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, inspection personnel must use the established IPC standards as the common rulebook, ensuring every acceptance or rejection decision is backed by shared definitions of "good" and "not good." Consistent visual cues, imaging tools, and clear acceptance classes allow fast decisions that hold up under scrutiny, protecting both the final product and the manufacturing process stability.

2.4.1 Acceptance Mandate: IPC Standards

The IPC-A-610 standard, Acceptability 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 across various product classes.
IPC-7711/7721: Defines the detailed procedures for rework and repair of defects and establishes the limits for how far a repair operation can go without compromising reliability.

The factory must augment these standards with limit samples (physical boards showing the acceptable borderline) and customer notes (specific void limits, cosmetic standards, etc.).

Product Acceptance Classes

The acceptance criteria are not universal; they depend on the product's intended service life and consequence of failure. The class must be posted on the traveler or work instruction.

Topic	Class 2 (General Industrial)	Class 3 (High Reliability/Life Support)
General Reliability	Functional reliability expected over service life.	Maximum reliability; essential performance and service life guaranteed.
Barrel Fill (THT)	Adequate vertical fill per IPC (often ≥ 75% from solder side).	Maximum vertical fill required; must show clear evidence of wetting on the top pad.
Solder Balls	Trapped, immobile, or benign balls may be allowed if no electrical risk.	Far stricter; virtually no loose particles allowed; minimal acceptable residue.
Rework	Allowed per 7711/7721 procedures.	More restricted; requires strict tracking of heat cycles and component limits.

2.4.2 Universal GO / NO-GO Cues

Inspection personnel must use these universal cues for rapid decision-making across all component types:

Acceptance Status	Criteria (GO)	Criteria (NO-GO)
Wetting	Solder thins out onto the pad/lead (concave fillet); wetting angle typically < 60°.	Non-wet/De-wet: Solder beads up like a raindrop; grainy, matte, or matte islands.
Geometry	Clean separation; no bridges or unintended solder balls.	Bridges/Shorts, Tombstones/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 (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 (a 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.
- Reject: Lifted corners, starved sides, massive central void that compromises thermal dissipation.

2.4.4 Rework and Repair Mandates

All repair work must be traceable 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 samples (photos of acceptable/rejectable borderlines) to ensure consistent decision-making across all shifts.

Final Checklist: Defect Evaluation and Acceptance

Mandate	Criteria	Verification Action
Standard Basis	Inspection must adhere to IPC-A-610 standards for the specified product Class (2 or 3).	Limit Samples and acceptance photos must be posted at the inspection station.
THT Acceptance	Must show a smooth bottom fillet and adequate vertical fill (top-side wetting) per class.	Reject immediately if bridging, icicles, or non-wetting is present.
Area-Array Acceptance	BGA/QFN must pass AXI for voids and collapse; no visible HIP seam.	Void percentage (e.g., ≤ 25%) verified via X-ray image analysis.
Rework Tracking	All repair activity must follow the 7711/7721 procedure and be logged.	Attempt count is recorded on the repair ticket; limit is enforced.
Cosmetics/Contamination	No loose debris, solder balls, or sticky, corrosive flux residue.	Foreign matter that can move or conduct fails the acceptance criteria.