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How to solder BGA chips without room for glue onto both sides of a PCB?

Discussion in 'Electronic Basics' started by Markus Zingg, Feb 22, 2007.

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  1. Markus Zingg

    Markus Zingg Guest

    I wonder how one can solder BGA devices to both sides of a PCB like
    they use it i.e. with DDR2 modules. The chips used there have no room
    left on their bottom side where one could apply glue - so how is it
    done?

    TIA

    Markus
     
  2. MassiveProng

    MassiveProng Guest

    The word/term for today is "surface tension".

    You have it done by professionals that can X-ray the resultant
    assembly. Period.
     
  3. Markus Zingg

    Markus Zingg Guest

    Errrr, so just because some professionals are suposed to do this, we
    are all not allowed to know HOW they do it?

    I was under the impression that I wrote "I wonder how" and not "I want
    to solder..."

    So, is there any kind soul out there willing to explain to me how it's
    done?

    TIA

    Markus
     
  4. Guest

    Well, my method is as follows;

    Equipment needed:
    1.) Hot Air gun
    2.) Hot Plate
    3.) flux pen
    4.) Solder paste
    5.) tweezers
    6.) small peice of aluminum (optional)

    Method:

    Set hotplate so that the temperature is just below the solder melting
    point.
    Place the small piece of aluminum stock on the hotplate to keep the
    hotplate solderfree(optional). Prep the BGA chip by apply flux to the
    ballgrid pins. Apply solderpaste to pcb where the chip is going.
    Carefully set the BGA chip on the solderpasted pcb. Set the pcb on the
    hotplate. Aim the hot air gun about 6-12 inches from the chip. Watch
    the solderpaste melt. take the tweezers and touch the chip it should
    suck right in place due to capillary action. turn off hotplate and let
    the pcb cool.

    HTH...
     
  5. MassiveProng

    MassiveProng Guest


    Do you have $200k for an X-ray machine?
     
  6. MassiveProng

    MassiveProng Guest

    Dumbass. READ THE POST. It is stated right there.

    SURFACE TENSION.
     
  7. MassiveProng

    MassiveProng Guest

    NOT capillary action. That is what brings solder through a thru hole
    via.

    SURFACE TENSION is what holds it on a surface mount assembly,
    nothing more. Nothing gets "sucked".
     
  8. maxfoo

    maxfoo Guest

    Well, there's both really.

    Capillary action is the result of adhesion and surface tension.

    The adhesive forces between solder molecules and the BGA are stronger than the
    cohesive forces resulting in a meniscus on the pcb pads and contribute to
    capillary action.
     
  9. MassiveProng

    MassiveProng Guest

    Yes, except that said action requires pathways, like a via or a via
    with a lead in it. On SMD, the ONLY force involved is surface tension,
    which by the way is the ONLY engine involved with capillary action as
    well.
     
  10. MassiveProng

    MassiveProng Guest

    There is no adhesive force in capillary attraction. The motion is
    due to surface tension. That is the engine by which capillary
    attraction works.

    You are going to lose this argument. Surface tension is the model
    all SMD design has centered around since the very beginning.

    And yes... it IS strong enough.
     
  11. Markus Zingg

    Markus Zingg Guest

    Dumbass. READ THE POST. It is stated right there.
    There's IMHO no reason to become offensive. I was reading your reply
    carefully including the two words "surface tension" but it was and
    still is too short for me to make all doubts go away.

    I'm just not sure if surface tension is enough to solder chips to BOTH
    sides of a PCB which still is and was my original question. I'm well
    aware that surface tension is responsible for the chips to align
    propprely during reflow soldering. Maybe I'm wrong but so far I
    thought that either the chips have to be glued to the PCB (at least if
    they reside on the bottom) or else it can't be done. The question
    arose when I first looked at one of those high density 2GB PC memory
    modules where there are BGA chips on both sides of the PCB.

    I simply figured that if one side of the PCB is solderd, those chips
    would fall off, or could be misaligned if the PCB is brought back into
    the oven with those already soldered chips on the bottom. I also could
    figure that the weight of the PCB itself would have a negative impact
    on the chips on the bottom and that there is special care needed if
    the chips on the bottom are different ones and not of the same height
    etc.

    So either "SURFACE TENSION" is not everything there is to say about
    it, or then you are right but you then may understand now where I
    have/had my doubhts and alas why I ask again.

    I don't care wether X-Ray equipement is $200K or $200 zillions. I just
    wonder how they do it for personal interest. Sometimes I just see
    something and wonder how it's done. I'm under the impression that this
    question is on topic in sci.electronics.basics. Please accept my
    apologies if not.

    Could you or someone else therefore either confirm that even for
    soldering BGA chips to both sides of a PCB "surface tension" is enough
    or then eventually be kind enough to elaborate one the topic a bit
    more?

    TIA

    Markus
     
  12. Markus Zingg

    Markus Zingg Guest

    [snip]
    [snip]

    Ok, I asked the same question in a german electronics newsgroup, and
    instead of getting answers like " You have it done by
    professionals..." and "period" and "dumb ass", they kindly explained
    that in fact the surface tension alone is strong enough to hold those
    chips on the bottom side in position during a second reflow even if
    the balls of the bottom side chips melt again.

    I just thought to share this here for other potential "dumb asses"
    like me :)

    SCNR

    Markus
     
  13. MassiveProng

    MassiveProng Guest


    You're the one that made the rule that it couldn't be glued on.
     
  14. Rich Grise

    Rich Grise Guest

    When you snipped, you snipped the "XXXX wrote" part, but whoever it
    was, I've filtered that person for being an offensive idiot.

    This is sci.electronics.basics, where there is no such thing as a dumb
    question - it's here for beginners, after all, which each and every one
    of us was once (or still is, which is OK). :)

    Unfortunately, I have no idea how to solder a BGA. )-;

    Good Luck!
    Rich
     
  15. MassiveProng

    MassiveProng Guest


    Which is your forte.

    Being an offensive idiot.
     
  16. MassiveProng

    MassiveProng Guest


    There is a lot you don't know.
     
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