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TMP007: Getting inconsistent values from temperature sensors

Tyler Gilbert
Prodigy 50 points

Part Number: TMP007

I have an adafruit TMP007 eval board which is working great. When I read the calibration data values they are ll set to the default. It outputs a consistent temperature that is consistent with what I expect. The problem is on a custom board.

I have a custom board with 32 tmp007 sensors. I can read all the registers and they all are showing the default values.  However, when I read the calculated temperature (register 3) I get numbers that are all over the place. Does anyone have any insight on what might be causing this? Could it be the sensors were damaged (got too hot) during assembly? Could it be the adafruit board is pre-calibrated but when I read the registers they show the default values? What values should the tmp007 give with the default calibration?

Thanks!

Tyler

  • 0
    TI__Mastermind 43835 points

    There's no magic in the coefficients. If you read the default values, that's what they are.

    It's likely that you've damaged your TMP007s. The device features a thermopile (see IR FAQ on E2E) in the center of the BGA solder balls on the bottom of the device. This thermopile is covered with a membrane that can be punctured. Additionally, any foreign materials (such as flux or loose solder) between the thermopile and PCB will prevent the device from operating correctly.

    Your thermopile should be able to produce a large positive voltage in the presence of a hot object. See the Sensor Voltage register. If you momentarily hold a soldering iron (or even just a hot coffee cup) above the device, you should see at least +100mV. If your voltage hovers around +/-100uV, then the thermopile is not working.


    Ren

  • 0 in reply to Ren Schackmann
    Prodigy 50 points
    Ren, thanks for the wisdom. Is there a recommended procedure for reworking these devices? Thanks!
  • 0 in reply to Tyler Gilbert
    TI__Mastermind 43835 points
    This type of packaging can't be soldered with an iron. It must be done with solder paste and air tool or reflow oven. I recommend using water soluble flux and rinsing with water afterwards. The water should be dried with warm air before energizing the circuit. The device should only be handled from the top with plastic tweezers or air suction tool. Ideally, I would only assemble at a contract manufacturer with automated placement, paste applied by stencil, and established cleaning flow.

    Ren
  • 0 in reply to Ren Schackmann
    Prodigy 50 points
    Ren, thanks that is very helpful. Is there a max temperature you can recommend for the air tool?
  • 0 in reply to Tyler Gilbert
    TI__Mastermind 43835 points
    Please see the following document.
    AN-1112 DSBGA Wafer Level Chip Scale Package
    www.ti.com/.../snva009ag.pdf

    Ren