I am using a MEMS microphone that I got from Digi Key ( Part Number: 1428-1021-1-ND). I soldered the mic on a PCB board using hot-air and then add an amplifier to increase the gain (Operational Amplifier Mouser Electronics 595-LPV802DGKR). I made sure to follow the datasheet and check that everything was power correctly by measuring the voltages in different terminals with a multimeter. However, the microphone is not working. I am measuring the output of the circuit with an oscilloscope and I am not getting anything. I noticed that the output of the microphone is less than what I was expecting. Any idea why the MEMS mic is not working? I have already done 4 of these and none is working.
Some IC's can only handle X °C for Y seconds. It may be possible that you've burned the IC's. You did use hot-air, who knows how hot it actually is right at the nozzle? And take a couple °C off that, that's how warm your IC got. Maybe a few hundred °C. Only you can tell, you got the instrument and you know what you did.
Or, I believe this is your datasheet, if you look at page 11 you'll see that it says "Do not pull air out of or blow air into the microphone port.". It's a very possible thing that you've done, add "very hot" to that problem and you've got yourself something that's probably broken.
If you keep reading on the same page, under "BOARD WASH it says the following:"When washing the PCB, ensure that water does not make contact with the microphone port. Do not use blow-off procedures or ultrasonic leaning.".
So it appears that your microphone is very sensitive, and can probably break if you just blow into the microphone port with your own breath.
Or something is actually wrong with the schematic.
Or something is wrong with some other component inside your circuit.
If you want to be very certain that the problem is not because of your hot-air soldering, then make a sixth and solder it with a regular hot iron.