5.2 IPC-A-610 Classifications & Criteria

IPC-A-610 "Acceptability of Electronic Assemblies" is the visual language of the electronics industry. It is not a suggestion box; it is the boundary between a shippable product and scrap. We do not inspect for "beauty"; we inspect for structural integrity and reliability physics. If a solder joint looks ugly, it is likely mechanically compromised.

The Three Classes (Risk Tiers)

You must define the Class before you open the book. Inspecting a consumer toy to aerospace standards is financial suicide; inspecting a pacemaker to toy standards is criminal negligence.

• Class 1 (General): "It turns on." Cosmetic defects are ignored. (e.g., Cheap Toys, Disposable LEDs).
• Class 2 (Dedicated Service): "It lasts." Uninterrupted service is desired. (e.g., Laptops, Home Appliances, Industrial Controls). This is the Default.
• Class 3 (High Reliability): "It saves lives." Failure is not an option. (e.g., Medical Life Support, Automotive Safety, Aerospace).

Pro-Tip: Never mix classes on the same assembly drawing. You cannot have "Class 2 soldering with Class 3 inspection on U1." The line moves too fast for that cognitive load.

Solder Joint Criteria (The Physics of Wetting)

A solder joint is an electrical connection and a mechanical anchor. It must show evidence of wetting (adhesion between the alloy and the base metal).

Visual States:

• Target: The ideal joint. Smooth, shiny, concave fillet.
• Acceptable: Not perfect, but mechanically sound. Ship it.
• Defect: A condition that compromises fit, form, or function. Reject.
• Process Indicator: A warning sign (e.g., a cold solder joint that passed electrical test). It’s "acceptable" for this unit, but signals the machine is drifting.

Universal Rules:

• IF the solder fillet is convex (bulbous) -> THEN Reject. This indicates "Cold Solder" or lack of wetting.
• IF the wire/lead is not visible in the solder -> THEN Reject. We must see the outline of the lead to verify it exists.
• IF flux residue is active/sticky -> THEN Clean it. Corrosive residues eat PCB traces over time.

Critical Differences: Class 2 vs. Class 3

The gap between Class 2 and 3 is often microns, but the cost difference is massive.

Through-Hole (THT) Barrel Fill:

• Class 2: 50% Fill required. (Gravity helps; heat transfer is harder).
• Class 3: 75% Fill mandatory. (Requires precise thermal profiling).

SMT Placement (Overhang):

• Class 2: 50% Overhang allowed. (If half the pin is on the pad, it holds).
• Class 3: 25% Overhang max. (Maximum shear strength required for vibration).

Toe Overhang:

• Class 2: Allowed (if joint length is sufficient).
• Class 3: Prohibited. (Risk of violation of minimum electrical clearance).

Final Checklist