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Discussion in 'Electronic Design' started by GregS, May 4, 2007.

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  1. GregS

    GregS Guest

    Why do I have to bend the leads every time I insert an IC into a socket.
    I'm sure this has been a long tradition, but I can only think that
    something didn't make solid contact with the leads at one time.
    Or perhaps it holds the IC in place on a board.

  2. It seems a sensible way to do it for mechanical insertion. The robot can
    get a good grip by squeezing the pins to the proper width. As an added
    plus, the pins would likely spring back enough to hold the part in place
    until it's soldered. I don't really know this to be a fact, but it at least
    sounds plausable. ;-)
  3. Phil Hobbs

    Phil Hobbs Guest

    One also used to use IC insertion tools that had a plunger running in a
    fixed-width slot--it held the DIPs the same way.

    This scheme has the very important advantage that it makes sure that the
    leads are in exactly the right place for insertion without bending. The
    leads are very stiff in the along-package direction, so that's less of a
    problem, but the lateral position depends on a not-very-precise lead
    frame bending operation.

    This way, you make the tooling accurate, once, and the spring force in
    the leads makes sure that all the pin positions are accurate thereafter.


    Phil Hobbs
  4. Rich Grise

    Rich Grise Guest

    I think I've read somewhere that it is, in fact, intentional, just for
    that purpose.

    When ICs first came out, the pins were parallel, and so the board
    stuffer would bend over two of the corner pins on the solder side to
    hold the chip in place. It made them a bitch to repair - it's almost
    impossible to unsolder and unbend a pin without damaging the board.

  5. linnix

    linnix Guest

    Usually, you can save the board or the chip, but not both.
  6. mpm

    mpm Guest

    I've seen these auto-insertion machines in operation (both DIP and
    surface mount).
    Very cool and fun to watch. The speed is AMAZING, but people who
    work with them everyday probably think they're slow.(?)

    One of the machines I saw used what looked like a whole bunch of
    bright red LED's. And you could feel the heat. (This was on a
    surface mount line.) I don't know if that was a pre-heater, or the
    thing doing the actual soldering.

    Anyway, when you see how fast these work, you understand there's no
    slop in the mechanicals.
    I wish I had a video to share.
  7. John Larkin

    John Larkin Guest

    The big mistakes were making the parts symmetrical, numbering the pins
    circularly, and putting Vcc and ground in the corners.

  8. Tam/WB2TT

    Tam/WB2TT Guest

    It's easier to set up a machine if you know up front that it has to sqeeze
    *all* the pins.

  9. I can see the problem with symmetry, but what's wrong with the numbering
    or the position of the power pins?

  10. Jeff L

    Jeff L Guest

    Yes they are. People who are interested in machinery find them fascinating.
    A friend spent hours just watching the chip shooter work once! Other people
    don't have the time of day for them. They don't even look at them as they
    are hammering parts down.

    The speed is AMAZING, but people who

    One of our pick and place machines (turret based chip shooter) can place
    parts at a sustained 0.15 seconds per part. After using it for a while it
    does seem much slower. Going back and using one of our older machines (also
    turret based chip shooter) that places parts at 0.25 seconds per part makes
    the machine look so slow.
    On an SMT line, the only major heat source should be the reflow oven. They
    can throw some heat off. The power consumption is usually between 10 and 20
    kW after startup (can be much more during start up) depending on oven size,
    speed, loading and profile, along with some other things like insulation and
    ventilation rate.
    When placing parts with a 3 sigma accuracy of 0.08 mm at a rate of 0.15
    seconds a part after everything is said and done, the machines have to be
    very tight. One machine is capable of 0.025 mm accuracy at 3 sigma, but is
    significantly slower.
    I have some that will be on our website when its updated in a few months,
    unfortunately, this thread will likely be forgotten about by then.
  11. Jeff L

    Jeff L Guest

    Since overall, very little quantity of DIPs were stuffed by had, people
    making DIPs optimized them to be machine placed by machines called "DIP
    Inserters". This meant the machine would squish the pins a bit so they would
    all be parallel and inline. Once the machine inserted the part, the leads
    would spring back some and hold it in place.

    Now most through hole is slowly dying along with DIPs as SMT is taking over.

    For the stuff that needs smaller productions of PCB's with DIP's that are
    not worth putting on an insertion machine, automatic lead formers are
    available that bend the leads vertical and parallel. We have such a machine
    and it works well and is very fast.
  12. MooseFET

    MooseFET Guest

    We would be better off if the power pins where like on a quad op-amp
    of a pair near the center on one side. The inductance of the ground
    and Vcc path is an issue when you get to high speeds.

    As far as I can see it, all simple numbering systems are about equal.
  13. Jeff,

    Please post a pointer to your website when you get it updated with
    something descriptive in the subjet line.
  14. DJ Delorie

    DJ Delorie Guest

    I've seen more and more chips with symmetrical power pins in the
    center of the part. If you insert it backwards, at least the Vdd/Vss
    pins are connected right.

    Probably still fry the chip though :p
  15. jasen

    jasen Guest

    distaance to the die is too far.

    cf lm339. power pins closer to die, easier to decouple.
    also the power trace forms a guard between siglals

  16. Tim Williams

    Tim Williams Guest

    Wouldn't it be easiest (and best) to put the supply pins on an end or side
    (e.g. 3842, 555)?

  17. Jim Thompson

    Jim Thompson Guest

    Engineers didn't used to be dummies ;-)

    ...Jim Thompson
  18. jasen

    jasen Guest

    aarg! lm324

  19. krw

    krw Guest

    IIRC, the reason most TTL power pins were put in the corners was to
    make wiring easier. One and two sided boards were all the rage then.
  20. Back when 2-layer boards were the norm and speeds were slower, having
    the pins consistently in the corners allowed for a nice Vcc/GND grid
    layout on top and bottom using traces too fat to go between DIP pins.

    Best regards,
    Spehro Pefhany
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