IPC-A-610 for PCB fabrication and IPC-J-STD-001 for assembly acceptance use 3 classes to define solder joint goalacceptability for various electronic products.

CLASS 1 –General Electronic Products

Includes products suitable for applications where the majorrequirement is function of the completed assembly. Toys

CLASS 2 –Dedicated Service Electronic Products

Includes products where continued performance and extendedlife is required, and for which uninterrupted service is desired but notcritical. Typically, the end-use environment would not cause failures.Computers & Phones

CLASS 3 –High Performance Electronic Products

Includes products where continued high performance orperformance-on-demand is critical, equipment downtime cannot be tolerated,end-use environment may be uncommonly harsh, and the equipment must functionwhen required, such as life support or other critical systems. Military &Medical 

The J-STD-001 and the 610 standardsare broken down into these definitions:

N = No requirement has beenestablished for this Class

A = Acceptable

P = Process Indicator

D = Defect

Examples:

[A1P2D3] is Acceptable Class 1,Process Indicator Class 2 and Defect Class 3

[N1D2D3] is Requirement Not EstablishClass 1, Defect Classes 2 and 3

[A1A2D3] is Acceptable Classes 1 and2, Defect Class 3

[D1D2D3] is Defect for all Classes

A defect for a Class 1 product means thatthe characteristic is also a defect for Class 2 and 3. A defect for a Class 2product means that the characteristic is also a defect for a Class 3 product,but may not be a defect for a Class 1 product where less demanding criteria mayapply.

Defect = Non-conformance to therequirements of this standard or other risk factors as identified by themanufacturer.

Process Indicator = A detectableanomaly, other than a defect, that is attributable to variation in material,equipment operation, workmanship or processes.

For additional information about how IPC compliance affects Footprint Land Patterns in Library Expert and Altium Designer read these posts: 

Thermal Pads

Chip Solder Joints

Gull Wing Terminal Leads

Who is IPC?