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My phone's microphone recently stopped working after falling. So I decided to try to repair it by buying this component (I guess a single microphone is in my phone, an xcover 4s, since calling with & without the speaker fails):

enter image description here

But the component is special in multiple ways:

  • it is way smaller than expected, the whole component is basically like 1mm wide, the width of the tip of my soldering iron… How can a microphone be that small??
  • it has no "legs", so I guess I need to solder the pads under it?? But how can I access them?
  • one of the pads is circular with a hole inside… Guess I don't want to solder the hole? Hopefully the sound is not supposed to enter this way.

So:

  • What is the name of these special components with no pads under them?
  • How am I supposed to solder this and unsolder the old one? Is it possible to do it with a regular soldering iron (mine is relatively thin with temperature control… but still not that thin), or do I need to get an expensive hot air solder? Do I need to solder the inner circle as well or only the two rectangular pads?
  • How can I test if the soldering has been done correctly since the "legs" are placed under the microphone?
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  • \$\begingroup\$ What is on the other side of the PCB where the microphone needs to be attached? If there is nothing, then it could be possible to heat the solder through the PCB if you tin the pads first. You would want to use leaded solder for the best chance; low melting temperature solder is available, but it might be too brittle. (I am not a phone repair technician.) \$\endgroup\$
    – Andrew Morton
    Commented Sep 17 at 17:51
  • \$\begingroup\$ @AndrewMorton That's a good point, I don't know yet (trying to grab as much information before opening my phone) \$\endgroup\$
    – tobiasBora
    Commented Sep 17 at 18:03
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    \$\begingroup\$ You could abandon the repair idea and use a plug-in or Bluetooth earphone with microphone. \$\endgroup\$
    – MTA
    Commented Sep 18 at 1:30
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    \$\begingroup\$ @tobiasBora I dont want to sound like a pain in the neck, but to my unprofessional ears it sounds like you do not actually know if this microphone part is responsible for the lack of sound on your phone. In fact it seems highly unlikely. More likely reason is: this part or some other part had bad solder and disconnected. If you are throwing the phone away, I would heat up the part of the phone where this part is with a blow drier, (removing the battery first obviously). \$\endgroup\$
    – Kphysics
    Commented Sep 18 at 11:24
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    \$\begingroup\$ If you don't know the answer to this, then it also means that you don't have the soldering skills to realistically pulls this off, even if you have access to a hot air soldering station and solder paste. Which means that the correct way is to hire a PCBA assembly shop and let it solder it in their reflow oven. Which is the most professional and safe way to do it either way. \$\endgroup\$
    – Lundin
    Commented Sep 18 at 13:57

5 Answers 5

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You use solder paste and hot air. This component is not possible to solder with a soldering iron.

Note that the word is "solder", not "weld"; welding is a very different process.

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  • \$\begingroup\$ Thanks, that seems quite a challenge (but I do like challenges ^^). But do you think I should solder the round pad around the hole? This one seems to be the most challenging one. Do you know if there is a place where I could get the documentation of this component? \$\endgroup\$
    – tobiasBora
    Commented Sep 17 at 15:48
  • \$\begingroup\$ You're probably supposed to. And no, I have no idea where you might find documentation. Ask the manufacturer is my best suggestion. \$\endgroup\$
    – Hearth
    Commented Sep 17 at 16:05
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Guess I don't want to weld the hole? Hopefully the sound is not supposed to enter this way.

Correct. You don't want to get solder in the hole. Probably that is exactly where the sound is sensed.

What is the name of these special components with no pads under them?

"Land Grid Array" or LGA.

How am I supposed to weld this and unweld the old one?

If the manufacturer had their way, you wouldn't. You'd throw it away and buy a new one.

In the factory they soldered (not welded) it with solder paste and a reflow oven.

do I need to get an expensive hot air welder?

You might be able to rework it with hot air solder system, but an experienced technician would have a much better chance of getting it right.

How can I test if the soldering has been done correctly since the "legs" are placed under the microphone?

You can inspect it with a $million x-ray inspection system.

Bottom line: phones are not designed to be re-worked by amateurs --- they are designed to fit an incredible amount of functionality into a very small device, even if that means they're very difficult to repair.

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  • \$\begingroup\$ Thanks, that seems quite a challenge (but I do like challenges ^^). But do you think I should solder the round pad around the hole? This one seems to be the most challenging one. Do you know if there is a place where I could get the documentation of this component? \$\endgroup\$
    – tobiasBora
    Commented Sep 17 at 15:48
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    \$\begingroup\$ YOU are not supposed to solder it. The original phone manufacturer is supposed to solder it. He has the equipment, and solders all the other components at the same time. This component is not expected to be replaced. \$\endgroup\$
    – Fred
    Commented Sep 17 at 16:34
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    \$\begingroup\$ While all the above is true, I watched a street vendor in Hong Kong repair the newest iPhone by replacing some BGA IC with a hot air gun. This was around iPhone 4 era though but still small BGA stuff. He did manage to fix it. \$\endgroup\$
    – winny
    Commented Sep 17 at 18:35
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    \$\begingroup\$ @tobiasBora Technicians/tinkerers experienced with the tooling & techniques are usually who buy components like the one you are asking about here. You are welcome to sacrifice your phone in an attempt to learn the same techniques - but if your intent is to have a working phone at the end of it, it may behoove you to find someone who already owns the tooling and has mastered the techniques. If you do intend to learn about hot air reworking, youtube has a wealth of video demonstrating both correct & incorrect techniques. Practice on scrap parts to master these skills for better odds of success. \$\endgroup\$
    – PowerLuser
    Commented Sep 18 at 5:01
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    \$\begingroup\$ Louis Rossmann has quite a few board repair videos where he goes over the equipment that he uses for microsoldering. It might be interesting to check out if you've never seen his work. \$\endgroup\$
    – Brian_Entei
    Commented Sep 18 at 18:10
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I will also try to answer my question to complete other questions based on my own research (and I'll update this thread if I manage to solve this). So, this microphone is a Micro Electro-Mechanical Systems (MEMS) microphone, that is basically a generic term to describe tiny sensors. This seems to be quite trendy now.

Searching for this brings several videos on youtube that can help:

  • https://www.youtube.com/watch?v=CF7jIAcRisM explains the different kinds of microphone MEMS. I have a bottom-port (aka 3 pin) MEMS microphone. The seal ring must be solded with solder paste, and seems to be used to guide the air to the hole (and indeed this hole is used to transport sound, so should not be covered).
  • https://www.youtube.com/watch?v=Oo07h9tbac8 shows a replacement of a MEMS microphone, with a different shape (4 connectors), using some solder paste and air gun. They also use some aluminium tape, maybe to make sure other components won't move, but I don't know if this is very standard, I would be afraid that some glue damage the circuit. See also this related one (longer one, but in indie https://www.youtube.com/watch?v=IOFk477IHv4)
  • https://www.youtube.com/watch?v=sCA7Pf3l-ug this one shows this time the exact same shape as mine. They also use solder paste, and they do put some on the ring part, just not in the middle. They manage to fix it without an air gun, by basically creating a big pile of solder paste next to the component (they glue it after removing the paint), and eating this pile to transfer the heat to the component… Not very professional, but if I'm desperate it might be helpful! And on the video, we can clearly see that some tin solder is present when they remove the first component, so this confirms that we also need to solder that part.
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You are discovering that the advances in electronic construction mean humans are not allowed. The good old days of components with legs are disappearing fast. If you fancy a little challenge then try soldering small wires to to component and then solder those wires to the board. You may then discover if the old component was at fault. Otherwise as suggested elesewhere support those guys at your local phone repair shop.

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You’ll need a hot air gun and solder paste (or just wet the pads with normal solder first). It can be tricky if there are other components nearby, though you can shield them with kapton tape.

If there is nothing under the PCB in that area you might be able to heat it up from the other side with your soldering iron (or maybe even a lighter or torch if you are super careful and cover the rest of the PCB in some protective foil or tape).

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    \$\begingroup\$ Specifically, you need a hot air rework station for soldering, not a plain hot air gun that you can buy in the local tool shop. \$\endgroup\$
    – Lundin
    Commented Sep 18 at 13:51
  • \$\begingroup\$ Also note that you need to have a quite good temperature regulation. That's not something that the hot air gun used to remove paint can do. \$\endgroup\$
    – jwo
    Commented Sep 20 at 17:42

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