How to Hand-solder a PowerPad IC

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Introduction: How to Hand-solder a PowerPad IC

About: I'm an electrical engineer, musician, and giant nerd. My school experience was mostly digital signal processing. My real-life work experience is with audio electronics: microphones, mixing consoles, guitar...

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.

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.

Step 2: Clean Up the Board

After getting the IC completely off the board, I got the pins off with the soldering iron, basically just scraping them until they stuck to it and then wiping them off on the sponge.

Then I used solder wick to remove all the excess solder from the board. The trick to using solder wick is to put a little solder on the tip of the iron first, so that it can soak into the wick and heat it up quickly. Then place the wick on the pads, holding it with needle-nose pliers, and put the wet soldering iron on top. Then I tend to pull the solder wick so it slides along the board, with the iron sliding along with it, and it wicks up the solder, leaving clean pads. (Slide lengthwise along the pads, and don't push hard, or it can pull the pads off the board.)  It can only absorb so much, though, so you need to keep cutting off the soaked part and exposing a fresh end.

The main pad in the middle sucks up heat much better, though (that's kinda the point), and the wick will tend to cool and get stuck, so do the main pad and the pin pads separately, at different temperatures.

It can be hard to see the structure of small shiny things (this IC is only 7 mm wide), so wait for it to cool, clean it with alcohol, and run your finger across it to feel for any bumps or leftovers. In this case, touch is better than sight (just like washing dishes!)

Now that it's clean, you can see all the vias that go through the center pad. You can also see some faint cut marks on the pads from cutting the pins off.

Step 3: Place the IC

So the next step, as with hand-soldering any surface-mount IC, is to put the IC on the pads, line it up, and "tack" it into place. Get it lined up as well as you can, then solder just one corner (one pin, if possible). This is just to hold it in place while you do other things. If it slips a little, you can easily melt the solder and reposition it until you get it just right, which you couldn't do easily if you soldered more than one pin.

I generally just hold the IC in place with my finger, but you might want to use masking tape or something if you don't trust yourself not to slip. ;)

Step 4: Solder the PowerPad

Now that the IC is in place, you need to solder the pad in the middle. Obviously you can't stick a soldering iron under the IC to melt it, so you need to solder it from the other side of the board.

While the pad is not yet soldered, you should still be able to lift the opposite corner of the IC off the board. When you can't do this anymore, you know it's being held down by solder on the pad, even though you can't see it.

Turn up the heat again, and hold the soldering iron to the pad on the other side of the PCB, adding solder and letting it wick through the vias.

This was my first time doing this, and I didn't watch the IC as I was doing it. Since the IC was free to separate from the board, it did, because more solder than I expected pooled underneath the IC and lifted it.

I was initially tempted to just melt it again and push the IC down flat, before I realized how stupid this would be. It would not push the excess solder through the vias! It would just squeeze out the sides of the IC (like squashing a peanut butter sandwich) and there would be solder bridges to every pin. Don't do this!

A better method would be to:
1. Watch the other side of the PCB and make sure the IC isn't lifting off the board.
2. Add solder in very small amounts, let it cool, and then test whether the IC is stuck down or not.

You might also be able to do this by tacking down two opposite corners, so the IC can't lift, and trusting the solder to only wick enough to fill the pad, and not to squeeze out and touch the pins. This would probably work even better, but I didn't try it, and you'd have to desolder one corner in order to make sure it couldn't lift anymore.

After this mistake, I used solder wick to suck the solder back out through the vias, until the chip lay flat again. Phew! Done with the tricky part.

Step 5: Solder the Pins

This is the way I solder pins on any surface-mount IC. Just glom solder all over the pins, so that it soaks underneath them, and then remove the excess with solder wick.

In my case, two of the pins got splayed out while wicking away solder, and I had to carefully bend them back into position with tweezers. I was very afraid of breaking them off and having to start over again. Luckily, they were redundant, so I could have broken one off and survived.

Step 6: Clean the Board and Check Everything

I always clean all the residue off the board to make it easier to see the pins and any solder bridges between them. Gently scratch the solid flux with a tweezer to make it come off in flakes, brush those away, and then put a paper towel over the chip and soak it in alcohol so the remaining flux residue will soak into the paper.

After visually confirming there are no solder bridges, use a multimeter to check every adjacent pin for shorts (usually by touching the components they are connected to, not the pins themselves), and then check every pin for shorts to the power pad (obviously it's ok if a grounded pin is connected to ground).

After you've confirmed that there are no shorts between any pins, you're done! Plug it in and try it.

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    40 Discussions

    wouldn't hurt to have a high accuracy temp probe on the ic. would give an idea when to back off.

    haha I know exactly what blew it out. I connected 120 VAC to the wrong wires. :D

    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.

    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.

    4 replies

    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. 

    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?

    2 replies

    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...)

    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.

    3 replies

    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.

    You could have used a solder suckerfor the vias and solder wick for thesurface pads and then alcohol to finish cleaning