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CC1101 PCA yield problem

gerg king
Prodigy 30 points
Other Parts Discussed in Thread: CC1101, SIMPLICITI

We are having issues with cc1101 boards. The problem is we can not communicate over the SPI bus from the 430. We are getting a 30 - 60 percent drop out of boards in  manufacturing and test depending upon the board type (we build about 5 different boards with the CC1101). With the very first runs of these boards we did not experience this problem but now it is pervasive. If I take a non functional board and have the CC1101 removed and replace the same part half of the time it fixes the PCA. If I replace the non functional CC1101s with new ones on the non functional PCAs I get90-100% fixed. We have X Rayed the boards looking for shorts and opens without effect we have used parts from about 5 different lo lot codes and we always have approximately the same results. We are now looking at changeing the paste mask under the part in hopes that this will yield better results. Has anyone else had these kinds of problems that you could give me a clue of what might be causing this.

Thanks, Greg

 

  • 0
    Mastermind 9802 points

    A couple ideas:

    1. Visually inspect the solder connection to the CC430 pads. The QFN package is a pain for manufacturing; look at it under a microscope to verify that the fillets look good.

    2. Don't over-paste; see TI's recommended stencil layout

    3. Verify your crystal is in spec (ppm over time/frequency etc.) Also verify crystal's capacitors.

    4. If the design is panelized, see if the failures are all in one place on the panel - that's a problem with your CM's reflow oven

     

    Good luck,

    Derek

     

  • 0 in reply to Derek
    Prodigy 30 points

    Thanks,

    We have been checking the boards and did notice that the earlier builds seem to have a better solder fillet around the outside pins. Apparently ther was a change in the solder paste to a no clean flux. At  this point we are having a batch of boards reworked with less paste in the center and we will see what the results are of that.

    Greg

  • 0
    Intellectual 350 points

    Hi Greg,

     We are experiencing the same problem, although have not gotten to so the same level of testing you appear to have done.

    Have there been any developments in your understanding of the problem as we are not sure what to do next ourselves. We have a very low pass rate some of which is due to the  manufacturer we used to populate the boards but there remains a doubt  that there may be other factors such as the software and variations in the manufacture of the chip. We are using the simpliciti stack and have avoided changing any software except where necessary so would not expect it to be a problem. However the boards stop at the point where the comms to the cc1101 is verified.

    If you have any further information that may be helpful it would be appreciated and in particular if there is a failure mode in the chip that can be avoided by design changes or otherwise it would be very helpful.

    Regards Kris