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    #1

    High melting point solders used on PCBs...

    I've noticed some boards are a pain to desolder, and others the solder melts quite readily. This is of course already considering large ground planes that will suck up all the heat from the joint. This by itself is a pain (do people just keep on applying heat to desolder caps on large ground planes or have some other tricks?)

    Take for instance my Antec SP400 PSU, the solder on the board took forever to melt. After I doped the solder on the board with some fresh eutectic 63/37 (or some high tin solder) it melted much more readily than before.

    Is it ROHS solder that's doing this? anyone know the exact formulation of common high melting point solder (metal ratios?)

    Then if you encounter this stuff, do you just use a really high watt iron to melt through it, or use a moderate iron and let it sit there till it melts (and for both, ever cause damage to board or components?)

    I have a spool of ROHS solder from Harbor Freight which I believe is mostly tin with a little copper in it, and has rosin core. This stuff melts more readily than the SP400 solder... (Then the other question is if the HFT ROHS solder is really lead free or not...) Also cheap 60/40 solder seems to melt faster than the SP400 solder... *shrug*
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    #2
    Re: High melting point solders used on PCBs...

    http://en.wikipedia.org/wiki/Solder#Solder_alloys

    The chart lists the melting temperature in the description for almost each alloy.

    Most solder used in hardware is tin with a percent or more silver and/or copper. Silver helps with surface mounted components.
    Usual temperatures are 217-225c in comparison with 60/40 solder that melts at about 180c or 63/37 that does it at 183c

    So yeah, you need to use 300c or more to desolder, and you usually add a bit of leaded solder to lower the melting temperature.

    Anything on a spool will melt faster than something already applied on pcb with big copper traces that could absorb heat.

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      #3
      Re: High melting point solders used on PCBs...

      For boards with big ground planes i usually use my "beefy" 100W iron. That gives loads less stress on the board since its loads quicker and usually means you don't heat it too much. Perfect for scavenging components from boards. My 50W just wont cut it, i can sit there and heat it until its all black and charred.

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        #4
        Re: High melting point solders used on PCBs...

        I came across a Biostar motherboard where none of the joints would melt...My iron got all the way up to 510C and none of the joints would melt at all, not even where the tip was. Tip was clean too...I just tossed the board

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          #5
          Re: High melting point solders used on PCBs...

          I use my heat gun to pre-heat the area then my 65w iron, it works.

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            #6
            Re: High melting point solders used on PCBs...

            There are so many different kinds of solder alloys so I was wonder which one was most common for the high melting point solder. The solder can't be very expensive either, after all, it's mass produced...

            I started to use my 100/140W solder gun to melt a couple of these but the tip is just way too big when dealing with motherboards... that's the other concern with the big guns...

            I've never tried using a heat gun to preheat, that seems like an idea to try...

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              #7
              Re: High melting point solders used on PCBs...

              I have never used the gun for the melting purpose but used the motherboard. Its nice but it takes some time to get melt. The advantage of using gun is it does not taker that much time compared to motherboard.
              ----------------------------------------------------------------
              The prix achat maison i.e the price of the house at the time of buying must be known before dealing with it.

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                #8
                Re: High melting point solders used on PCBs...

                will 80W soldering iron be enough ? I put the temperature to 420 but it's still hard on unsoldering the caps....any other tricks ?

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                  #9
                  Re: High melting point solders used on PCBs...

                  it's the tip used and speed the iron reacts to temp loss as much as anything.

                  a T12 tip will be worlds ahead of most other irons.

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                    #10
                    Re: High melting point solders used on PCBs...

                    Originally posted by stj View Post
                    it's the tip used and speed the iron reacts to temp loss as much as anything.

                    a T12 tip will be worlds ahead of most other irons.
                    Exactly!

                    This:
                    https://www.circuitspecialists.com/l...l-display.html
                    +
                    https://www.circuitspecialists.com/lf-52d.html
                    =
                    haven't had a motherboard I couldn't recap or remove a MOSFET from. Makes my life so much easier!

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