Electronic – Incorrect resonator/crystal PCB layout

Your placement is fine.

Your routing of the crystal signal traces is fine.

Your grounding is bad. Fortunately, doing it better actually makes your PCB design easier. There will be significant high frequency content in the microcontroller return currents and the currents thru the crystal caps. These should be contained locally and NOT allowed to flow accross the main ground plane. If you don't avoid that, you don't have a ground plane anymore but a center-fed patch antenna.

Tie all the ground immediately associated with the micro together on the top layer. This includes the micro's ground pins and the ground side of the crystal caps. Then connect this net to the main ground plane in only one place. This way the high frequency loop currents caused by the micro and the crystal stay on the local net. The only current flowing thru the connection to the main ground plane are the return currents seen by the rest of the circuit.

For extra credit, so something similar with the micro's power net, place the two single feed points near each other, then put a 10 µF or so ceramic cap right between the two immediately on the micro side of the feed points. The cap becomes a second level shunt for high frequency power to ground currents produced by the micro circuit, and the closeness of the feed points reduces the patch antenna drive level of whatever escapes your other defenses.

For more details, see https://electronics.stackexchange.com/a/15143/4512.

Added in response to your new layout:

This is definitely better in that the high frequency loop currents are kept of the main ground plane. That should reduce overall radiation from the board. Since all antennas work symmetrically as receivers and transmitters, that also reduces your susceptibility to external signals.

I don't see the need to make the ground trace from the crystal caps back to the micro so fat. There is little harm in it, but it is not necessary. The currents are quite small, so even just a 8 mil trace will be fine.

I really don't see the point to the deliberate antenna coming down from the crystal caps and wrapping around the crystal. Your signals are well below where that will start to resonate, but adding gratuitous antennas when no RF transmission or reception is intended is not a good idea. You apparently are trying to put a "guard ring" around the crystal, but gave no justification why. Unless you have very high nearby dV/dt and poorly made crystals, there is no reason they need to have guard rings.

1. Crystal, or quartz crystal. Crystal resonator is not at all incorrect but they have been called just crystals for over 50 years to no harm...

2. Ceramic resonator; maybe just resonator, but certainly not crystal or oscillator.

3. Basically yes. (The middle terminal will be ground). However there are also ceramic filters with this configuration, so be careful and double check the datasheet. (Especially if they are marked with common radio IF frequencies, 455 kHz or 10.7 MHz!)

4. I don't know; most likely no.2 in different packaging, I have never seen quartz crystals packaged this way.

5. Yes.

6. No, though connected to the right pins on an IC it might be. A crystal oscillator is either:

   a. something like package (1) with 4 pins; it takes 3.3V or 5V in, and puts out a clean signal (making it dead easy to use), or

   b. a circuit involving these components, possibly a resistor, and some kind of amplifier (inside the IC, or a separate transistor) or a misused logic gate, to drive the crystal. In the latter case you can usually substitute a ceramic resonator, but you may have to change the capacitors and a gain setting resistor (or drive limiting resistor) to make it work at all, or work reliably.