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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Using QX3 microscope for SMT
References: <email@example.com> <3D9E2EBF.535EE22A@mfi.net> <3D9E50EE.181E992D@webaccess.net> <3D9E628C.701D166D@mfi.net>
Date: Sat, 05 Oct 2002 05:06:24 GMT
NNTP-Posting-Date: Fri, 04 Oct 2002 22:06:24 PDT
"Michael A. Terrell" wrote:
> Chuck Simmons wrote:
> > In general, you want a moderate NA not high) to get depth of field and
> > built in top illumination to get a bright field. Microscopes in this
> > class are non-standard but available new for about $200US and up.
> > Younger people and myopic people can get by with low powers like 2X or
> > 3X for 0.5mm pin pitch. The reason myopia can help is that the myopic
> > has a very short working distance with the uncorrected eye. My
> > comfortable working distance without glasses is about 3 inches. I need a
> > lot of light to get good depth of field with my unaided eye.
> Chuck, I used a stereo inspection microscope on my bench for almost
> four years to do rework myself, rather than wait for the usual rework
> cycle. I could do it on the fly, sometimes without unhooking the board
> or module i was working on, then go right back to testing. Then the
> board went to the cleaning room before going to QC.
Yes, stereo works best. Comfortable for viewing and the depth perception
is very helpful. I do some rework but we consider 10 boards a production
run for us. The boards are evaluation boards for a chip set - sort of a
reference design. The customer base is a bit small for that sort of
thing. The first board is free to a viable customer and additionals are
sold at various prices all below our cost. It's a cruel world. We send
out all rework that I and the younger enginers won't do. I don't know if
it is good or bad but if you get one of our boards, three to four
engineers on the design team (including me) have blessed it. We have no
technician to do test and rework.
> My uncorrected vision is poor. It was 20/200 and 20/400 when I went
> into the service in 1972, and its worse now. I have lost the fine
> focus, so even though I can see things close up, I can't make out the
> details without the microscope. I have lineless trifocals for normal
> work and driving, but they have to come off to do the fine stuff. I'm
> trying to get a good stereo microscope with zoom so I can work from
> home. Hopefully, I can talk the VA into getting me one when they finally
> get my medical benefits straightened out. I have most of the other
> tools I need, and I am going to try to set up a board repair service, if
> the VA can help me with the constant migraines.
I can work on small stuff without my glasses but I am literally afraid
of burning my nose with the soldering iron when I do. A large magnifier
with ring illumination is excellent for me because I can use it without
my glasses and my nose is not in the middle of everything at risk from
tools. I should be in trifocals but I put it off. I got into bifocals
when my accomidation range early in the morning was so bad that the only
way to read the paper was to prop it on a chair across the room and view
it with binoculars.
Vision is a kind of fickle thing. I had a board with a problem with a
particular chip. Even with my glasses off I could see nothing wrong. I
inspected again under our 20X microscope and discovered a solder bridge.
I then noticed that when I looked without glasses, I could see it
because I knew where it was. Then I noticed I could see it with my
glasses. When the 22 year old kid that does my rework came to get the
board, he could not see it. I told him the pin numbers and suddenly he
could see it too. Since the kid can't come inside the building without
some messing about, I showed him the problem in bright sunlight where it
was, in fact, easy to see. There is some psychology involved in what you
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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