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LMT85: Could you tell me where Thermal Response is faster?

Part Number: LMT85

Hi, support team

My customer has the questions as follow:

Surface mounted Temperature sensor, such as LMT85DCKT or TMP235AEDCKT.

Top temperature (surface air temperature),
bottom temperature (Substrate temperature in contact with bottom surface),
and the temperature conducted from pins,
Could you tell me where Thermal Response is faster in the above three?

Thanks so much.

Best regards,

  • Hi Yuki,

    Conduction will always be faster than convection (air) transfer.

    For the two conduction paths you mentioned, I would use direct contact with the package if it were available to me. Generally, it's not desirable to manufacture this way, so I would settle for the pin metal conduction path. 

    Please refer to SNOA967. However, I'll offer some additional details specific to your devices.

    The DCK package for both of these devices has the DAP (Die Attach Pad) connected to Pin 2 GND. This DAP is a metal flag that the device is mounted on, and the metal is formed into Pin 2 as it exits the mold compound. This makes pin 2 a better thermal path to the sensor than other pins. If your object can be electrically connected to Pin 2 GND without violating the sensor's Abs Max Voltage ratings, I recommend doing so.

    Figure 8 in SNOA967 is incorrect. Both DBV and DCK are 'flip chip' packages. This means the leadframe is loaded upside-down, known as 'dead-bug' with the legs upward. This means the mold compound is not very thick on top, and this provides a good thermal path to the sensor and DAP as well. 

    Note that in these images, 'die' is the silicon IC device which incorporates the temperature sensor.