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SolderTip #39: Class 2 vs Class 3 Assemblies

Question:  Can you give me a basic definition of the differences between Class 2 and Class 3 products and where these differences show up in the IPC documents?

Possible Solution:  Class 2 products are defined as products where continued performance and extended life are required and for which uninterrupted service is desired, but not critical. Class 3 products demand continued high performance or require performance-on-demand, both being critical, and equipment downtime cannot be tolerated. The end use environment may be uncommonly harsh and the equipment must function when required, such as life support or other critical systems.

By reviewing the requirements of Class 3 vs. Class 2 products within the IPC documents, there are some differences in the requirements between the documents, those being IPC-A-610 and J-STD-001. In IPC-A-610 some of the differences are found in component placement for surface mount components, hole fill requirements for plated through holes and cleanliness requirements based upon residual contaminants on the surface of the product, whereas in J-STD-001, the differences also include process requirements defining how materials are selected and used. These individual issues can impact the performance requirements of Class 3 products hindering their ability to function on demand.

Some examples of Class 3 products are medical equipment used in life support systems, aeronautics, and certain military applications.