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SN74CB3T16211: Max Die Junction Temperature?

Vince Hadley
Prodigy 50 points
Part Number: SN74CB3T16211

The datasheet indicates that the part performance specifications are qualified up to +85 deg C (Ambient).  The question is, what is a max allowable Die junction temperature under normal operation?  Is it capable of higher temp (say up to 125 Deg C Junction Temp) assuming not much power is being dissipated by the switch currents flowing through the part?  Or is there some other concern about exceeding 85 deg C?

  • 0
    TI__Intellectual 2900 points
    Hello,

    The high temperature consideration is for device reliability concern. For example, the interconnect of the device is made of metal. Given the same amount of current, higher temperature will decrease the lifetime of the metal interconnect. In other words, metal is easier to break at higher temperature. This mechanism also applies to other compononets on the silicon.

    We specify 85C ambient temperature is because PCB designer has no easy way to probe the junction temperature. From our chip design point of view, since SN74CB3T16211 does not heat itself too much, we will push our junction temperature up to 90C when we design the silicon.

    If no voltage or current applied on this device, which is the storage situation, the device can survive up to 150C. We normally specify the storage temperature in the table of "Absolute Maximum Ratings".
  • 0 in reply to Fan.Wang
    Prodigy 50 points

    Hello Fan,

         Thank you for the detailed response.  In our application we expect the board/ambient temperature to reach as high as 105 deg C.  I know that in many cases higher temp qualification (above 85 deg C) is something that is only done if there is a strong enough market demand for it.  So the question is, is there a design reason/limit for the 85 Deg C spec or is there a strong likelihood that *this particular part* (SN74CB3T16211ZQLR - VFBGA Package) would operate reliably up to 105 deg C, but just lacks the formal qualification for it?

    Thank you,

    -VH

  • 0 in reply to Vince Hadley
    TI__Intellectual 2900 points
    As you suggested, without a formal qualification, we are not able to confidently gurantee the reliabity and performance at 105C ambient.

    The design limits mostly come from two sources. One is the metalization from layout perspective. The other is the transistor size of all current conducting paths.

    Since there are so many potential failure spots when extending a legacy design from 85C to 105C, we will have to analyze the likelihood of reliabliably operating up to 105C by layout review, design re-simulation, bench re-charaterazation and stress test for mass production. Therefore, given the datasheet claims 85C today, it is very hard to tell if SN74CB3T16211ZQLR can reliability support 105C in the future.