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Order of placing SMTs?

Discussion in 'Electronic Basics' started by Glenn Ashmore, Mar 16, 2005.

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  1. What is the best plan for placing surface mounted compinents on a board?
    Should you place the bigger stuff, SOICs and D2paks first and then fill in
    the resistors and caps or do the small one first? Or should you just start
    and one side and work towards the other?

    If you get a little shakey placing a D2pak you risk bumping several small
    parts off their pads. OTOH it is harder to place the smaller ones once the
    big ones are placed.

    The only thing I know for sure is that coffee and Mountain Dew don't help.
    :)

    --
    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at: http://www.rutuonline.com
    Shameless Commercial Division: http://www.spade-anchor-us.com
     
  2. Chris

    Chris Guest

    Hi, Glenn. I'm assuming you're doing this by hand. Manual pick 'n'
    place is the same as automatic pick and place in this respect. Best
    just to go from one side to the other. For P&P machines, that
    minimizes head travel/time. For hand placement, going from the end of
    the board farthest from you in to the edge closest keeps you from
    knocking components or jostling the board. I'm right-handed, so I go
    from the upper left to the lower right. Trying to place all of one
    type of component all over the board before moving on to the next
    component is false economy and an invitation to mistakes. Use some
    double-stick tape, and affix and label the individual embossed tapes on
    the bench beside you beforehand. You can then pull them out one at a
    time as you need them. The printout of the component layout goes on a
    clipboard behind the board you're working on. That's what works for
    me, anyway.

    If you've got an air source and a bin of spare pneumatic blivets, and
    you're planning to do a lot of this stuff, you might want to try using
    a venturi and a little Clippard push button valve to make a small
    vaccuum pipette to pick and place the smaller components. With a
    little practice and tweaking, it can speed things up over the tweezers
    routine, especially when removing parts from the embossed tape. It
    lets you pull individual parts one at a time right from the tape, which
    avoids all kinds of problems.

    I also find it helps to place a dictionary or other prop under my
    forearm to limit the wobble while I'm placing. Great lighting and a
    low distortion magnifier help, too. Make sure to clamp the board down
    while you're working on it, but use something that won't cause the
    board to bounce when you release it.

    Being a coffee achiever myself, I try to limit consumption on SMT days.

    I like this part:

    "If I were going to make this my profession I might invest in a special
    cable cutter for the 1/0 and 2/0 battery cable but I am only going to
    make 15 or 20 cuts in my lifetime. I have found that a regular pair of
    compound pruning shears makes a nice clean, square cut." from
    www.rutuonline.com

    Good luck
    Chris
     

  3. I don't know about the coffee but Mt Dew never bothered me. My hands
    were rock steady and I drank a 2 liter bottle a day. It also helped
    take the edge off my migraine headaches.
     
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