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Reflow soldering on a custom PCB

Discussion in 'Electronic Basics' started by Chris W, Jun 5, 2005.

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  1. Chris W

    Chris W Guest

    I recently had some through hole custom PCBs made by
    http://custompcb.com. Everything worked great. Now I am thinking that
    the next project I do will use surface mount components. What I am
    wondering is, is there enough solder on those custom PCBs to do reflow
    soldering? I don't see anywhere on that web site where it talks about
    that although they do talk about a tin/silver plating. Another
    prototype surface mount adapter board I got didn't look like there was
    any solder to reflow but it did work fine. I just don't want to spend
    the money on a custom PCB till I know for sure it will have enough
    solder on there to do reflow soldering of surface mount chips.

    --
    Chris W

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  2. John Larkin

    John Larkin Guest


    People normally apply solder paste through a stencil, then place the
    parts and reflow. I don't think any normal solder coating would be
    enough to make reliable joints.

    John
     
  3. Chris,

    AFAIK the plating on the PCB is never used for reflow. That's to say, not on
    its own. In the reflow proces a fine grained solder and flux mixture is used
    that is put on the PCB by screen print. Then the components are placed and
    the PCB is heated by infrared to "reflow" the solder.

    petrus bitbyter
     
  4. PeteS

    PeteS Guest

    As stated, the short answer is no, there is insufficient solder from
    the plating process.

    That said, I have had surface mount boards soldered by hand. The
    difference is simply the amount of solder used. The person I use has
    successfully dealt with 0.5mm pitch ICs and 0201 passives. The one area
    you'll really need reflow is BGAs.

    If you want a proper reflow, then you'll need to have a stencil made,
    as John noted. This is a standard cost item when producing surface
    mount boards using a contract manufacturer.

    Cheers

    PeteS
     
  5. Art

    Art Guest

    Also, in normal manufacturing using multiple smd components. an adhesive is
    applied to the pcb surface to hold the smd components in place during the
    rest of the processes. Otherwise some of the components either shift
    position, fall off the pcb, or short to adjoining pads and components.
     
  6. Bob Eldred

    Bob Eldred Guest

    No, there is not enough solder on the boards to solder on parts. The solder
    there is basically tinning so additional solder will wet the pads cleanly.

    Since I only do a few boards at a time, I solder surface mount boards
    manually without paste, masks, glue, stencils or other production methods or
    devices. I use a small tip Weller iron and 20mil wire solder. On the board,
    I flow a dab of solder on one of the component pads for each device to be
    mounted. Holding the device in position with a pair of tweezers, I reflow
    the solder dab sticking the part to the board by one pin. After aligning the
    part so that all of the pins are in the proper position, I apply solder to
    another pin on its pad. I push the component to the board and reflow this
    second pad insuring that the component seats onto the board and is aligned
    properly. I then solder all of the other pins to their pads in the normal
    manner. When solder accidentally bridges more than one pin, which happens
    occasionally in .5mm parts, I use solder wick to sop up the excess which
    leaves a clean joint. My eyes aren't to good so I work under a microscope,
    some people can do it with the naked eye. For small quantities, there is no
    need for paste, Infrared reflow equipment and the rest.
    Bob
     
  7. Art

    Art Guest

    Sounds like a plan, where labour is not an essential cost. Have at it and
    post your results. Cheers.
     
  8. Wayne

    Wayne Guest


    These new QFN packages are not much fun either..
     
  9. Kat

    Kat Guest

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    I've been using this method for years, works very well for me.

    *tin the pads with ample solder for reflow
    *use a dab of expoy (if working with multiple pin componets)
    *alined the chip on the pads and let the expoy set (10-15 min is good)
    *flux pen the leads
    *and now reflow :)

    This is a longer method but I have found over and over this saves me time
    and money in the long run. Because the chip is already alined you only need
    to heat the chip for 15 seconds (a 16pin QSOP atleast) or so.

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