EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Rob Lo on August 01, 2016, 03:33:36 pm
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Hi, I am relatively new to DIY and soldering as well. Long story short I purchased a set of pcb's from a synth based DIY site. The board which is the control surface for the synth was already populated.
I soon realized my error in buying the board because the LED's were soldered too low and sit too recessed when the face panel is attached.
So I have to desolder roughly 80 LED's and some diodes.
I've done two rows so far with a desoldering braid and some liquid flux pen as I don't have a desoldering gun and/or a solder sucker, and I didn't want to buy a hot air gun for this purpose only (even though eventually I will). I am a bit worried about doing it this way and I'm not sure if I am damaging the pads or not. I've attached some close up of the rows done so far. Am I killing the board? Also, the parts do not need to be reused. I will be installing all new LED's
Any help is appreciated
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Also, not sure how bad this is...but i thought it was just flux but apparently I delaminated the board..and killed a trace? This is the botyom.
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lots of heat for a short time on braid, use a large tip as if you can't get the heat in fast enough you will be sitting there waiting for it to heat and just burn it up mean time.
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If you're not going to re-use the LEDs, I would cut them off, desoldering the lead ends when they're separated from each other should be much easier.
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Yea that's what I did, cut the leads from the top them use the braid on the bottom. Then heat the leads on bottom til they wiggle and pull them with tweezers or just push with the iron til they fall out the bottom.
In the second post is it possible to see if I burned the trace?
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The pads do look a bit mashed up.
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In my experience, desoldering with solder-wick will almost inevitably ruin the board. Pads will lift, vias (through-hole plating) will be damaged, etc.
A few years back I bought a Hakko 808 desoldering tool and it is magnificent for working on through-hole components. Unfortunately, it has been discontinued and replaced by something else. Like:
http://www.testequipmentdepot.com/hakko/desoldering-irons/desoldering-iron-kit-fr300-05p.htm (http://www.testequipmentdepot.com/hakko/desoldering-irons/desoldering-iron-kit-fr300-05p.htm)
I know, it's terribly expensive and I don't believe I paid anything like that for my 808 but if saving the board is important, using the right tool makes a lot of sense.
You're in and off the pad in a couple of seconds and wiggling the tip side to side guarantees the component won't still be soldered to the edges of the via.
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Yea that's what I did, cut the leads from the top
In that case I'd be just heating the lead from top or bottom and then tapping the board on the edge of the desk so that the lead and most of it's solder drops through. You have to do it so that the straight part of the lead is to drop through the hole and not the bent end. Of course this is a very messy but quick way.
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I have done a lot of desoldering with solder wick. It is certainly possible to damage boards with solder wick, but I don't find it inevitable.
I don't see any real problems with your board. This won't be suitable for high reliability (space, medical, aerospace) applications, but I don't doubt that it will function and last for years for you. There is a solder splash that should be cleaned up in your follow up photo. A touch of the iron, or just mechanical removal with an exacto knife or equivelant will do it quickly. It is possible that the trace underneath is damaged, but from the photo it doesn't seem likely.
The heat and tap method is good. If you have access to compressed air, heating and blowing out the solder also works well. Don't wear shorts when using either of these techniques, and evaluate your own position on lead safety. Some would find this hazardous to you and the environment. Is not a concern to me.
When desoldering it is easy to overlook keeping the iron tip clean and tinned. It really helps on heat transfer, which then reduces the time heat is applied and reduces the chances of board damage.
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but heat it enough, it could be that the braid is soldering to the pads and the pads are being pulled with the braid, lots of heat, fast, in and out!
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I have a much better result using the solder wick using a higher temperature and a larger tip.
Shorter time applying heat helps a lot.
Also run the wick in rosin solder flux beforehand.
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I've been using a 3.2 chisel tip. The temp I've been careful to not go over 600f (about) because I have no reliable way to test my iron temp and I'm using a hakko clone (936b).
Thanks so much for the input everybody.
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I find that desoldering wick (braid) is almost useless without applying a little flux to the wick braid first. I put a little flux paste on my fingers and rub it up the wick. Once the wick is fluxed, get in and out, and with a hot enough iron, you will see a large amount of solder get sucked all the way up the wick, sometimes up to 1" up the wick... Properly fluxed and with a hot iron, solder wick can definitely be used without damaging the board.
It's impossible to judge if you are destroying the board with the flux not cleaned off. With the flux still on the board, it looks pretty bad.. but with the flux cleaned off, it might still be in perfect condition. It's just hard to tell.
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I don't go by the temperature, I go by how quick the solder joint melts. In your top picture where the lead ends are still showing I would expect that to be fully molten in 1 to 1.5 secs, especially if the length of remaining lead on the other side is very short, another 1 sec to allow the heat to travel through the hole to the other side, and tap it quick.
Don't forget, you only need to have the holes clean enough to be able to get the new LED's leads through the holes, a bit of solder still left around the hole won't matter when you come re-solder them.
Yes, you've got to keep the tip clean and tinned so it makes a good quick thermal contact with the joint.
What you've done so far looks fine to me, I could do worse than that and I've been desoldering since about 8.
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I've been taking breaks doing this because it's been a nightmare.
I've gotten about 85% of it done. Basically I've used wick and tacky flux to suck the solder then pull the lead out of the top side with tweezers.
The issue i have now is there are a handful holes that have become blocked with solder and im unable to push leads for the new component through. It's near impossible to get the wick on it.
Anybody have anytips?
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The issue i have now is there are a handful holes that have become blocked with solder
a mechanical spring loaded solder sucker is cheap and quite effective for clearing holes,
https://www.google.com.au/search?q=solder+sucker&newwindow=1&source=lnms&tbm=isch&sa=X&biw=1118&bih=749 (https://www.google.com.au/search?q=solder+sucker&newwindow=1&source=lnms&tbm=isch&sa=X&biw=1118&bih=749)
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The issue i have now is there are a handful holes that have become blocked with solder
a mechanical spring loaded solder sucker is cheap and quite effective for clearing holes,
https://www.google.com.au/search?q=solder+sucker&newwindow=1&source=lnms&tbm=isch&sa=X&biw=1118&bih=749 (https://www.google.com.au/search?q=solder+sucker&newwindow=1&source=lnms&tbm=isch&sa=X&biw=1118&bih=749)
+1
I've got one the same as the 2nd one top row, a MUST HAVE item for soldering/desoldering.
You can stick your braid, I rarely if ever need to use it.
OP, get yourself some old PCB's, anything at all, practice salvaging components and replacing them, all invaluable skills.
That said, most construction these days is with lead free solders that require higher temps and as a consequence PCB's can be easier to damage for the unwary. When the Pb free muck is encountered first dilute it with some leaded solder to reduce the melting temp, suck off excess, rinse and repeat and solder and components will be easy to remove.
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The issue i have now is there are a handful holes that have become blocked with solder and im unable to push leads for the new component through. It's near impossible to get the wick on it.
You simply put the iron on the hole and then add a bit of new solder to the iron/joint, when your new solder flows into the hole tap it or suck it out.
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You don't need solder wick at all for this. Just pull the leads out with pliers, and reopen the holes with a toothpick (in both cases while applying the soldering iron).
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no need braid no need flux, just a normal tip iron at the right angle with the right hand at right temperature to melt both lead, left hand to pull the led hard from another side. LEDs can be reused for other purpose, no need cutting leads.
The issue i have now is there are a handful holes that have become blocked with solder and im unable to push leads for the new component through. It's near impossible to get the wick on it.
same method as above except pushing new LED to holes while both holes solder melted, you need to add solder on recessed dried solder so iron tip will reach it while doing acute angle solder. you are getting me? good!
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What's wrong with plain generic solder sucker? Set your iron to about 220-250c, lay the tip almost flat on the pcb, touch both leads of the led with the iron, when the solder melts put the solder sucker over the lead/iron tip and suck solder.
Or just heat both leads of leds and let them fall down from the board (tap the pcb gently if needed to make the led fall off), then you could use solder wick to clean but i personally don't like wasting wick for this.. solder sucker is good enough for this.
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no need braid no need flux, just a normal tip iron at the right angle with the right hand at right temperature to melt both lead, left hand to pull the led hard from another side. LEDs can be reused for other purpose, no need cutting leads.
The issue i have now is there are a handful holes that have become blocked with solder and im unable to push leads for the new component through. It's near impossible to get the wick on it.
same method as above except pushing new LED to holes while both holes solder melted, you need to add solder on recessed dried solder so iron tip will reach it while doing acute angle solder. you are getting me? good!
+1 with this.
I would not use solder wick for these diodes. Just a plain tip large enough to heat both leads at the same time.
Do not bother to remove the solder.
Put the board vertically, and heat the solder on one side, put the led on the other side starting with the long lead.
This will help you to position more precisely the second lead so it is in the hole.
Heat both holes at the same time.
Add a little bit of solder if needed, to help to melt the solder that is in the holes.
This should work without any problem.
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Or just heat both leads of leds and let them fall down from the board (tap the pcb gently if needed to make the led fall off).
those led wont fall off easily as the OP tried to mimick professionally made mass produced units by bending led's lead end at different angle before soldering them.. i had lot of fun salvaging passive components with that kind of bended leads termination, including using small tip plier or tweezer to pull them off forcefully...
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You don't need solder wick at all for this. Just pull the leads out with pliers, and reopen the holes with a toothpick (in both cases while applying the soldering iron).
I do this with a cheap flea market dental pick that I heat directly instead of the pad.
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When I need to open a hole,
I use small drill bits of the suitable diameter
http://www.electrodragon.com/product/20pcs-straight-pcb-drill-bit-variable-0-50-70-81-0mm-diameter/ (http://www.electrodragon.com/product/20pcs-straight-pcb-drill-bit-variable-0-50-70-81-0mm-diameter/)
with a small manual drill
http://www.ebay.fr/itm/272336482733?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.fr/itm/272336482733?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT)
Which I heat directly with the soldering iron. Of course, it is not good for the steel, but these bits are very cheap, and can be reserved for this kind of use. If needed, one can finish by drilling the hole a little, but need to be careful about removing the tin of the hole. For the present case, as there is a lead across, it does not matter.
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Oh deer, I don't know what to suggest. I can't say I've ever had such a problem with de-soldering LEDs, even when I was a total beginner and had a crappy old unregulated soldering iron.
Don't cut the legs off the LEDs. It will make it more difficult to remove them. There should be no need to add any more flux. If anything, add a little more solder to help it wet the contacts. Use a large enough soldering iron tip to enable you to heat both leads at the same time, then the LED should just fall out.
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I have sucked a lot of solder over the years, so all of the above posts contain good advice especially about a hot iron. I prefer a 'hoof' tip but without much recess- like the old Weller TCP1 tips.
I have a Pace desoldering iron tool but often still reach for the spring solder sucker if I can't be bothered to wait for the Pace to heat up.
I have some green anodised Radio Spares teflon-tipped suckers that go back to the 70s. They still work fine.
A while ago my friend's son wanted some advice on a his dead aircon unit, so we isolated the fault and I sent him off to buy a soldering iron and sucker. The sucker was absolutely unuseable, I think because the hole was too big, and the recoil was like a Colt 45.
We did the job with one of my RS suckers but try as I did, I could not teach him how to use it- he could not synchronise touching the iron on the lead and then pulling it away as he fired the sucker.
Practice and practice with a scrap board from the dumpster.
BT
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When I need to open a hole,
I use small drill bits of the suitable diameter
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with a small manual drill
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Which I heat directly with the soldering iron. Of course, it is not good for the steel, but these bits are very cheap, and can be reserved for this kind of use. If needed, one can finish by drilling the hole a little, but need to be careful about removing the tin of the hole. For the present case, as there is a lead across, it does not matter.
While a Pin Vise is useful for holding tools for clearing holes, I would question the use of twist drill bits for that purpose. A lightly oiled mounted steel needle is my preferred tool for clearing difficult holes as there is far less risk of damaging the copper barrel plating inside the hole. Heat whichever side has the best access and thermal contact, adding a little fresh solder if you cant get it to melt right through the hole, push the needle through, removing the iron, and wobble the needle slightly to maintain a clearance as the solder cools. As long as the needle is bright polished it will slide back out easily.
Mount needles in a 3" length of 1/4" dowel as a handle in a close fitting hole 1/3 the needle length, abrading the eye end of the needle, using a small amount of epoxy.
If you know anyone who rigs dinghies, or keelboats who can give you some offcuts of 1x19 stainless rigging wire of various diameters, unlay it to salvage the straight center strand, which can also be used to make useful mounted probes for hole cleaning and general prodding around in solder joints. Flatten the handle end of the wire by hammering it on an anvil to give the epoxy a better grip. 316 stainless wire is even less likely to stick to solder than steel needles, and is virtually impossible to snap if abused. You can even bend a hook on the end for unwrapping soldered terminal pins.
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The nice thing with drill bits is that they are well calibrated.
The other good aspect is that they are made with very hard steel that does not easily stick to solder.
It is true that one needs to be cautious, unless it is with a single side board. But an easy way to overcome that if
you wonder about the possibility to damage the plating of the hole, is to mount your drill bit in the reverse way.
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i dont recommened drill bit... it will screw hole plating and pad, it risk breaking your bit, the hassle to bring out everything on the bench etc. it can be done with simpler thing as a single soldering iron i dont see much reason why an advice of the overkill. if anything, i will advice the OP to buy a decent solder sucker, its more general purpose, drill bit is only applicable to this very specific application where you dont have anything in the hole except a dried blob.
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While a Pin Vise is useful for holding tools for clearing holes, I would question the use of twist drill bits for that purpose.
They work nicely if you know the trick. Which is: put them in the pin vise backwards. In other words, put the cutting end in the pin vise and use the smooth, non-cutting back end.
I heat one side of the board and push the smooth end of the bit through the other side. This leaves a little tube of solder that can be cut off flush.
The drill-style welding tip cleaners include a low-quality pin vise and a handy assortment of drill sizes that store in the handle.
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I use the drill trick to clear holes, or even enlarge it a bit for the component wire, but only on single-sided boards or on one-sided traces.
On double sided board, unless you insert a wire in there and make sure there is solder on both sides, you run the risk of disconnecting the top and bottom traces (if connected) from each others. You would be surprised how many board use an inner plating in a component hole (just like a via) to interconnect or are even cheaper and assume the component lead is the interconnect. On multi-layer boards (like 5 layers in motherboards) there might even be an intermediate connection that gets damaged. Only once did I come across that issue, troubleshooting a Dage tension meter controller board. The person that did the previous repair had "cleaned" the through hole well on both sides and soldered the capacitor wire on the back. However the top of the board was completely clean around the top trace. Of course the capacitor was masking the fact there was no electrical contact to the top trace.... took a while to find the issue.
Get a good sucker that is powerful enough to clean the hole clear of all solder. Before I got my Pace rework station with an active pump desolderer, I used to melt the solder in the hole with my soldering iron and then use a can of compressed "air" with a tube to give it a point blast. It would eject all the solder out the other side.
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IIRC in the days before suckers and most of the desoldering stations the "book" procedure was 1 of 2 methods:
Use a drinking straw to blow away the solder.
Rubber bulb puffers to blow away the solder.
Both still valid when caught in the field short of tools. :phew:
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I always start by ADDING fresh solder quickly to each joint. Then if is easy to use either a desoldering station (even the cheap ones from China work pretty well. See Dave's review) or solder wick. If you don't get it the first time ADD more fresh solder and do it again. Don't just try to hold the iron and wick there longer.
But get Chem Wick from Chemtronics. Most other wick is trash. Make sure you trim the wick before each desoldering. This makes it much easier than trying to use different parts on the wick.
Never pull hard on anything, wether it be pulling on a part to get it out, or trying to pull off stuck solder wick. Pulling these often pulls pads right off the board.
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So I have to desolder roughly 80 LED's and some diodes.
Here are my suggestions:
1) flux is your friend. If you don't have any, then adding *more* solder is your friend. The new solder contains flux which will help the old solder behave better. Solder tends to oxidize, and oxidized solder just doesn't behave correctly. Like it doesn't melt. Or flow. Flux fixes this, mostly.
2) Don't be afraid to add more solder. Often it's the fastest way to get the old solder out.
3) Gravity is your friend. So is a bit of tapping. Assuming you've cut the led's off the board, try heating the solder, and then tapping the board semi-gently against your work bench while the solder is hot - you'll be surprised how quickly those leads fall out of the hole, and often all of the solder comes out of the hole with it. Just be careful and wear eye protection. For something with two leads, like a LED, unless the leads are crimped/bent, often heating both leads at the same time (i.e. alternating between them) and tapping will result in the entire component falling out.
4) My experience is wick is best for cleaning up afterwards, not actually doing the desoldering. I'm spoiled in that I have a vacuum desoldering iron which sucks all the solder out. Before that, I'd almost always use gravity and/or the tapping method to get the lead out, then wick to clear out any remaining solder.
5) Beware of pad lift, and try to heat the lead/solder and not the board. If a pad gets too hot, it will unglue from the board, and will often cause a failure. Fast work is the best. If you aren't able to get a pad cleaned within a very short time, move on and come back after it's cooled.
6) If you've got a crappy iron, we'll all feel sorry for you (but not enough to buy you a inexpensive but nice iron). If you have a decent iron, try different settings: Too low, and you won't be able to work quickly enough. Too hot, and you'll destroy everything. There's a fine line in the middle.
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Another suggestion, if it's not a modern board ignore all the temperature advice. If you use high temp on an older board you're likely to burn the board. It's a lot like soldering, you use the lowest temperature you can get away with, it will take some experience because too low and you'll do nothing but too high and you'll start burning things. Know what kind of solder you're working with, lead-free is high temp, old leaded solder is low temp. Sometimes you need to adjust based on the component like having to take off.
Our shop does repairs for several hospitals and some of their equipment still uses CRTs. Those need a lot less heat or you'll burn up the board and lose the trace. I'm barely above leaded solder melting point.
A dab of ChipQuik will save you a lot of headaches but learn how to do it properly and don't use ChipQuik as a crutch because that's an expensive crutch. https://www.amazon.com/ChipQuik-SMD1-Leaded-Temperature-Removal/dp/B0019UZP7I (https://www.amazon.com/ChipQuik-SMD1-Leaded-Temperature-Removal/dp/B0019UZP7I)
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read this:
https://www.eevblog.com/forum/beginners/desoldering-bulb/ (https://www.eevblog.com/forum/beginners/desoldering-bulb/)