problem is with placing the crystal on the PCB design.

[Diagoco1]

Hi

,

 

I'm new to PCB design. I'm planning to build a handmade board for a project that uses the STM32F103C8T6, and I've run into some issues in certain parts of the PCB design. My board only has copper on one side (single-sided). For the HSE 8MHz and LSE 32.768kHz crystal oscillators, the body needs to be placed on the bottom layer, with the pins passing through holes to reach the top layer where they will be soldered.

 

I'm concerned about the soldered area where the solder forms a fillet on the top layer, and whether this fillet, being in line with the OSC traces running toward the MCU, could cause problems.

 

To put it simply: could the solder fillet of the crystal on the top layer cause frequency issues, reduced performance, or make it completely unusable?

 

Since my project is currently in the experimental stage, I haven't built the board yet. The images I've included are just for better understanding and were collected from a few websites.

 

What's your opinion on this?

[TDK]

could the solder fillet of the crystal on the top layer cause frequency issues, reduced performance, or make it completely unusable?

A solder fillet and/or placing the crystal on the other side of the board, will not affect functionality.

[mƎALLEm]

Hello ​@Diagoco1 and welcome to the ST community,

No impact on the oscillator when the crystal is on the other side. 

The recommendation is to place it as much as possible to the MCU as well as their CL capacitors.

An example of PCB layout is provided in the AN2867 “Guidelines for oscillator design on STM8AF/AL/S and STM32 MCUs/MPUs” for through-hole crystal

 

[STOne-32]

Dear ​@Diagoco1 ,

Only particular care is required for the 32.768KHz crystal , in general the watch / cylinder one have 12.5pF Of CL by default and are not compatible with STM32F103, Just double check to have a crystal of CL=6pF , or 7pF worst case. In general their ESR is low 

Hope it helps ,

STOne-32