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DRA829J-Q1: Impedance test failed during production

guobing.zhou
Prodigy 10 points

Part Number: DRA829J-Q1
Other Parts Discussed in Thread: DRA829

Dears, 

What we tested was the impedance between VDA_DLL_0V8 and DGND. When the first batch of PCBAs were produced (total: 36 PCS PCBA), 95% of the PCBAs had an impedance value between VDA_DLL_0V8 and DGND of 11k-12K (Expected Value: 5K-20k) , when producing the second batch of PCBA (total: 70 PCS PCBA), we found that nearly 50% of the PCBA, the impedance value between AVDA_DLL_0V8 and DGND was around 400Ω.
This VDA_DLL_0V8 is generated by TPS65941213RWERQ1, and then directly provides the working voltage to N9_ VDDA_0P8_PLL_DDR and Y9_ VDDA_0P8_DLL_MMC0 of MCU_ DRA829.
Should I appropriately relax the Expected Value based on the production situation? Are there any big risks?

   Thanks

  • 0
    TI__Guru 57645 points

    Was there any design change in this area between batch 1 and batch 2?  Have you tested a batch 2 board with lower impedance to see it its functional?  The other 50% boards of batch 2 that are above 400-ohms...are they all matching batch 1 (~10K-ohms)?

  • 0 in reply to Robert Eschler
    Prodigy 10 points

    Hi Robert,

    This area did not change in design between batch 1 and batch 2. I tested a batch 2 board with lower impedance and all other functions were normal.

    The other 50% boards of batch 2 that are above 400-ohms have impedances between 11K-12K.

    Should we appropriately relax the expected value based on actual production conditions? Are there any big risks in doing this?

  • 0 in reply to guobing.zhou
    TI__Guru 57645 points

    I do not know what is driving the difference in impedance, so I cannot comment.  There is some variation in process from device to device, but this seems larger than I would expect.  It does provide some confidence that boards tested OK across all measurement levels.