This is a teardown of a second-generation Amazon Echo Dot (purchased around January 2017, UK). The photos are fairly high-res and can be clicked to enlarge.
There is a lot of intricate detail in the design.
The underside has a peeling part before the self-tap screws can be removed.
Almost the entire unit comes out, but there is still some stuff in the black plastic shell : ) Notice the two metal contacts for the speaker.
What the unit looks like outside of its shell.
The speaker unit can be extracted. The side that was hidden from view is now visible, and you can see the speaker grille too (it's where the arrow is pointing), and there are small holes for it in the outer shell too as you can see. Also notice the radio tag stuck inside.
Closeup of the speaker unit:
The top removed. Now the buttons are visible. The array of holes all around the unit are for the microphones. The are six mics around the circumference, you can see the holes for them in the foam shaped pad. There is also a center microphone.
The other side; this is the underside of the main control board. That flat flex has a black piece that flips up to open it, easy to miss and damage while removing it : (
The PCB antennas are visible here too, near the top and bottom of the photo:
The main PCB removed. There is a SIL-PAD type thing for thermal transfer, and two pads for presumably electrical contact to the metal chassis for shielding.
The metal chassis portion of it can be removed from the black plastic:
The top PCB is removed here too, and the underside of it can be seen. The white plastic acts as a light diffuser for the ring of LEDs.
The plastic removed from the top PCB. Now the microphones and LEDs can be seen.
Closeup of the two boards:
Closeup of the top board, microphone soldered side (the buttons and holes for the mics are on the other side).
The top facing side of the top board:
The main processor board:
Other side of the main processor board: