Fitting the RTC crystal on Teensy 3.2

Status
Not open for further replies.
C

ChrisRowland

Active member
I've a suggestion when fitting the RTC crystal on the Teensy 3.2, fit the crystal to the top of the board and solder it from the bottom.

I tried doing it the other way and a slight slip of the soldering iron deposited solder on some of the pins of the MK20 IC shorting them out. If you solder on the bottom of the board, with the crystal on top, there's much less to disturb.

Not sure if I can recover it, the pins involved are 22 to 27 which involve the MKL device and the USB. Blink runs, the USB connection seems to be partially made but the device isn't recognised as a Teensy. Not sure if my very limited surface mount rework skills are up to this.

I'm not blaming anyone, other than myself, just hoping this will help others avoiding getting into this state.

Chris
 
I assume the ground plane and ideal location matches the silk screen below by design - Crystals do their work by being hyper active and sensitive - putting them up top may defeat the purpose of having them be accurate/reliable due to undo influences of the parts/noise there.

I've done at least half a dozen crystals without problem - all below. I have bridged the two pins - but there is room there to work that out. The last were placed below and soldered below as the gap for the pin arch left room - away from any nearby components, flux carries the heat and the solder well through the hole. A blob of solder paste is good too - lots of flux in it and keeps a free hand and the solder out of the way - just heat the two halves.

To resurrect the solder bridges perhaps review these sparkfun SMD tips. #7 looks like it offers promise - or at least hope. I wouldn't power it with bridges in place or expect it to work well or maybe long depending on what is bridged where.
 
Thanks for the feedback. I'd bought two devices so still had one to use and it's fine.

Yes, I'll work up the nerve to be a bit more adventurous with the SMD rework process, I've a number of vintage PC components I can practice on.

I see the point of keeping the crystal away from noise. I'm not sure how much this matters when most of the time power is off and this is the only thing that's running.

I've done a small amount of SMD work and what seemed to work was applying too much solder, then removing the excess with desolder braid. It's something I need to work up to.

Thanks everyone,

Chris
 
There are some good YouTube videos re drag soldering chips and other SMD techniques. I'd put as little heat into a device as possible, however. So heating it multiple times (initial solder application, removal via braid, etc) will stress the component.

For most of my boards, I now use solder paste and a stencil for the initial application of SMD components. You can solder these in an oven or use a soldering iron to individually melt each pad.
 
Last edited:
Status
Not open for further replies.
Back
Top