2.5 Workmanship and Acceptance Criteria

Quality cannot be negotiated after the solder has cooled. Subjective terms like "good enough," "neat," or "strong" have no place in manufacturing; they are breeding grounds for disputes between the EMS provider and the client. To ensure consistent output, the Golden Data Pack must lock the workmanship standard to a binary Pass/Fail logic governed by industry-validated specifications.

The Governing Standards

Distinguish between the process of soldering and the inspection of the result.

1. J-STD-001: The Process Standard

• Function: Defines the materials, methods, and process controls required to build the assembly (e.g., flux types, gold removal, cleanliness testing).
• Usage: Used by Process Engineers to set up the line.

2. IPC-A-610: The Acceptance Standard

• Function: Defines the visual acceptance criteria for the final product. It provides the "Target," "Acceptable," "Process Indicator," and "Defect" conditions.
• Usage: Used by Quality Control (QC) inspectors and AOI machines.

Defining the Class (The Reliability Tier)

Inspection criteria change drastically based on the Class. A 25% overhang on a component is a Pass for Class 2 but a Fail for Class 3.

• Rule: The Data Pack must explicitly state the IPC Class.
• Default Protocol: If the customer does not specify a Class, Then the Project Manager must declare IPC-A-610 Class 2 as the default before the build begins.

The Three Classes:

• Class 1 (General Electronic Products): Consumer electronics, toys. Function is primary; cosmetic imperfections are acceptable.
• Class 2 (Dedicated Service Electronic Products): Laptops, appliances, industrial controls. Uninterrupted service is required, but not critical.
• Class 3 (High Performance/Harsh Environment): Medical, Automotive, Aerospace. Equipment must function on demand; no downtime allowed.

Pro-Tip: Do not default to Class 3 "just to be safe." Class 3 requires stricter barrel fill (75% vs 50%) and tighter component alignment, driving up cost and inspection time without necessarily improving function for a consumer device.

Critical Acceptance Logic

Convert the 400-page IPC manual into focused inspection rules for the line.

1. Solder Joint Geometry

A joint is verified by the wetting angle and fillet shape.

• Wetting: The solder must form a concave meniscus.
  • Fail: Convex (bulbous) shapes indicate non-wetting or excess solder.
  • Fail: Contact angle > 90° (beading) on the pad.
• Vertical Fill (Through-Hole):
  • Class 2: ≥ 50% vertical fill of the barrel is required.
  • Class 3: ≥ 75% vertical fill is required.

2. Component Placement & Alignment

• Side Overhang:
  • Class 2: Component termination may overhang the pad width by ≤ 50%.
  • Class 3: Component termination may overhang the pad width by ≤ 25%.
• Toe Overhang: Strictly Forbidden. The component termination must not overhang the pad length (toe) in any Class.

3. Cleanliness & Residue

• Flux Residue:
  • No-Clean: Visible residue is acceptable if it is non-sticky and does not obstruct visual inspection.
  • Water Soluble: Zero visible residue allowed. White powder indicates a cleaning process failure.
• Solder Balls: Any solder ball that is not entrapped (i.e., can be dislodged by a brush) is a Defect.

Inspection Magnification

More magnification is not better. Over-magnification leads to "false failures" by highlighting surface graininess that is structurally sound.

Standard Magnification Levels (J-STD-001):

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

Final Checklist