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Hot Plate for Soldering

Discussion in 'Electronic Design' started by James Morrison, May 2, 2006.

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  1. Hello all,

    I'm looking for a hot plate to help with both soldering small runs of
    PCB's or rework of the same. I've seen these devices, I've even used
    them at previous jobs. But I can't find any info on the web. There are
    lots of hot plates for chemical lab use but I can't find anything like
    what I expect to see.

    Does anyone know who manufacturers these types of units? Something in
    North America is preferred as they are pretty heavy so I imagine
    shipping would be costly. But I"m open to any and all ideas here.

    Here are the things I think I require. These are soft requirements:
    1) a way to set the temperature (labelled in degrees rather than cold
    to hot would be better)
    2) heating area approximately 6"x10", larger would be better
    3) 110VAC 60Hz
    4) a cover that can be placed over the hot surface for safety

    If anyone had something like this sitting around in their lab collecting
    dust I may be interested in taking it off your hands.

    Thanks a lot.

  2. Guest

    Under the "I'm open to any and all ideas" category...a $30 hotplate
    from Target!

    James Arthur
  3. Roy L. Fuchs

    Roy L. Fuchs Guest

    Surface mount repair using a hot plate for the reflow segment of the
    process is very bad if the PCB assembly has parts on both sides of the

    Also, the board should be pre-heated in a chamber (read toaster oven)
    before placing it on the "reflow bench" (read hot plate) for the

    Reflow benches, as they are called are old school and can be very
    bad for many parts. Ceramic capacitors, in particular, can lose the
    layer connections to the end "caps" (platings actually).

    This is why a modern reflow oven ramps up the temp, reflows the
    assembly, and gets the product out the other end in a very timely
    fashion, and is also why hand soldering is detrimental, because a
    would be assembler or repair "technician" invariably turns up their
    irons far far too high for such tasks.

    550 F is good... maybe 600F, but NOT 800F, which I see all the time
    at workstations. It takes a well trained tech with knowledge of how
    components are made to really appreciate the processes in the
    industry, as opposed to merely stating "I know how to solder".

    It reminds me of the argument I had with the girl that insisted on
    attaching resistors and caps to the board with two irons, even going
    so far as to pick the part up with the two irons.

    Me? Tweezers, and one side at a time, and that is Solder it fast
    (less than 2 seconds), and NO big blobs on the pad. Just a tiny drop
    of solder on the tip of the iron, and lots of flux present is all that
    is required for hand operations. Less IS more!

    The word for today is "FILLET".

    When I assemble, it looks like it came from a machine. In fact, one
    cannot tell the difference.

    The crap I see others build is so blobby that a rocket launch would
    rip the pads and parts right off the board, they are so big.

    Sad that we cannot educate our kids so well these days.

    Anyway, hand assembly of short runs by skilled soldering personnel is
    far far better for the life of your product than a hot plate or
    toaster oven reflow process could ever be. I mean you aren't talking
    about 12" x 18" digital HDTV processing CCAs (I have done them).

    If you are stenciling paste onto the PCB, you have six hours to get
    the parts placed and get it reflowed, before the paste begins to
    express major performance issues like tombstoning and flux popping
    parts clean off the board.

    I am Solder Man (Black Sabbath inflection).

    NASA certification is the best, most comprehensive soldering cert.
    followed by mil 2000, then IPC 610-A.

    MTBF goes right out the window.
  4. Pooh Bear

    Pooh Bear Guest

    For lead free ?

  5. Roy L. Fuchs

    Roy L. Fuchs Guest

    No. It would be a higher temperature. Sad, that.

    The whole RoHS thing is utter crap.

    Metallic form lead does not pose an environmental threat.

    It was certain European nations' way of boosting the eurodollar and
    that's about it.

    Now an entire industry in the US has to switch gears. The flux
    makers, and the PCB makers, etc. etc. all get screwed to play into
    some lame pissy country's baby bullshit directives.

    I am only glad that military product makers got an exemption.

    If it were such a big problem, lead would have been showing up in the
    water tables near dumps decades ago, and it never did. Nor was there
    an increase in cancer rates near such water tables.
  6. Pooh Bear

    Pooh Bear Guest

    I totally agree. Furthermore, WEEE is supposed to stop electronics being
    dumped anyway.

  7. Guest

    Thou art forsooth Solderman, and all thy points hard and true, and I
    acknowledge all except perhaps the bit about hand-soldering caps one
    side at a time seems inconsistent with your earlier admonitions.

    Although this is exactly how I solder caps, doesn't it throw all that
    careful ramping / thermal profile stuff right out the window and apply
    maximum thermal and mechanical shock to an brittle, inflexible part?
    And yet, carefully done, these connections seem very secure and

    Of course I'm just doing small stuff for fun this way, not launching
    anything into space, but perhaps there's a little more lattitude in the
    soldering process than is otherwise acknowledged, yes?

    For single-sided soldering, I'd think one could do a really good job
    on a skillet, as you can ramp the temperature up to suit, and ramp it
    back down the instant you see the solder flow. That should be very
    gentle on the components, exposing them to the minimum temperature
    needed, and for the shortest time.

    Soldering double-sided boards on an electric skillet would of course
    be a good way to roast the parts riding on the skillet surface, as well
    as preventing proper heat flow through the printed circuit board
    substrate. Ergo, double-sided needs a double-sided, controlled heat
    source...a toaster !

    From SED's own Robert Lacoste, a toaster oven controller:

    The Seattle Robotics Society has a manually operated scheme:

    If you're too busy, here's a pre-built toaster oven controller for

    And the Sparkfun guys are at it too:

    If you read through their discussion of the merits,
    they prefer their hot plate to their commercial, bought reflow oven, as
    the latter melts connectors. That failing of the commercial product,
    in fact, was what spurred them to roll their own soldering setup.
    Ultimately it seems they liked the skillet so much that they aborted
    their toaster project.

    All in good fun!
    James Arthur
  8. Guest



    Here are a few possibly-related discussions that I found interesting
    (mainly was looking for through-hole whole-board-at-once soldering
    ideas, at the time):


    Tom Gootee

  9. DJ Delorie

    DJ Delorie Guest

    FYI the matcal talon recommends picking up tiny parts with the tips
    *cold*, holding them in place, then turning the iron on. That gives
    you a 10-15 sec ramp-up and you can let go as soon as the solder
  10. Guest

    That sounds kind to the parts (but the thermal cycling will be rough
    that lovely Metcal).

    There was a rather contentious thread discussing this topic on s.e.d.
    a few eons ago... ah, here we go: Soldering surface mount components,

    Therein Clarence reported reliably hand-soldering caps in hi-rel
    (space) hardware, while others gave a dimmer view. All in the
    technique, perhaps?

    James Arthur
  11. Roy L. Fuchs

    Roy L. Fuchs Guest

    Hold on pads with tweezers, solder one pad, then the other in
    succession. Both together is where to part is held by two irons in
    tweezer like fashion, soaking far too much heat into them for far too
    long. Very, very bad. Quite consistent.
  12. Roy L. Fuchs

    Roy L. Fuchs Guest

    The single iron ramps it up faster, and it doesn't ramp back down
    between the two sub second operations. Absolutely proper. Iron temp
    should only be a few tens of degrees over the 495F 63/37 typical melt
    point. Minimal attack on the part. Circuit boards are a lot hardier
    these days, but the parts are susceptible. It becomes very apparent
    when working with high voltage ceramic SMDs. If done right,
    everything works fine. DOne wrong, and the thing won't make voltage,
    and sinks a lot of power. Testing the cap doesn't show anything as
    the problem only exhibits itself at working voltages.

    It is cheaper at that point to replace all six caps in a three stage
    multiplier with fresh, than it is too attempt to determine which cap
    is leaking. Ceramic terminations are actually contacting a huge number
    of "plate ends". Such attachments are weak at best. Far weaker than
    say a plated through hole's integrity is. Heat damage is one of the
    only ways to damage a ceramic that has never been overvoltaged.

    Back to the heat issue...

    The two iron approach, however has the full iron temp on the part,
    on both terminations with nowhere for the heat to go until you lace it
    on the board. Very, very bad.
  13. Roy L. Fuchs

    Roy L. Fuchs Guest

    There has to be a lot of flux present, a fume hood, and unless you are
    using a paste, you may as well hand solder the entire assembly. Also,
    one should remove the board immediately after reflow, not even attempt
    waiting for a huge thermal mass like an iron skillet face to cool
    down. Bad move. It will hold its temp a while. It also sports a very
    high emissivity, which is a factor in this case. A teflon coated
    griddle would be best as even the REAL reflow benches are teflon
    coated. They also pass the PCB OFF the plate area. There is a ramp
    up heat plate, and a reflow plate, and the boards are slid across in
    continuous fashion. With skillets or griddles, one would be about
    480F (just below reflow temp), and the other should be at about 525F.
    That is a high temp and an electric stove would have a hard time
    creating a uniform temp over the surface (evenly). Flame is much
    better at this in this case. The board would go one the ramp griddle
    for about 15 secs, then over to the reflow griddle until a few secs
    after one sees reflowing taking place as they do not all flow together
    when getting their heat through the bottom.
    Gentle? The solder process is by far the most damaging event in the
    life of an assembly. That discounts circuit/part failures and shorts
    etc.. I am talking about proper operation.

    The water or solvent wash after soldering should be followed by a
    60C dry chamber (often "aired out") bake out for about 30-45 min.
    This especially important if EL caps with rubber mount faces, or any
    transformers, inductor, etc. are on the board. Hell, even the SMD
    versions. Baking is important step. The PCB itself is hygroscopic.
    A vacuum step, then bake is ideal
  14. Roy L. Fuchs

    Roy L. Fuchs Guest

    Metcals are famous for coming up to temp in 5 seconds flat.
  15. Roy L. Fuchs

    Roy L. Fuchs Guest

    They are meant to be turned of after each and every use. The life of
    your $45 plus tip depends on only using it when needed. The supply
    they hit it with is designed to handle it, and meant to be used just
    that way.
  16. Guest

    Nice units, those Metcals.

    James Arthur
  17. Guest

    I don't have any data to judge the thermal time constant of an
    electric skillet. It seems to me a very lossy device, but if it cools
    too slowly, one might simply add a cooling fan blowing underneath, or a
    2nd adjacent skillet at a lower temperature, as you suggested. But
    then, I'm talking about hobby / fun / proto stuff, and you're talking

    Certainly being awash in molten metal isn't gentle in the ordinary
    sense. I meant 'gentle' in that the skillet produces less thermal
    shock (dT/dt) to the components than being suddenly contacted by a blob
    of molten solder sitting on a soldering iron.

    Such a thermal shock--and more particularly, the resulting thermal
    gradient across the part, and resultant mechanical strain--could
    shatter a component with sufficient thermal mass, such as a large
    ceramic capacitor.

    James Arthur
  18. Roy L. Fuchs

    Roy L. Fuchs Guest

    Still, simply removing the PCB to another surface IS what you WANT
    to do.

    Actually time at reflow stage should be minimal required to perform
    full reflow. After that, the ramp down has traditionally always been
    faster than the ramp up. The ramp up passes through four or more step
    in a big reflow oven, then the last stage IS reflow temp area, then it
    passes out the end into a room temp environment, seconds after it
    actually got soldered.

    Id say it matters.

    I'd also still say that hand soldering the first article, if not the
    entire run, by a skilled soldering personage is the best route.
    Especially for short runs.
  19. Thank you one and all for all of your input. It was a bit more than I
    originally asked but its all good.


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