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Desoldering ICs

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  • vldmrrr
    replied
    Originally posted by Chuck(G) View Post
    How do you clear the holes in the PCB after the IC's been removed?
    I just use a round wooden toothpick that I sharpen a bit with razor blade. With that I poke holes from component side melting solder with regular solder iron from opposite side (board mounted vertically). Then I cut off some of excessive solder on the opposite side with fine flat clippers. This make the site ready for replacement in a short time.

    I usually put a socket with round gold-plated connectors instead of soldering replacement chip directly. Having sockets facilitates troubleshooting and later, when the board is working, it can be used for testing other questionable chips of the same kind.

    Leave a comment:


  • Agent Orange
    replied
    Originally posted by Chuck(G) View Post
    There used to be U-channel shaped adapters for irons that did a similar thing.

    How do you clear the holes in the PCB after the IC's been removed?
    Once up on a time I used to use a Dremel with a very very fine bit. Not kosher for some, but worked fine for me in some instances. My Pace station was known wreak havoc on cheaper PCB's eyelets even while attempting to be very careful.

    Leave a comment:


  • Chuck(G)
    replied
    There used to be U-channel shaped adapters for irons that did a similar thing.

    How do you clear the holes in the PCB after the IC's been removed?

    Leave a comment:


  • maxtherabbit
    replied
    that's brilliant

    Leave a comment:


  • Dwight Elvey
    replied
    This is a great idea. Fantastic idea.
    Dwight

    Leave a comment:


  • vldmrrr
    replied
    Copper pipe desoldering tool

    Here is a homemade tool that I've used for removing through hole DIP parts up to 40 pins.

    I've cut a piece of 3/4" copper pipe to the length of the part to be de-soldered. Then I cut the pipe lengthwise with hack saw. For wider parts I made a second cut removing a segment of copper, but depending on density of board, the pipe with a single cut probably can be just bent to create sufficient opening. Then I heat the pipe with butane torch and covered the edge with solder. Here is a picture of three different sizes.

    pipes.jpg

    The tool works by fitting it tight over pins and heating the top with small butane torch. The heat is transferred to the pins melting solder around them. At that stage the part can be lifted with flat forceps, for longer part lift one side first, move the forceps deeper under the part and lift the whole. After lifting I quickly remove the pipe from the part. Here is a staged photo of two pipes fitted over the board - for illustration, not a real rework.

    board.jpg

    I used these on several occasions, not too often yet to develop a good skill, so I am still quite nervous during operation, but results were all good thus far. For example, I removed Z80 CPU and few other similar sized chips, and I later re-installed them on sockets into the same board, and it worked well. On couple of boards I removed a complete set of DRAM chips to find bad ones and returned good ones back into newly installed sockets. Never damaged a single trace yet.
    Last edited by vldmrrr; July 7, 2020, 08:28 PM.

    Leave a comment:


  • Dwight Elvey
    replied
    The most important thing is that it is non-conductive. Even slight conductivity can cause problems over years.
    Dwight

    Leave a comment:


  • Gary C
    replied
    Stuff I have been using is acid free and hasn't corroded anything (yet !) but it does get everywhere

    Leave a comment:


  • Chuck(G)
    replied
    Better to just clean the board well. Solder doesn't stick to oxidized/corroded copper.

    Plumber's flux is mostly ammonium chloride which, when heated tends to get everywhere you don't want it to be, leading to corrosion in unexpected places.

    Leave a comment:


  • DeltaDon
    replied
    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.

    Leave a comment:


  • Chuck(G)
    replied
    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.

    Leave a comment:


  • lowen
    replied
    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 4, 2020, 06:33 AM.

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  • maxtherabbit
    replied
    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

    Leave a comment:


  • Chuck(G)
    replied
    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.

    Leave a comment:


  • Dwight Elvey
    replied
    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

    Leave a comment:

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