How to unsolder & replace BGA IC?

[mitaux8030]

My worst electronic nightmare has come true. Want to learn how to unsolder & replace a BGA ICs.

Unsoldering is going to be easy, right? - just use a SMD hot air station to blast the IC and remove with tweezers? What is the success rate of removing a good BGA device unharmed from a PCB?
Probably should use some reflective foil tape placed strategically around the BGA device to prevent too much heat going into surrounding components, too?

And what about replacing with a new BGA device... what's the technique used to resolder them to the PCB? Will surface tension of molten solder help 'pull' the BGA device into perfect alignment, or....?

I'm fairly experienced at SMD soldering of regular components eg: SOIC etc.

[hinekadon]

practice and good eyesight works

[wotnot]

What size BGA?

edit:

[wotnot]

My worst electronic nightmare has come true. Want to learn how to unsolder & replace a BGA ICs.

I've got time now for a better answer, but hopefully you had a look at various youtube vids linked to above. It sounds like you nightmare is of your own making - can't help that =)

Unsoldering is going to be easy, right? - just use a SMD hot air station to blast the IC and remove with tweezers?

There's lot of variables, and it differs from board to board. One has to start somewhere to form a mental picture, and the actual size of the BGA is about the first thing you look at. Then, it depends on what other SMD components may surround the chip being removed, and if there's any components underneath the area being reworked..and in a general sense, this matters more on large chip packages and PCB structures that absorb/dissipate a lot of heat. For example, some large BGA chips, you need a heater plate underneath the PCB. to heat up the PCB to just under (lead-free) solder melting temperature, and only increase the heat on the chip area to achieve melting just there.

What is the success rate of removing a good BGA device unharmed from a PCB?

Really depends on the chip itself, and how quickly the rework is performed...ie; keep the periods of high temperature excursion as short as possible

Probably should use some reflective foil tape placed strategically around the BGA device to prevent too much heat going into surrounding components, too?

Indeed, this is a strategy often employed, especial when there's plastic connector bodies adjacent the rework area - typically one uses 'kapton' heat proof sticky tape to hold the shrouding in place

And what about replacing with a new BGA device... what's the technique used to resolder them to the PCB? Will surface tension of molten solder help 'pull' the BGA device into perfect alignment, or....?

Many new chips, do not come pre-balled. Often one has to do that prepping the chip, using stencils and solder paste, or the right sized solder balls..then, yes...you align the chip correctly and bring it up to solder melting temp, and surface tension does the final work. Most times, there's package alignment marks in the PCB silkscreen to aid alignment.

I'm fairly experienced at SMD soldering of regular components eg: SOIC etc.

Good, hopefully you appreciate the difference between 'good' flux, and 'junk' flux , because BGA rework requires a good flux =)

practice and good eyesight works

Lol...it's actually sound advice, although good eye-sight might be optional these days, as electronic microscopes abound...you can read & study everything about BGA reworking, and it'll still take you some time in practice (often months) to hone your skills enough to become 'confident' you've done it correctly, every PCB will dissipate heat a little differently, to your horror, you discover some lead-free solder has a melting temp so high, you have to wonder what they replaced the lead with...aluminium? =)

Thing is, what do you practice with? Well, assuming you've got all your gear together for the rework task itself (as above), your cheapest BGA rework patients, are probably USB thumb devices, and you could see how you go swapping ram/driver chips from one device to another, and you can easily verify if you got it right or not...you obviously have to go out and buy a couple of 3packs of the -same- USB stick, and a board holder would be handy, and blablablah... If you just want to practice removal technique, PM me and I can send you a bag of old PCBs you can practice on to your heart's content =)

[mitaux8030]

Thanks for that detailed primer wotnot - absolutely brilliant. Some of those YouTube videos make it look incredibly easy, though I'm sure any skill like that is 'easy' after loads of experience. Good thing there are a few practice junk PCBs laying around here to help get that experience first. Feeling a lot more positive about tackling BGAs now, but of course that's a bit of Dunning-Kruger creeping in. Will see how far down the curve I manage to slide after some practice.
Ultimately the size of BGAs I will be working with are small to medium, 9x10 up to 19x19.

[wotnot]

Thanks for that detailed primer wotnot - absolutely brilliant. Some of those YouTube videos make it look incredibly easy, though I'm sure any skill like that is 'easy' after loads of experience. Good thing there are a few practice junk PCBs laying around here to help get that experience first. Feeling a lot more positive about tackling BGAs now, but of course that's a bit of Dunning-Kruger creeping in. Will see how far down the curve I manage to slide after some practice.
Ultimately the size of BGAs I will be working with are small to medium, 9x10 up to 19x19.

Don't they just...but then, tight-rope walkers between two hi-rise building make that look like a doddle as well =) As I alluded to above, -every- PCB tends to be different, and in saying that, every brand/manufacturer tends to do the same thing with all their PCBs. You can niche things out, and specialize in specific rework tasks, just based on what equipment you have. Incidentally, is a good channel for looking for USB drive rework tips&tricks. When one becomes familiar with a specific brand/design, it becomes second nature to tailor your technique, to suit that particular rework job, so it takes as little time as possible to do the task.

If there's any 'inner magic' involved, it would be the operator's familiarity with their hot-air gun, and the type of PCB it is ; it'd be about as sublime as picking up on body language, uh-huh? As you're heating things up, you're watching the PCB surface, flux, and the solder joints surrounding the component to be removed, looking for visual signs clues to how close you are to melting point. You will see vids suggesting you use such'n'size size nozzle, this temp, that much air...and you'll find other vids of blokes doing the same job, with a household paint-stripped heat gun to equal success, and others who say full hot, and just enough air to avoid blowing any of the surrounding smaller components off the board.

Essentially, the hot-air gun must be -more- than capable of delivering enough heat energy, required to melt the solder balls of a BGA mounting, within a limited temperature increase slope measured in time -- the actual temperature control (of the rework area) is how close the operator holds the hot-air output to the device/rework area, and how they move/steer the hot-air around to achieve equal heating. Technically speaking, there's a pre-heat ramp (bring device/PCB up to 150C or so), the ramp from there up to solder melting point, and then a long cooldown ramp to operating temp range again...it looks like this;



The lead-free solders have a similar curve, but higher temperature ranges, that can be tolerated for a shorter amount of time, but as I mentioned before, some lead-free solder alloys are horrorshow to work with, and going north of 250C 'for a moment' is sometimes required....as I understand it, some of these lead-free solder alloys do some weird change state crystallize voodoo (heat being the catalyst), and weld to the PCB pad..and the melting temp of this stuff is higher again.

As long as you're aware reflow heat/time specifics are generally part of device datasheets, you can work out what your rework time 'window' looks like (most of them are similar). Trouble is, this is all relative to the solder alloy used, and it's a BIG variable. This is why, the best flux you can get, and copious amounts of it, are really important nowadays to deal with these nasty, 'one time use' solder alloys =)

Where most folks come unstuck, is not ensuring all balls reach melting point at the same time (equally so for removal/replacement) - when I was taught this stuff billygoats ago, one training tip I can give you, is learn 'to float the chip' - using the graph above as a guide, practice getting getting through pre-heat, and into reflow, within the allotted times, just long enough to 'dance' the chip on the meniscus of all those balls, by giving it a little tap on the side with your tweezers... then let it all cool down without removing the chip. It's really good practice, as you're learning both removal/replacement skills at the same time sort of thing.

Same goes for reballing, practicing that is rather insightful, due to th visual feedback of the balls/paste melting, and how the movement of the hot-air gun/airflow heat affects how quickly that melting propagates across the chip/stencil.

Get a fume extractor if you at all care about the health of your lungs and/or what ends up stuck to the ceiling & walls =)