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My understanding of electrical engineering is pretty much non-existent, so please forgive any obvious oversights on my part.

I am currently trying to recover the data from an eMMC chip from a dead phone through soldering direct connections from the chip to a microSD adapter. This example shows in pictures what I am trying to achieve. As I cannot afford an eMMC socket (cannot post more than two links so you can find it on Amazon with product number B01LYUHB33) and the data I'm trying to recover is of sentimental value for my partner's grandmother, I am very keen to try to do it myself.

As it is one of the few times I'm actually soldering my questions are:

  1. Is this wire that I bought appropriate? If not, do you have any recommendations?
  2. Do I need to somehow strip the (possibly) very thin coating? Could I use a knife to do this?
  3. It is my understanding from the example above that the VCC and VCCQ pins should be connected to each other on the chip. Is this necessary? I'd like to avoid as much soldering as possible (lacking both microscope and steady hands), so I'm already skipping connections DAT1-DAT3.
  4. I'm assuming that I do not need solder balls if the wires are directly connected to the chip (as this is a BGA chip). Is this correct?

If there's any other tips that you can give me, they'd be greatly appreciated. Many thanks in advance.

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  • \$\begingroup\$ In addition to question (1), is there any other wire 'around the house' I could use (if the one linked is not appropriate), say, for example single strands of a USB cable wire / SATA cables / ribbon cables? Thanks again. (Don't fully know why there are multiple strands in the same "wire" of the USB cable, e.g., in the red wire there are multiple strands of the same type of material instead of a thicker one.) \$\endgroup\$ – Alia Atreides Oct 24 '16 at 18:40
  • \$\begingroup\$ You could salvage wire, but it may be advisable to use the same type of wire throughout. \$\endgroup\$ – 0-60FPS Oct 24 '16 at 18:44
  • \$\begingroup\$ Thanks, only meant if the one I already bought is not appropriate. \$\endgroup\$ – Alia Atreides Oct 24 '16 at 18:45
  • \$\begingroup\$ The wire you chose looks like it could do the job. Looking through the tutorial you mentioned, the soldering that needs to be done looks extremely difficult without a microscope due to the scale and required precision. The socket you mentioned looks like it would reduce the risk of soldering and connection mistakes greatly. Perhaps you could search for a used one? \$\endgroup\$ – 0-60FPS Oct 24 '16 at 18:50
  • \$\begingroup\$ VCC is going to be the supply for the actually flash memory and VCCQ is the supply for the controller. They are not necessarily the same voltage, so you really need to look up the specific chip. \$\endgroup\$ – ks0ze Oct 24 '16 at 18:55
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You have embarked on a challenging task.

  1. You pick the correct wire size for the job, 38AWG, it will not break pads. But still be very careful and do not bend wires, secure them with capton tape.

  2. You don't need to strip ends. All you need is a slightly hotter iron tip, 250-300C. Using a solder with resin core, just touch the solder tip with solder wire, and while the blob still has melting resin core, stick the wire into it. The insulation will gently burn out, and you will have a perfectly wet wire tip.

  3. Voltage rails should be connected. By SD/MMC specification, memory chip must be tolerant to default 3.3V, so it should work, although less power efficient. However, I am not sure if you can skip DAT1-DAT3. The SD controller will first access the eMMC in one-wire mode, which will tell the controller that the chip is 8-bit wide. The SD host will then try the connection at advertised frequency and bus width. I am not sure if your SD host will fall back into one-wire mode if it has no right response.

  4. Not sure what do you mean here about the balls. The wire is either soldered, or not to the spot.

Having done this kind of workaround myself many times, I would not try this without a professional grade soldering iron with 0.1-0.2mm tip, and a good stereo microscope.

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  • \$\begingroup\$ Thanks very much for your detailed response @AliChen! I had tried with a soldering iron tip of 0.6mm and 60%-tin-40%-lead solder (now that I checked), but may not have 'stripped' the ends correctly in this way (also leaving the iron at the lowest temperature it goes). I had managed after some good hours to make the connections, but did not connect DAT1-DAT3. The eMMC chip/SD card was not recognised, so gave up on it for a while. \$\endgroup\$ – Alia Atreides Oct 24 '16 at 20:49
  • \$\begingroup\$ And with regards to (4), please ignore me, I did not think it through. \$\endgroup\$ – Alia Atreides Oct 24 '16 at 20:51
  • \$\begingroup\$ @AliaAtreides - You need to strip and tin the wire ends separately from connecting them. When stripping, use a high iron temp to burn off the insulation. Since there is no pad to damage at this point, get the temperature up. The result should be a wire end with a smooth coat of solder on it. Then turn down the iron and solder to the board. \$\endgroup\$ – WhatRoughBeast Oct 27 '16 at 21:44
  • \$\begingroup\$ Yes, you need to tin wire tips BEFORE soldering the wire to balls. I do not change soldering tip temperature when doing this kind of job. \$\endgroup\$ – Ale..chenski Oct 27 '16 at 21:58

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