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Dms12444
February 12th, 2010, 04:30 PM
Category:How_To
While the principles involved in desoldering an IC 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
Soldering ICs

acenewman
May 1st, 2020, 09:08 PM
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.

Gary C
May 2nd, 2020, 05:27 AM
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.

Chuck(G)
May 2nd, 2020, 07:44 AM
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.

Gary C
May 2nd, 2020, 10:26 AM
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.

Chuck(G)
May 2nd, 2020, 11:28 AM
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.

maxtherabbit
May 2nd, 2020, 12:30 PM
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

Chuck(G)
May 2nd, 2020, 02:18 PM
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.

maxtherabbit
May 2nd, 2020, 02:55 PM
exposure to chimney fires!

Gary C
May 2nd, 2020, 03:25 PM
I will just keep sniffing then :)

bladamson
May 3rd, 2020, 06:47 AM
I love the smell of soldering. It brings back recollections of happier times. I guess if it gives me cancer someday, that's alright.

Dwight Elvey
May 3rd, 2020, 08:26 AM
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

ibmapc
May 3rd, 2020, 06:39 PM
Anyone use CHIPQUICK? (https://www.chipquik.com/store/index.php?cPath=200_210)

hornbetw
May 3rd, 2020, 06:57 PM
Kester 186 is your friend! You can get it through Amazon.

Tom

Dwight Elvey
May 3rd, 2020, 09:51 PM
Anyone use CHIPQUICK? (https://www.chipquik.com/store/index.php?cPath=200_210)

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

Chuck(G)
May 3rd, 2020, 10:58 PM
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.

maxtherabbit
May 4th, 2020, 05:09 AM
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

lowen
May 4th, 2020, 06:08 AM
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-Stainless-Steel-Needle-Set-Through-Hole-Desoldering-Welding-0-7-1-3mm/232745078300?hash=item3630b00e1c:g:~XsAAOSwkcBa3vb 6

The ones I've used:
https://www.ebay.com/itm/8pcs-Stainless-Steel-Hollow-Needles-Desoldering-Tool-Core-Desoldering-HVXI/383370852013?hash=item5942aef6ad:g:ts4AAOSw5kBbOGs m

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.

Chuck(G)
May 4th, 2020, 08:31 AM
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.

DeltaDon
May 30th, 2020, 04:54 PM
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.

Chuck(G)
May 30th, 2020, 05:44 PM
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.

Gary C
June 20th, 2020, 08:13 PM
Stuff I have been using is acid free and hasn't corroded anything (yet !) but it does get everywhere

Dwight Elvey
June 20th, 2020, 09:23 PM
The most important thing is that it is non-conductive. Even slight conductivity can cause problems over years.
Dwight

vldmrrr
July 7th, 2020, 08:01 PM
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.

61879

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.

61880

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.

Dwight Elvey
July 7th, 2020, 10:04 PM
This is a great idea. Fantastic idea.
Dwight

maxtherabbit
July 8th, 2020, 05:34 AM
that's brilliant

Chuck(G)
July 8th, 2020, 05:56 AM
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?

Agent Orange
July 8th, 2020, 06:51 AM
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.

vldmrrr
July 8th, 2020, 07:05 AM
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.