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Microsoldering with Weller WHA-900 HotAir

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  • Microsoldering with Weller WHA-900 HotAir

    Hi,
    I´m new to Microsoldering.
    I use this Equipment:
    - Weller WHA-900 with bent Nozzle (see attached, 6mm)
    - Weller WSM-1 Soldering Machine
    - Weller WTCP-51 Soldering Machine
    - Amtech Flux NC-559-V2-TF (Age 07/11/16)
    - PreHeater "Wozniak PPD 120E"
    - Microscope AmScope https://www.amscope.com/3-5x-90x-cir...al-camera.html

    My Problem is to desoldering the Chips. I saw a lot of your Videos Jessa, and practice on faulty Boards. After a few Time the desoldering worked well.
    But now I tested it on 2 iphone 7 Audio IC´s and both takes a long Time until the Chip comes off, leaving a few Pads on the Chip

    I use Preheater with 185 degrees and HotAir with 410 and Air Pressure 5-6.

    Can someone help me please....


  • #2
    Hi there--welcome to the forum!

    For learning bga, iPhone 7 audio ic is not the place to start. Start with tristar on a 5s or 5c. Get one that charges (it doesn't have to boot to ios, it can be icloud locked, it just needs to charge on a usb ammeter). Then change the tristar chip and make sure it still charges. Do that a few times and then graduate up to the next bigger chip, meson touch ic. After mastering that, move up to audio ic.

    Other tips:
    Audio ic on iPhone 7 is different than chips on other boards because the iPhone 7 is a bigger heat sink.
    Audio ic on iPhone 7 gets into trouble because of flexion of the board---and that pulls up pads. It is common for many pads to already be loose, especially along the edge of the chip near the sim tray. Sometimes you will take pads off with the chip--because those pads were already separated from the board due to flexion damage. This is another reason to perfect your microbga technique on something other than iPhone 7 audio ic.
    185C sounds pretty hot., although it is typical for those preheaters to be all over the map with calibration. If you haven't calibrated it then do that first. Then you have to find the sweet spot for each preheater. The one I use at home is at 128C, the one I use at work is at 150C.

    Let us know how it goes!
    Jessa

    Comment


    • #3
      Hi Jessa,
      Thanks for your Answer!

      I changed a few iPhone 5S and 6 Tristar (not a lot, about 5 Pcs). Sorry, i forgot to mention
      I calibrated the preheater using your Calibrate Video before Repair.
      But I'm not sure if the HotAir Temp is ok, because in your video "Fast Method" the chip was really quickly desoldered.
      Is the Nozzle perhaps too big with 6mm ?

      Regards
      Mike

      Comment


      • #4
        the Flux is not too old?

        Comment


        • #5
          Flux doesn't get too old in my experience, and you are worrying too much about small details. iPhone 7 does take longer to get the chip off when not on a preheater. I think 185C on a preheater is way too high, but everyone has their own style. The hot air temperature can either be very hot with very low flow speed, or high flow speed and moderately hot---that is personal preference. It is these small details that you work out on straightforward jobs like iPhone 5c tristar. Then you move up to boards that you don't want to kill after you have microbga figured out. The difference between a 5c tristar and an iPhone 7 ON A PREHEATER will be very small. You will use the same nozzle size and same basic hot air controls within 10% between a 5c tristar and iPhone 7 audio IC on a preheater.

          If you are struggling the MOST LIKELY reason is poor positioning of the nozzle and a lack of awareness of where your nozzle is pointed in space. Have someone take a close side view video of you using hot air so that you can see where you were actually aiming once done.

          Also--forget about the 'quick method' video--that is a fancy technique that we don't even use anymore. It works fine, but every now and then one will overheat. We prefer to use the standard technique on a preheater and reballing the audio ic with leaded paste.
          Last edited by Jessa_the_Professa; 01-07-2019, 06:08 PM.

          Comment


          • #6
            Ok, thanks for your Answer again
            I will try it again.

            Comment


            • #7
              - which Temp on preheater do you use on iPhone 7?
              - I used Kapton tape on the Backside of Logicboard to protect Chips again Preheater. Was this wrong?

              Update 13.02.2019
              After a few successfully Tristar and iPhone 6 Plus Touch IC i managed to change the Audio IC
              Last edited by mimk97; 02-13-2019, 03:29 PM.

              Comment


              • Jessa_the_Professa
                Jessa_the_Professa commented
                Editing a comment
                We never use kapton tape at all, other than to hold something in place. You need to experiment with this idea of "protect from heat" Would you put a piece of kapton tape on your finger and then aim your hot air at your finger expecting it to "protect" you? Do some experiments on donor boards taking the same chip off of two different boards, one with "protection" and one without. Which one comes off faster?

                My experience training students is that after you are comfortable using hot air, most microsolderers do not use any kind of heat protection at all. They know that the board MUST get hot in that one spot faster than the heat is being sucked through the whole board by the ground planes. Heat "protection" often creates the problem we are trying to solve. I think in the last week I put a quarter on a job one time, the rest--no tape, no heat shielding.

                So how can this be?

                The answer is the nozzle position. If you have changed the same chip 100 times, you have muscle memory for where to direct your nozzle to *just* heat that specific spot in a targeted way. Most beginners will *eventually* heat up the target spot, but they are often all over the place or aiming heat directly at an adjacent spot and therefore overheating that spot quite a lot before that heat spreads to the target chip and it comes off. This is how beginners get "heat problems"

                You asked what temperature on the preheater---I use somewhere between 128-150C on mine and I will change that as I see how the board reacts.

                One of the best ways to learn the nozzle positioning and angles is to just sit there and reball a bunch of chips, or to take something like a donor iPad mini and take off the digi/lcd connectors and then tin with an iron. Heat the board so that you can see WHEN the solder gets liquid and balls up. These techniques will help you master the art of heat control.
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