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TSSOP reflow soldering problem

Marco2002
Prodigy 200 points
Other Parts Discussed in Thread: MSP430G2553

Hi everybody,

I’m a novice on microcontrollers; I’m having a hard time in soldering my MSP430G2553 in TSSOP28 package.
I’m using the SAC305 (lead free) solder paste, and I never have problems soldering smd parts with my reflow oven.
But when I soldered the microcontroller, and I tried to program it, I had this message:
 
Error connecting to the target:
Could not find device (or device not supported)
 
So I decided to lower the temperature at a minimum, turning off the oven immediately after the point at which the paste melts, but never changed.
I tried to use my hot gun, but the problem still occurs.
So I tried to program my microcontroller before soldering, and it works great, but I’m unable to reprogram it.
So, my question is: am I blowing the internal fuse?
Has anyone else had this problem?
 
Thank you for your reply.
  • 0
    Guru 46710 points

    Marco2002 said:
    So I tried to program my microcontroller before soldering, and it works great, but I’m unable to reprogram it.

    Did you try to solder chip using soldering iron so you are absolutely sure it is not overbaked? Results?

  • 0 in reply to Ilmars
    Prodigy 200 points
    Hi llmars, and thank you for your reply;
     
    soldering the chip using a soldering iron is the next step; actually, it looks like it's the ONLY step I can do.
     
    But I find being really very very strange that I’ve not been able to solder an SMD device with a reflow oven, nor with an hot air gun, especially considering that the temperature I’ve used in my last attempts was 225°C, well below the peak temperature for the MSP430G2553 (260°C), and that I immediately turn off the device after the point at which the solder paste melts.
  • 0 in reply to Marco2002
    Guru 46710 points

    Marco2002 said:
    But I find being really very very strange that I’ve not been able to solder an SMD device with a reflow oven, nor with an hot air gun, especially considering that the temperature I’ve used in my last attempts was 225°C

    So maybe your problem is not soldering at all. - That's why I suggested to use soldering iron and supposedly have same results. Maybe it's just PCB routing or manufacturing or chip orientation error or something like that, not related to how you solder chip..

  • 0 in reply to Ilmars
    Prodigy 200 points
    Hi llmars,
     
    you're absolutely right; I won’t post any new consideration until I’ll try to sold it manually.
  • 0 in reply to Marco2002
    Prodigy 200 points

    Hi everybody,
     
    finally, I found the problem; let me summarize.
     
    I made six TSSOP / DIP adapters, on which I soldered: one MSP430G2553 (28 pins, TSSOP package), one 47K resistor and one 10nF capacitor.
    No one of them was working, even if I tried to lower the soldering temperature. I always had the same message:
     
    Error connecting to the target:
    Could not find device (or device not supported)
     
    So, I removed them, and I soldered new MCUs manually, with an iron: still the same error message.
    But when I programmed the MCUs before soldering, they worked perfectly, even if I wasn’t able to re-program them.
    Finally, I found the problem: the 10nF capacitor.
    Removing it, they worked as expected, and I was able to solder them still maintaining the possibility to re-program them.
    I remembered that on the MSP430 family user’s guide there was written something about the capacitance of that capacitor:
     
    “The pulldown capacitor should not exceed 2.2 nF when using devices with Spy-Bi-Wire interface in Spy-Bi-Wire mode or in 4-wire JTAG mode with TI tools like FET interfaces or GANG programmers.”
     
    I replaced the 10nF capacitor with a 2.2nF capacitor, and now everything is working as expected.
  • 0 in reply to Marco2002
    Guru 227245 points

    Marco2002 said:
    I replaced the 10nF capacitor with a 2.2nF capacitor, and now everything is working as expected.

    Things usually start working when done right :)

    Instead of using a 2.2nF cap (which makes the timing for the reset lien quite short) a larger one can be used if there is a series resistor between the pullup/capacitor combo and the RST pin. This way, the SBW signals are decoupled from the capacitor by the series resistor (1k should be enough) while the pulldown effect of the capacitor at power-up is maintained.

    VCC
    |
    R
    ----R----RST/SBW
    |
    C
    |
    GND

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