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Airflow and temperatures

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  • Airflow and temperatures

    I know there is no “right” temperature for hot air because each hot air station is different and I need to find what works for mine. My question is more around the thought process when deciding weather I need high temp and high flow, low temp high flow etc. are there some general guides to follow when deciding how to set my station for any particular area of an iPhone logic board? For example when removing a shield I know to set high flow and high temperature for easy removal but when I’m removing overfill I reduce the temperature and flow so I don’t inadvertently knock small components off. When working around IC’s I’m concerned about hurting surrounding components and IC’s by using improper flow and temperature. I guess my question is: is there a sweet spot I’m looking for and what’s the best way to dial it in?

  • #2
    My experience the last few months is trying out. For ic removal u2 size around 360 with 60 airflow. I have a quick hotair station. Also depend on the size of the tip you use, that will change a lot of the temperture and removal time. I think there will be a balance not to heatup the board to long and other components. Normally i can remove ic within 1,5 minute. I think its normal that sometimes other parts will move because of the small size. Best way is to play with a donor board and see whats the best way. Grz Remco

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    • #3
      Like Remco Ross said, you will learn the proper temperatures by practicing with donor boards.

      Your worst enemy are underfill IC, but not all of them are underfill, and if so, can be safely reflown.

      Luckily, you can use a heat sink (a penny for example) over an IC your protecting. This will make it more likely that the component or the IC you are trying to remove will melt before the one that the penny is sucking some of the heat out of. For the regular overfill components, you can simply remove the overfill.

      Timing is key, and we all have are own technics.

      Personally, I like to warm up the area I'm about to work on with 1/3 to 1/2 the temperature I will use to melt the solder for a few seconds with a big nozzle,
      and then I switch hot air station with a smaller nozzle that just a little bigger than the chip I want to remove and heat it up at fairly high temperature so it melts quickly and before anything else.

      They are bad ways to do this work, but not ONE golden way. Over time you will develop your own style naturally as you learn by trial and error (and some guidance).



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      • #4
        TBH I use max temp and get in and out within 5 seconds or less. The art of repair 'YouTube' tested this technique the other day and the temp on the back of the board worked out a lot less than using lower temps and waiting. If I get an undefilled ic il pretty much always grind it out if it's near any other undrfilled ics, unless it's nand,small like tristar or it's an ic that is by itself on a section of the board, otherwise you just end up having to reball all nearby ics. If you grind it out you can use a ic with leaded balls which will melt before the lead free ones squeeze out a ball. Il use bits of copper sheet or coins to cover anything sensitive or liable to melt like connectors etc.
        For connectors il use 200-250 as they just melt into mush if you use above that.
        Shields I just hit them with max temp and then remove heat straight away. They'll come off by a matter of seconds.

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        • #5
          Your goal is simply time. You want to figure out how to get a chip off in 15-20 seconds. There are waaaaay too many variables to start posting actual temp/airflow and applying from one station to another. Your nozzle size, height above chip, angle of airflow, and your stations actual temp and flow vs what it says here are HUGE variables. For example—just from the advice given here, if I were to attempt to remove a chip at 360C/60 flow on my station I’d roast the board and deliver waaay too much heat and it would take about 3 full minutes to get the chip off. 380/80 worked for me up until about a month ago, but today it is also too low on my station. If I went from my station to the one next to me and put 380/80 I’d be fire blasting the board and the chip would come off instantly, which is also too much stress and would bother underfilled chips. Similarly 200 recommended above for connectors would never get a connector off, I honestly don’t see how that can work for anyone since solder melts well above 200. I use the same temp I use for chips for connectors.

          the point here is that taking internet advice from someone else’s station and applying it to your own—even within this thread!—will kill boards. How do you know what is the right temp/flow for you? The time. And practicing on donor boards.

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          • crea2k
            crea2k commented
            Editing a comment
            I think 200c on my station isn't 200c lol it's just what I know works without melting the connector. I'm 99.9% sure it's not calibrated anywhere near spec as it's just a cheap station but does the job. But this fact alone backs up what you're saying about not having one temp for particular things as just station to station varies greatly. Iv got two of that same station and both melt solder at different temps.

          • BigN8
            BigN8 commented
            Editing a comment
            Thanks jessa . That was the answer I was looking for. How long should it take to remove a chip. I know some people talk about going slow and warming the board first and others say hit it hot and hard as fast as possible.

        • #6
          Jessa's advice looks like the American Idol performance: it must only last up for 30 seconds!

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