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Thread: Desoldering ICs

  1. #1

    Default Desoldering ICs

    [wiki]Category:How_To[/wiki]
    While the principles involved in desoldering an [wiki="Integrated Circuit"]IC[/wiki] are the same as those for any other part, the delicate nature of the component and the large number of pins can present a challenge.
    If the chip to be removed is to be used again, great care is required to ensure all joints are completely free of solder. Just one partially soldered pin is enough to hold a stubborn IC in place and locating which pin is still connected can be tricky. If a pin is not completely clear of solder, it is often easier to flow new solder into the joint and start again. Take care not to apply excessive heat which may damage the IC or fine traces on the circuit board. When done correctly, very little force will be required to remove the IC from the board; ideally, turning the board over and giving it a good tap should make the IC fall out. If you find yourself prying the chip out, check again for stuck pins. When possible, it pays to practice on junk boards and ICs before tackling important or rare ICs.
    If the chip to be replaced is defective, it is often easier to cut the body of the chip away from the pins before starting, then desolder the individual pins. This approach can also be gentler on the circuit board from which the chip is being removed. As each pin is removed individually, it?s easier to detect when the pin is free so excessive heat and pressure can be avoided. With all pins removed, the holes can then be cleared of solder using a desoldering pump or solder wick. Small traces of solder are not always worth removing and can, after heating, be poked through with a wooden toothpick. It is sometimes easier and/or safer to leave the old pins in place and simply solder the new chip to the old pins sticking out from the board.
    See Also

    • [wiki]Soldering ICs[/wiki]

  2. #2

    Default

    I am troubleshooting a card mounted 286 processor from a Telex 1280 at the moment. I wanted to be able to work on it on the bench and not inserted in the computers backplane. To make it easier to power the board and make the needed connections I desoldered a 16 bit card slot from an old junk motherboad a couple nights ago. It had been a while, but by the time I got that slot out I was desoldering like a pro

    I can personally attest to the adding a little solder back trick. If you have a pin that isn't quite clear or just didn't have a lot of solder to start with it really helps.

  3. #3
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    Its all I have been doing lately. Socketed up a Issue 1 ZX81 and an Einstein VPU/VRAM for fault finding, the ZX81 has heavy corrosion and resoldering is the only way to get a flow. I do use plumbers flux as well on difficult highly oxidised boards.

    I am using a very old green RS components sucker and I thing its getting past its use by date.

    I am tempted by one of the desktop vacuum desoldering irons units similar to the ones at work. They make desoldering a breeze.

    However, I'm thinking I really need an extraction system to stop me breathing in all that lead etc.

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    I think you're over-reacting on the lead stuff. You'd get more lead in your system by using Grecian Formula 16 to darken your graying hair.

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    Quote Originally Posted by Chuck(G) View Post
    I think you're over-reacting on the lead stuff. You'd get more lead in your system by using Grecian Formula 16 to darken your graying hair.
    Hey !

    My hair is still naturally black, with no 'enhancement' thank you very much !



    Interesting about the fumes, I stopped actively doing soldering professionally around 96 and since then fume extraction (and everything else) has become so much more restrictive. After an hour of sniffing flux and solder fumes I did think it might be worth a small fan or some such.

    Do we think there is little hazard ?, not really looked into it myself.

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    Lead, like mercury is most dangerous when it takes the form of organic compounds, which can be metabolized.

    Consider the dreaded mrecury, for example. You can hold the metallic element in your hands without significant danger to yourself. Calomel, (mercury chloride. Hg₂Cl₂) is an inorganic salt that was widely used as a purgative. Dimethyl mercury (CH₃)₂Hg) is an organic compound that's been documented as being able to slowly kill from a single droplet on the skin (cf. the tragic story of Karen Wetterhahn).

    Lead is much the same way--it's still used as flashing for roofs, in stained glass work, in storage batteries, fishing sinkers and a host of other things, including solder in metallic form). On the other hand, Lead Acetate ("sugar of lead" Pb(CH₃COO)₂) is somewhat toxic. It's used in Grecian Formula as a hair darkener, only because you're not likely to ingest it. Old flaking lead paint is dangerous, mostly to young children because it interferes with brain development if they eat it. But everything from battleships to bridges was painted with lead-based paint, so not so much for adults. My home town was home to American Lead Products. I think I'm still more-or-less functional. I've been soldering since age 10 and still use 50-50 solid-core solder in metalwork.

  7. #7

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    I agree, the lead is a non-issue. The flux fumes are probably a greater threat, but I don't really worry about them either

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    Old-style Sn-Pb solder uses a rosin flux. I've taken (string) bass rosin and dissolved it in alcohol and used it--works fine.

    You're probably in more danger of exposure if you burn pine in your fireplace.

  9. #9

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    exposure to chimney fires!

  10. #10
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    I will just keep sniffing then

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