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35827Re: CRT monitor dying?

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  • Mariss Freimanis
    Nov 30, 2006
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      That certainly will work but is impractical in production conditions.
      We produce a product that has 151 SMT components per board and we
      build about 200 boards a day. These boards are visually inspected
      after reflow under a low-power stereo microscope. All that can be
      caught are missing parts, upside down parts, tombstoned parts and bad
      solder joints.

      The fractured X7R caps were only caught during electrical test of the
      assemblies. The problems appeared when we switched to ROHS compliant
      parts, board and solder paste. Our solution was to ban X7R caps from
      the entire design. NPO and COG parts were designed in. No problems
      since then.

      The Y5V problem started then too but is rare (1:10,000 or so).

      I really hate ROHS.

      Mariss



      --- In Electronics_101@yahoogroups.com, "jverive" <jverive@...> wrote:
      >
      > You can see the cracks in an SMD ceramic device by conducting light
      through the device from the side. In tight spaces, I have used single
      optical fibers. I have also custom ground and polished small glass
      rods (with square cross-sections) to serve as miniature inspection
      "periscopes". Together with conducted side illumination, I've been
      able to obtain photos and microscope images of single failed ceramic
      SMD caps buried among countless other parts. The images are quite
      striking, since the conducted light intensity drops off at the crack
      due to the refractive index changes.
      >
      > - Jeff
      >
      > --- In Electronics_101@yahoogroups.com, "Mariss Freimanis"
      <mariss92705@> wrote:
      > >
      > > Ceramic SMT capacitors have their very own charming eccentricities.
      > > Examples:
      > >
      > > X7R caps are mechanically fragile. Reflow thermal stresses fracture
      > > the caps unless the reflow process is under very tight control. Result
      > > is zero capacitance even though the cap is visually perfect. On
      > > hot-air rework the cap comes off in 2 pieces with the fracture near
      > > the metallized end.
      > >
      > > Y5V caps (multi-uF) develop shorts even when operating at small
      > > fractions of their rated voltages. Capacitance varies greatly with
      > > applied voltage.
      > >
      > > Mariss
      > >
      > >
      > >
      > > --- In Electronics_101@yahoogroups.com, "Stefan Trethan"
      > > <stefan_trethan@> wrote:
      > > >
      > > > On Thu, 30 Nov 2006 21:09:10 +0100, lcdpublishing
      > > > <lcdpublishing@> wrote:
      > > >
      > > > > Wow, That is very disturbing. For something as common as Caps
      > > > > which are in just about anything electronic, you would think that
      > > > > their useful life would be better than 10 years. Then again, what
      > > > > electronic components have an active life that long. Hmmm, I do
      > > > > have a stereo that is about 25 years old - all the TVs are
      less than
      > > > > 20, most less than 10. Computers are all less than 6 years
      old. I
      > > > > suppose, most of this stuff isn't intended to last 25 years - just
      > > > > seems strange at first glance.
      > > > >
      > > >
      > > >
      > > > The useful life often is much longer.
      > > > But because of their construction - a little like batteries - they
      > > have a
      > > > higher chance of failing than other stuff.
      > > > When nothing goes wrong and they are used right (= not hot),
      they will
      > > > last 30 years and more.
      > > > Most of the time nothing goes wrong, but they are still a high
      risk
      > > > component compared to others.
      > > >
      > > > You'll see, wait a few decades and 90% of 'lytics will be replaced
      > > with
      > > > ceramics or some other technology.
      > > > Operating frequencies and circuit speeds go up and up all the time,
      > > that
      > > > means there's less need for large filter capacitors, on the
      other hand
      > > > ceramic capacity goes up dramatically as well, i remember only a few
      > > years
      > > > ago someone was so amazed about 1u ceramic caps in 0805 that he
      > > actually
      > > > put them in the RLC bridge before he believed it's true ;-)
      > > >
      > > > Wet aluminum technology will not be around forever. They also fit
      > > badly
      > > > with modern manufacturing and SMD technology, all that can stuff
      and
      > > > sealing stuff and wet stuff and large stuff and.. nah.. not nice ;-)
      > > > You'll see, they'll eventually go away.
      > > >
      > > > Now i'm not saying that things will get more reliable because of it,
      > > but
      > > > that's not because of bad components, that's just bad
      engineering and
      > > > economics.
      > > >
      > > > ST
      > > >
      > >
      >
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