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From: "Michael A. Terrell"
Subject: Re: Using QX3 microscope for SMT
Date: Sat, 05 Oct 2002 01:40:17 -0400
Organization: I'm trying!
X-Mailer: Mozilla 4.61 [en]C-CCK-MCD (Win95; U)
References: <email@example.com> <3D9E2EBF.535EE22A@mfi.net> <3D9E50EE.181E992D@webaccess.net> <3D9E628C.701D166D@mfi.net> <3D9E7354.A1124AD1@webaccess.net>
Chuck Simmons wrote:
> "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
I was involved in testing and aligning board and modules on a
(US)$80,000+ telemetry system. Plenty of 288 pin chips, and poor
control of the solder process. The humidity was too high, and even
though the assemblers did a fair job placing the SMT parts, it took too
long. The flux started to dry out before the boards hit the reflow
oven. So I had to check every pin on every chip before power up. QC
would miss all kinds of things coming from assembly, then try to nail
the test department for things they missed to start with. In a way it
is a good thing that they closed the plant and moved it. Al the old,
dead wood was laid off or retired, and only a couple people went with
the engineers to another state. They let me and another good tech go
because we couldn't work 12 to 16 hour days, six days a week. I just
hope they didn't take any of the management team that screwed everything
Michael A. Terrell
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