![]() my modus operandi for video and hifi has been discrete components for decades. Only do this with good ventilation and try to not breathe any of the fumes!Ī fume-extractor would be very good to have and use.īit of a tangent from me, should you wreck it. Looking at the picture you posted, you have at the very least, one capacitor on the bottom left corner that needs protection as well as the plastic ports in the top left that would melt at such temperatures.Īs piranha said, flux is very important and should not be used sparingly.īut you need to also watch out for your health. I personally usually use around 370☌ air temperature and even turn it up to 450☌ sometimes if the parts won't budge soon enough.ĭepending on the shoddiness of your hot-air, you need to turn heat and airflow to the max, to get anything to budge reasonably quickly.Īt least that was the case for me with my first chinesium 858D. In this case it simply means that you have to get everything hot enough for the solder to melt, even below the chip.Ī preheater would help with that a lot, though you can also simply go a bit higher in temperatures and duration with a long time on like 200☌ air temperature to soak the board. If you have no experience in working with SMD chips, I recommend to practice first on scrap boards.Ĭlick to expand.That is what has called a "thermal pad underneath". It is tacky, and requires cleanup after work but holds the components during soldering. Good flux is the key to success when working with SMD components, don't be shy with it. Water removes the dirty IPA, and clean IPA removes water.Īs you may have noticed, I mentioned flux many times. After rinsing in water, rinse again in IPA and let the board dry. Rinse with IPA frequently during the operation.Īfter you're done, rinse again with clean IPA, and then rinse the IPA with water. Start by scrubbing the board with IPA and the brush until there are no residues of the flux on the board. I use a tooth brush, isopropyl alcohol, and clean water. It is a good idea to cover components around the chip with a kapton tape, or aluminum foil.Īfter mounting the chip, you have to clean the board. Flow rate has to be big enough to deliver enough heat, but not too big, to not blow other components off the board. Set the temperature by trying to melt a piece of solder on a sheet of paper. I set the hot air temperature and flow rate by experimenting. It has to be the right amount of solder: too little will result in a poor thermal connection, too much will float the chip too high to solder the pins to the board, and can result in shorts. Since you can't access it from outside, you have to put some solder on the pcb before mounting the chip, and reflow it by heating the chip from the top. Once the chip is removed, clean the solder with a wick. With a warm board, a light blow of hot air is usually sufficient to melt the solder. I usually heat the board up to 150-200C before using hot air. There is a big plane of copper under the chip which drains away the heat, and it is difficult to heat up the pad through the chip to the point of melting solder. The point is to keep the board warm during the entire operation. If you don't have a board preheater, you can use an electric skillet. I highly recommend preheating the board before the rework. With enough experience it is possible to replace it with just a hot air station, but you have a very good chance of damaging the board. The operation gets more complicated if the chip has a thermal pad underneath. Search YT for "drag soldering".Īs for temperature, for leaded solder I heat up the soldering iron to 300-320C, Occasionally I'll bump the temperature to 350C if 300 is not enough. Don't worry about bridging pins, you can clean bridges later. There is a simple trick, which makes mounting the new chip a breeze: Flux the pads well, put enough solder on the tip to make a big drop, and drag it along the pins holding the tip submerged in the molten solder, but without touching the pins. Flux the pads again, put some solder on the tip, drag along the pads to wet them, and clean again. Don't try to drag across the pads, it's too easy to damage them. Put the wick on the pad, press gently with soldering iron, wait until the solder melts, and drag along the length of the pad. ChipQuick is a low melting point solder, which will stay liquid for long enough to heat all sides and remove the chip. After removal, clean the flux with isopropyl alcohol, and clean the pads well using solder wick. Generously cover all pins, in the flux and ChipQuick, make sure that the solder is liquid on all sides, and remove the chip. For desoldering, get some good flux and Chip Quick solder. If the chip has no metal pad underneath, removing the IC is a pretty simple job. Click to expand.If you have no experience in working with SMD chips, I recommend to practice first on scrap boards.
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