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Newbie - Hand Soldering TO-220 SMD - HELP!

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    Newbie - Hand Soldering TO-220 SMD - HELP!

    I have a lot of experience with PCB thru-hole repairs but only some SMD replacements such as 0805 parts or SOT-23 transistors where i have tacked the pins to the pads manually with a fine solder tip. I am now replacing several TO-220D-A1 diodes on a TV pcb and all of these need the cathode backside of the component soldered to a large ground pad. I have a XYtronic LF-8800 80W hot air pencil (minimum setting is 300C, max is 450C) and used Chipquick low temp lead free solder paste. I have pre-warmed the SMD with the hot air pencil at 300C held about 1" above the SMD for about 1-2mins then turned up the heat to 400C and held that for another 1-2 minutes. Slowly cooled off and the SMD was still not soldered to the ground pad. I unbderstand the ground pad is basically the entire pcb copper plane so big heat sink. How do you do this without destroying things? I have a small IR over for small parts < 6" but this TV board is 18" x 7". Any advice would be greatly appreciated.

    Jerry NY2KW

    #2
    Re: Newbie - Hand Soldering TO-220 SMD - HELP!

    Use a solder iron with a fairly large tip, add some flux and add some new solder, the solder iron will heat the copper and the transistor easier than the hot air.

    Comment


      #3
      Re: Newbie - Hand Soldering TO-220 SMD - HELP!

      Originally posted by R_J View Post
      Use a solder iron with a fairly large tip, add some flux and add some new solder, the solder iron will heat the copper and the transistor easier than the hot air.
      Sorry if I wasn't clear, the part to solder is not visible/accessible. It is the entire backside of the component which is mounted flat to the PCB - I assume it is constructed so to allow the PCB ground plane act as a large heat sink since these TV diodes (RN1501 or DAF30A) are rated at 20A with 100A surge. Are you saying I should apply the iron tip directly onto the SMD body?

      Jerry

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        #4
        Re: Newbie - Hand Soldering TO-220 SMD - HELP!

        NO. not to the plastic body part. you apply the solder tip to where the metal tab meets the copper board. the heat will transfer under the transistor, melting the solder, It works best with the addition of some solder flux
        Watch these:
        https://www.youtube.com/watch?v=L_DIpklxXcI
        https://www.youtube.com/watch?v=uFev4JbVG1U
        Last edited by R_J; 02-05-2018, 06:14 PM.

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          #5
          Re: Newbie - Hand Soldering TO-220 SMD - HELP!

          OK, will give it a try... the exposed metal tab is line a pretty thin strip, less than 1/16" wide. Few questions please:

          1) what temp would you use? I have a Weller 100W iron with 600F, 700F and 800F tips?

          2) would you use Chipquick or other low temp solder?

          3) how long? Is there someway of knowing when the solder has flowed enough under the SMD?

          Many, many thanks

          Jerry

          Comment


            #6
            Re: Newbie - Hand Soldering TO-220 SMD - HELP!

            How long is a piece of string?
            It depends on the thickness and size of the solder pad, try the 700F tip and see how it works, I just use normal 60/40 solder
            Did you watch the video?
            If you are using a small sized tip, place it along side of the tab where it meets the board to get a better heat transfer. More heat quicker works better than low heat for a long time
            with some practice you will see when the solder flows under the part and you can remove the heat
            Last edited by R_J; 02-05-2018, 06:29 PM.

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              #7
              Re: Newbie - Hand Soldering TO-220 SMD - HELP!

              The first video was outstanding. Seems very straightforward... for some reason I thought hot air would be less destructive but this video makes it seem pretty fast. thank you for taking the time to help me.

              Comment


                #8
                Re: Newbie - Hand Soldering TO-220 SMD - HELP!

                You can assist the soldering iron with the hot air wand if it is not too powerful by itself. But with a 80W iron i doubt you will be having any kind of issues. If you're having trouble you are likely using the wrong tip for the job, soldering such a component requires a chisel tip at least 3mm wide.
                Originally posted by PeteS in CA
                Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                A working TV? How boring!

                Comment


                  #9
                  Re: Newbie - Hand Soldering TO-220 SMD - HELP!

                  For SMD replacement work in general, what's your opinion on using pre-heating plates?

                  Comment


                    #10
                    Re: Newbie - Hand Soldering TO-220 SMD - HELP!

                    Usually avoidable, but they make life a lot easier when you're dealing with boards with large copper areas. If you can get one, please do.
                    Originally posted by PeteS in CA
                    Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                    A working TV? How boring!

                    Comment


                      #11
                      Re: Newbie - Hand Soldering TO-220 SMD - HELP!

                      Thanks to all, replaced 7 bad diodes and IGBT's in an old Panasonic plasma TV and works perfectly again.

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