Beginner question : can I layout / put a crystal on the back side of the 51822 / 52832 ?

[sprhawk]

I'm doing a very space limited PCB layout.

I have a thought what if I put the crystal on the back side of the PCB ?

Does it hurt something ?

[RK]

Can you do it? It might be possible. However the capacitance between the crystal and the chip is critical for proper operation and the capacitance needs to be pretty small, a few pF. The closer to the chip you mount the crystal, the less stray capacitance there is, so you can adjust the components to get it right. The further you move the crystal, the more capacitance there is, the less room you have to adjust it. If there is too much stray capacitance, the crystal won't work.

Putting it on the other side of the board, even very close, adds a through hole (with capacitance) and distance, so you might find it very hard, or impossible, to tune.

Using a crystal with load capacitance towards the top end of the range and keeping it as close as you can to the chip may work .. but really .. try hard not to do that if you can avoid it.