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I have read a lot of articles on epoxy and glues for PCB especially with a ripped off pad. I am in the same situation myself and was hoping to get some suggestions here.

Ripped of pads.

The MEMS microphone looks as follows:

enter image description here

The PCB still has metal connections jutting out, and I tried soldering without glue. The microphone works, but it is not held in place since the solder connection with the metal does not form a strong bond. The way I see it there are multiple ways of dealing with the situation:

  1. Buy a silver based epoxy, coat the metal and nearby area where pads originally were, and then solder the microphone using silver epoxy as pads. There is only one epoxy 8331 from MG chemicals which seems to be most preferred yet most expensive. Can anyone suggest a cheaper version?

  2. Apply a non conductive epoxy and stick some solder pads if I can find one. Once the epoxy is cured, solder back the microphone. However this looks to be difficult task since I need to find solder pads matching the one on the board and I have not found any yet.

  3. Simply solder the microphone and then make sure that the microphone connectors are touching the metals, and apply super glue to keep it in place. but this is not a clean solution.

I would really appreciate if anyone can give me a cleaner solution. Also names of epoxy/adhesives/glues will be helpful.

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    \$\begingroup\$ If you've got a workable connection with the solder, just use regular epoxy for mechanical strength. \$\endgroup\$
    – Tom Carpenter
    Commented Jul 10, 2018 at 12:19
  • \$\begingroup\$ Epoxy is strong but may have poor adhesion. I suggest Polyurethane is better. ( architectural adhesive) \$\endgroup\$
    – D.A.S.
    Commented Jul 10, 2018 at 14:50
  • \$\begingroup\$ @TomCarpenter: Yes but can you please name any? \$\endgroup\$
    – RAN
    Commented Jul 10, 2018 at 16:58
  • \$\begingroup\$ I would dig down with a scapel and expose more metal and then solder with a hot air gun and solder paste, but thats just me. \$\endgroup\$
    – Voltage Spike ♦
    Commented Jul 10, 2018 at 18:11
  • \$\begingroup\$ @laptop2d, that was my initial idea. But I have no clue which other traces are buried down there. Morever the pcb is too thin and flimsy, so it was kind of risky. Thank you for your suggestion anyway. \$\endgroup\$
    – RAN
    Commented Jul 11, 2018 at 21:01

1 Answer 1

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The microphone works, but it is not held in place since the solder connection with the metal does not form a strong bond.

If 4 soldering points cannot hold practically weightless component in place then you did not solder it properly.

solder the microphone and then make sure that the microphone connectors are touching the metals, and apply super glue to keep it in place. but this is not a clean solution.

IMHO it is actually the best solution. I don't understand why you think it is "not clean".

Here is what I would do (basically a variant of @laptop2d suggestion in comments):

  • clean MEMS contacts thoroughly. Put a drop of solder paste on each pad and heat it up to form round blobs. You can also make a simple solder mask by punching 4 holes in suitable material, but it is not required. I recommend watching some "BGA reballing" videos for example.

  • clean PCB contacts thoroughly, use some no-clean flux, cover them with solder, then remove as much solder as you can with a wick.

  • add solder paste to PCB contacts. Here that mask will come handy again. Position MEMS in place so that the balls you made earlier sink into paste blobs. Heat the whole thing up to solder it in place.

  • Make sure MEMS works, then put a drop of thick CA glue at the MEMS edge. It should seep under the part on its own.

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  • \$\begingroup\$ thank you for the advice. First off, i was not aware of solder paste. That already solves quite a lot. Also i read on some forums that CA based glue like Super Glue damages the PCB. Some say it dissolves through the pcb. Is that true? The reason why i thought it was not a clean solution was because if for some reason the MEMS moves after soldering and checking whether it works and then I put the super glue in, then it would be even more difficult to remove the component off the PCB. \$\endgroup\$
    – RAN
    Commented Jul 10, 2018 at 21:39
  • \$\begingroup\$ I don't know how you managed to solder it without paste in the first place. I believe everybody responding assumed just as I did that you have hot air soldering station and paste. You can try it with iron, I guess, but the risk of damaging the part is high. I am not aware of any damage to PCB from a drop of CA except from online myths . As soon as solvent vaporizes the glue is inert. however it does produce toxic fumes when heated. If you planning on doing more soldering then consider other types of glue. Or simply cover the hole and put hot glue all over. \$\endgroup\$
    – Maple
    Commented Jul 10, 2018 at 22:03
  • \$\begingroup\$ I used a hot air soldering station, applied some solder on the mems, a blob like you mentioned before, and soldered it down with hot air. Anyway, i think i will go with the solder paste+CA. Any brand recommendations for solder paste? \$\endgroup\$
    – RAN
    Commented Jul 10, 2018 at 22:15
  • \$\begingroup\$ Avoid very low temperature and wash-away types. Kester is usually recommended by people "in the know". For me it is rather expensive, so I switched to cheap leaded Chinese brands. Haven't had any problems yet. But you better ask somebody with more experience or search forums. \$\endgroup\$
    – Maple
    Commented Jul 10, 2018 at 23:20
  • \$\begingroup\$ Hi, so i finally soldered the MEMS to the PCB, checked whether it is working and super glued it. Unfortunately the connection is not as strong as i expected. A very delicate touch also disconnects the MEMS from board. I am not sure whether it is the PCB itself which has disfigured or the MEMS loosing contact with the PCB. Anyway i plan to give it one more try. Now comes the process of removing super glue off the PCB \$\endgroup\$
    – RAN
    Commented Aug 22, 2018 at 18:52

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