Magic smoke escape from atmega 32ua but still working

[redben]

Hi, I post this into the beginner section cause today I made a mistake which is making me look like a real noob.
I am working on a custom made robot controller board which is working with an Atmega 32ua.
When I jumped from one power source to another the microcontroller started to smoke.
Then I thought that I made some bad solder point but I had just inverted the polarity.
Anyway, the magic smoke came out of this puppy but I can still implement code and everything is running perfect.
My soldering is a bit crusty but there is no physical traces of damage.
My questions are :
What can be damage that i don't know anything about ?
Can the magic smoke escape without damaging the chip ?

Sorry for my poor english skills ... But this forum is far the best I know !!

[Stonent]

It is possible you burned out something that you're not using in the current project.

[c4757p]

Or nothing at all - the smoke is from the plastic, not the silicon! But don't trust it for anything high reliability. For all you know, you just shaved off all but its last five hours of lifetime.

[Simon]

the heat will have come from the protection diodes but could have done damage or weakened the chip. if it's non critical just keep going

[sync]

Is this pin still working? It looks like that the smoke escaped here.

[Simon]

doe he need it ? 

[hans]

To answer your questions in a different way..

I once made a switch mode power supply that had an enable/disable pin. I thought it was tolerant for working at the input voltage. That would be 30 Volts sir. So a wire ran happily to the enable pin. The power supply was working fine and easily supplied 3 Amps though it was getting a bit warm, even with no load attached.

After an afternoon of testing, the power supply wouldn't turn on anymore. No smoke escaped. I was puzzled. Adjusting the input voltage down to ~7V, and it came to life again. So I read the datasheet once more, and yep.. absolute max rating EN pin: -0.5V to 6.0V. So I modded a zener diode on it to put 5V on the enable pin, and it still worked after that. As it was a very early prototype, I did the remaining tests and carefully stored the board in a circular shaped archive, also called 'the thrash can'.

You probably burnt up some protection device, diode, or plastic housing of the chip. Or maybe an I/O pin of the chip is blown. In other words, if you are writing software for this chip and are getting crazy weird things and issues, I would try to get a replacement. Staring at issues for hours because of a broken component (that costs a few $) is so frustrating.
If it's still running OK and it's a struggle to get a replacement fitted, you maybe can get away with it for now.. but I still wouldn't trust it for too long.

[Zbig]

This made me think. Some time ago I've let the magic smoke out of some LCD by reversing polarity. Now I realized that I haven't really checked it afterwards but rather sort of assumed it has to be dead now. Then proceeded straight to gutting the thing thinking at least I'll get some educational value out of it. Hmm, this makes me feel little weird now...

[cloudscapes]

It is possible you burned out something that you're not using in the current project.

I did that once. Fried the micro's ADCs but as far as I could tell the rest of it worked.

[amyk]

I think the magic smoke is still inside if you didn't hear any loud pop or crack. What you saw might've been from some flux or other residue on the PCB.

[tszaboo]

I think the magic smoke is still inside if you didn't hear any loud pop or crack. What you saw might've been from some flux or other residue on the PCB.

There was this microcontroller, got 12V driven on the pin. The thing exploded, I've seen a small piece of it fly 20cm. And it was still working, although it was getting hot. The other time I fryed a hot swap controller, and it was emitting smoke slowly, every time I turned it on. It was still working.
Did I keep them on the board? Hell no!

[redben]

Thanks for all !!

This project is not a big deal !! It's pure fun design for some hobby robotic application.
So I think I will let the micro as it is until it death.

I also don't know how to replace the chip...

Does someone has the skills to unsolder those kind of chip without damaging the board ??
Actually I'm worried about damaging the board.
But I only have access to a soldering iron (good JBC), no hot air gun.

I would really appreciate unsoldering tutorial.
I allready destroyed too many things from poor soldering skills.

Thanks again for all the answers and coming...

[c4757p]

I'd recommend either getting some Chip Quik SMD removal solder alloy, or carefully shearing off the pins with a blade. Only press downward, don't swipe or you will rip pads. Then you can gently remove the pins with your iron.

Obviously method B won't save the chip, but you can at least avoid wrecking the PCB. Method A will only save the chip if you're careful. If you want to be able to just reach in and pluck it off, you need hot air.

[Galaxyrise]

I'd recommend either getting some Chip Quik SMD removal solder alloy, or carefully shearing off the pins with a blade. Only press downward, don't swipe or you will rip pads. Then you can gently remove the pins with your iron.

Side cutters may be easier to cut the pins on that chip, but it's hard to say from the picture.

I desolder all sorts of stuff with Chip Quik.  Dave did a video on it, too.

[c4757p]

If you can't get the side cutters around one single pin, but instead have to cut multiple at once, you are applying massive shear forces to the pads. You're going to need some freaking tiny side cutters to get the pins on a QFP individually...

redben, from looking at your PCB, just a side comment: If you spin a second revision of this board, I'd recommend increasing the annular ring width on the vias. A few of them are drilled with the hole actually over the edge of the copper!

[redben]

Thanks, the Chip Quick sounds a great way to go.
I'll take note you're comments for the vias in future improvement.

How many chip can you unsolder with the Chip Quick ? cause it cost much more than my pcb (china made) and the micro.

[Galaxyrise]

It's not a fixed amount per chip; it's based on how much space you need to heat.  If the QFP has half an inch of pins on a side, and you get 16 feet of chip quik (aka 192 inches), you can remove roughly 96 of them.  I clip off a small amount of Chip Quik, place it up against the pins, then melt it with the iron and spread it around.  It's too brittle to apply like regular solder, and this way I know I'm using a conservative amount.

[westfw]

If the chip still works, you obviously only released some "ordinary smoke", and the required amount of "magic smoke" is still inside  :-)

Does someone has the skills to unsolder those kind of chip without damaging the board ??
Actually I'm worried about damaging the board.

When replacing a bad part on a board that must be preserved, the usual procedure is to cut off all the leads and then remove the pins individually.  That may have limits for SMT chips :-(
(This is the opposite of the "apply blowtorch to board and smack on table", which is useful for getting working chips off of a board you don't care about.)
(chipquick will preserve both chip and board, but is relatively expensive.)