Instructables
I made a really stupid mistake at work the other day and ended up blowing up an IC on a one-of-a-kind prototype. :'(

Dying of embarrassment, I decided to try the impossible and replace it before anyone found out what happened. I've soldered surface-mount ICs before, but never any with a PowerPad on the bottom. These are especially tricky to do by hand, since you need to melt the solder under the chip, without making any solder bridges between the pins and the pad. I wasn't sure it was even possible to hand-solder.

(The reason I was able to do this is because there are vias connecting the PowerPad to the other side of the PCB, so that the ground plane on the other side acts as a heatsink. If your design doesn't have these vias, or the holes in the vias are too small for solder to travel through, this method won't work.)

But I was successful! Now no one needs to know my secret shame.
 
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Step 1: Remove the old chip

In my case, the old chip was destroyed, so it didn't matter what happened to it. If you want to salvage the old chip, and you don't have a hot-air rework tool, you'll have to figure out something clever and post your own Instructable. That's beyond my skillz.

To remove the busted chip, I first cut all the pins off of it. That way I didn't have to desolder both the pad and the pins at the same time; I could just focus on the pad. I used an exacto knife and pressed it carefully against the pins, one at a time, as close to the chip as possible, until they were all broken off. I ended up cutting into the PCB a little, as you can see in other images, but it didn't harm the layout.

Since the PowerPad-style chips use the PCB as their heatsink, you're supposed to create a bunch of vias right under the IC. This is the key to removing it. If you don't have these vias, I don't know what to tell you. Get a hot-air rework tool, or try to wick solder under the chip from the sides, I guess.

So then I turned my soldering iron up to a higher temperature than normal and held it to the pad/vias on the other side of the board until the solder melted all the way through. The chip came loose and separated from the PCB, and I was then able to get under it to free it the rest of the way.
zack2474 years ago
did they ever figure out the ic blew out? and what went wrong with the first ic?
endolith (author)  zack2474 years ago
haha I know exactly what blew it out. I connected 120 VAC to the wrong wires. :D

that stinks, 120vac to the wrong wires.

I blew an IC in a similar manner. I was testing the voltage drop across the current sense resistor to see if the current sense amp was reporting correctly. However, the resistor was on the bottom of the board, so I decided to directly probe one of the pins on the chip. Needless to say, the probe slipped, and suddenly 5v line on the board was connected to 24V. Every single 5V part on the entire board got fried, blowing up about 50 bucks worth of IC. The MEGA128L had a similar divot as the one in this pic.

The one thing that I do slightly differently is tin the pad on the first pin before soldering it down. That way I get it perfectly in can get it perfectly in place and solder it down at the same time.
haha. oops.
kenoconnor4 years ago
Unfortunately, unless you have access to an x-ray machine, you will never know if there is sufficient solder coverage to transfer the necessary heat out of the die inside the case of the part.
Sounds like a good excuse to get an x-ray machine.

Just use plenty of flux and it will probably be fine.  Then put a knuckle on the chip and run full power through it.  If it gets so hot you can't touch it, then there isn't enough solder.  Either that or it needs a heat sink. 
or you could just use the x-ray machine, just dont forget your led underware.
I want LED underwear! :P
endolith (author)  hintss3 years ago
Make some! Be sure to document it for an Instructable.
did it on a wireles desktop receiver pcb... well after a sucsessful practice on desoldering and soldering again the rf chip everything looks good but i get continuous errors the pc refuzes to recognize it.... i guess i held the soldering iron many time on the contacts i fried it... Btw Is it possible to use a cheap hot air gun for acrylic colors etc to do soldering and desoldering instead of using an expensive hot-air soldering station?
endolith (author)  paleologos_the_greek4 years ago
Are you sure you overheated it?  Did you check for short circuits?
Dear endolith im 100000% sure about that when i tried to desolder it again i saw a crack on the plastic package of the chip (after removing it from the pcb it separated in two pieces)... i d never used much force so i belive it is from the rapid temperature rising... (like filling a glass with hot water :P disaster!) any way i decided to buy a cheap acryllic dye hot-air gun (about 10 euros/dollars) and use it as hot-air solderer/desolderer... it does good work... however if you try this you have to protect the near components with aluminium foil... (cheap hot air guns can reach the prefered temperature but they cannot focus in very small areas as the worth & expensive hot air stations...)
nolte9194 years ago
So just to be clear. You blew the IC on a one-of-a-kind prototype, decided to fix it before anyone noticed, and still took the time to take pictures? You are admirably devoted to the Instructable trade.
endolith (author)  nolte9194 years ago
Well, I wasn't sure if it was going to work or not, so I wanted to document it in case something went wrong. Instead of labeling wires before I take something apart, for instance, I just take a picture of the wires in their original configuration, and then I can refer to it later if I forget where something goes. Digital cameras are very convenient.
I do exactly the same when unmounting modular equipment, if later someone says "you connected it wrong", i just show them the picture after unmounting and problem solved.
Also, taking pictures when disassembling complicated equipment helps later if you don`t know where some part goes.

i do the same thing when reparing computer components. i like to take them for my memory as far as where stuff goes and incase i get the return customer that says his computer only worked for a day after he picked it up and i dident fix it right, then i find half a glass of wine spilled in it. i gess his wife was hoping i dident notice. or keep picture records of my work.
navyredman4 years ago
You could have used a solder suckerfor the vias and solder wick for thesurface pads and then alcohol to finish cleaning
endolith (author)  navyredman4 years ago
I used alcohol to clean it.  I only have the plunger-type soldersucker and I don't like it.  The recoil often damages the board,and it produces lots of lead dust, which isn't exactly healthy. Solder wick works better for most things.

The spring loaded one?  I've never had a problem with damage or dust. It's all sealed and after I'm done with one project I open it and dump everything out. To each his own I guess.

endolith (author)  navyredman4 years ago
Maybe mine are defective.  The dust falls back out the nozzle after it plunges and gets in the air.  And the recoil often damages more delicate traces.  I didn't like solder wick at first but now that I'm used to it I prefer it.  I have a vacuum desolderer at work, too, but it gets clogged very easily.
navyredman4 years ago
A method I use for removal is heat the bottom of the PCB at thevias, stick a flat chissel tip exacto blade under the IC and lift alittle at a time.

I also forgot to mention that if you heat the solder wick too muchit with pull the coating off the PCB then the whole thing will short. Ifyou're going to solder wick that much stuff you cannot move the wickaround on the board. You have wick and lift straight up
navyredman4 years ago
A method I use for removal is heat the bottom of the PCB at thevias, stick a flat chissel tip exacto blade under the IC and lift alittle at a time.
Kii4 years ago
The ideal method when soldering ICs is to use drag soldering.

endolith (author)  Kii4 years ago
That looks pretty good!  Is that flux in the tube?
thereza4 years ago
wait,i can do to convey useful information and not violate the policy - by avoiding the critisism and offering advice wich would allow others to not bother using this technique :

if this happens to you, do yourself a favor and buy a hot air station.  you can get them cheap all over.  it's the right way to do this.  your hair (or lack thereof) looks good on you.

that's a nice comment, and instructive.  yay!

thereza4 years ago
It says that my comments have to be nice, and positive, but I feel that there is some bad information in this post - if I point out the problems with the technique, then I wouldn't be nice, but if I don't point out the problems, then there is a chance someone can cause damage.   I think this policy sucks (I can be negative towards the policy, but not towards the author, right?)

*sigh*

yeah, I just tried to explain the problems without using words like "cringe" and I just can't do it.  I belive in honesty and treating people like adults - especially if they're resoldering ICs.  But if instructables want to treat their users like kindergardeners, then that's their perogative. 
dagenius4 years ago
I find it neater to use a really small soldering iron, and really small lead solder. Then go and do each and every pad. This makes for a neater final product, and you have less of a chance of overheating the ic.
drbaldyphat4 years ago
Another way to do this is to use solder paste on the power pad as this will flow beter when heated from the other side and the surface tension of the molten solder will suck it to the pcb in the correct place.
I had to do something similar for a similar part, TPA2008D2, last week. Now I can see the technique is used somewhere else. Great Instructable!
mattccc4 years ago
what is the prototype suppose to do and coud i have mor pics tyu
Bigev4 years ago
Well done! Not only did you teach me about soldering a power pad chip, you also taught an easier way to solder surface mount components.
lol "what one of a kind " piece of machinery did you break you just showed the chip
endolith (author)  albylovesscience4 years ago
It's a prototype of a product that doesn't exist yet. Of course I only showed the chip. :)
carlos66ba4 years ago
Very good instructable and VERY HIGH QUALITY PHOTOGRAPHS (if only others could learn how to use the macro function, sigh!).
why dont you make an instructable about it. i can never figure out how to take close up shots this nice.
endolith (author)  Berserk874 years ago
1. Set auto-focus to "center" 2. Press the "Macro" button 3. Get as close to the object as you can 4. Make sure there's plenty of light, but not causing a glare 5. Half-hold the shutter 6. If the box is yellow, move back a smidge and do #5 again until the box is green 7. Take several shots and pick the best one after you put them on your computer 8. Crop the parts you don't need. There. That was much easier than an Instructable.
there are no less than 5 bazmillion 'how to use macro mode' instructables. As cpo says, if only everyone would do this good :D Not a HUGELY useful skill - but great problem solving and prototyping prowess are shown here...with great photos!