Overheating components with soldering iron - hierarchy?

Discussion in 'Electronic Equipment' started by Don W, Apr 23, 2006.

  1. Don W

    Don W Guest

    I removed some small electolytic capacitors from a modern circuit board
    to use elswhere which meant that the wires of the electrolytics were
    really very short. I then soldered some "extension" leads onto the
    electrolytics.

    Of course, it's possible I may have overheated them.

    This mead me think which components are more prone and which less prone
    to being overheated by the applying a soldering iron for too long or too
    close?

    I guess at the top of the list is some sort of semiconductor. But what
    is the least prone? Resistors? Tantalum capacitors? Is there a
    hierachy of common components which can be listed?

    And what happens when a type of component overheats? ISTR that
    resistors can lose up to one-third of their resistence. At least that
    was in the good old days and maybe it has changed now.
     
    Don W, Apr 23, 2006
    #1
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  2. Don W

    Rich256 Guest

    Don W wrote:
    > I removed some small electolytic capacitors from a modern circuit board
    > to use elswhere which meant that the wires of the electrolytics were
    > really very short. I then soldered some "extension" leads onto the
    > electrolytics.
    >
    > Of course, it's possible I may have overheated them.
    >
    > This mead me think which components are more prone and which less prone
    > to being overheated by the applying a soldering iron for too long or too
    > close?
    >
    > I guess at the top of the list is some sort of semiconductor. But what
    > is the least prone? Resistors? Tantalum capacitors? Is there a
    > hierachy of common components which can be listed?
    >
    > And what happens when a type of component overheats? ISTR that
    > resistors can lose up to one-third of their resistence. At least that
    > was in the good old days and maybe it has changed now.



    To try to cut down of overheating is one of the reasons I usually try to
    use a rather hot iron to get in and out as fast as possible. I don't
    know if this is a valid reasoning or not.

    And of course try to put some sort of clamp on the device itself to
    absorb some of the heat.
     
    Rich256, Apr 23, 2006
    #2
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  3. In article <Xns97AEDBE9DE95D74C1H4@127.0.0.1>,
    Don W <> writes:
    > I removed some small electolytic capacitors from a modern circuit board
    > to use elswhere which meant that the wires of the electrolytics were
    > really very short. I then soldered some "extension" leads onto the
    > electrolytics.
    >
    > Of course, it's possible I may have overheated them.
    >
    > This mead me think which components are more prone and which less prone
    > to being overheated by the applying a soldering iron for too long or too
    > close?
    >
    > I guess at the top of the list is some sort of semiconductor. But what


    Germanium semiconductors -- you pretty much had to use a heat shunt.
    I've overheated LEDs once or twice, resulting in dim operation.
    I'm not aware that I've ever damaged any silicon semiconductors
    or other components -- I tend to use a hot iron as quickly as
    possible.

    --
    Andrew Gabriel
     
    Andrew Gabriel, Apr 23, 2006
    #3
  4. Rich256 <> wrote in
    news:T6S2g.72184$:

    > Don W wrote:
    >> I removed some small electolytic capacitors from a modern circuit
    >> board to use elswhere which meant that the wires of the electrolytics
    >> were really very short. I then soldered some "extension" leads onto
    >> the electrolytics.
    >>
    >> Of course, it's possible I may have overheated them.
    >>
    >> This mead me think which components are more prone and which less
    >> prone to being overheated by the applying a soldering iron for too
    >> long or too close?
    >>
    >> I guess at the top of the list is some sort of semiconductor. But
    >> what is the least prone? Resistors? Tantalum capacitors? Is there
    >> a hierachy of common components which can be listed?
    >>
    >> And what happens when a type of component overheats? ISTR that
    >> resistors can lose up to one-third of their resistence. At least
    >> that was in the good old days and maybe it has changed now.

    >
    >
    > To try to cut down of overheating is one of the reasons I usually try
    > to use a rather hot iron to get in and out as fast as possible. I
    > don't know if this is a valid reasoning or not.
    >
    > And of course try to put some sort of clamp on the device itself to
    > absorb some of the heat.


    I go along with that. Trying to quantify the various damage thresholds is
    FAR harder to do than to develop ways to avoid them.

    A strong temperature controlled iron is good, and tinning wires beforehand
    is vital if they're not extremely clean. I bring the solder in with the
    iron and remove both together to let the residual heat and flux make a
    clean melt and solidification. For heat shunts I often just leave excess
    wire to snip off afterwards.

    The components most easily damaged I've found are those with thermoplastics
    in them, like some small capacitors. Peltiers are dodgy too, they use very
    low temperature solder, so if you break a wire on them, it's screwed unless
    you can get low temperature solder. Laser diodes are very sensitive too,
    but not just from heat.

    Hand soldering surface mount stuff is dodgy too, I've found that practising
    various tricks is needed to get those right.
     
    Lostgallifreyan, Apr 23, 2006
    #4
  5. Don W wrote:
    > I removed some small electolytic capacitors from a modern circuit board
    > to use elswhere which meant that the wires of the electrolytics were
    > really very short. I then soldered some "extension" leads onto the
    > electrolytics.
    >
    > Of course, it's possible I may have overheated them.
    >
    > This mead me think which components are more prone and which less prone
    > to being overheated by the applying a soldering iron for too long or too
    > close?
    >
    > I guess at the top of the list is some sort of semiconductor. But what
    > is the least prone? Resistors? Tantalum capacitors? Is there a
    > hierachy of common components which can be listed?
    >
    > And what happens when a type of component overheats? ISTR that
    > resistors can lose up to one-third of their resistence. At least that
    > was in the good old days and maybe it has changed now.


    The key is getting everything right before applying the soldering iron -
    as with most thing, preparation is everything.

    The most common thing damaged by overheating, I would say, is printed
    circuit boards themselves, with tracks coming off the board.

    The most difficult to damage are, perhaps, air-spaced high voltage (eg
    transmitter) capacitors - which you could probably take a blowlamp to.

    I can't, off-hand, remember *ever* damaging anything (other than the
    afore-mentioned printed circuit tracks) by over-heating.

    My standard way of bulk-removing components from scrap printed circuit
    boards is to hold it component side down and play an electric hot-air
    gun over the top - tapping the board edge against the bench so the
    components fall out. The components even seem to take that abuse and
    still work with no apparent ill-effects...

    --
    Sue
     
    Palindr☻me, Apr 23, 2006
    #5
  6. Don W

    Mr Fixit Guest

    "Palindr?me" <> wrote in message
    news:...
    > Don W wrote:
    >> I removed some small electolytic capacitors from a modern circuit board
    >> to use elswhere which meant that the wires of the electrolytics were
    >> really very short. I then soldered some "extension" leads onto the
    >> electrolytics.
    >>
    >> Of course, it's possible I may have overheated them.
    >>
    >> This mead me think which components are more prone and which less prone
    >> to being overheated by the applying a soldering iron for too long or too
    >> close?
    >>
    >> I guess at the top of the list is some sort of semiconductor. But what
    >> is the least prone? Resistors? Tantalum capacitors? Is there a
    >> hierachy of common components which can be listed?

    a lot of PCB are soldered in an oven its not the heat that kills its the
    thermal shock of a cold component with a very hot leg
     
    Mr Fixit, Apr 24, 2006
    #6
  7. Don W

    Arfa Daily Guest

    "Palindr?me" <> wrote in message
    news:...
    > Don W wrote:
    >> I removed some small electolytic capacitors from a modern circuit board
    >> to use elswhere which meant that the wires of the electrolytics were
    >> really very short. I then soldered some "extension" leads onto the
    >> electrolytics.
    >>
    >> Of course, it's possible I may have overheated them.
    >>
    >> This mead me think which components are more prone and which less prone
    >> to being overheated by the applying a soldering iron for too long or too
    >> close?
    >>
    >> I guess at the top of the list is some sort of semiconductor. But what
    >> is the least prone? Resistors? Tantalum capacitors? Is there a
    >> hierachy of common components which can be listed?
    >>
    >> And what happens when a type of component overheats? ISTR that resistors
    >> can lose up to one-third of their resistence. At least that was in the
    >> good old days and maybe it has changed now.

    >
    > The key is getting everything right before applying the soldering iron -
    > as with most thing, preparation is everything.
    >
    > The most common thing damaged by overheating, I would say, is printed
    > circuit boards themselves, with tracks coming off the board.
    >
    > The most difficult to damage are, perhaps, air-spaced high voltage (eg
    > transmitter) capacitors - which you could probably take a blowlamp to.
    >
    > I can't, off-hand, remember *ever* damaging anything (other than the
    > afore-mentioned printed circuit tracks) by over-heating.
    >
    > My standard way of bulk-removing components from scrap printed circuit
    > boards is to hold it component side down and play an electric hot-air gun
    > over the top - tapping the board edge against the bench so the components
    > fall out. The components even seem to take that abuse and still work with
    > no apparent ill-effects...
    >
    > --
    > Sue
    >


    All of the above posts give valid and good experiences and advice. There is
    much nonsense and urban myth spoken on this subject in some circles. When
    thinking about it, just bear in mind that when the boards are produced, they
    are pre-baked, wave soldered, control-cooled, and then probably baked again,
    allbeit at a lower temperature, during burn-in soak testing. All of these
    actions subject the board and its components to far worse stress than you're
    ever going to give them, with standard hand soldering gear.

    As one of the other posters said, static, and failure to take proper
    handling precautions against it, is the biggest killer of 'delicate'
    electronic components - LSIs, laser diodes, some MOSFETs, memory chips etc.

    Arfa
     
    Arfa Daily, Apr 24, 2006
    #7
  8. Don W

    Tim Shoppa Guest

    Don W wrote:
    > I removed some small electolytic capacitors from a modern circuit board
    > to use elswhere which meant that the wires of the electrolytics were
    > really very short. I then soldered some "extension" leads onto the
    > electrolytics.
    >
    > Of course, it's possible I may have overheated them.
    >
    > This mead me think which components are more prone and which less prone
    > to being overheated by the applying a soldering iron for too long or too
    > close?
    >
    > I guess at the top of the list is some sort of semiconductor. But what
    > is the least prone? Resistors? Tantalum capacitors? Is there a
    > hierachy of common components which can be listed?
    >
    > And what happens when a type of component overheats? ISTR that
    > resistors can lose up to one-third of their resistence. At least that
    > was in the good old days and maybe it has changed now.


    My opinion:

    Damage caused not necessarily by overheating but by lead stress during
    desoldering is what you'll see more commonly.

    Decoupling the two effects is not always possible. In particular, with
    typical hobbyist desoldering setups, you can either overheat the
    component OR overstress the component leads.

    As to components most sensitive to fairly normal soldering
    temperatures, polystyrene caps that have their dielectric melt at 85C
    have to be at the top. Of course these parts have really skinny wires
    for good reason - to not conduct too much soldering heat into the
    capacitor body!

    Typically carbon composition resistors go up in value (sometimes by a
    factor of several hundred percent) in response to overheating.

    With old electrolytics it's entirely possible they were bad/dried out
    before you desoldered them!

    Tim.
     
    Tim Shoppa, Apr 24, 2006
    #8
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