[afandian]

How are people sticking stuff to quartz? I know less than nothing, but the pieces of quartz you find in rock don't look like they'd take a solder bond.

I'd assumed that with piezo crystals etc there was a mechanical connection rather than an electrode bonded to the crystal?

But if you can add solder presumably there is some kind of molecular connection with the metal?

[adrian_b]

Electrodes are deposited on the crystal in vacuum, e.g. by metal evaporation or sputtering, in the same way as they are deposited on the semiconductor crystals used to make transistors or integrated circuits.

The electrodes may consist of multiple layers, a base layer that adheres strongly to quartz and a top layer that is solderable, e.g. made of nickel or silver.

The pins of the package that hosts the crystal resonator are soldered on the electrodes, in places well chosen so that they will not damp much the oscillations of the crystal.

When the mass of the crystal must be increased to shift the resonance frequency, excess solder may be deposited on the electrodes.

[afandian]

Thanks, that's fascinating. I imagine they use a mask and large spread? Or a stepper?

Fun video of 'metallization' on a coarser scale! https://www.youtube.com/watch?v=e-QcseGvU5o

[jacquesm]

There is already a silver patch bonded to the crystal where the wire connects to. Adding weight to that obviously will not make the load curve any better but if you do it with just enough to drop you back down below where you wanted to be then it can be a saving move. You could also put a trimmer in parallel, but that might not have enough range (and can also end up overloading the crystal so the oscillator won't start).