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I design a lot of PCBs that uses microcontrollers with external clocks. For some reason a lot of the example designs always tend to use the big generic HC-49 package. Even factory made modules that I purchase tend to use that package. I typically source my components from LCSC which has a large variety of components. Are there any disadvantages to using the smaller packages for crystals other than price and availability?

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  • \$\begingroup\$ Big packages (HC-6, HC-49) holding big crystals tend to withstand higher drive levels than small crystals in small packages. High drive can improve noise floor. \$\endgroup\$ – glen_geek Dec 17 '18 at 15:42
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This is probably mostly because of cost per unit reason as you mentioned. For scale projects unless the PCB area is not concerned, I would chose the cheapest and high volume solution. Therefore, HC-49 package crystals and oscillators are preferred in most cases.

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  • \$\begingroup\$ I like the 6x3.5mm SMD package, 406 family, such as CTX856CT. May cost a little more, but take up a lot less room, and low height. You can see one on the bottom of the 4th board here www.crossroadsfencing.com/BobuinoRev17. Or the XC1776, like a small SMD version of the HC49 thru hole parts. \$\endgroup\$ – CrossRoads Dec 17 '18 at 15:40
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Crystals have much more important properties than frequency, size and cost. These are operating temperature, frequency and temperature tolerance, load and shunt capacitances and ageing.

Obvious advantages of HC-49's size - easiness to mount and power dissipation.

But I did not see industrial or enterprise designs using HC-49 last decade (even on big boards where HC-49 will fit). The biggest they use is HC-49S, or chip crystals.

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Certain packages can offer different sets of frequencies. For example, the 3.2x2.5 package can be had with frequencies up to 80MHz, and with tolerances of 10ppm.

Parasitic capacitance and inductance also comes into play, the 2 vias of the HC-49 and the 2 large pads of the HC-49S have larger parasitic capacitance than the pads of a small SMT device.

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