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    Questions about PCB thickness and dimensions, options of casing for BMI085 and BMG250

    Questions about PCB thickness and dimensions, options of casing for BMI085 and BMG250

    Occasional Visitor

    Dear Community,

    Our team is using BMI085 and BMG250 sensors in our devices.

    We would appreciate your suggestions regarding the following:

    1. Mounting of the PCB. We know that the deformation of PCB leads to decreased performance of MEMS gyros. Therefore, we were planning to use a thicker PCB that has higher rigidity. However, in section 5.1 of the document bst-mis-hs000.pdf  Bosch recommends using a thinner PCB. This does not really make sense to me, could you please provide some clarifications?

    2. In our design, along with four gyros, a number of other elements are installed on the board. Does it make sense to install gyros on the separate PCB with smaller dimensions to decrease stress and deformation? Or gyros can be installed on the same board where other elements are mounted?

    3. Based on our experience, the type of the sensor casing also affects the performance of the sensing element. (a) Will the installation of the Bosch sensor into the ceramic LCC package improve the sensor's characteristics? (b) What if in addition to (a) the package will be vacuumized? Will this improve the characteristics?

    4. Could anyone please provide us with plots of Bias and SF over the temperature for BMI085 and BMG250? 

    Thank you!

    1 REPLY 1

    Occasional Contributor

    Hi Akaalka,

    About question 1----you know pcb is multi-layer, if the pcb thickness is more thicker, the inner layer is easier to make deformation and it will generate more intrinsic stress, so that's why it's recommended that the pcb thickness should be less than 0.8mm in datasheet.
    About question 2---you can mount you sensors together with your other elements on one board, how to put the sensors, you can refer to the document bst-mis-hs000.pdf, section 5.1 for details.
    About question 3--- I think there is no necessary to cover the sensor with ceramic LCC package, maybe metal shield is enough.
    About question 4---we don't have the plots of bias over temperature, you can refer to the parameter TCO.

    And what's the meaning of SF you mentioned?