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For data recovery I need to desolder a BGA 153 eMMC chip from a dead phone. I'd like to maximize my chances of NOT destroying the eMMC chip in the process (the other remains of the phone do not matter since these are dead already). I've already watched various instruction videos and I'd say I have an idea of the general process.

I do have a cheap Chinese hot air station where the temperature can be set between 100-500 degrees Celsius (but I don't know how accurately that actually works) and where air speed can also be selected.

For target practice I just unsoldered some DDR3 chips from some old PC's memory PCB (these chips where not glued on - it was just the solder that held them in place). I used a nozzle about the same size as the chip and put flux all around the chip before heating. I always used a low air speed (2 on a scale to 8). I progressively increased temperature and each time heated for 2 minutes to test at which minimum temperature the chip would come loose. For the DDR3 chip it actually took me 385 degrees celsius (but maybe the displayed temperature is just wrong)!

With regards to the eMMC chip I had so far found information that 240 degrees should be sufficent to unsolder it (supposedly its solder melts at 225 degrees).

Is it to be expected that an eMMC chip would come off at a so much lower (240 instead of 385) temperature than a DDR3 chip? Or is this just an indication that the temperature reading on my hot air station is way off?

Should I rather be using some higher air speed for this kind of job?

Would it make sense put some thermal isolation on the backside of the phone's PCB to reduce heat emission?

What type of low melting point solder should I use if I wanted to directly solder some wires to the eMMC chip? Or what would be the right type for reballing (leaded, lead-free, etc) if I was so put it onto some kind of breakout board?

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    \$\begingroup\$ To maximize the chances, let someone handle it that has experience. \$\endgroup\$ – PlasmaHH Feb 14 '18 at 16:40
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    \$\begingroup\$ "Would it make sense put some thermal isolation on the backside of the phone's PCB to reduce heat emission?" On the contrary, pre-heating the back side of the board to just below the soldering temperature would actually make it easier and quicker to get the chip off the board. \$\endgroup\$ – Dave Tweed Feb 14 '18 at 16:54
  • \$\begingroup\$ Search out "Louis Rossmann" on YouTube and watch him repair a bunch of MacBook Pro laptops. Much (most) of what he does is boring but you will learn some invaluable tips. I've been doing rework for decades and still learned much. It's worth the time investment. PS - he does BGA transplants between boards regularly and (for him) easily. He also shows how to re-ball BGA using solder paste instead of pre-fab balls. \$\endgroup\$ – Dwayne Reid Feb 14 '18 at 21:46
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The easiest and less destructive way would be to turn your board upside-down, and heat the chip area from the PCB side. Use some powerful heat gun instead of a tiny hot-air pencil. As soon as the solder temperature gets to the soften/melting point (which you don't know and shouldn't guess), the chip will fall down by itself, maybe with a little help.

You can't afford re-balling, plus you will need to develop a PCB interposer for the BGA with breakout pins, etc. Best way would be to use a very thin magnet wire, AWG36 to AWG40, and break the connection to some DIP-40 socket, or something. Solder 60/40 would be just fine, if you have a 10X stereo stand and fine-tip soldering iron.

ADDITION: Here is your other option without soldering the chip back:

enter image description here

You just need to clean your eMMC thoroughly.

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  • \$\begingroup\$ I like the idea. However I noticed something around the edges of the eMMC chip that might be epoxy (might be that Huawai put some extra glue to hold it in place?). I guess there is a risk that the IC might still stick to the board after the solder has molten and with the big paint removal heat gun the stuff might get real hot quickly.. (or should it be OK if I just tried to scrape that stuff off before?) \$\endgroup\$ – wothke Feb 14 '18 at 19:57
  • \$\begingroup\$ What you mean by "can't afford": The extra risk of reheating the chip once again without the proper equipment? (it's a pity since these kind of cheap adapters aliexpress.com/item/… seemed to be made for my purpose.. but of course they are useless if I kill the chip in the process..) \$\endgroup\$ – wothke Feb 14 '18 at 19:58
  • \$\begingroup\$ I just experimented with my scrap DDR3 chips (I think their pads have the same spacing as the eMMC chip) and I managed to solder 0.1mm enameled copper wire to them so I can do that if necessary. However I need to use at least 270 degrees centigrade (on my Ersa soldering station) before it even starts melting my 60/40 solder.. would that be a risk to the chip? \$\endgroup\$ – wothke Feb 14 '18 at 19:58
  • \$\begingroup\$ About re-balling: it seems that service prices came down considerably, e.g. reballing of RSX Playstation3 chip is now just about $100. Sorry for outdated info. \$\endgroup\$ – Ale..chenski Feb 14 '18 at 20:23
  • \$\begingroup\$ regarding reballing: actually I had thought about buying a respective stencil and a bottle of solder balls (less than 10$ on aliexpress) and do it myself.. that's why I'd like to know the right type of solder balls with a respective low melting point.. \$\endgroup\$ – wothke Feb 14 '18 at 20:51
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The big danger, regardless of your method, is getting your chip too hot for too long. You don't want to pump enough heat through your IC to heat up the PCB beneath it.

One good solution is in @AliChen's answer. Another method is to preheat the whole pcb (from underneath) to just under the solder melt temperature. Then you can add heat to the IC with your hot air station and remove it with tweezers.

I would recommend an IR preheating station. If you don't have one, you'll have to decide if your data is worth the investment. You can probably find a new cheap one for under $100 USD.

Here's an example image from AliExpress. I haven't used this one, so I can make no recommendations:

preheater

By the way, you certainly don't want your IC hot enough to melt solder for two full minutes at a time!

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    \$\begingroup\$ The highly trained technicians in my electronics lab use a hot air preheater below the board, and a focused hot air station directed at the chip on the top side of the board. Just err on the side of low heat and only crank it up if it doesn't release within a minute or so. \$\endgroup\$ – Selvek Feb 14 '18 at 18:07
  • \$\begingroup\$ It is a friend's phone and he would certainly be pleased to recover his photos - but not enough so to spend that kind of money. The phone would go into the trash - if I managed to recover some data that would be a bonus. But what you are saying is also, that the same temperature (e.g. 225 for 50secs would be OK) may destroy the chip if it is applied too long (e.g. 225 for 120secs).. that's good to know. \$\endgroup\$ – wothke Feb 14 '18 at 19:13
  • \$\begingroup\$ @Selvek Supposing the correct temperature was 230 and I start with 200 cranking it up by 10 after each unsuccessful 1-minute-attempt. By the time I hit the right temperature the chip would have been heated above 200 for more than 3 minutes.. might that not damage the chip - or are sub melting point temperatures safe even when used for extended periods of time? \$\endgroup\$ – wothke Feb 14 '18 at 20:16
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    \$\begingroup\$ Cranking up 10C each step would be the worst scenario. Better use 360-400C air one time. \$\endgroup\$ – Ale..chenski Feb 14 '18 at 20:26
  • \$\begingroup\$ For reference, I just checked the hot air stations in my lab and they are set to 415C. But I wouldn't rely too heavily on that number since pressure, distance, and nozzle have a big impact as well. Also, FWIW, reflow ovens bring chips to a preheat temp of maybe 200C over a few minutes (this is the goal of the preheater) before increasing the temp. \$\endgroup\$ – Selvek Feb 14 '18 at 20:57

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