5.2 IPC-A-610 Classifications & Criteria

IPC-A-610 "Acceptability of Electronic Assemblies" serves asis the primary visual acceptancelanguage standard forof the electronics industry. It definesis thenot "Target,"a "Acceptable,"suggestion "Processbox; Indicator," and "Defect" conditions for solder joints and mechanical assembly. Adherence to the correct Classit is the primaryboundary determinantbetween ofa manufacturingshippable costproduct and reliability.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 Electronic Products)General): Function"It isturns the primary requirement.on." Cosmetic imperfectionsdefects are acceptable.ignored. Example:(e.g., Cheap Toys, disposableDisposable electronics.LEDs).
• Class 2 (Dedicated Service): Continued"It performance and extended life are required.lasts." Uninterrupted service is desireddesired. but not critical. Example:(e.g., Laptops, microwaves,Home generalAppliances, industrial.Industrial Controls). This is the Default.
• Class 3 (High Reliability): Downtime"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 behave tolerated;"Class end-use2 environmentsoldering maywith beClass harsh;3 equipmentinspection 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 functionshow onevidence demand.of Example:wetting Life(adhesion support,between aerospace,the automotivealloy engineand control.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:

• Through-Hole Vertical Fill:
  • Class 2: 50% verticalFill fillrequired. of(Gravity thehelps; barrelheat transfer is permitted (with exceptions for thermal mass)harder).
  • Class 3: 75% verticalFill fillmandatory. (Requires precise thermal profiling).

  SMT Placement (Overhang):

  • Class 2: 50% Overhang allowed. (If half the pin is mandatory.on Thisthe requirespad, preciseit wave solder profiling and often necessitates selective soldering for heavy copper boards.holds).
• SMT Component Overhang (Lateral):
  • Class 2: Up to 50% of the component termination width may overhang the pad.
  • Class 3: Maximum 25% overhangOverhang allowed.max. This ensures maximum mechanical(Maximum shear strength required for vibration resistance.vibration).

• SMT Toe Overhang:

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

Final Checklist

FeatureControl Point	Class 2Critical Requirement	ClassNon-Negotiable 3 RequirementRule
VerticalClass SolderDefinition	Defined on Drawing/PO.	Default to Class 2 if undefined.
Wetting	< 90° Contact Angle (Concave).	Non-wetting / De-wetting = Scrap.
THT Fill	Class 2: 50% Minimum/ Class 3: 75%.	75%0% MinimumFill (invisible on solder side) is always a defect.
SideSMT OverhangAlignment	MaxPin 50%must ofsit Leadon Widthpad.	MaxMisplaced 25%component of= LeadReflow Widthprofile failure.
End Joint WidthMagnification	Min1.75x 50%to of4x Lead Width(Standard).	MinDo 75%not ofuse Lead40x Width
Cleanliness	Visuallymicroscopes Clean	Ionicfor Contaminationgeneral Testinspection Required(False Fails).