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possibilty of short circuit

Discussion in 'Electronic Design' started by sudheervemana, Dec 15, 2003.

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  1. Hi all,

    I am novice in the field of debugging an circuit board,can
    anyone help me on the possibilty of getting short circuit in an pcb.In
    my circuit board i found out that 3 components have benn short
    circuited .I dont know why it has been shorted ,i have checked my
    schematics and layout file too.but there is no way a getting
    shorted.even when i got the bare board after fabrication with out
    placing the components,there is no short circuit on my board ,when
    after getting assembled i found that at a few places the components
    were shorted and and at the time of debugging a few capacitors were
    shorted,i have removed the shorted components on my pcb ,even then at
    that points i am getting shorted on those components(like capasitors
    and diode).please help me in finding a solution such that how to avoid
    this shorted components and what could be the possibilties of
    discretes(like cap,diodes and res) getting shorted.
    Thanks in advance.

    With Regards,
    sudheervemana.
     
  2. Are these through hole or surface mount components?

    Do you have a temperature controlled soldering iron?
     
  3. Maybe you could link to a photo of the bit of the board where this bad
    stuff is happening?

    Best regards,
    Spehro Pefhany
     
  4. Mac

    Mac Guest

    This may be a red herring, but capacitors, particularly large ones, will
    briefly (until they charge up) appear as short circuits with a simple
    audible testing device.

    And of course, all items connected to ground are, in fact, shorted
    together. ;-)

    Mac
     

  5. the components are surface mount and i used an ordinary soldering iron
    which doesn't have any temperature display.how it had happenned even
    when i had removed the component(capasitor) it was showing the
    continuity at the two pads on the pcb.please tell me the temperature
    to keep at the time of soldering an smd and through hole
    components,and also what are the tools that are needed for placing and
    removing an component on the board.the pad to pad spacing in my board
    is 8 mills,then i should have what range of solder bit.please give
    your valuable suggestions .

    With Regards,
    sudheervemana.
     
  6. YD

    YD Guest

    What kind of short? Are the parts in question behaving like a short or
    are they shorted to some adjacent part? Take a very close look at the
    solder joints, if the pads are too close together there may be all but
    invisible whiskers between them. Run a knifepoint between the shorted
    points and see what happens.

    - YD.
     
  7. So the PCB is what is shorted, not the component?
    Heat is destructive of many components, so the lower temperature you
    can use, and the less heating time, the less likely you will damage
    the components. The smaller the components, the more important it is
    to have an iron that keeps its temperature just above the solder
    melting point. Also, using low melting temperature solder (e.g. 63 %
    tin, 37 % lead, not 50 % tin 50% lead) allows lower soldering
    temperature. Shorts on the PCB traces are simple bridges of solder
    between nearby traces which you should be able to see with good
    lighting and some magnification. You can often wipe them off with a
    bit of solder removal wick (fine stranded wire coated with solder
    flux) heated by a soldering iron.
     
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