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Thread: Desoldering ICs

  1. #11

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    I love the smell of soldering. It brings back recollections of happier times. I guess if it gives me cancer someday, that's alright.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): TRS-80 Model II,12,16,6000, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  2. #12

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    How I desolder chips.
    If I intend to toss the chip, I use a pair of flush dikes ( that means the cutting edge is not offset from the edge of one side of the cutters ). I cut the leads as close to the IC body as I can. I then use a small bench vice or similar holder to heat the solder from the bottom side of the board. I use sharp tweezers to grab the lead and quickly pull them out before the tweezers remove too much heat. If you miss reheat and try again. I use a full length pull-it to suck the solder out.

    If I intend to remove the IC intact it is different. First, I heat the board from the bottom. Most leads are flared out in the hole. It is almost impossible to remove 100% of the solder with the lead up against the inside of the hole. While the solder is molten I bend the lead so it is half way across the width of the hole. ( the solder must be completely molten to the top of the board. ) I then use the pull-it to remove the solder. Heat from the top and remove the iron at the instant I energize the pull-it. I then use what I call the tink test. I use a small flat screw driver and stroke across the lead ( careful to not push so much it bends ) and listen to the sound. A dull tink means it still has solder. Refill the hole and repeat, never try to suck an almost empty hole.
    No matter what, at the top of the board, the shoulders of the lead will be touching the board. Even with the best of suckers, there will be a little meniscus of solder between the two. I then use a pair of short needle nose pliers such the one blade is right at the board and the other is at the package and squeeze. If you've done good at removing the solder, it will easily pop from the board. Before doing this, always inspect to make sure you really did remove any visible solder.
    If all went well the IC should now easily lift from the hole.
    I didn't mention through this that always keep clean fresh solder in the joint and a clean fresh tinned iron. Never attempt to heat with an oxidized iron. You can remove old oxidized solder with the pull-it and replace with fresh flux and solder. Use the correct heat level for the joint you are desoldering. A 4 layer ground pin takes about a 700F heat while a feed through lead takes about 600F tip ( with 60-40 or better 63-37 solder ).
    Never use plumber flux on a board. It is impossible to clean completely and will cause long term failures. Don't use water soluble unless you intend to completely submerse the board in water. Use a good rosin flux. Experiment on a clean fresh board. This is a test I often do with new unknown flux. I take a new clean board I solder two close leads but let the flux get between the leads. I then let it sit for a few days. I then measure the resistance between the leads. If it measures anything on my highest resistance, I don't use that flux. Remember, even if you can remove the flux from the bottom of the board it is almost impossible to remove it all from the top under the part without special cleaning equipment ( that is no longer legal in the US ).
    With water soluble flux, I once used some that claimed I didn't need to remove the old flux after solder ( from a known brand ). This was on an analog board. Nothing worked right until I soaked and rinsed the board several times. For most digital, a small leakage is not an issue. For most analog, as seen recently it one of the board I helped fix on the MB, a tiny leakage makes a difference for a 555 reset circuit. Know your flux!
    I've used solder wick in some cases. Use with care. it takes a hotter iron than you'd normally use on a regular lead. Make sure to bend it so it doesn't touch traces the don't have solder mask that you are not working on. I've seen too many ripped traces. It can be used well but it has its problems as well. With a large hot iron, it is good at removing solder from power plane joints. I have some in my tool box but prefer the pull-it type.
    I generally don't like to use combined iron and sucking systems. You can't see how much you are bending the lead under the round end. They also are harder to keep clean unless you are moving fast. An oxidized tip is a real hazard. Many will turn up the temperature to compensate. When it does finally make thermal contact, it will often damage the bond between the board and the trace. Learn how much heat is needed for each joint use a tiny amount of fresh solder or a little flux to make first contact. On really old oxidized solder, always remove and replace with fresh.
    Good luck
    Dwight
    Last edited by Dwight Elvey; May 3rd, 2020 at 08:31 AM.

  3. #13
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    Anyone use CHIPQUICK?

  4. #14
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    Philadelphia,PA area
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    Kester 186 is your friend! You can get it through Amazon.

    Tom

  5. #15

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    Quote Originally Posted by ibmapc View Post
    Anyone use CHIPQUICK?
    I've used it once. A friend gave me a small piece. It seems to work but I'm not all that sure what the potential of things like migration are. Metals are funny. It did seem to work. Once the solder was diluted, I could just warm it with a heat gun, much less than an iron's heat.
    I've seen what high tin on copper does over time. It is not pretty. These low temperature alloys may not have any long term issues but I'd love to see what effect it has on boards that are 30 years old. One should clean it good and dilute with regular solder, in my thinking. I guess I'll never know, as I doubt I'll be able to wait that long.
    Dwight

  6. #16
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    I use Cerrobend 158, powdered, which is again, a low-temp alloy. I pack it around the device and then use a 150W PAR spotlight in the area to be desoldered. After the device is removed, I use a toothbrush to clean the excess solder+alloy off before resoldering. I've used it only for SMT, but it hasn't failed in about 10 years.

    I do a fair amount of nonferrous metal work and the Cerrobend makes a great filler when bending thinwall tubing. Much easier to work with than pitch.

  7. #17

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    I tend to side with Dwight on this. Don't like the idea of corrupting my solder alloy, even slightly. Not like removing parts with a good vacuum desoldering pump or hot air tool is hard

  8. #18
    Join Date
    Jan 2014
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    Western North Carolina, USA
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    For through-hole parts, here lately I've been using a vacuum desolder gun first, then using those cool little stainless steel hollow pins to completely disconnect the component lead from the plated-through hole. In a pinch I've found that that 45W desoldering iron RadioShack sold years ago (I have three, and a dozen or so replacement tips; Weller made a very similar device that probably works better, but I use what I have on-hand) works almost as well as the commercial vacuum gun, and even the little teflon nozzle desolder bulb RS sold in their cheap kits works well enough to get the majority of the solder. I never have been able to get the 'soldapult' style solder-suckers to work well for me, just never learned the right technique I guess. The little stainless steel hollow pins ( youtube video https://www.youtube.com/watch?v=NlkebIBpw80 ) work a treat, especially on re-cap jobs, and they're cheap enough to have several sets available for use. Those re-cap jobs tend to be difficult since the negative lead is typically connected to the ground plane, which is a really good heatsink.

    A representative eBay link:
    https://www.ebay.com/itm/10-Kinds-St...sAAOSwkcBa3vb6

    The ones I've used:
    https://www.ebay.com/itm/8pcs-Stainl...4AAOSw5kBbOGsm

    I've not done enough SMD yet to intelligently comment about anything that works 'best' for me, as I'm still experimenting with those techniques.
    Last edited by lowen; May 4th, 2020 at 06:33 AM.
    --
    Thus spake Tandy Xenix System III version 3.2: "Bughlt: Sckmud Shut her down Scotty, she's sucking mud again!"

  9. #19
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    For the Soldapullt suckers, only the large ones (DS017) work. I've got various small ones from third-party sources, include a Swedish! one. None of those is worth owning. The trick to the DS017 is keeping it clean (clear out old solder) and keeping it greased. I've had mine for 30 years and it still works well.

  10. #20
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    Oct 2016
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    Quote Originally Posted by Gary C View Post
    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.
    Plumbers flux is acid based and not good for PC boards. If you have real stubborn solder and a chip doesn't want to desolder without a lot of heat, even after adding 60-40 solder, you can try adding some low temperature melt (tin bismuth based) solder to the pins. Expensive so use only if needed.
    Crazy old guy with a basement full of Pentium 1 laptops and parts

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