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How to desolder DRAMs from a large PCB?

Krille

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I was "dumpster diving" in the e-waste bin at work some time ago and I found a large board made by ABB (in -94 judging by the date codes on various components). The board itself is not that interesting to me but it's got quite a few 1 MBIT DRAM chips that I think would be nice to salvage.

Today I made a rather pathetic attempt to desolder the chips and quickly realized that I'm either using the wrong tools or the wrong technique - probably both as I'm a complete n00b at (de)soldering stuff.

So, how would you guys go about this?

Pictures of the board here.
 

GiGaBiTe

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I'd use a desoldering gun, like the Hakko FR-301 or its Chinese equivalent, the ZD-985 or ZD-915 if you're on a budget.

Desoldering wick can also work, but it takes a lot longer and is more prone to damaging the chips from heat. I wouldn't recommend using a spring loaded desoldering pen because the force can rip traces off the PCB.
 

tipc

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Someone posted on a thread where they mounted half of a piece of copper (or brass) pipe to the end of a conventional iron, of a suitable diameter that would span the pins of an ic. You heat up the iron-pipe sufficiently and apply it to the bottom of the board, providing ample cooling on the chip side. You also have to have a simpler chip extractor in place, ready to go when it's no longer being held to the board.
 

bladamson

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I've never been able to get those desoldering suction plunger doodads to work worth a hoot, and solder wick takes too much heat and doesn't get enough solder out for my taste (still breaks pins sometimes when you start prying).

I use the aforementioned FR-301. It's a really great tool (far far far far better than the Chinesium desoldering station that it replaced), but rather pricey. Probably costs more than the RAM is worth.

However..... Here's what I used to do back in high school and college, to salvage ICs from boards, as long as it's for *salvage* rather than repair......

Grab the IC with a pair of channel locks on the ends, such that you're not holding onto any of the pins, and hold the board up at an angle with the component side up-ish. Heat all the pins at once with a propane torch and give the board a shake so it drops off the IC. Yeah, you read that right. Be careful not to over-cook. Garnish with parsley and serve with a dark lager. It's tricksy, but probably costs a good bit less than the FR-301.

Alternately, if you have some kind of big flat griddle, the way the skeevy Chinese electronics salvage operations work is they put the whole board on top of a hot griddle, solder side down. Wait for board to heat up and all the solder to melt. Grab board with pliers, turn over, and rap against the concrete. All the ICs should fall out. I 'spect it's difficult to control the amount of heat using this method, though, which may be why such operations have such a bad reputation.
 

kc8eyt

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I'd use a desoldering gun, like the Hakko FR-301 or its Chinese equivalent, the ZD-985 or ZD-915 if you're on a budget.

Desoldering wick can also work, but it takes a lot longer and is more prone to damaging the chips from heat. I wouldn't recommend using a spring loaded desoldering pen because the force can rip traces off the PCB.

I have the Hakko FR-301 and ZD-915. If you go this route spend the extra for the Hakko. The ZD-915 is a nightmare to use. I chose it first because it was cheap. You get what you pay for.

The Hakko will have those chips removed for you in no time. I use mine to pull dead Dallas chips ... works like a charm.
 

GiGaBiTe

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I never said the ZD-985 or ZD-915 were perfect, but they do the job they were intended for. I've had the ZD-985 for several years and it does require periodic maintenance. Cleaning the gun isn't terrible, but the vacuum pump does need to be internally cleaned from time to time as the reed valves foul up with solder flux, even with two felt filters.
 

Chuck(G)

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So long as the board itself is sacrificial, I use a hot air gun applied to the solder side of the inverted board, then bang the board over a 5 gallon pail. Most iCs just fall out. Clean them up later. Do it outdoors, as the stank from the PCB is pervasive. I've also heard of folks using an electric skillet filled with peanut oil to heat the board.

If you were in China, you'd be using a charcoal brazier, pulling the components out with a pair of long-nosed pliers. Then sell the pulls to the local internet parts-flogger for cleanup and relabeling.

Old-school crudeness at its utmost.
 

kc8eyt

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I never said the ZD-985 or ZD-915 were perfect, but they do the job they were intended for. I've had the ZD-985 for several years and it does require periodic maintenance. Cleaning the gun isn't terrible, but the vacuum pump does need to be internally cleaned from time to time as the reed valves foul up with solder flux, even with two felt filters.

Sorry, didn't mean to insinuate that, I was just offering my experience between the devices if the OP chose to go the desolder tool route.

As you said, the ZD-915 requires cleaning too often and the suction is a lot less than you would think from such a large unit. Too often I have to apply more solder to remove solder using the 915, resulting in even more cleaning sessions. I rarely have to do that with the Hakko.
 

gekaufman

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So long as the board itself is sacrificial, I use a hot air gun applied to the solder side of the inverted board, then bang the board over a 5 gallon pail. Most iCs just fall out. Clean them up later. Do it outdoors, as the stank from the PCB is pervasive...

Back in the 1970's I built up many systems using ram and ttl parts that I recovered using a pliers and a propane torch. Ironically I don't think I ever had a chip failure, even with a rather crude technique. Not elegant, but if you don't have a hot air gun it does work. Also Harbor Freight has a fairly inexpensive hot air gun that is nice.
 

GiGaBiTe

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Too often I have to apply more solder to remove solder using the 915, resulting in even more cleaning sessions. I rarely have to do that with the Hakko.

This happens because the nozzle doesn't have enough thermal mass. The way I get around it is to touch my soldering iron to the tip to double up on the heating and thermal mass, which will make quick work of stubborn solder joints. Having enough flux helps too, old crusty solder doesn't like melting well.

On PCBs with massive power or ground planes like ATX power supplies, I'll get out my Hakko 551. It cuts through huge blobs of solder like a knife through butter. Gotta be careful with it though so you don't burn the board, it gets up to about 1200 degrees.
 

Chuck(G)

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Back in the 1970's I built up many systems using ram and ttl parts that I recovered using a pliers and a propane torch. Ironically I don't think I ever had a chip failure, even with a rather crude technique. Not elegant, but if you don't have a hot air gun it does work. Also Harbor Freight has a fairly inexpensive hot air gun that is nice.

Yup, done that one too. The hot air gun makes for less smoke.
 

Krille

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What tools are you using?

I have a "dibotech soldering station pro 60" and used a solder sucker and also tried with some solder wick. I gave up after trying to remove just two of the chips in the corner of the board (the result should be visible on the image with the solder side of the board).

So long as the board itself is sacrificial, I use a hot air gun applied to the solder side of the inverted board, then bang the board over a 5 gallon pail. Most iCs just fall out. Clean them up later. Do it outdoors, as the stank from the PCB is pervasive.

This seems to be the easiest and cheapest option so, hot air gun it is then! :D

Thanks to everyone for the input and advice!
 

Dwight Elvey

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Years ago, I helped a friend using peanut oil. It was relatively easy. You do want to wear a face shield, thick gloves and a bib of some kind. Do make the electric skillet so no one would want to use it for food. He scratched a skull and cross bones in it. The lead from the solder will contaminate it. You never want to use it for food again.
As for removing ICs with other methods. The main trick is to get the pins free so when you extract the solder, the pin has little surface touching the inside of the via hole. Most manufactures use insertion tools. When done by hand the first thing you do is straighten the pins so it slides easily into the pin holes. You can tell if it is hand inserted or used an insertion tool by looking to see if a couple of the corner pins have been bent to hold the IC in, for later wave solder. Using an insertion tool, the pins still have outward tension and will stay in place for wave soldering.
In either case, you need to remove any outward tension on the pin or unbend the pin before doing much desoldering. To do this, first apply flux or use flux core solder and heat each pin from the bottom. Make sure the pin has heated to the IC side of the hole. Power pins on 4 or more layer boards take more time and/or heat.
When the solder is melted, push the pin inwards. The idea is to bend it just enough that it is floating in the hole and no longer up tight against the outside or inside of the hole. One can usually tell by feel. There will be some springiness with a slight push either way. Remember, with the solder melted, it doesn't take much force to bend the pin. It takes a likely practice to learn how hard to push. Do this for all of the pins so that they are all not tight against the edge of the holes. At this point, I like to go around the IC by holding it so the the pins are down and wiping the iron along each pins, long enough at each pin so that the solder will melt at the top of the board and any excess will run down to the iron. Some will stay in the hole but the thick blobs will melt and run down to the iron.
I then clamp the board in a vice ( I've been known to set it flat on a table but it is better to have the board vertical so the you are not fighting gravity when sucking the solder ). I then use a sucker ( or solder wick if that is you preference ) to remove the solder from each pin. After a first pass, I go along each pin with a small flat blade screw driver. If the hole is properly cleaned the pin will make a distinct tink sound. It is hard to describe but you'll know it when you hear it. If it doesn't tink right check the top of the board and look to see if you properly got the solder from the top. Sometimes, it there isn't too much holding the top, I'll use a pair of short needle nose to pop it loose from the top of the board by squeezing the pin towards the IC a little, with the tip of the pliers next to the board.
If a pin is found to not have been cleaned well of solder, I will add solder, just enough to close to the hole and suck it again. I find that I can then remove the IC with little effort by prying at the ends with a small screw driver. Remember you can always go back and work on an individual pin.
In doing this, remember, never use an oxidized tip. Keep it clean and properly tinned. I prefer the iron clad tips as they don't rot out as fast as the cheap copper tipped irons. The copper ones always require a lot of filing to get a nice flat surface, as the solder dissolves the copper. ( never use a file on an iron clad tip ).
Dwight
 
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Krille

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Thanks for the very detailed explanation Dwight! The pins seems to be bent slightly outward so I guess an insertion tool was used - making it a lot harder and more time consuming than I had hoped. :/
 

bladamson

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Thanks for the very detailed explanation Dwight! The pins seems to be bent slightly outward so I guess an insertion tool was used - making it a lot harder and more time consuming than I had hoped. :/

If you can put the board in a vise and use the pliers + propane torch / heat gun method, you can give it a good yank and get it out even with the bent pins.
 

Chuck(G)

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Three things: (1) invert the board and apply heat to the solder side such that most of the heat is radiated upwards. (2)I use a long small flat-blade screwdriver to get under the DIPs and pry them out if necessary while the solder is hot. Many components will simply fall out. (3) Wear gloves.

Don't bother with resistors and capacitors--they'll likely be affected by the heat. Be gentle with connectors, if you're salvaging them (usually not worth the effort).
 

Hugo Holden

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Generally the method depends on whether you want to save the IC, the board or both.

In most cases, not yours the board is of utmost importance and the IC expendable, so the method seeks to minimize pcb damage, for that, for DIL IC's, I cut the IC pin with very fine needle nose pliers close to the IC body, remove each pin one by one and clear the pcb holes with the sucker, with minimal heat stress to the pcb and its pads and tracks.

Or, the sucker method one by one to save the IC and the pcb. But, there are various quality suckers and you have to be patient, adding fresh solder and making sure after the suck that the pcb hole is clear and when you push the IC pin sideways in the hole, it breaks free and every pin has to be perfectly free before you pull on the IC, or it can damage tracks and pads.

The other method that works very well, if done correctly is a tool like this on your soldering iron:

https://www.buerklin.com/en/IC-desoldering-head/p/09L6127

Again fresh solder is added first, all the solder on all pins is heated until you are confident it has liquified, then the IC is pulled from the board.

I use similar tools to remove surface mount IC's and the tool goes over the top of the IC and all the pins heated at once (after applying a lot of solder over the the pin arrays first) then the pcb is cleaned with wick and IPA .

Another trick to remove surface mount IC's , but on a pin by pin basis, is to thread some thin enameled copper wire in the gap under the pin and the IC body, down one row of pins and tie it somewhere nearby. Pull on the other end of the wire, keeping the wire low and parallel to the pcb surface, not pulling upwards on the wire, while heating a pin, the wire lifts the pin off the pcb track, but without putting any upward pulling forces on the track, in fact it pushes the track toward the pcb, preserving the fine tracks.

The problem with blowtorches, the heat can rise very quickly to uncontrolled and unknown levels, destroying the pcb and any parts you are trying to salvage, I would never use one.
 

Agent Orange

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If I'm not saving the IC's and have no other use for them, I'm using a pair of dykes to crush them apart and taking my time heating the pins and pulling out what's left with a set of needle nose pliers.
 

Dwight Elvey

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If I'm not saving the IC's and have no other use for them, I'm using a pair of dykes to crush them apart and taking my time heating the pins and pulling out what's left with a set of needle nose pliers.

On some boards I use this method but many times, I want to keep the IC and find that if I take my time, it is not an issue. Only once when first doing it, I lifted a trace. I as for centering the pin, I get best results when centering while hot with solder. Still, sometimes, if there is a tiny touch to the side of the hole, rather then filling and recentering, I find that if I'm careful I can put the iron to the pin, without touching the board and with a side pressure have it pop loose. It is even more touchy-feelly so I didn't mention it. It also take practice. You are just getting enough heat on the pin for only the solder on the pin to soften. If not done right, fill the hole with solder and suck again. Take your time and always inspect before forcing. I've had time when done the the IC literally falls from the board.
Dwight
 
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