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Warming devices fail

Peter Borenstein
Mastermind 8695 points

Other Parts Discussed in Thread: CC2541

Hello all,

My CC2541 chips have been bricking when warmed from ~1°C.  The device works fine at low temperatures. I can connect even at -30°C. As soon as the device starts to warm, it locks. I can no longer see advertising packets. I also have a periodic event flashing an LED. That stops too.

I'm powering the device with a coin cell battery. I hooked the device up to an O-scope and Vcc never went below 2.1V

I do have the watchdog timer going, but it doesn't help. I can reset the device with the reset pin once its warmed. The device sometimes brings itself back to life.

  • 0
    Guru 22270 points

    Hello Peter,

    One possible cause for this is condensation.  Repeat the experiment again but this time:

    1. Heat one of those silica pouches you get with componets to above 100 deg C in a dry oven for at least 15 minutes then put it in a sealed dry bag to cool.

    2. Put the cooled silica pouches and your controller in another sealed bag and cool it below -1

    3. Let it warm up.

    Thanks,

  • 0 in reply to Greenja
    Mastermind 8695 points

    Thank you greenja,

    It was indeed condensation issues. I had guessed that before, but never tested with silica pouches. Do you have any thoughts on how to water-proof small PCBs? I'm using a Panasonic module that covers sensitive circuitry with a ground shield. Good for noise reduction, hard for getting at pins. Please forgive me for hijacking my own post with secondary questions.
     

  • 0 in reply to Peter Borenstein
    Guru 22270 points

    It depends on your budget and availability of materials.  There are serveral non conductive sprays from 3M that have a very high dialetric strenghts.  Most of the silicone adhesives you get at the hardware store will work.  Glue from a glue gun works (you see them all the time holding down capacitors).  I have actually used wood glue once for an i2c device.

    Your main concern is how permanent you want your waterproofing to be.   With the sprays, you can always scrape away the layer to get at pins.  With the glue and adhesives, you may pull off pins if you try to remove it.

    You can do a test on a test circuit with a clear coat automotive spray or event clear coat wood protectors to see if it works.  The things to look out for would be the impedance between traces and if any of the ingredients react with the copper, other metals or plastic.

    BTW, it sounds like you are getting ready to send something to outer space :-)

    Good luck!