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I'd like to remove all the ICs from the below PCB, hopefully preserving them for future use:

enter image description here

This was a failed (ish) reflow attempt using paste and a hot plate.

I have a hot plate, a hot air machine and a soldering iron, plus soldering stuff: wick, solder sucker, and lead-free solder.

How do I do it?

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Here's what I'd do... To start with, read my answer to the question of "Solder very close together contacts". That answer won't tell you what to do to remove these parts, but it will tell you the type of soldering iron tip to use and what to do once the parts are off.

Now, as for getting the parts off... I would use a pair of curved fine-tip tweezers, and a super pointy dental pick with a 60-70 degree bend in the end. Most dental picks are not sharp enough for this. You need one that's narrow enough to get at least a little bit of the tip under the part. You might be able to use an X-Acto knife instead of a dental pick.

Now, let's separate this into chips with two rows of pins (SOIC's, TSSOP's, etc). We'll tackle the chips with 2-rows first...

Start with lots of flux on the chip. Clean off the soldering iron tip and then put on a good amount of solder. Touch one row of pins and run the soldering iron back and forth across the entire row of pins. The idea here is that you get the solder on the entire row melted and keep it melted. You need to use enough solder so that there is enough thermal mass to keep it molten as you move the tip back and forth.

While that one side is melted, put the dental pick under the chip and pry it up. You are not going to get it up very much, maybe 1 mm. You shouldn't need much pressure (or you could damage things). When you're done, one row of pins should be about 1 mm higher than the other row.

Let me be clear here. With one hand, you are running the iron across the pins, keeping the solder molten. With the other hand, you're gently prying up that row of pins.

Repeat this process for the other row. Now both rows should be about 1 mm higher. Repeat again, alternately jacking up each side until one side comes completely loose. Now, grab the chip with the tweezers and heat up the remaining row. The chip should be loose.

Clean up the chip's pins, and the pads on the PCB with some flux and solder braid. It's important to get the pins back as straight as possible before trying to solder it down again. If it's a cheap chip, and you have more of them, then consider throwing it away and starting with a fresh chip-- it's that important that they are all straight and even.

Now, on to chips with 4 rows of pins (QFP, TQFP, PLCC, etc). I hate to say it, but you can't use the previous method with those chips. The only way I have been able to remove a QFP and not destroy the chip in the process is to use a hot-air rework station with a nozzle that is made for the chip package that I'm removing. You might be able to kludge something together using a standard heat gun or toaster oven or whatever, but I have never had luck with that. Whatever you do, practice, practice, practice. Actually, that goes for everything else too.

So, here's how you remove a QFP/PLCC by destroying the chip (and not destroying the PCB): Get an X-Acto knife. You might consider putting a fresh blade in it. And run the blade across each row of pins where the pin enters the plastic/ceramic body of the chip. You'll have to go across 10-20 times, each time scoring the pin a little bit deeper. Eventually you will cut through the pins. Do that for each row. Remove the plastic/ceramic part of the chip. Then use a soldering iron with a gob of solder on it to remove the pins from the pads. Clean up the PCB as before.

The danger with any type of PCB rework is that you could damage the PCB-- lifting pads and traces off of the board. Mostly this comes from applying too much heat for too long, or prying things off when the solder is not completely melted. I recommend that you practice any of this before working on a PCB that you actually care about. Get some old piece of gear and start unsoldering things. This will save you much frustration and broken PCB's.

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I would use Chip Quik. It works very well, in my experience, and is very fast. The board and parts aren't damaged in any way, and the removed devices can be reused if necessary. Ideally, it's used with a temperature-controlled soldering station on a low temperature setting. They will send you a free sample kit if you want to try it out, which will remove a couple of QFP parts.

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  • \$\begingroup\$ Hmm, nice stuff but I looked up a price for 6.5" of the stuff, and it's £7, given that that probably wouldn't remove many components (dsPIC is £4, sync sep £2) it's too expensive for me. :( \$\endgroup\$ – Thomas O Apr 17 '11 at 12:34
  • \$\begingroup\$ Given the price of the board that will usually be repaired with it, it's very good value. \$\endgroup\$ – Leon Heller Apr 17 '11 at 14:12
  • \$\begingroup\$ I get my boards for £2 each from China. \$\endgroup\$ – Thomas O Apr 17 '11 at 17:13
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I would try using the hot plate to warm the board, combined with the hot air tool to heat up the ICs and the solder joints. With patience (and some luck) you'll get the ICs off.

Tweezers and/or a utility knife can be helpful getting the parts off once the solder is flowing.

Does your air tool have nozzles that line up with the IC packages? They help with the larger parts.

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For SOIC it can be done with normal tin, by using 'a whole lot' of it and getting both sides liquid so you can get the chip off.

Personally I don't use flux with this, because if I desolder chips I am 100% sure I'm not reusing them. You have putten them through >3 times their heat cycle, by soldering/desoldering/soldering. For TSSOP, TQFP etc that's probably even more the case with certain soldering tricks. If a chip is broken in the process but you're unaware of , it can be a very time consuming mistake to figure out why. And then you have the desolder the chip again if you want to use the same PCB.

There is also 'special desoldering' tin that stays liquid at a lower temperature. By using that you can possibly get all sides liquid for long enough to desolder it. I haven't tried this myself on QFP, so I don't know if the chip survives. I know for a fact that the PCB does, because they did this a couple of times to an ARM development board at my internship where the chip was already broken (blown up). As always, heat is the danger of destruction, so desoldering QFPs is always a pain.

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  • \$\begingroup\$ That's the Chip Quik I mentioned in my answer. \$\endgroup\$ – Leon Heller Apr 17 '11 at 14:34
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Use flux + solder wick to gently remove the majority of the solder from the part.

Run the board through the reflow process again, on a hot plate. When you hit the molten solder point, remove the parts with tweezers.

Most reflow profiles call for 60-150 seconds in a liquidous state, you should be able to remove the components at this time with tweezers and thats plenty of time to remove a couple parts. You'll also have 10-30 seconds within 5C of the peak temperature where you can definitely just remove the parts.

If you don't want to do this just pre-heat the board to 100-150C and use a hot air gun. Trying to remove a package as large as that PIC with a regular old solder gun is a meticulous hit or miss process and not really worth it.

The SOIC 8 you can lift with just a pair of tweezers and a wide chisel tip, just lift one side then the other.

Just keep in mind using any method other than heating the entire package and lifting it straight off the board will require a fair bit of clean up and bending of pins to get the package back into a state that it will reliably reflow.

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Here's what I've done:

Put the board in a toaster oven. Cut off a few mm of wire solder and place it on top of the black QFP part. Set to "dark brown" and begin toasting.

When the solder goes from wire-shaped to ball-shaped, quickl y open the toaster oven, grab the edge of the board with pliers, hold it vertically over your desk and knock the edge on the desk a couple times. The parts will fall off. You might need to clean the parts and board up with braid before reuse.

You could also pick the part up with tweezers, but just letting the part slide off the board is better in my opinion, because there is no way it can put significant stress on the pads or pins.

If you overheat the board this way it will discolor the silkscreen (the white browns a bit) but will be perfectly functional.

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  • \$\begingroup\$ Oh, you have hot air, so you could put the board in a vise and blow air at it until the part slides off. This is an easy application of air because you aren't concerned about disturbing neighboring parts, so crank up the air volume and blow the chip off the board... \$\endgroup\$ – markrages Apr 19 '11 at 16:06

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