Mike,

If you read the rest of the paragraph on page 3 where it gives information on
magnification used for inspection it is stated that measurements of the
dimensions of  specific defects is to be done with the appropriate instruments
and/or microscopes of that have magnifications that can accurately measure the
defect size. This specification and it derivation IPC-RB-276 Amendment 1 Para
3.6 and IPC 6012 para. 3.3 so stae this requirement..  It would be unusual to
try to measure a defect in gold plating that near 0.013mm in length; therefore
the specifications state that dimensional requirements shall be measured at
other magnifications and with devices that allow accuracy of these
measurements.  It is your choice to use what you want to determine the
dimensional size of possible defects, many fabricators use a 80X or 100X hand
held instrument to measure small defects, line width, spacing etc.  The 40X
was placed in the specification to aleviate the visual inspection problem
wherein the inspector looked at an anomoly at 1.75 X and rejected the board
because he saw a spot that looked like a void, but a look at 10 X determine
that it was spot of resist that could be flicked off.

A similar circumstance occurs when a board or internal layer are inspected
with AOI.  All facilities that I am familiar with recheck the non-obvious AOI
indicated defects with a magnification of about 10X.  This would not seem to
be a violation of A-600.

Phil Hinton

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