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BGA Decoupling Capacitors Placement

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  • BGA Decoupling Capacitors Placement

    Hi,
    I am trying to place decoupling capacitors under BGA processor. If I understand strategy correctly - goal is to place one capacitor for each two power supply pins. I have a question regarding 1V5_DDR power supply on attached picture. There are 2 kind of capacitors: 220nF (smaller) and 22uF (bigger bulk capacitors). The arrow is pointing to 220nF decoupling capacitor which is to far away from any 1V5_DDR ball. Is that ok? I suppose that bigger bulk capacitor (22uF) doesn't have to be very close to power supply pins. My concern are 220nF decouple capacitors.

    Best regards,
    Milos
    milos.stankovic
    Member
    Last edited by milos.stankovic; 09-11-2015, 03:03 AM.

  • #2
    I suppose that bigger bulk capacitor (22uF) doesn't have to be very close to power supply pins
    milos.stankovic
    Member
    milos.stankovic Yes, you are right - the 22uF doesn't have to be directly under the pins, placing the 220nF directly under the pins is more important.

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    • #3
      Maybe there are more 220nF caps than number_of_vcc_pins/2. I will check. What is the puprose of two 220nF caps adjacent to 22uF? The more is better in any case.

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      • #4
        Maybe there are more 220nF caps than number_of_vcc_pins/2. I will check
        Normally you may want to use 1 small CAP per 1 PIN.


        What is the puprose of two 220nF caps adjacent to 22uF?
        Smaller caps will react much faster than bigger caps.

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        • #5
          I understand. Thanks

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