Post by thread:[EE][OT] Repair goes bang?

I just worked on a circuit board (the one I need the SRAM for) and had a very unusual thing happen. While soldering on the vias, and on a couple of the SRAM chips, with the board entirely removed from the system, I had several instances of what appeared to be explosions as I heated the joints. These were NOT any kind of bubbling, these were bright noisy POPs, which threw red and yellow sparks. The board has a couple of 100uF caps, and a bunch of 0.1uF, but had not been powered in months, and in any case, I was only touching the one point, no possibility of a short. The lithium coin cell had leaked over this area, which had a number of lead solder joints, and copper traces of course. I am wondering if there's a possible chemical reaction there that leads to an explosive? Never saw anything like it before. -- Feel the power of the dark side! Atmel AVR

Is your iron grounded? Is it possible that they contain high enough voltage that the iron may bring two conductors close enough to arc? I'm noticing a lot of static electricity in southeast michigan due to the cold weather - perhaps you are starting a spark which provides a path for a capacitor to discharge. I like the chemical reaction thought - lithium is a very reactive metal. Test a few caps with a multimeter. Very interesting - let us know what you find if you discover the cause. -Adam On 1/19/07, Micro Brix <spam_OUTmicrobrixTakeThisOuTgmail.com> wrote: {Quote hidden}> I just worked on a circuit board (the one I need the SRAM for) and had a > very unusual thing happen. > > While soldering on the vias, and on a couple of the SRAM chips, with the > board entirely removed from the system, I had several instances of what > appeared to be explosions as I heated the joints. These were NOT any kind > of bubbling, these were bright noisy POPs, which threw red and yellow > sparks. The board has a couple of 100uF caps, and a bunch of 0.1uF, but had > not been powered in months, and in any case, I was only touching the one > point, no possibility of a short. > > The lithium coin cell had leaked over this area, which had a number of lead > solder joints, and copper traces of course. > I am wondering if there's a possible chemical reaction there that leads to > an explosive? > > Never saw anything like it before. > > -- > Feel the power of the dark side! Atmel AVR > -

On 1/19/07, M. Adam Davis <.....stienmanKILLspam@spam@gmail.com> wrote: > > Is your iron grounded? It is, but the board was not connected to anything else, no current path. Is it possible that they contain high enough > voltage that the iron may bring two conductors close enough to arc? Not even remotely. I'm noticing a lot of static electricity in southeast michigan due to > the cold weather - perhaps you are starting a spark which provides a > path for a capacitor to discharge. No. not static, or charged capacitors. I've shorted a lot of caps, and I'd say what I saw, in each instance, looked like 1500+uF at 12V or more, and this board only has a 5V rail on it, and no caps bigger than 100uF.

> > > iirc some of the stuff in lithium batteries as pretty explosive even > without something to react with. I know people say they "explode", but I've always held that to be a boiling liquid "explosion" when the vent fails. This was a definite "BANG", which threw sparks. Happened in several places, notably where a lot of black "crud" had built up, in the vias, and between the pins near VCC on the SRAM. Some of them were address lines to the SRAM, definitely NOT where any cap would exist to store up energy.

> From: piclist-bouncesKILLspammit.edu > [.....piclist-bouncesKILLspam.....mit.edu] On Behalf Of Micro Brix > -- > Feel the power of the dark side! Atmel AVR > -- Just a quick note to point out that "Micro Brix" is David VanHorn. gmail apparently changed Daves outgoing email setup without his knowledge. ...in case anyone cares. --- James Newton: PICList webmaster/Admin EraseMEjamesnewtonspam_OUTTakeThisOuTpiclist.com 1-619-652-0593 phone http://www.piclist.com/member/JMN-EFP-786 PIC/PICList FAQ: http://www.piclist.com

> I just worked on a circuit board (the one I need the SRAM for) and had a > very unusual thing happen. > > While soldering on the vias, and on a couple of the SRAM chips, with the > board entirely removed from the system, I had several instances of what > appeared to be explosions as I heated the joints. These were NOT any kind > of bubbling, these were bright noisy POPs, which threw red and yellow > sparks. The board has a couple of 100uF caps, and a bunch of 0.1uF, but > had > not been powered in months, and in any case, I was only touching the one > point, no possibility of a short. > > The lithium coin cell had leaked over this area, which had a number of > lead > solder joints, and copper traces of course. > I am wondering if there's a possible chemical reaction there that leads to > an explosive? Sounds like you might have ignited a little bit of lithium. It melts and burns rather easily and quite violently. The low temperature burn (around 400 degrees F) is crimson red, as it burns and reacts with oxygen the flame gets hotter and turns white. Kind of like a magnesium flare. It's definitely something you don't want to ignite, you can't even put it out with water because lithium reacts with water - not as bad as sodium, but bad enough. -- Cris Wilson Information Resource Consultant College of Architecture, Arts, and Humanities Clemson University crisspam_OUTclemson.edu Report problems to: @spam@aah_computersKILLspamclemson.edu

Micro Brix <microbrix <at> gmail.com> writes: > The lithium coin cell had leaked over this area, which had a number of lead > solder joints, and copper traces of course. > I am wondering if there's a possible chemical reaction there that leads to > an explosive? This is common with boards that got lithium battery electrolyte leaked on them. I do not know what the chemical is but it goes bang from heat. Wear safety lab glasses when doing such jobs, and close all solvent bottles etc. Peter P.

>> It's definitely something you don't want to ignite, you can't >> even put it out with water because lithium reacts with >> water - not as bad as sodium, but bad enough. > > If it was Li, would humidity hydrate it over a period and make > it safe ? Pure Lithium will react with high humidity and spontaneously ignite. So the pure stuff is usually stored in oil, and held down under the oil by a weight of some kind (because lithium will float) Lithium doesn't stay pure very long, it reacts with just about everything and oxidizes in a matter of minutes to normal air exposure. Once it has reacted with air, nitrogen, oxygen, whatever it is harmless. BUT, if you heat it up (like from a soldering iron) it melts and becomes highly reactive again. Since it is an alklai metal - it definitely doesn't react well to the acidity of solder flux and will ignite when in contact with it. To remove the stuff that leaks out of Lithium batteries, I usually do repeated alcohol washes and scrub out as much of it as I can before soldering near it. And even after the washes, if I have to solder near a Lithium spill I wear glass safety glasses, welding gloves, and a long sleeve shirt. The stuff feels like molten solder when it lands on you while it's still burning. It's not likely to lit anything on fire, but you will probably drop your soldering iron in your lap and get a worse burn from that - in a place you don't really want to be burned. So the final point is, remove as much of the lithium junk from the board as possible before soldering, be ready for the popping noise and sparks, and where long sleeves. -- Cris Wilson Information Resource Consultant College of Architecture, Arts, and Humanities Clemson University KILLspamcrisKILLspamclemson.edu Report problems to: RemoveMEaah_computersTakeThisOuTclemson.edu

Do you feel somber and indifferent after it lands on you? -- Martin K Cris Wilson wrote: {Quote hidden}> And even after the washes, if I have to solder near a Lithium spill > I wear glass safety glasses, welding gloves, and a long sleeve shirt. > The stuff feels like molten solder when it lands on you while it's > still burning. It's not likely to lit anything on fire, but you > will probably drop your soldering iron in your lap and get a worse > burn from that - in a place you don't really want to be burned. > > So the final point is, remove as much of the lithium junk from > the board as possible before soldering, be ready for the popping > noise and sparks, and where long sleeves. >

If it did that I probably would solder naked around it ;-) Seriously, though, the lithium used for depression is usually in the form of lithium carbonate or lithium citrate - and you have to take it orally. I don't think I'm going to try and catch a burning/molten piece of metal on my tongue. I'm not really sure what type of lithium salt you end up with after the batteries leak onto the board. Next time I have to repair one, I'll try to remember to scrap the goop off and have it analyzed. At 10:48 AM 1/22/2007, you wrote: {Quote hidden}>Do you feel somber and indifferent after it lands on you? >-- >Martin K > >Cris Wilson wrote: > > And even after the washes, if I have to solder near a Lithium spill > > I wear glass safety glasses, welding gloves, and a long sleeve shirt. > > The stuff feels like molten solder when it lands on you while it's > > still burning. It's not likely to lit anything on fire, but you > > will probably drop your soldering iron in your lap and get a worse > > burn from that - in a place you don't really want to be burned. > > > > So the final point is, remove as much of the lithium junk from > > the board as possible before soldering, be ready for the popping > > noise and sparks, and where long sleeves. > > > >

At 11:14 AM 1/22/2007, you wrote: >I just found the whole thing interesting. After working with millions of >systems with these batteries, this is the first one I've seen where lithium >escaped from the cell. I've only seen a couple cells rupture. I suppose >this is because we were very careful with our design, not allowing any >measurable current back into the cells, and buying quality cells. The majority of the repairs I have had to do with leaking Li batteries were because someone had spilt a drink or beaker of something into the equipment. _____________________________________________________________ Cris Wilson Information Resource Consultant College of Architecture, Arts, and Humanities Clemson University spamBeGonecrisspamBeGoneclemson.edu To report problems email: TakeThisOuTaah_computersEraseMEspam_OUTclemson.edu

> > > The majority of the repairs I have had to do with leaking Li batteries > were > because someone had spilt a drink or beaker of something into the > equipment. Hmm.. We had tons of those, "guess the beverage" became a game in the repair department. But the vast majority of our battery failures were simply "dead". I only remember one coming back with a ruptured battery, and it was reported to have caused the device to partially disassemble, but they put it back together before they shipped it to us.

David VanHorn wrote: > I just found the whole thing interesting. After working with millions of > systems with these batteries, this is the first one I've seen where lithium > escaped from the cell. I've only seen a couple cells rupture. I suppose > > this is because we were very careful with our design, not allowing any > measurable current back into the cells, and > buying quality cells. > That's the key. --Bob

Just a little joke... -- Martin K Cris Wilson wrote: {Quote hidden}> If it did that I probably would solder naked around it ;-) > > Seriously, though, the lithium used for depression is usually in the form > of lithium carbonate or lithium citrate - and you have to take it orally. > I don't think I'm going to try and catch a burning/molten piece of metal > on my tongue. > > I'm not really sure what type of lithium salt you end up with after the > batteries leak onto the board. Next time I have to repair one, I'll try > to remember to scrap the goop off and have it analyzed. > > At 10:48 AM 1/22/2007, you wrote: > >> Do you feel somber and indifferent after it lands on you? >> -- >> Martin K >> >>