Help me understand the differences between the Class 1, 2, and 3 in the
ANSI/J-Std-001A.

First, I understand that they are set up for different applications, ie,
Gameboys, switchgear, Aircraft electronics.  I want to understand what
reliability goals or targets these classes represent.

Why do I want to understand this?
I have a Class 3 application.  The supplier delivers a board with a slightly
off center 20 mil pitch component, ie 1/3 of the lead width.  This meets
Class 2 requirements, but not Class 3.  Now, what are the reliability risks
associated with accepting a part to Class 2 requirements?  Do I accept the
additional risks and accept the part as is, or do I attempt to rework the
part?  In my experience, rework operations often rework a board from an
uncertain condition to a known bad quality condition.  While this makes the
reliability call easier to make, but is not usually viewed as the wisest
course of action.  On the other hand, I don't fully understand what the
additional reliability risks are of accepting the part as delivered.

What would I like to have?
I'd like to see data like this, or even acknowledgement that the standard
has a "fictionalized targeted reliability goal" in mind something like this:
Given: Three groups of 1000 Assemblies are subjected to the same conditions.
After some period of time the number of failures are totaled.
Of the Class 3 Assemblies X of the 1000 failed.
Of the Class 2 Assemblies 10X of the 1000 failed.
Of the Class 1 Assemblies 75X of the 1000 failed.

Thanks for the input.

George Franck
Raytheon Systems
Falls Church Virginia
"My Opinions are just that."

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