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  • PCB screw position problem - how to validate?

    Discussion in 'The main mechanical design forum' started by kenny82, Aug 2, 2009.

    1. kenny82

      kenny82 Well-Known Member

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      I am designing an enclosure where I need to mount four PCBs. Each PCB with all components fitted weighs around 35g. The equipment is likely to encounter vibrations with a maximum acceleration of 40m/s^2. Originally I had planned to mount the PCBs using four M2.5 screws - one in each corner. A senior colleague recommends five - one in each corner and one in the middle. I think this is overkill and I want to keep it to 4 screws. What would be the best way to validate my design? :?: :?:
       
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    3. aknotley

      aknotley Active Member

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      Using 5 screws (4x on corners and 1 in the center of the PCB) will make the natural resonance frequency higher than using only 4x corner screws. It will also reduce the amplitude of vibrations in the center of the PCB.

      An alternative option is to support your PCB's on springs that would behave as shock absorbers. Hope this helps.
       
    4. Karl A Petersen

      Karl A Petersen Member

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      What are you trying to minimize? If it is flexure and you must use four screws, put them on the diagonals (an X) about 1/5 the length of the diagonal from each corner. This also maximizes the axial load on the screws, but, hey, you can make them any size you want.
       

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