NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

Independent NASA Test of
Actel SX-A, SX-S, and SX-SU
Field Programmable Gate Arrays (FPGAs)

KM1 Anomalies: S/N 37990

S/N 37990: t_PD anomaly

Summary

S/N 37990 was observed to have a t_PD anomaly at the conclusion of KM1-5 (-55 ºC).  Previously, the device had been subjected to 1,000 hours of +125 ºC testing.

The failure is attributed to a damaged F antifuse.

Analysis and Discussion

• Passed all testing after 1000 hours of HTOL (+125 ºC)

• After 250 hours of LTOL (-55 ºC)

  • ATE Low to High (t_PLH) delay measurement increased by 11 ns with respect to time 0 delay measurement and 7 ns increase with respect to the 1000 hours HTOL measurement

  • Mean t_PLH delay delta for the entire KM1 lot was +4 ns (~0.5%)

   

  

   

  • 1009th delay stage verified to have net responsible for 11 ns of the t_PLH with the Silicon Explorer

  • The suspected anomalous net (1009) is routed via 3 antifuses: F, X, and I

  •  The 3 suspected antifuses were verified with the manual antifuse check

    • The F-antifuse was checked first

      • Check indicated a higher resistance in the programming path

    • The X-antifuse was checked second and the I-antifuse third

      • Both the X-antifuse and the I-antifuse showed normal programming path resistance with respect to a reference unit

    • After each manual antifuse check the Silicon Explorer was used to verify that the delay characteristics of the net were not affected by the check.  The manual antifuse check, designed to be as benign as practical, has some level of risk associated with it's use.

    
    Reference (net 1009 to 1010) = 0.8 ns

     

    • Silicon Explorer is used to verify the characteristics of the net during the manual antifuse check.

S/N 37790 delay from net 1009 to net 1010 is 11.2 ns prior to the manual fuse check (left).
The delay is unchanged and remains at 11.2 ns after the F antifuse check using the MFC process.

 

 

Similarly, there is no change in the devices propagation delay after checking the X
antifuse (left) or the I antifuse with the MFC.  The delay remained constant at 11.2 ns.

 

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