2.5 Workmanship and Acceptance Criteria

Quality cannot be negotiated after the solder has cooled. Subjective terms like “good enough” or “looks neat” are insufficient and can lead to disputes between the EMS and the client.

To guarantee a stable, predictable yield, the Golden Data Pack must clearly define the workmanship standards into a clear Pass/Fail logic governed by validated industry specifications.

The Governing Standards

A strict differentiation must be made between the standard governing the process of soldering and the standard governing the inspection of the result.

1. J-STD-001: The Process Standard

• The Function: This standard governs the materials, methods, and process controls required to build the assembly (e.g., flux chemistries, gold removal requirements, cleanliness testing methodologies).
• The Owner: It is used by Process Engineers to dial in the SMT line and the wave soldering parameters.

2. IPC-A-610: The Acceptance Standard

• The Function: Defines the visual acceptance criteria for the finalized product. It categorizes every joint into one of four states: “Target,” “Acceptable,” “Process Indicator,” or “Defect.”
• The Owner: Exclusively used by Quality Control (QC) inspectors and Automated Optical Inspection (AOI) machines to Pass or Reject the board.

Defining the Class (The Reliability Tier)

Inspection criteria change significantly depending on the defined Class. A component pushed 25% off its pad is a Pass for Class 2, but a Defect for Class 3.

• The Rule: The Data Pack must explicitly declare the target IPC Class in the Fab Notes.
• The Default Protocol: When the client fails to declare a Class, the Project Manager should document IPC-A-610 Class 2 as the default baseline before assembly begins.

The Three Classes:

• Class 1 (General Electronic Products): Consumer electronics, toys. The primary requirement is functionality; cosmetic defects are generally acceptable.
• Class 2 (Dedicated Service Electronic Products): Laptops, appliances, industrial controls. Uninterrupted performance is expected, but the application is not life-critical.
• Class 3 (High Performance/Harsh Environment): Medical life-support, automotive ADAS, aerospace. The equipment must function reliably on demand; downtime is unacceptable.

Engineering Warning: Defaulting to Class 3 “just to be safe” is prohibited. Class 3 mandates extensive barrel fill requirements (75% vs. 50%) and highly accurate component alignment. This increases the PCBA cost and AOI inspection time without adding functional value to a standard consumer device.

Critical Acceptance Logic

The comprehensive IPC manual must be distilled into focused, enforceable inspection rules for the factory floor.

1. Solder Joint Geometry

A joint is structurally evaluated based on its wetting angle and fillet shape.

• Wetting (The Bond): The solder must form a smooth, concave meniscus blending into the pad.
• The Defect: Convex (bulbous/fat) shapes indicate non-wetting or excess solder.
• The Defect: A contact angle > 90° (beading up like water on wax) on the pad is a rejection.
• Vertical Fill (Through-Hole):
  • Class 2 Target: Requires ≥ 50% vertical flow up through the plated barrel.
  • Class 3 Target: Requires ≥ 75% vertical flow up through the plated barrel.

2. Component Placement & Alignment

• Side Overhang:
  • Class 2 Matrix: The component termination may laterally overhang the physical pad width by ≤ 50%.
  • Class 3 Matrix: The component termination may laterally overhang the physical pad width by only ≤ 25%.
• Toe Overhang: Prohibited. The component termination should avoid overhanging the length (toe) of the pad under any Class requirement.

3. Cleanliness & Flux Residue

• Flux Residue:
  • No-Clean Chemistry: Visible baked-on residue is fully acceptable provided it is chemically inert (non-tacky) and does not obstruct Automated Optical Inspection (AOI).
  • Water Soluble Chemistry: Zero visible residue is permitted. A white, powdery haze indicates a wash process failure and is highly conductive.
• Solder Balls: Any isolated solder sphere that is not entrapped (e.g., stuck permanently under a component or under mask) and can be dislodged with a stiff brush is a Defect.

Inspection Magnification

More magnification is not always better. Excessive magnification creates “false failures” by exposing microscopic surface grain structures that are actually metallurgically sound.

The Magnification Baseline (J-STD-001):

• Pad Width ≥ 1.0 mm: 1.75X – 4X Magnification
• Pad Width 0.5 – 1.0 mm: 4X – 10X Magnification
• Pad Width 0.25 – 0.5 mm: 10X – 20X Magnification
• Pad Width < 0.25 mm: 20X – 40X Magnification

Final Checkout: Workmanship and acceptance criteria

The Control Point	The Operational Requirement
Standard Declaration	Invoke IPC-A-610 (Visual) + J-STD-001 (Process).
Class Selection	Explicitly declared (1, 2, or 3). Assumed Class 2 by default.
Wetting Angle	Must be Concave (< 90°). Convex = Reject.
PTH Barrel Fill	≥ 50% (Class 2 baseline) or ≥ 75% (Class 3 baseline).
Toe Overhang limit	0% permitted. The lead must sit entirely on the pad.
Inspection Zoom	Cap manual inspection at 10X for standard SMT to prevent false AOI rejects.
Gold Removal Rule	Mandatory tinning requirement if gold plating > 2.54 µm to prevent embrittlement.