2.4.3 Feature-Specific Visual Inspection

    A) Through-Hole Technology (THT)

    THT joints require a fast check for mechanical integrity and solder flow.

    • Solder Fillet (Bottom): Must be smooth, concave, and wet the pad and lead uniformly. Reject if icicles/spears are present, or if there is voided "ball on a plate" non-wetting.
    • Top-Side Evidence: Must show visible wetting at the top land (chips)a small, shiny crown) confirming adequate vertical barrel fill.
    • Protrusion: Lead length after soldering must be 0.5 – 1.5 mm above the top pad.

    B) Area-Array (BGA, QFN)

    Visual inspection is insufficient for these hidden joints. Acceptance relies on high-end imaging.

    • BGA (Ball Grid Array): Acceptance is based on AXI (Automated X-ray Inspection).
      • Accept: Uniform collapse (hourglass shape); no missing balls; voiding within limit (e.g., typically ≤ 25% per ball).
      • Reject: HIP (BGAa seam).dark seam between the ball and reflowed paste); non-collapsed center field; solder shorts between balls.
    • QFN/LGA (Quad Flat No-Lead): Acceptance is based on AXI for the thermal pad and 3D AOI for the perimeter.
      • Accept: Continuous perimeter fillet visible along the edges (if wettable flanks are present); thermal pad void percentage within the customer specification.
      • DamageReject:: crackedLifted bodies,corners, chippedstarved lenses,sides, liftedmassive pads/traces.
      • Residuecentral void: sticky/charred deposits or foreign matter that couldcompromises move.thermal dissipation.

    2.4.4 Rework and Repair Mandates

    IfAll you’rerepair onwork themust fence,be comparetraceable and adhere to the IPC-7711/7721 standard.

    • Rework: (Green status) Standard, repeatable procedures (part replacement, touch-up, BGA reballing) following strict documented steps and thermal limits (Chapter 2.3).
    • Repair: (Yellow status) Non-routine fixes (e.g., pad or trace repair) requiring specialized certification and detailed logging.
    • Attempt Count: The repair ticket must track the attempt count (number of times the joint or component was heated). Exceeding the max cycle limit (e.g., BGA ≤ 2 reflows) requires Material Review Board (MRB) approval.

    2.4.5 Evidence and Documentation

    Evidence is required to justify any rejection or repair action. This protects the quality decision from dispute and feeds accurate data into the CAPA system (Chapter 5.5).

    • Mandatory Evidence: All failures must have supporting images or data attached to the repair ticket (e.g., AXI slice image for a BGA void; AOI photo for a bridge).
    • Inspection Setup: The inspection station must display the product class (2 or 3) and the current limit samplesamples for(photos thisof productacceptable/rejectable borderlines) to ensure consistent decision-making across all shifts.

    Final Checklist: Defect Evaluation and class; when in doubt on critical nets, fail → rework.



    2.4.4 SMD (chips, SO/DFN/QFP) — fast cuesAcceptance

    FeatureMandate

    AcceptCriteria

    RejectVerification Action

    ChipsStandard (0201–1206)Basis

    BothInspection endsmust wetted,adhere centered;to slightIPC-A-610 meniscusstandards visiblefor the specified product Class (2 or 3).

    Limit SamplesTombstone, drawbridge,and skewacceptance offphotos pad,must exposedbe baseposted metalat the inspection station.

    Gull-wingsTHT (SO/QFP)Acceptance

    Toe/heel/Must show a smooth bottom fillet and adequate vertical fill (top-side filletwetting) visible;per no solder on body; leads parallelclass.

    Bridges,Reject liftedimmediately heel,if solderbridging, wickingicicles, upor lead,non-wetting bentis leads that break coplanaritypresent.

    DFN/QFNArea-Array edges

    Solder visible along edge; even fillet height on sides

    Starved corners, voided or flooded thermal pad that floats the body

    Drag solder finish

    Uniform “combed” shine; no icicles

    Solder webs between pins, dull/crumbly look

    Tip: judge fillet shape and symmetry, not mirror shine (finish/mask color can fool you).



    2.4.5 THT joints — what to look for in seconds

    FeatureAcceptance

    Accept

    Reject

    Insertion & lead

    Lead centered; protrusion ~0.5–1.5 mmBGA/QFN post-solder

    Leaning pins, mushroomed clinch that blocks wetting

    Solder fillet (bottom)

    Smooth concave fillet, wets pad & lead

    Icicles/spears, voided craters, non-wet “ball on plate”

    Top-side evidence

    Visible wetting at top land; adequate vertical fill per class

    Dry top, black hole appearance, resin voids

    Cleanliness

    No bridges row-to-row

    Bridges, solder balls that can dislodge

    If marginal on fill, check design factors (hole size, thermals) and process data (flux/preheat). Don’t grade design sins as operator faults.



    2.4.6 BGAs / area arrays — what images must show

    • AOI can’t judge hidden balls; usepass AXI for acceptance.
    • Accept:voids uniformand collapse (“hourglass” ball shape),collapse; no missing balls, voiding within limit per spec (often ≤ ~25% per ball, dispersed).
    • Reject:visible HIP (dark seam between sphere and paste), non-collapsed center field, large voids clustered at the pad interface, solder shorts between balls.

    Escapes here hurt; bias to fail and route to rework if the image is ambiguous on Class 3.



    2.4.7 QFN / LGA — easy pass/fail pattern

    • Perimeter: continuous wetting line on all sides; even stand-off.
    • Thermal pad: acceptable void percentage/pattern per customer (dispersed small voids better than one crater).
    • Reject: lifted corners, starved sides, solder balls squeezing from under body, massive central voids.



    2.4.8 Cosmetics & contamination (don’t debate—class it)

    Item

    Class 2

    Class 3

    Flux residue (no-clean)

    Thin, clear, non-sticky OKseam.

    Minimal,Void non-corrosive;percentage no(e.g., residues≤ that25%) couldverified migratevia X-ray image analysis.

    MaskRework nicks/silkTracking

    MinorAll thatrepair don’tactivity exposemust copperfollow OKthe 7711/7721 procedure and be logged.

    Attempt countStricter; nois copperrecorded exposureon the repair ticket; limit is enforced.

    Foreign matterCosmetics/Contamination

    No loose particles;debris, trapped, immobile tinysolder balls, mayor passsticky, corrosive flux residue.

    EssentiallyForeign none;matter removethat can move or failconduct fails the acceptance criteria.

    If it can move or conduct, it fails any class.



    2.4.9 7711/7721 rework & repair — green/yellow/red

    • Green (common rework): touch-up solder, part replacement (SMD/THT), wick and re-solder, BGA/QFN reflow per procedure.
    • Yellow (controlled repair): pad repair with adhesive, trace repair, mask repair—follow 7721, qualified tech only, record it.
    • Red (no-go without deviation): structural laminate damage, repeated heat beyond limits, repairs in prohibited zones for Class 3. If in doubt, MRB.

    Always log attempt count and repair type on the ticket.



    2.4.10 Fast decision trees (print these)

    Bridged fine-pitch pins?

    → Flux + clean sweep with chisel → If still bridged, wick lightly → If mask damage risk or repeats → Rework station → If BGA-style hidden short → AXI.

    Suspect BGA?

    → AXI slice at ball plane → If HIP/voids over limit → Rework → AXI verify.

    THT low top-fill?

    → Check flux/preheat record → If in band, spot reflow with preheat → If chronic on same refdes/lot → Design/PCB lot review (hole/finish) + process CAPA.



    2.4.11 Evidence that ends arguments (attach it)

    • AOI/AXI images (before/after for rework) with refdes overlay.
    • Macro photos of THT topside and suspect SMD joints.
    • Process snippets: SPI map for the area, reflow plot, selective/wave settings.
    • Class note (“Inspected to IPC-A-610 Class 3 + Customer Void Spec Rev C”).

       Put it in the ticket—don’t paste into chat apps.



    2.4.12 Pocket checklists

    Inspector setup

    • Product Class visible (2 or 3)
    • Limit sample photos loaded (good / borderline / reject)
    • AOI/AXI program rev matches traveler

    Per board

    • Polarity/markings correct; no missing/wrong parts
    • SMD fillets wet & symmetric; no bridges/balls
    • THT: clean bottom fillet, adequate top-side evidence for class
    • BGAs/QFNs: image check (AXI/AOI 3D) within limits
    • Cosmetics per class; nothing loose

    If unsure

    • Compare to limit sample for this product/class
    • Escalate Class-A doubts to QE; attach image + class note
    • Never “pass by vibe” on BGAs/QFNs—get the image



    Conclusion: Applying IPC standards, limit samples, and consistent documentation ensures that acceptance is clear, fast, and defensible. This disciplined approach minimizes disputes, strengthens reliability, and keeps workmanship aligned across operators, shifts, and customers.


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