Desoldering Chips Safely

Is there a way to de-solder RAM chips safely from a circuit board (DIP 28 package), and clean the legs so they can then be used in a socket?

Every time I desolder, either the chips become dead, or the legs have solder on them that get stuck, and then can't be used in sockets.

De-soldering chips safely is a long lost art... Took me years to master as a service tech at Commodore Computers, especially boards with Multiple layers of copper clad. The more layers, the tighter the holes are (less flexible), but sure...I'll share some golden rules I've learned over the years:

1) Have a good de-soldering pump, with a nice clean head. A desoldering hand pump will do just fine.

2) Fill up on solder before you de-solder (yes, solder the pads that already have solder on them), this is because you want to have as much solder as you can in order to get a good distribution of the heat when its time to desolder.

Here is how you actually do it:

3) After re-soldering the pads, make sure your soldering tip is super clean, and give it some extra solder just to make it easy to connect with the pads.

4) Operate quickly, but firmly. Tilt the soldering iron about 45-60 degrees away from the solder pads, and press gently into the pads (not too hard, or you'll destroy the pads and pcb).

5) Wait for it...after it starts to melt, wait a few seconds extra for the solder to heat up around the entire chip-leg and trough hole...

6) Now, have a flat-head screwdriver handy, gently push back and forth the chip leg still in the through hole... until you can hear it snap off, or feel lose enough to wiggle until you center it in the hole. Centering is important.

7) Now..super quickly switch to the solder pump (have it pump ready ahead so you don't waste precious time), FIRMLY press it over the ENTIRE hole/chipleg. and Suck-release! You can almost feel the flow of solder coming off if you do it right. It's this FEEL you must work towards.


If unsuccessful, there are still hope - that you did a fairly decent job, just grab that flathead screwdriver again, and gently but firmly wiggle the chip-pin back and forth until you hear a nice snapping sound (which means it's free from the pcb, and through hole.)

Repeat for all the other pins. It's difficult, takes training and patience, don't expect to become a natural at this the first few days. It WILL frustrate you, but patience and training is your friend.


Now, for cleaning the pins after desoldering, just add some extra solder on it with the soldering iron, and kind of like "paint" the solder on it, and scrape it off quickly with your soldering iron. The trick is a smooth surface. Just use some smooth head pliers to straighten the pins, And it should be perfectly socketable.

PS. Don't use those tight holed sockets, use the ones that have a flexible feather like socket.

Good luck

Ok, thank you, I will try this, and hopefully this turns out well.

If you intend to do a 'lot' of ICs then investing in a desoldering head (shaped to heat all the IC pins at once) is by far the easiest and quickest way. You might want to try making your own if you have any experience with 'metal bending'.

If the circuit board isn't being reused use the old blow torch and BE QUICK!

I tend to 'chisel' at a very shallow angle by placing the flathead and giving it a light tap, but the idea is still the same: you're not always going to have a chip suddenly jump off the board with a pump and iron. Note also, we're not talking about arse loads of remaining solder in the hole here. the joint should look clean and it should be obvious that there's only that last little bit of wetting remaining.

Another hint to success is pass on pins that don't go nicely the first time and go back to them at the end instead of fiddling.

As mentioned, a hot clean iron tip is key. If you intend to salvage both the board and the IC then patience will pay off. Don't look at it as a ten minute job, Allow the iron to come up and clean the tip between pin operations.

I prefer to do this mechanically with a small flat file although it strips the (tin?) plating from the legs.

The only thing I disagree with is socket type. I personally prefer machined sockets whenever possible to use them. Wiper types seem to be all over the board for quality these days.

I either use wick, or hot air if im at work and there isnt too many pins

To clean the leads I put rosin on them, and hit them with the iron, wiping on a sponge between.. that usually takes most excess solder off, and makes it nice and uniform. Could hit it with wick if it won't come for some reason...

These are 28-pin DIPs, but luckily I just sourced some NOS chips, so keeping the originals intact is no longer required (but would be nice to do though.)

Also, I will be removing the 68000 CPU too, now THAT sucker is going to take a long time..

"chip quick" ... this will create a low melting temp alloy with the solder .
it isn't just about the max temp applied to the chip via the leg or body ... it is about temperature and time .

i have removed 48+ leg dip ICs with the stuff ... no lead straightening needed (unless they are kinked at the tips on the soldered side) .
use a decent iron , a couple of nylon "prybars" (you don't want to scratch the top mask/traces) .
melt the "chip quick" with the iron as you feed it to all the leads ... don't worry about being too neat ... make a "trailing blob" .
it is essential to keep the temp at just the melting point ... this will allow the alloy to penetrate the solder down through the board .
ya just keep walking/sliding the around and around the IC .
the speed at which you move will determine the temp (along with the setting of the iron , i cranked mine up) ... after a bit , slow down the speed and let the temp come up .
then you are ready for the extraction ...

use the two nylon pry bars to lift the IC from the board as evenly as possible .
clean up the leads with solder wick .
the old chip quick can be sucked/blobbed up easily and saved for re-use .
the whole application/alloying operation should not take more than about 30 seconds for the types of ICs i described above .

practice makes perfect .
i made several tools for chip removal ... these were mostly simple levers with different angled/length heads .
remember that static is a killer ... always use the proper anti-static precautions .
oh yeah ... the stuff acts differently than solder , it is like slightly viscous mercury when melted ... this will change as the alloy gets more tin and lead into it (re-use) .

@ joOngle ...
did you ever repair those dedicated arcade game boards (say the "street fighter" series from the 80s-90s) ?
uuuggghhh !

You dont say ... Many a time i wanted to they used to packup so quicky, had several that would last only a few days, then be back for the same problem..

Although I personally used to do the Video system repairs, Tv board, (Heavy board and we nicknamed it)

However there most of the times, when a chip had to come out it was because it was now dead, So we just clipped the legs off the chip, and removed them one by one, clean and easy...

BTW did you know about the Bug in PacMan .. You could get the ghosts to follow each other in circles in the bottom right corner.. Came across a PacMan once in a corner Cafe, with no one attending to it but the game was in play... Personally i've never been able to get it into that state, (came close once with three in the loop for a while)..

https://www.google.com/doodles/30th-anniversary-of-pac-man

At work, we have a vacuum desoldering iron, so I don't have to worry about it. Put the hollow tip over the pad, wait a few seconds, press the "suck" button, and move on to the next...

If you don't necessarily need the board intact, fire works wonders. With some discipline, you can play a torch over the board, slowly and gently enough to avoid burning traces off, then use a screwdriver or pliers to remove individual parts, or firmly rap the board to shake loose the entire heated area.

Tim

The fastest and quickest way is to place the board over a gas burner and pull on the chip with a chip-puller.
Hold the board with one hand and pull on the chip with the other. The chip comes away in a few seconds and it is not over-heated at all.

Yes, not Streetfighter per see, but many MANY others. They were mostly all dedicated, albeit you could find some "bootleg" versions that had eg. Galaxians on a Pac-Man board etc...

The amount of wire wrap wires I've used on those boards... uuughhh indeed.

@Tim, yep...have one of those "suck-o-matic" de-soldering machines myself. It's an Ersa Vac 5000, some German product I think, works a treat. Heck...I even have an Automatic SOLDERING machine as well...feeding solder via an extra tube that follows the tip. That one is fairly rare though, Weller - even!

I need to save the board I'm taking the chips from too.

Removing DIPs on double sided boards (soldered both sides) drives me insane!!!!

Sometimes I try to cut the chip off and remove the pins one by one if I can't get it loose enough to start levering the ends with a screwdriver.

Removing a 68000 sounds like hard work.

Removed the first 28pin ram chip. The chip is dead, traces on the board were damaged.

Basically I couldn't get the chip out, and then overheated it trying. Then the solder pads popped off the board.

Argh! I'm afraid now to work on the CPU.

one more time ...
"chip quick" .

Extremely easy job...

I just bought some Chip Quik and its F-ing amazing.
Chemtronics desoldering wick is also incredible (half the brands out there do absolutely nothing, I pitty the cheap bastards who haven't used chemtronics).

But chip quick says it's for SMD. These aren't SMD.

PS: Got the 68000 removed. That was actually FAR easier to do oddly. Just took longer.

The traces weren't as bad as I thought, still worked and the solder pads that fell off were NC.

Put sockets on, replaced the chips with my stock, and the system still boots up.

Anyway, progress so far.

http://img.photobucket.com/albums/v395/Evi...on/IMG_1510.jpg

The chips removed, are the ones that are now on sockets.

This Chip Quick, I'm going to be looking it up if it'll work on DIP.

I hadn't realised sega used a 68k. I presume you swapped in the CERDIP..?

Yes, I installed that. I also installed the fast 10ns SRAM. Sega used 120ns PSRAM.

"for smds only ..." ?
naaaa ...
if that were the case then something i have used successfully for over 20 years to remove all manner of dips , 150+ lead "postage stamp" ics , etc ... on all types of boards : multilayer , plated through hole , double sided , etc ...
has all been a figment of my imagination .

@ mike :
heh ... the other tech at a shop i worked for said pretty much the same thing .
he had never seen a successful extraction and transplant of a bad controller/processor postage stamp ic in a certain brand of vcr that was known for failure of that ic .
a replacement board was on the order of 125 bucks ... the ic was available for 27 bucks .

then there was a proprietary controller board for the automation at an FM station ... plated through holes .
the replacement had a price tag of 1200 bucks and a one week lead time ... unacceptable .
i ordered up the parts , shipped in overnight (the cost was around 55 bucks as i recall) , pulled the old parts and replaced them ... the owner and GM of the station were watching me .
(i will admit it made me a bit nervous)
i installed the board , fired up the machine , and after a few set-up items it worked perfectly .
that one earned me a bonus of a steak dinner .

Yup, 68k main processor, and a Z80 running the sound chip. Between those and the blitter (2D graphics), they did pretty well!

The best the IBM-PC did was something like Commander Keen. The 8086 processor is roughly contemporary with the 68k, but the EGA/VGA graphics adapter wasn't nearly as advanced, severely limiting graphical features... plus, computers didn't come with any kind of sound function beyond the PC speaker for years.

Tim

Just had to make a minor correction. The Genesis doesn't have a blitter.