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Solder not reflowing - what am I doing wrong?

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    #1

    Solder not reflowing - what am I doing wrong?

    I'm trying to fix a broken MacBook Air, and got a parts board to salvage components from. Following the suggestions of many folks here, I wanted to get in a little practice of using my hot air station (A Quick 957DW+) on the parts board so I know what kind of behavior to expect.

    For the life of me, I can't get anything done with this thing. I have tried multiple temperatures (from 210-425c), different air speeds, preheating the board (with the hot air, just warming it all around). I have applied what feels like excessive amounts of flux (Amtech V2-TF-559) and the solder on these components (specifically a fuse) won't budge. I don't think I'm being impatient in expecting the solder to start liquifying after a couple of minutes.

    One thing that stands out that might be contributing is that I'm using a digital microscope - I don't have a good sense of depth when doing this - which maybe means I'm not perfectly pointed at the component. But I'm also not seeing success when I put aside the microscope.


    I don't know what I'm doing wrong. Is there some special trick to reflowing solder with hot air that I'm just not getting? Suggestions are welcome.

    Tags: None
    #2
    try to remove something without the microscope just to get used to how close your putting the air nozzle

    Comment

      #3
      I hardly use the microscope to take anything off using hot air. Hot air takes practice. At the beginning I went full bore and way too close so much I made a huge bubble underneath the traces. Basically the PCB separated. These days I use two settings on my hot air and don't pay much of attention on exact airspeed and temperature values.

      The next thing becomes the nozzle. My bet is you use a too small of nozzle. I use only 2, basically one 1. A small nozzle for little simple SMT buggers, or none (I take the nozzle right off) if I need more spread out heat for an IC. I also only fan the hot air around the PCB at the beginning, then center that hot air over the IC or whatever get closer and then wait until it becomes floating and pick it off.

      Another Problem: under fill and glue. SMD or T components can either have an under fill or even glue underneath. Making it appear they do not come off. Be careful what you doing here, you can rip of traces or pads in no time. Same with using too much heat.
      Vague, eh? That's why I said it needs practice. It's kinda like riding a bike.

      Now let's see what you are trying to do. Maybe it is as simple as adding a little flux and some new quality leaded solder and it should come off. I got spoiled and got some hot tweezers for my Weller WD-1.

      Crap: here is the next point… SOLDER. I use 3 different types. A very low melt solder paste, Kester leaded 60/40 solder wire and “silver solder”. Use good solder, not the Chinesium crap.

      Comment

        #4
        I tried again last night and it went a little better than it had previously. I switched to the big nozzle and tried to preheat the board a bit, and messed around bit more with the air speed and temperature. It was still tough and took more effort than I expected. I guess in a lot of ways this is a practice thing.

        I don't think anything is glued on (not that I'm dealing with anyway). FWIW, I'm using Weller silver solder, and I think the leaded stuff I have is kester (i'd have to pull it out). I think the MBA I'm working on would use lead-free, but it is a 2015 era, so I don't know how aggressive Apple was at the time for RoHS compliance.

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          #5
          I hardly use that silver solder. A spool of it lasts me many years. The 60/40 is use to 95%. I assume you are taking ICs off the board. Take the nozzle right off and blast the IC. Poke at it and once it moves pick it off with the tweezers.

          Comment

            #6
            time for a solder talk.

            silver solder is only needed when soldering onto oxide deposited onto ceramic backing - like hybrid circuits or piezo transducers.
            it may melt faster and flow a little better, but once it's on it's harder to reflow or melt later.

            i use 60/40 solder to clean boards or lower the melting point of chinese leadfree solder joints,
            when i put stuff back i use leadfree solder with NiGe in it.
            thats not cheap btw.

            Comment

              #7
              Hi,
              Mix lead solder with non lead.
              https://www.eptac.com/blog/leaded-vs...hich-is-better

              Comment

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