TechNetters, here are my comments on the points raised by Pete Duncan,
Steve G, Jiang Ping, and John Fahey.
As Daan and Kathy noted, Table 1-2 in 610C gives inspection magnifications
and refers to "When magnification is required by contract". Above that,
there is a statement "Magnification aids use for inspection need to be
appropriate". Given those statements, it is the use, by an inspector, of
the magnifier that produces the inspection activity and introduces the
uncertainty or variability.
For more specifics about magnification, look at IPC OI-645, Standard for
Visual Optical Inspection Aids.
I have been saying that the inspector's job is not to find nonconformances,
but to get conforming product to the customer as quickly as possible and to
get nonconforming product back where it came from as quickly as possible.
And for the nonconforming product, to assure that its supplier understands
why the product is being rejected. And, ideally, the inspector can assist
in reducing the probability of recurrence of the nonconformance.
Regarding inspecting quality into a product, I count on inspectors to
protect us from disasters like 20/20 assemblies missing a component. I do
not expect them to find 1/1000 solder joints with a hole only 70% filled.
By the way, I had a discussion with some of my colleagues in production
about some holes that were 90% filled and well-wetted. The production
worker wanted to rework them. The supervisor asked my opinion, and I, of
course, referred to 610.
Lou Hart
Compunetix QA
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