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Solder surface-mounts by hand?

Discussion in 'Electronic Basics' started by eromlignod, Jan 12, 2004.

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  1. eromlignod

    eromlignod Guest

    Hi guys:

    Is it possible/practical to solder surface-mount resistors onto a PCB
    by hand? Have any of you ever tried this? I'm making a prototype of
    a very small circuit and the resistors are taking up a lot of space.
    Surface mounted ones would considerably reduce the overall size, but
    are they too tiny and tedious to do myself?

    Thanks for any replies.

    Don
     
  2. Soldering a few isn't so bad. I have done this by tinning one pad on
    the board, and then placing the resistor with a pair of pointy
    tweezers, while heating the edge of that pad. Then I solder the other
    end. It helps to have a fine point on the soldering iron. But it
    gets old after a few dozen parts.
     

  3. Lots of people solder surface mount resistors of pretty much all sizes by
    hand without difficulty. This is done both in indutry and by hobbiests.

    It reminds me of learning how to color with crayons between the lines rather
    than just scribbling all over the place. It really isn't diffcult in the
    slightest, although it may have seemed like it was before actually doing it.
    You hands are versatile (unless maybe you got a natural shake or something)
    and are readily adapted to this sort of thing so long as you excersize a
    little bit of control when first starting out.

    I like 0805 resistors since it is still pretty easy to read the numbers on
    them, but on the other hand my more recent trend is to use 0603 parts since
    they take up less space.

    I usually tin one of the pads on the board, use tweezers to place the part
    over the tinned pad, and then reapply the soldering iron to the tinned
    region. Assuming the resistor leads are clean and adequate flux is laying
    around it should make a nice bond thus holding the part in place so you can
    solder down the other side.
     
  4. David Knaack

    David Knaack Guest

    If I'm doing more than a few I use a very small drop of fast drying glue
    to hold them down. The tiny dot of glue is easy to break off if I screw
    up and have to move them, but it holds them in place long enough that I
    don't have to be particularly delicate while soldering them.

    The only other thing I've found to be very useful is to grid my
    soldering iron tips down to pencil sharpness (steeply sloped sides, very
    pointy tip) and run it at 30 watts. The tip wears out much faster, but
    iron tips are cheap and I get more work done.

    DK
     
  5. Use two irons at the same time for resistors and capacitors. You
    don't need any glue, and they will self center like they do in a reflow
    oven. You have to be careful with glue. some types break down and become
    conductive, while others eat the copper traces. PCB manufacturing uses a
    type of epoxy to hold parts to a circuit board because it is more
    stable, and can be removed with a hot soldering iron tip.

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    Central Florida
     
  6. Wayne

    Wayne Guest

    Get yourself own of those big lighted magnifiers.

    Better yet a Mantis scope if you can afford or borrow one.

    I lucked out and found one at a business that was liquidating.
     
  7. Thanks guys. I'm going to give it a shot.

    Don
     
  8. Mantis? What's that? Looks like a U.K. product. Probably hard to
    find in the U.S.
    http://www.vtech-smt.co.uk/Catalogue/microscopes/it010004.htm


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  9. ptaylor

    ptaylor Guest

    I hand soldered a SMD resistor that had come loose,back onto a PC
    Motherboard once...,of course after I found it first!I had dropped it
    onto the carpet!! I thought I was doomed! A bright flashlight
    helped,while I was on my hands and knees searching for it..Finally found
    it and soldered it back in place with my trusty Radio-Shark soldering
    iron,and the Motherboard didn't randomly lock-up anymore! Yay!
    FWIW,it was an Intel ("Socrates") P-100 board,now out in the "scraps" pile.
     
  10. Johnboy

    Johnboy Guest

    You can also use the Intel microscope that sells for $65.00
    with good results.

     
  11. As an Engineering Tech, part of my job responsibilities includes assembling
    prototype PCBAs -- lots of SMT devices, some with small-pitch (0.010") lead
    spacing. My tools include:
    1) lighted magnifier (5 diopter) for larger parts
    2) small 2x - 4x microscope for smaller parts
    3) soldering pencil w/ 0.010" dia tip
    4) various size wire solder -- as small as 0.010" diameter
    5) 250W heat gun
    6) hot plate
    Those tools have enabled me to even remove parts from one PCBA and put them
    down on other boards! Beyond the tools, a little technique goes a long
    way -- practice, practice, practice!
    Bryan
     
  12. mike

    mike Guest

    There are a bunch of issues. There are many different resistor sizes
    that qualify as "surface mount".
    You have to be able to see it. I use a head-mounted magnifier.
    You have to be able to hold it. Tiny tweezers and a steady hand.
    You need a soldering iron with a tiny tip and (effective) high thermal
    mass. Something with temp control feedback measuring the tip temp.
    Metcal makes some irons that are way cool in this area. Heat guns work
    well in many circumstances. A temp controlled hot plate can work in
    some circumstances. Mine looks like it came from a chemistry lab.
    You need solder tiny enough to fit where it goes. Solder paste works best.
    The typical pad layout for a SMT resistor is HUGE compared to the
    size of the resistor. Great for automated place and reliable soldering,
    but you can modify the pads and squeeze 'em a LOT closer together if
    you're only gonna build one by hand. If you have two of the same size
    component, like a parallel R-C, you can stack 'em on their sides on
    one pad set.
    mike




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