From Tom Clifford

Chris -
Thanks for feedback.  Let's sidestep the human-too-hot-to-touch issue. Make no mention of acuity etc. The value of the target goes beyond that. All the other elements (lighting, focus, optics, mag, etc) determine whether a tiny feature can be detected and characterized.
The target should be used as a reference and as a qualifier for a particular microscope system.  It can be used for all trouble-shooting and accept/reject tasks that require good discrimination and descriptions ie " we can help, because our system has been shown to be able to discriminate between a category B and category C feature."
It also can be used in image transmittal: "...when you print this image out at your end, can you see the difference between Grade 5 and Grade 6? ... " or "... we could help with virtual trouble-shooting your cracked-capacitor, but we cannot make out the details. Please send some target pix so we can be sure we can really see what you're seeing ..." or " we can visually distinguish between class 8 and class 9, but our print-out in the Workmanship Standards Book makes them both look the same! ..."

anyway... the industry needs something like this   let's keep in touch  Tom
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]]On Behalf Of Chris Mahanna
Sent: Thursday, September 08, 2005 7:32 AM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] IPC A-600 6012 and 2221 task group at Expo 2005

Right on target Tom.  Pun intended.  These creatures are called "targets".
The USAF has had a system in place for what....30-40 years?
Robisan and other independent labs have been pushing for this kind of stuff ever since at least the late 80s. Jack Crawford has explicitly told me that IPC legal believes assessment of the "human part" too-hot-to-touch.  And actually the "Visual Acuity Testing" from IPC-QL-653 is supposed to be stricken in the next revision. My father was on the front lines arguing this issue for the Navy against the union.  To the best of my knowledge the Navy won, but that was 20 years ago. Is the human the largest ingredient in the "uncertainty of observation" budget?  I don't know.  Probably.  At any rate, it sure is hard (if not impossible) to assess the system without the observer. Today-- quality optical system manufactures state resolution on the device's specs.  You could simply use these numbers in conjunction with IPC-OI-645 to build the "better than nothing"  table. The bottom line is... the bottom line.  As features become smaller and smaller, it will without question, become cost prohibitive to use human inspection. Unless, of course, you redefine your sample.  The microsection part of 600/6012 has always used this human inspection-very small sample model.
Chris Mahanna  Quality Manager
Robisan Laboratory Inc.